| @c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002 |
| @c Free Software Foundation, Inc. |
| @c This is part of the GCC manual. |
| @c For copying conditions, see the file gcc.texi. |
| |
| @node Target Macros |
| @chapter Target Description Macros and Functions |
| @cindex machine description macros |
| @cindex target description macros |
| @cindex macros, target description |
| @cindex @file{tm.h} macros |
| |
| In addition to the file @file{@var{machine}.md}, a machine description |
| includes a C header file conventionally given the name |
| @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. |
| The header file defines numerous macros that convey the information |
| about the target machine that does not fit into the scheme of the |
| @file{.md} file. The file @file{tm.h} should be a link to |
| @file{@var{machine}.h}. The header file @file{config.h} includes |
| @file{tm.h} and most compiler source files include @file{config.h}. The |
| source file defines a variable @code{targetm}, which is a structure |
| containing pointers to functions and data relating to the target |
| machine. @file{@var{machine}.c} should also contain their definitions, |
| if they are not defined elsewhere in GCC, and other functions called |
| through the macros defined in the @file{.h} file. |
| |
| @menu |
| * Target Structure:: The @code{targetm} variable. |
| * Driver:: Controlling how the driver runs the compilation passes. |
| * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. |
| * Per-Function Data:: Defining data structures for per-function information. |
| * Storage Layout:: Defining sizes and alignments of data. |
| * Type Layout:: Defining sizes and properties of basic user data types. |
| * Escape Sequences:: Defining the value of target character escape sequences |
| * Registers:: Naming and describing the hardware registers. |
| * Register Classes:: Defining the classes of hardware registers. |
| * Stack and Calling:: Defining which way the stack grows and by how much. |
| * Varargs:: Defining the varargs macros. |
| * Trampolines:: Code set up at run time to enter a nested function. |
| * Library Calls:: Controlling how library routines are implicitly called. |
| * Addressing Modes:: Defining addressing modes valid for memory operands. |
| * Condition Code:: Defining how insns update the condition code. |
| * Costs:: Defining relative costs of different operations. |
| * Scheduling:: Adjusting the behavior of the instruction scheduler. |
| * Sections:: Dividing storage into text, data, and other sections. |
| * PIC:: Macros for position independent code. |
| * Assembler Format:: Defining how to write insns and pseudo-ops to output. |
| * Debugging Info:: Defining the format of debugging output. |
| * Cross-compilation:: Handling floating point for cross-compilers. |
| * Mode Switching:: Insertion of mode-switching instructions. |
| * Target Attributes:: Defining target-specific uses of @code{__attribute__}. |
| * Misc:: Everything else. |
| @end menu |
| |
| @node Target Structure |
| @section The Global @code{targetm} Variable |
| @cindex target hooks |
| @cindex target functions |
| |
| @deftypevar {struct gcc_target} targetm |
| The target @file{.c} file must define the global @code{targetm} variable |
| which contains pointers to functions and data relating to the target |
| machine. The variable is declared in @file{target.h}; |
| @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is |
| used to initialize the variable, and macros for the default initializers |
| for elements of the structure. The @file{.c} file should override those |
| macros for which the default definition is inappropriate. For example: |
| @smallexample |
| #include "target.h" |
| #include "target-def.h" |
| |
| /* @r{Initialize the GCC target structure.} */ |
| |
| #undef TARGET_COMP_TYPE_ATTRIBUTES |
| #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes |
| |
| struct gcc_target targetm = TARGET_INITIALIZER; |
| @end smallexample |
| @end deftypevar |
| |
| Where a macro should be defined in the @file{.c} file in this manner to |
| form part of the @code{targetm} structure, it is documented below as a |
| ``Target Hook'' with a prototype. Many macros will change in future |
| from being defined in the @file{.h} file to being part of the |
| @code{targetm} structure. |
| |
| @node Driver |
| @section Controlling the Compilation Driver, @file{gcc} |
| @cindex driver |
| @cindex controlling the compilation driver |
| |
| @c prevent bad page break with this line |
| You can control the compilation driver. |
| |
| @table @code |
| @findex SWITCH_TAKES_ARG |
| @item SWITCH_TAKES_ARG (@var{char}) |
| A C expression which determines whether the option @option{-@var{char}} |
| takes arguments. The value should be the number of arguments that |
| option takes--zero, for many options. |
| |
| By default, this macro is defined as |
| @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options |
| properly. You need not define @code{SWITCH_TAKES_ARG} unless you |
| wish to add additional options which take arguments. Any redefinition |
| should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for |
| additional options. |
| |
| @findex WORD_SWITCH_TAKES_ARG |
| @item WORD_SWITCH_TAKES_ARG (@var{name}) |
| A C expression which determines whether the option @option{-@var{name}} |
| takes arguments. The value should be the number of arguments that |
| option takes--zero, for many options. This macro rather than |
| @code{SWITCH_TAKES_ARG} is used for multi-character option names. |
| |
| By default, this macro is defined as |
| @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options |
| properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you |
| wish to add additional options which take arguments. Any redefinition |
| should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for |
| additional options. |
| |
| @findex SWITCH_CURTAILS_COMPILATION |
| @item SWITCH_CURTAILS_COMPILATION (@var{char}) |
| A C expression which determines whether the option @option{-@var{char}} |
| stops compilation before the generation of an executable. The value is |
| boolean, nonzero if the option does stop an executable from being |
| generated, zero otherwise. |
| |
| By default, this macro is defined as |
| @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard |
| options properly. You need not define |
| @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional |
| options which affect the generation of an executable. Any redefinition |
| should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check |
| for additional options. |
| |
| @findex SWITCHES_NEED_SPACES |
| @item SWITCHES_NEED_SPACES |
| A string-valued C expression which enumerates the options for which |
| the linker needs a space between the option and its argument. |
| |
| If this macro is not defined, the default value is @code{""}. |
| |
| @findex TARGET_OPTION_TRANSLATE_TABLE |
| @item TARGET_OPTION_TRANSLATE_TABLE |
| If defined, a list of pairs of strings, the first of which is a |
| potential command line target to the @file{gcc} driver program, and the |
| second of which is a space-separated (tabs and other whitespace are not |
| supported) list of options with which to replace the first option. The |
| target defining this list is responsible for assuring that the results |
| are valid. Replacement options may not be the @code{--opt} style, they |
| must be the @code{-opt} style. It is the intention of this macro to |
| provide a mechanism for substitution that affects the multilibs chosen, |
| such as one option that enables many options, some of which select |
| multilibs. Example nonsensical definition, where @code{-malt-abi}, |
| @code{-EB}, and @code{-mspoo} cause different multilibs to be chosen: |
| |
| @example |
| #define TARGET_OPTION_TRANSLATE_TABLE \ |
| @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \ |
| @{ "-compat", "-EB -malign=4 -mspoo" @} |
| @end example |
| |
| @findex CPP_SPEC |
| @item CPP_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to CPP@. It can also specify how to translate options you |
| give to GCC into options for GCC to pass to the CPP@. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @findex CPLUSPLUS_CPP_SPEC |
| @item CPLUSPLUS_CPP_SPEC |
| This macro is just like @code{CPP_SPEC}, but is used for C++, rather |
| than C@. If you do not define this macro, then the value of |
| @code{CPP_SPEC} (if any) will be used instead. |
| |
| @findex NO_BUILTIN_SIZE_TYPE |
| @item NO_BUILTIN_SIZE_TYPE |
| If this macro is defined, the preprocessor will not define the built-in macro |
| @code{__SIZE_TYPE__}. The macro @code{__SIZE_TYPE__} must then be defined |
| by @code{CPP_SPEC} instead. |
| |
| This should be defined if @code{SIZE_TYPE} depends on target dependent flags |
| which are not accessible to the preprocessor. Otherwise, it should not |
| be defined. |
| |
| @findex NO_BUILTIN_PTRDIFF_TYPE |
| @item NO_BUILTIN_PTRDIFF_TYPE |
| If this macro is defined, the preprocessor will not define the built-in macro |
| @code{__PTRDIFF_TYPE__}. The macro @code{__PTRDIFF_TYPE__} must then be |
| defined by @code{CPP_SPEC} instead. |
| |
| This should be defined if @code{PTRDIFF_TYPE} depends on target dependent flags |
| which are not accessible to the preprocessor. Otherwise, it should not |
| be defined. |
| |
| @findex NO_BUILTIN_WCHAR_TYPE |
| @item NO_BUILTIN_WCHAR_TYPE |
| If this macro is defined, the preprocessor will not define the built-in macro |
| @code{__WCHAR_TYPE__}. The macro @code{__WCHAR_TYPE__} must then be |
| defined by @code{CPP_SPEC} instead. |
| |
| This should be defined if @code{WCHAR_TYPE} depends on target dependent flags |
| which are not accessible to the preprocessor. Otherwise, it should not |
| be defined. |
| |
| @findex NO_BUILTIN_WINT_TYPE |
| @item NO_BUILTIN_WINT_TYPE |
| If this macro is defined, the preprocessor will not define the built-in macro |
| @code{__WINT_TYPE__}. The macro @code{__WINT_TYPE__} must then be |
| defined by @code{CPP_SPEC} instead. |
| |
| This should be defined if @code{WINT_TYPE} depends on target dependent flags |
| which are not accessible to the preprocessor. Otherwise, it should not |
| be defined. |
| |
| @findex CC1_SPEC |
| @item CC1_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language |
| front ends. |
| It can also specify how to translate options you give to GCC into options |
| for GCC to pass to front ends. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @findex CC1PLUS_SPEC |
| @item CC1PLUS_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to @code{cc1plus}. It can also specify how to translate options you |
| give to GCC into options for GCC to pass to the @code{cc1plus}. |
| |
| Do not define this macro if it does not need to do anything. |
| Note that everything defined in CC1_SPEC is already passed to |
| @code{cc1plus} so there is no need to duplicate the contents of |
| CC1_SPEC in CC1PLUS_SPEC@. |
| |
| @findex ASM_SPEC |
| @item ASM_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to the assembler. It can also specify how to translate options |
| you give to GCC into options for GCC to pass to the assembler. |
| See the file @file{sun3.h} for an example of this. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @findex ASM_FINAL_SPEC |
| @item ASM_FINAL_SPEC |
| A C string constant that tells the GCC driver program how to |
| run any programs which cleanup after the normal assembler. |
| Normally, this is not needed. See the file @file{mips.h} for |
| an example of this. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @findex LINK_SPEC |
| @item LINK_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to the linker. It can also specify how to translate options you |
| give to GCC into options for GCC to pass to the linker. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @findex LIB_SPEC |
| @item LIB_SPEC |
| Another C string constant used much like @code{LINK_SPEC}. The difference |
| between the two is that @code{LIB_SPEC} is used at the end of the |
| command given to the linker. |
| |
| If this macro is not defined, a default is provided that |
| loads the standard C library from the usual place. See @file{gcc.c}. |
| |
| @findex LIBGCC_SPEC |
| @item LIBGCC_SPEC |
| Another C string constant that tells the GCC driver program |
| how and when to place a reference to @file{libgcc.a} into the |
| linker command line. This constant is placed both before and after |
| the value of @code{LIB_SPEC}. |
| |
| If this macro is not defined, the GCC driver provides a default that |
| passes the string @option{-lgcc} to the linker. |
| |
| @findex STARTFILE_SPEC |
| @item STARTFILE_SPEC |
| Another C string constant used much like @code{LINK_SPEC}. The |
| difference between the two is that @code{STARTFILE_SPEC} is used at |
| the very beginning of the command given to the linker. |
| |
| If this macro is not defined, a default is provided that loads the |
| standard C startup file from the usual place. See @file{gcc.c}. |
| |
| @findex ENDFILE_SPEC |
| @item ENDFILE_SPEC |
| Another C string constant used much like @code{LINK_SPEC}. The |
| difference between the two is that @code{ENDFILE_SPEC} is used at |
| the very end of the command given to the linker. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @findex THREAD_MODEL_SPEC |
| @item THREAD_MODEL_SPEC |
| GCC @code{-v} will print the thread model GCC was configured to use. |
| However, this doesn't work on platforms that are multilibbed on thread |
| models, such as AIX 4.3. On such platforms, define |
| @code{THREAD_MODEL_SPEC} such that it evaluates to a string without |
| blanks that names one of the recognized thread models. @code{%*}, the |
| default value of this macro, will expand to the value of |
| @code{thread_file} set in @file{config.gcc}. |
| |
| @findex EXTRA_SPECS |
| @item EXTRA_SPECS |
| Define this macro to provide additional specifications to put in the |
| @file{specs} file that can be used in various specifications like |
| @code{CC1_SPEC}. |
| |
| The definition should be an initializer for an array of structures, |
| containing a string constant, that defines the specification name, and a |
| string constant that provides the specification. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @code{EXTRA_SPECS} is useful when an architecture contains several |
| related targets, which have various @code{@dots{}_SPECS} which are similar |
| to each other, and the maintainer would like one central place to keep |
| these definitions. |
| |
| For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to |
| define either @code{_CALL_SYSV} when the System V calling sequence is |
| used or @code{_CALL_AIX} when the older AIX-based calling sequence is |
| used. |
| |
| The @file{config/rs6000/rs6000.h} target file defines: |
| |
| @example |
| #define EXTRA_SPECS \ |
| @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, |
| |
| #define CPP_SYS_DEFAULT "" |
| @end example |
| |
| The @file{config/rs6000/sysv.h} target file defines: |
| @smallexample |
| #undef CPP_SPEC |
| #define CPP_SPEC \ |
| "%@{posix: -D_POSIX_SOURCE @} \ |
| %@{mcall-sysv: -D_CALL_SYSV @} %@{mcall-aix: -D_CALL_AIX @} \ |
| %@{!mcall-sysv: %@{!mcall-aix: %(cpp_sysv_default) @}@} \ |
| %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" |
| |
| #undef CPP_SYSV_DEFAULT |
| #define CPP_SYSV_DEFAULT "-D_CALL_SYSV" |
| @end smallexample |
| |
| while the @file{config/rs6000/eabiaix.h} target file defines |
| @code{CPP_SYSV_DEFAULT} as: |
| |
| @smallexample |
| #undef CPP_SYSV_DEFAULT |
| #define CPP_SYSV_DEFAULT "-D_CALL_AIX" |
| @end smallexample |
| |
| @findex LINK_LIBGCC_SPECIAL |
| @item LINK_LIBGCC_SPECIAL |
| Define this macro if the driver program should find the library |
| @file{libgcc.a} itself and should not pass @option{-L} options to the |
| linker. If you do not define this macro, the driver program will pass |
| the argument @option{-lgcc} to tell the linker to do the search and will |
| pass @option{-L} options to it. |
| |
| @findex LINK_LIBGCC_SPECIAL_1 |
| @item LINK_LIBGCC_SPECIAL_1 |
| Define this macro if the driver program should find the library |
| @file{libgcc.a}. If you do not define this macro, the driver program will pass |
| the argument @option{-lgcc} to tell the linker to do the search. |
| This macro is similar to @code{LINK_LIBGCC_SPECIAL}, except that it does |
| not affect @option{-L} options. |
| |
| @findex LINK_COMMAND_SPEC |
| @item LINK_COMMAND_SPEC |
| A C string constant giving the complete command line need to execute the |
| linker. When you do this, you will need to update your port each time a |
| change is made to the link command line within @file{gcc.c}. Therefore, |
| define this macro only if you need to completely redefine the command |
| line for invoking the linker and there is no other way to accomplish |
| the effect you need. |
| |
| @findex LINK_ELIMINATE_DUPLICATE_LDIRECTORIES |
| @item LINK_ELIMINATE_DUPLICATE_LDIRECTORIES |
| A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search |
| directories from linking commands. Do not give it a nonzero value if |
| removing duplicate search directories changes the linker's semantics. |
| |
| @findex MULTILIB_DEFAULTS |
| @item MULTILIB_DEFAULTS |
| Define this macro as a C expression for the initializer of an array of |
| string to tell the driver program which options are defaults for this |
| target and thus do not need to be handled specially when using |
| @code{MULTILIB_OPTIONS}. |
| |
| Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in |
| the target makefile fragment or if none of the options listed in |
| @code{MULTILIB_OPTIONS} are set by default. |
| @xref{Target Fragment}. |
| |
| @findex RELATIVE_PREFIX_NOT_LINKDIR |
| @item RELATIVE_PREFIX_NOT_LINKDIR |
| Define this macro to tell @code{gcc} that it should only translate |
| a @option{-B} prefix into a @option{-L} linker option if the prefix |
| indicates an absolute file name. |
| |
| @findex STANDARD_EXEC_PREFIX |
| @item STANDARD_EXEC_PREFIX |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @file{/usr/local/lib/gcc-lib/} as the default prefix to |
| try when searching for the executable files of the compiler. |
| |
| @findex MD_EXEC_PREFIX |
| @item MD_EXEC_PREFIX |
| If defined, this macro is an additional prefix to try after |
| @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched |
| when the @option{-b} option is used, or the compiler is built as a cross |
| compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it |
| to the list of directories used to find the assembler in @file{configure.in}. |
| |
| @findex STANDARD_STARTFILE_PREFIX |
| @item STANDARD_STARTFILE_PREFIX |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @file{/usr/local/lib/} as the default prefix to |
| try when searching for startup files such as @file{crt0.o}. |
| |
| @findex MD_STARTFILE_PREFIX |
| @item MD_STARTFILE_PREFIX |
| If defined, this macro supplies an additional prefix to try after the |
| standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the |
| @option{-b} option is used, or when the compiler is built as a cross |
| compiler. |
| |
| @findex MD_STARTFILE_PREFIX_1 |
| @item MD_STARTFILE_PREFIX_1 |
| If defined, this macro supplies yet another prefix to try after the |
| standard prefixes. It is not searched when the @option{-b} option is |
| used, or when the compiler is built as a cross compiler. |
| |
| @findex INIT_ENVIRONMENT |
| @item INIT_ENVIRONMENT |
| Define this macro as a C string constant if you wish to set environment |
| variables for programs called by the driver, such as the assembler and |
| loader. The driver passes the value of this macro to @code{putenv} to |
| initialize the necessary environment variables. |
| |
| @findex LOCAL_INCLUDE_DIR |
| @item LOCAL_INCLUDE_DIR |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @file{/usr/local/include} as the default prefix to |
| try when searching for local header files. @code{LOCAL_INCLUDE_DIR} |
| comes before @code{SYSTEM_INCLUDE_DIR} in the search order. |
| |
| Cross compilers do not search either @file{/usr/local/include} or its |
| replacement. |
| |
| @findex MODIFY_TARGET_NAME |
| @item MODIFY_TARGET_NAME |
| Define this macro if you with to define command-line switches that modify the |
| default target name |
| |
| For each switch, you can include a string to be appended to the first |
| part of the configuration name or a string to be deleted from the |
| configuration name, if present. The definition should be an initializer |
| for an array of structures. Each array element should have three |
| elements: the switch name (a string constant, including the initial |
| dash), one of the enumeration codes @code{ADD} or @code{DELETE} to |
| indicate whether the string should be inserted or deleted, and the string |
| to be inserted or deleted (a string constant). |
| |
| For example, on a machine where @samp{64} at the end of the |
| configuration name denotes a 64-bit target and you want the @option{-32} |
| and @option{-64} switches to select between 32- and 64-bit targets, you would |
| code |
| |
| @smallexample |
| #define MODIFY_TARGET_NAME \ |
| @{ @{ "-32", DELETE, "64"@}, \ |
| @{"-64", ADD, "64"@}@} |
| @end smallexample |
| |
| |
| @findex SYSTEM_INCLUDE_DIR |
| @item SYSTEM_INCLUDE_DIR |
| Define this macro as a C string constant if you wish to specify a |
| system-specific directory to search for header files before the standard |
| directory. @code{SYSTEM_INCLUDE_DIR} comes before |
| @code{STANDARD_INCLUDE_DIR} in the search order. |
| |
| Cross compilers do not use this macro and do not search the directory |
| specified. |
| |
| @findex STANDARD_INCLUDE_DIR |
| @item STANDARD_INCLUDE_DIR |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @file{/usr/include} as the default prefix to |
| try when searching for header files. |
| |
| Cross compilers do not use this macro and do not search either |
| @file{/usr/include} or its replacement. |
| |
| @findex STANDARD_INCLUDE_COMPONENT |
| @item STANDARD_INCLUDE_COMPONENT |
| The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}. |
| See @code{INCLUDE_DEFAULTS}, below, for the description of components. |
| If you do not define this macro, no component is used. |
| |
| @findex INCLUDE_DEFAULTS |
| @item INCLUDE_DEFAULTS |
| Define this macro if you wish to override the entire default search path |
| for include files. For a native compiler, the default search path |
| usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, |
| @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and |
| @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} |
| and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, |
| and specify private search areas for GCC@. The directory |
| @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. |
| |
| The definition should be an initializer for an array of structures. |
| Each array element should have four elements: the directory name (a |
| string constant), the component name (also a string constant), a flag |
| for C++-only directories, |
| and a flag showing that the includes in the directory don't need to be |
| wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of |
| the array with a null element. |
| |
| The component name denotes what GNU package the include file is part of, |
| if any, in all upper-case letters. For example, it might be @samp{GCC} |
| or @samp{BINUTILS}. If the package is part of a vendor-supplied |
| operating system, code the component name as @samp{0}. |
| |
| For example, here is the definition used for VAX/VMS: |
| |
| @example |
| #define INCLUDE_DEFAULTS \ |
| @{ \ |
| @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ |
| @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ |
| @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ |
| @{ ".", 0, 0, 0@}, \ |
| @{ 0, 0, 0, 0@} \ |
| @} |
| @end example |
| @end table |
| |
| Here is the order of prefixes tried for exec files: |
| |
| @enumerate |
| @item |
| Any prefixes specified by the user with @option{-B}. |
| |
| @item |
| The environment variable @code{GCC_EXEC_PREFIX}, if any. |
| |
| @item |
| The directories specified by the environment variable @code{COMPILER_PATH}. |
| |
| @item |
| The macro @code{STANDARD_EXEC_PREFIX}. |
| |
| @item |
| @file{/usr/lib/gcc/}. |
| |
| @item |
| The macro @code{MD_EXEC_PREFIX}, if any. |
| @end enumerate |
| |
| Here is the order of prefixes tried for startfiles: |
| |
| @enumerate |
| @item |
| Any prefixes specified by the user with @option{-B}. |
| |
| @item |
| The environment variable @code{GCC_EXEC_PREFIX}, if any. |
| |
| @item |
| The directories specified by the environment variable @code{LIBRARY_PATH} |
| (or port-specific name; native only, cross compilers do not use this). |
| |
| @item |
| The macro @code{STANDARD_EXEC_PREFIX}. |
| |
| @item |
| @file{/usr/lib/gcc/}. |
| |
| @item |
| The macro @code{MD_EXEC_PREFIX}, if any. |
| |
| @item |
| The macro @code{MD_STARTFILE_PREFIX}, if any. |
| |
| @item |
| The macro @code{STANDARD_STARTFILE_PREFIX}. |
| |
| @item |
| @file{/lib/}. |
| |
| @item |
| @file{/usr/lib/}. |
| @end enumerate |
| |
| @node Run-time Target |
| @section Run-time Target Specification |
| @cindex run-time target specification |
| @cindex predefined macros |
| @cindex target specifications |
| |
| @c prevent bad page break with this line |
| Here are run-time target specifications. |
| |
| @table @code |
| @findex CPP_PREDEFINES |
| @item CPP_PREDEFINES |
| Define this to be a string constant containing @option{-D} options to |
| define the predefined macros that identify this machine and system. |
| These macros will be predefined unless the @option{-ansi} option (or a |
| @option{-std} option for strict ISO C conformance) is specified. |
| |
| In addition, a parallel set of macros are predefined, whose names are |
| made by appending @samp{__} at the beginning and at the end. These |
| @samp{__} macros are permitted by the ISO standard, so they are |
| predefined regardless of whether @option{-ansi} or a @option{-std} option |
| is specified. |
| |
| For example, on the Sun, one can use the following value: |
| |
| @smallexample |
| "-Dmc68000 -Dsun -Dunix" |
| @end smallexample |
| |
| The result is to define the macros @code{__mc68000__}, @code{__sun__} |
| and @code{__unix__} unconditionally, and the macros @code{mc68000}, |
| @code{sun} and @code{unix} provided @option{-ansi} is not specified. |
| |
| @findex extern int target_flags |
| @item extern int target_flags; |
| This declaration should be present. |
| |
| @cindex optional hardware or system features |
| @cindex features, optional, in system conventions |
| @item TARGET_@dots{} |
| This series of macros is to allow compiler command arguments to |
| enable or disable the use of optional features of the target machine. |
| For example, one machine description serves both the 68000 and |
| the 68020; a command argument tells the compiler whether it should |
| use 68020-only instructions or not. This command argument works |
| by means of a macro @code{TARGET_68020} that tests a bit in |
| @code{target_flags}. |
| |
| Define a macro @code{TARGET_@var{featurename}} for each such option. |
| Its definition should test a bit in @code{target_flags}. It is |
| recommended that a helper macro @code{TARGET_MASK_@var{featurename}} |
| is defined for each bit-value to test, and used in |
| @code{TARGET_@var{featurename}} and @code{TARGET_SWITCHES}. For |
| example: |
| |
| @smallexample |
| #define TARGET_MASK_68020 1 |
| #define TARGET_68020 (target_flags & TARGET_MASK_68020) |
| @end smallexample |
| |
| One place where these macros are used is in the condition-expressions |
| of instruction patterns. Note how @code{TARGET_68020} appears |
| frequently in the 68000 machine description file, @file{m68k.md}. |
| Another place they are used is in the definitions of the other |
| macros in the @file{@var{machine}.h} file. |
| |
| @findex TARGET_SWITCHES |
| @item TARGET_SWITCHES |
| This macro defines names of command options to set and clear |
| bits in @code{target_flags}. Its definition is an initializer |
| with a subgrouping for each command option. |
| |
| Each subgrouping contains a string constant, that defines the option |
| name, a number, which contains the bits to set in |
| @code{target_flags}, and a second string which is the description |
| displayed by @option{--help}. If the number is negative then the bits specified |
| by the number are cleared instead of being set. If the description |
| string is present but empty, then no help information will be displayed |
| for that option, but it will not count as an undocumented option. The |
| actual option name is made by appending @samp{-m} to the specified name. |
| Non-empty description strings should be marked with @code{N_(@dots{})} for |
| @command{xgettext}. Please do not mark empty strings because the empty |
| string is reserved by GNU gettext. @code{gettext("")} returns the header entry |
| of the message catalog with meta information, not the empty string. |
| |
| In addition to the description for @option{--help}, |
| more detailed documentation for each option should be added to |
| @file{invoke.texi}. |
| |
| One of the subgroupings should have a null string. The number in |
| this grouping is the default value for @code{target_flags}. Any |
| target options act starting with that value. |
| |
| Here is an example which defines @option{-m68000} and @option{-m68020} |
| with opposite meanings, and picks the latter as the default: |
| |
| @smallexample |
| #define TARGET_SWITCHES \ |
| @{ @{ "68020", TARGET_MASK_68020, "" @}, \ |
| @{ "68000", -TARGET_MASK_68020, \ |
| N_("Compile for the 68000") @}, \ |
| @{ "", TARGET_MASK_68020, "" @}@} |
| @end smallexample |
| |
| @findex TARGET_OPTIONS |
| @item TARGET_OPTIONS |
| This macro is similar to @code{TARGET_SWITCHES} but defines names of command |
| options that have values. Its definition is an initializer with a |
| subgrouping for each command option. |
| |
| Each subgrouping contains a string constant, that defines the fixed part |
| of the option name, the address of a variable, and a description string. |
| Non-empty description strings should be marked with @code{N_(@dots{})} for |
| @command{xgettext}. Please do not mark empty strings because the empty |
| string is reserved by GNU gettext. @code{gettext("")} returns the header entry |
| of the message catalog with meta information, not the empty string. |
| |
| The variable, type @code{char *}, is set to the variable part of the |
| given option if the fixed part matches. The actual option name is made |
| by appending @samp{-m} to the specified name. Again, each option should |
| also be documented in @file{invoke.texi}. |
| |
| Here is an example which defines @option{-mshort-data-@var{number}}. If the |
| given option is @option{-mshort-data-512}, the variable @code{m88k_short_data} |
| will be set to the string @code{"512"}. |
| |
| @smallexample |
| extern char *m88k_short_data; |
| #define TARGET_OPTIONS \ |
| @{ @{ "short-data-", &m88k_short_data, \ |
| N_("Specify the size of the short data section") @} @} |
| @end smallexample |
| |
| @findex TARGET_VERSION |
| @item TARGET_VERSION |
| This macro is a C statement to print on @code{stderr} a string |
| describing the particular machine description choice. Every machine |
| description should define @code{TARGET_VERSION}. For example: |
| |
| @smallexample |
| #ifdef MOTOROLA |
| #define TARGET_VERSION \ |
| fprintf (stderr, " (68k, Motorola syntax)"); |
| #else |
| #define TARGET_VERSION \ |
| fprintf (stderr, " (68k, MIT syntax)"); |
| #endif |
| @end smallexample |
| |
| @findex OVERRIDE_OPTIONS |
| @item OVERRIDE_OPTIONS |
| Sometimes certain combinations of command options do not make sense on |
| a particular target machine. You can define a macro |
| @code{OVERRIDE_OPTIONS} to take account of this. This macro, if |
| defined, is executed once just after all the command options have been |
| parsed. |
| |
| Don't use this macro to turn on various extra optimizations for |
| @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for. |
| |
| @findex OPTIMIZATION_OPTIONS |
| @item OPTIMIZATION_OPTIONS (@var{level}, @var{size}) |
| Some machines may desire to change what optimizations are performed for |
| various optimization levels. This macro, if defined, is executed once |
| just after the optimization level is determined and before the remainder |
| of the command options have been parsed. Values set in this macro are |
| used as the default values for the other command line options. |
| |
| @var{level} is the optimization level specified; 2 if @option{-O2} is |
| specified, 1 if @option{-O} is specified, and 0 if neither is specified. |
| |
| @var{size} is nonzero if @option{-Os} is specified and zero otherwise. |
| |
| You should not use this macro to change options that are not |
| machine-specific. These should uniformly selected by the same |
| optimization level on all supported machines. Use this macro to enable |
| machine-specific optimizations. |
| |
| @strong{Do not examine @code{write_symbols} in |
| this macro!} The debugging options are not supposed to alter the |
| generated code. |
| |
| @findex CAN_DEBUG_WITHOUT_FP |
| @item CAN_DEBUG_WITHOUT_FP |
| Define this macro if debugging can be performed even without a frame |
| pointer. If this macro is defined, GCC will turn on the |
| @option{-fomit-frame-pointer} option whenever @option{-O} is specified. |
| @end table |
| |
| @node Per-Function Data |
| @section Defining data structures for per-function information. |
| @cindex per-function data |
| @cindex data structures |
| |
| If the target needs to store information on a per-function basis, GCC |
| provides a macro and a couple of variables to allow this. Note, just |
| using statics to store the information is a bad idea, since GCC supports |
| nested functions, so you can be halfway through encoding one function |
| when another one comes along. |
| |
| GCC defines a data structure called @code{struct function} which |
| contains all of the data specific to an individual function. This |
| structure contains a field called @code{machine} whose type is |
| @code{struct machine_function *}, which can be used by targets to point |
| to their own specific data. |
| |
| If a target needs per-function specific data it should define the type |
| @code{struct machine_function} and also the macro |
| @code{INIT_EXPANDERS}. This macro should be used to initialize some or |
| all of the function pointers @code{init_machine_status}, |
| @code{free_machine_status} and @code{mark_machine_status}. These |
| pointers are explained below. |
| |
| One typical use of per-function, target specific data is to create an |
| RTX to hold the register containing the function's return address. This |
| RTX can then be used to implement the @code{__builtin_return_address} |
| function, for level 0. |
| |
| Note---earlier implementations of GCC used a single data area to hold |
| all of the per-function information. Thus when processing of a nested |
| function began the old per-function data had to be pushed onto a |
| stack, and when the processing was finished, it had to be popped off the |
| stack. GCC used to provide function pointers called |
| @code{save_machine_status} and @code{restore_machine_status} to handle |
| the saving and restoring of the target specific information. Since the |
| single data area approach is no longer used, these pointers are no |
| longer supported. |
| |
| The macro and function pointers are described below. |
| |
| @table @code |
| @findex INIT_EXPANDERS |
| @item INIT_EXPANDERS |
| Macro called to initialize any target specific information. This macro |
| is called once per function, before generation of any RTL has begun. |
| The intention of this macro is to allow the initialization of the |
| function pointers below. |
| |
| @findex init_machine_status |
| @item init_machine_status |
| This is a @code{void (*)(struct function *)} function pointer. If this |
| pointer is non-@code{NULL} it will be called once per function, before function |
| compilation starts, in order to allow the target to perform any target |
| specific initialization of the @code{struct function} structure. It is |
| intended that this would be used to initialize the @code{machine} of |
| that structure. |
| |
| @findex free_machine_status |
| @item free_machine_status |
| This is a @code{void (*)(struct function *)} function pointer. If this |
| pointer is non-@code{NULL} it will be called once per function, after the |
| function has been compiled, in order to allow any memory allocated |
| during the @code{init_machine_status} function call to be freed. |
| |
| @findex mark_machine_status |
| @item mark_machine_status |
| This is a @code{void (*)(struct function *)} function pointer. If this |
| pointer is non-@code{NULL} it will be called once per function in order to mark |
| any data items in the @code{struct machine_function} structure which |
| need garbage collection. |
| |
| @end table |
| |
| @node Storage Layout |
| @section Storage Layout |
| @cindex storage layout |
| |
| Note that the definitions of the macros in this table which are sizes or |
| alignments measured in bits do not need to be constant. They can be C |
| expressions that refer to static variables, such as the @code{target_flags}. |
| @xref{Run-time Target}. |
| |
| @table @code |
| @findex BITS_BIG_ENDIAN |
| @item BITS_BIG_ENDIAN |
| Define this macro to have the value 1 if the most significant bit in a |
| byte has the lowest number; otherwise define it to have the value zero. |
| This means that bit-field instructions count from the most significant |
| bit. If the machine has no bit-field instructions, then this must still |
| be defined, but it doesn't matter which value it is defined to. This |
| macro need not be a constant. |
| |
| This macro does not affect the way structure fields are packed into |
| bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. |
| |
| @findex BYTES_BIG_ENDIAN |
| @item BYTES_BIG_ENDIAN |
| Define this macro to have the value 1 if the most significant byte in a |
| word has the lowest number. This macro need not be a constant. |
| |
| @findex WORDS_BIG_ENDIAN |
| @item WORDS_BIG_ENDIAN |
| Define this macro to have the value 1 if, in a multiword object, the |
| most significant word has the lowest number. This applies to both |
| memory locations and registers; GCC fundamentally assumes that the |
| order of words in memory is the same as the order in registers. This |
| macro need not be a constant. |
| |
| @findex LIBGCC2_WORDS_BIG_ENDIAN |
| @item LIBGCC2_WORDS_BIG_ENDIAN |
| Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a |
| constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be |
| used only when compiling @file{libgcc2.c}. Typically the value will be set |
| based on preprocessor defines. |
| |
| @findex FLOAT_WORDS_BIG_ENDIAN |
| @item FLOAT_WORDS_BIG_ENDIAN |
| Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or |
| @code{TFmode} floating point numbers are stored in memory with the word |
| containing the sign bit at the lowest address; otherwise define it to |
| have the value 0. This macro need not be a constant. |
| |
| You need not define this macro if the ordering is the same as for |
| multi-word integers. |
| |
| @findex BITS_PER_UNIT |
| @item BITS_PER_UNIT |
| Define this macro to be the number of bits in an addressable storage |
| unit (byte). If you do not define this macro the default is 8. |
| |
| @findex BITS_PER_WORD |
| @item BITS_PER_WORD |
| Number of bits in a word. If you do not define this macro, the default |
| is @code{BITS_PER_UNIT * UNITS_PER_WORD}. |
| |
| @findex MAX_BITS_PER_WORD |
| @item MAX_BITS_PER_WORD |
| Maximum number of bits in a word. If this is undefined, the default is |
| @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the |
| largest value that @code{BITS_PER_WORD} can have at run-time. |
| |
| @findex UNITS_PER_WORD |
| @item UNITS_PER_WORD |
| Number of storage units in a word; normally 4. |
| |
| @findex MIN_UNITS_PER_WORD |
| @item MIN_UNITS_PER_WORD |
| Minimum number of units in a word. If this is undefined, the default is |
| @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the |
| smallest value that @code{UNITS_PER_WORD} can have at run-time. |
| |
| @findex POINTER_SIZE |
| @item POINTER_SIZE |
| Width of a pointer, in bits. You must specify a value no wider than the |
| width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, |
| you must define @code{POINTERS_EXTEND_UNSIGNED}. |
| |
| @findex POINTERS_EXTEND_UNSIGNED |
| @item POINTERS_EXTEND_UNSIGNED |
| A C expression whose value is greater than zero if pointers that need to be |
| extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to |
| be zero-extended and zero if they are to be sign-extended. If the value |
| is less then zero then there must be an "ptr_extend" instruction that |
| extends a pointer from @code{POINTER_SIZE} to @code{Pmode}. |
| |
| You need not define this macro if the @code{POINTER_SIZE} is equal |
| to the width of @code{Pmode}. |
| |
| @findex PROMOTE_MODE |
| @item PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) |
| A macro to update @var{m} and @var{unsignedp} when an object whose type |
| is @var{type} and which has the specified mode and signedness is to be |
| stored in a register. This macro is only called when @var{type} is a |
| scalar type. |
| |
| On most RISC machines, which only have operations that operate on a full |
| register, define this macro to set @var{m} to @code{word_mode} if |
| @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most |
| cases, only integer modes should be widened because wider-precision |
| floating-point operations are usually more expensive than their narrower |
| counterparts. |
| |
| For most machines, the macro definition does not change @var{unsignedp}. |
| However, some machines, have instructions that preferentially handle |
| either signed or unsigned quantities of certain modes. For example, on |
| the DEC Alpha, 32-bit loads from memory and 32-bit add instructions |
| sign-extend the result to 64 bits. On such machines, set |
| @var{unsignedp} according to which kind of extension is more efficient. |
| |
| Do not define this macro if it would never modify @var{m}. |
| |
| @findex PROMOTE_FUNCTION_ARGS |
| @item PROMOTE_FUNCTION_ARGS |
| Define this macro if the promotion described by @code{PROMOTE_MODE} |
| should also be done for outgoing function arguments. |
| |
| @findex PROMOTE_FUNCTION_RETURN |
| @item PROMOTE_FUNCTION_RETURN |
| Define this macro if the promotion described by @code{PROMOTE_MODE} |
| should also be done for the return value of functions. |
| |
| If this macro is defined, @code{FUNCTION_VALUE} must perform the same |
| promotions done by @code{PROMOTE_MODE}. |
| |
| @findex PROMOTE_FOR_CALL_ONLY |
| @item PROMOTE_FOR_CALL_ONLY |
| Define this macro if the promotion described by @code{PROMOTE_MODE} |
| should @emph{only} be performed for outgoing function arguments or |
| function return values, as specified by @code{PROMOTE_FUNCTION_ARGS} |
| and @code{PROMOTE_FUNCTION_RETURN}, respectively. |
| |
| @findex PARM_BOUNDARY |
| @item PARM_BOUNDARY |
| Normal alignment required for function parameters on the stack, in |
| bits. All stack parameters receive at least this much alignment |
| regardless of data type. On most machines, this is the same as the |
| size of an integer. |
| |
| @findex STACK_BOUNDARY |
| @item STACK_BOUNDARY |
| Define this macro to the minimum alignment enforced by hardware for the |
| stack pointer on this machine. The definition is a C expression for the |
| desired alignment (measured in bits). This value is used as a default |
| if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, |
| this should be the same as @code{PARM_BOUNDARY}. |
| |
| @findex PREFERRED_STACK_BOUNDARY |
| @item PREFERRED_STACK_BOUNDARY |
| Define this macro if you wish to preserve a certain alignment for the |
| stack pointer, greater than what the hardware enforces. The definition |
| is a C expression for the desired alignment (measured in bits). This |
| macro must evaluate to a value equal to or larger than |
| @code{STACK_BOUNDARY}. |
| |
| @findex FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN |
| @item FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN |
| A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is |
| not guaranteed by the runtime and we should emit code to align the stack |
| at the beginning of @code{main}. |
| |
| @cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY} |
| If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned |
| to the specified boundary. If @code{PUSH_ROUNDING} is defined and specifies |
| a less strict alignment than @code{PREFERRED_STACK_BOUNDARY}, the stack may |
| be momentarily unaligned while pushing arguments. |
| |
| @findex FUNCTION_BOUNDARY |
| @item FUNCTION_BOUNDARY |
| Alignment required for a function entry point, in bits. |
| |
| @findex BIGGEST_ALIGNMENT |
| @item BIGGEST_ALIGNMENT |
| Biggest alignment that any data type can require on this machine, in bits. |
| |
| @findex MINIMUM_ATOMIC_ALIGNMENT |
| @item MINIMUM_ATOMIC_ALIGNMENT |
| If defined, the smallest alignment, in bits, that can be given to an |
| object that can be referenced in one operation, without disturbing any |
| nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger |
| on machines that don't have byte or half-word store operations. |
| |
| @findex BIGGEST_FIELD_ALIGNMENT |
| @item BIGGEST_FIELD_ALIGNMENT |
| Biggest alignment that any structure or union field can require on this |
| machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for |
| structure and union fields only, unless the field alignment has been set |
| by the @code{__attribute__ ((aligned (@var{n})))} construct. |
| |
| @findex ADJUST_FIELD_ALIGN |
| @item ADJUST_FIELD_ALIGN (@var{field}, @var{computed}) |
| An expression for the alignment of a structure field @var{field} if the |
| alignment computed in the usual way is @var{computed}. GCC uses |
| this value instead of the value in @code{BIGGEST_ALIGNMENT} or |
| @code{BIGGEST_FIELD_ALIGNMENT}, if defined. |
| |
| @findex MAX_OFILE_ALIGNMENT |
| @item MAX_OFILE_ALIGNMENT |
| Biggest alignment supported by the object file format of this machine. |
| Use this macro to limit the alignment which can be specified using the |
| @code{__attribute__ ((aligned (@var{n})))} construct. If not defined, |
| the default value is @code{BIGGEST_ALIGNMENT}. |
| |
| @findex DATA_ALIGNMENT |
| @item DATA_ALIGNMENT (@var{type}, @var{basic-align}) |
| If defined, a C expression to compute the alignment for a variable in |
| the static store. @var{type} is the data type, and @var{basic-align} is |
| the alignment that the object would ordinarily have. The value of this |
| macro is used instead of that alignment to align the object. |
| |
| If this macro is not defined, then @var{basic-align} is used. |
| |
| @findex strcpy |
| One use of this macro is to increase alignment of medium-size data to |
| make it all fit in fewer cache lines. Another is to cause character |
| arrays to be word-aligned so that @code{strcpy} calls that copy |
| constants to character arrays can be done inline. |
| |
| @findex CONSTANT_ALIGNMENT |
| @item CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align}) |
| If defined, a C expression to compute the alignment given to a constant |
| that is being placed in memory. @var{constant} is the constant and |
| @var{basic-align} is the alignment that the object would ordinarily |
| have. The value of this macro is used instead of that alignment to |
| align the object. |
| |
| If this macro is not defined, then @var{basic-align} is used. |
| |
| The typical use of this macro is to increase alignment for string |
| constants to be word aligned so that @code{strcpy} calls that copy |
| constants can be done inline. |
| |
| @findex LOCAL_ALIGNMENT |
| @item LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) |
| If defined, a C expression to compute the alignment for a variable in |
| the local store. @var{type} is the data type, and @var{basic-align} is |
| the alignment that the object would ordinarily have. The value of this |
| macro is used instead of that alignment to align the object. |
| |
| If this macro is not defined, then @var{basic-align} is used. |
| |
| One use of this macro is to increase alignment of medium-size data to |
| make it all fit in fewer cache lines. |
| |
| @findex EMPTY_FIELD_BOUNDARY |
| @item EMPTY_FIELD_BOUNDARY |
| Alignment in bits to be given to a structure bit-field that follows an |
| empty field such as @code{int : 0;}. |
| |
| Note that @code{PCC_BITFIELD_TYPE_MATTERS} also affects the alignment |
| that results from an empty field. |
| |
| @findex STRUCTURE_SIZE_BOUNDARY |
| @item STRUCTURE_SIZE_BOUNDARY |
| Number of bits which any structure or union's size must be a multiple of. |
| Each structure or union's size is rounded up to a multiple of this. |
| |
| If you do not define this macro, the default is the same as |
| @code{BITS_PER_UNIT}. |
| |
| @findex STRICT_ALIGNMENT |
| @item STRICT_ALIGNMENT |
| Define this macro to be the value 1 if instructions will fail to work |
| if given data not on the nominal alignment. If instructions will merely |
| go slower in that case, define this macro as 0. |
| |
| @findex PCC_BITFIELD_TYPE_MATTERS |
| @item PCC_BITFIELD_TYPE_MATTERS |
| Define this if you wish to imitate the way many other C compilers handle |
| alignment of bit-fields and the structures that contain them. |
| |
| The behavior is that the type written for a bit-field (@code{int}, |
| @code{short}, or other integer type) imposes an alignment for the |
| entire structure, as if the structure really did contain an ordinary |
| field of that type. In addition, the bit-field is placed within the |
| structure so that it would fit within such a field, not crossing a |
| boundary for it. |
| |
| Thus, on most machines, a bit-field whose type is written as @code{int} |
| would not cross a four-byte boundary, and would force four-byte |
| alignment for the whole structure. (The alignment used may not be four |
| bytes; it is controlled by the other alignment parameters.) |
| |
| If the macro is defined, its definition should be a C expression; |
| a nonzero value for the expression enables this behavior. |
| |
| Note that if this macro is not defined, or its value is zero, some |
| bit-fields may cross more than one alignment boundary. The compiler can |
| support such references if there are @samp{insv}, @samp{extv}, and |
| @samp{extzv} insns that can directly reference memory. |
| |
| The other known way of making bit-fields work is to define |
| @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. |
| Then every structure can be accessed with fullwords. |
| |
| Unless the machine has bit-field instructions or you define |
| @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define |
| @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. |
| |
| If your aim is to make GCC use the same conventions for laying out |
| bit-fields as are used by another compiler, here is how to investigate |
| what the other compiler does. Compile and run this program: |
| |
| @example |
| struct foo1 |
| @{ |
| char x; |
| char :0; |
| char y; |
| @}; |
| |
| struct foo2 |
| @{ |
| char x; |
| int :0; |
| char y; |
| @}; |
| |
| main () |
| @{ |
| printf ("Size of foo1 is %d\n", |
| sizeof (struct foo1)); |
| printf ("Size of foo2 is %d\n", |
| sizeof (struct foo2)); |
| exit (0); |
| @} |
| @end example |
| |
| If this prints 2 and 5, then the compiler's behavior is what you would |
| get from @code{PCC_BITFIELD_TYPE_MATTERS}. |
| |
| @findex BITFIELD_NBYTES_LIMITED |
| @item BITFIELD_NBYTES_LIMITED |
| Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited |
| to aligning a bit-field within the structure. |
| |
| @findex MEMBER_TYPE_FORCES_BLK |
| @item MEMBER_TYPE_FORCES_BLK (@var{field}) |
| Return 1 if a structure or array containing @var{field} should be accessed using |
| @code{BLKMODE}. |
| |
| Normally, this is not needed. See the file @file{c4x.h} for an example |
| of how to use this macro to prevent a structure having a floating point |
| field from being accessed in an integer mode. |
| |
| @findex ROUND_TYPE_SIZE |
| @item ROUND_TYPE_SIZE (@var{type}, @var{computed}, @var{specified}) |
| Define this macro as an expression for the overall size of a type |
| (given by @var{type} as a tree node) when the size computed in the |
| usual way is @var{computed} and the alignment is @var{specified}. |
| |
| The default is to round @var{computed} up to a multiple of @var{specified}. |
| |
| @findex ROUND_TYPE_SIZE_UNIT |
| @item ROUND_TYPE_SIZE_UNIT (@var{type}, @var{computed}, @var{specified}) |
| Similar to @code{ROUND_TYPE_SIZE}, but sizes and alignments are |
| specified in units (bytes). If you define @code{ROUND_TYPE_SIZE}, |
| you must also define this macro and they must be defined consistently |
| with each other. |
| |
| @findex ROUND_TYPE_ALIGN |
| @item ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) |
| Define this macro as an expression for the alignment of a type (given |
| by @var{type} as a tree node) if the alignment computed in the usual |
| way is @var{computed} and the alignment explicitly specified was |
| @var{specified}. |
| |
| The default is to use @var{specified} if it is larger; otherwise, use |
| the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} |
| |
| @findex MAX_FIXED_MODE_SIZE |
| @item MAX_FIXED_MODE_SIZE |
| An integer expression for the size in bits of the largest integer |
| machine mode that should actually be used. All integer machine modes of |
| this size or smaller can be used for structures and unions with the |
| appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE |
| (DImode)} is assumed. |
| |
| @findex VECTOR_MODE_SUPPORTED_P |
| @item VECTOR_MODE_SUPPORTED_P(@var{mode}) |
| Define this macro to be nonzero if the port is prepared to handle insns |
| involving vector mode @var{mode}. At the very least, it must have move |
| patterns for this mode. |
| |
| @findex STACK_SAVEAREA_MODE |
| @item STACK_SAVEAREA_MODE (@var{save_level}) |
| If defined, an expression of type @code{enum machine_mode} that |
| specifies the mode of the save area operand of a |
| @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). |
| @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or |
| @code{SAVE_NONLOCAL} and selects which of the three named patterns is |
| having its mode specified. |
| |
| You need not define this macro if it always returns @code{Pmode}. You |
| would most commonly define this macro if the |
| @code{save_stack_@var{level}} patterns need to support both a 32- and a |
| 64-bit mode. |
| |
| @findex STACK_SIZE_MODE |
| @item STACK_SIZE_MODE |
| If defined, an expression of type @code{enum machine_mode} that |
| specifies the mode of the size increment operand of an |
| @code{allocate_stack} named pattern (@pxref{Standard Names}). |
| |
| You need not define this macro if it always returns @code{word_mode}. |
| You would most commonly define this macro if the @code{allocate_stack} |
| pattern needs to support both a 32- and a 64-bit mode. |
| |
| @findex CHECK_FLOAT_VALUE |
| @item CHECK_FLOAT_VALUE (@var{mode}, @var{value}, @var{overflow}) |
| A C statement to validate the value @var{value} (of type |
| @code{double}) for mode @var{mode}. This means that you check whether |
| @var{value} fits within the possible range of values for mode |
| @var{mode} on this target machine. The mode @var{mode} is always |
| a mode of class @code{MODE_FLOAT}. @var{overflow} is nonzero if |
| the value is already known to be out of range. |
| |
| If @var{value} is not valid or if @var{overflow} is nonzero, you should |
| set @var{overflow} to 1 and then assign some valid value to @var{value}. |
| Allowing an invalid value to go through the compiler can produce |
| incorrect assembler code which may even cause Unix assemblers to crash. |
| |
| This macro need not be defined if there is no work for it to do. |
| |
| @findex TARGET_FLOAT_FORMAT |
| @item TARGET_FLOAT_FORMAT |
| A code distinguishing the floating point format of the target machine. |
| There are five defined values: |
| |
| @table @code |
| @findex IEEE_FLOAT_FORMAT |
| @item IEEE_FLOAT_FORMAT |
| This code indicates IEEE floating point. It is the default; there is no |
| need to define this macro when the format is IEEE@. |
| |
| @findex VAX_FLOAT_FORMAT |
| @item VAX_FLOAT_FORMAT |
| This code indicates the ``D float'' format used on the VAX@. |
| |
| @findex IBM_FLOAT_FORMAT |
| @item IBM_FLOAT_FORMAT |
| This code indicates the format used on the IBM System/370. |
| |
| @findex C4X_FLOAT_FORMAT |
| @item C4X_FLOAT_FORMAT |
| This code indicates the format used on the TMS320C3x/C4x. |
| |
| @findex UNKNOWN_FLOAT_FORMAT |
| @item UNKNOWN_FLOAT_FORMAT |
| This code indicates any other format. |
| @end table |
| |
| The value of this macro is compared with @code{HOST_FLOAT_FORMAT}, which |
| is defined by the @command{configure} script, to determine whether the |
| target machine has the same format as the host machine. If any other |
| formats are actually in use on supported machines, new codes should be |
| defined for them. |
| |
| The ordering of the component words of floating point values stored in |
| memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}. |
| |
| @end table |
| |
| @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type}) |
| This target hook returns @code{true} if bit-fields in the given |
| @var{record_type} are to be laid out following the rules of Microsoft |
| Visual C/C++, namely: (i) a bit-field won't share the same storage |
| unit with the previous bit-field if their underlying types have |
| different sizes, and the bit-field will be aligned to the highest |
| alignment of the underlying types of itself and of the previous |
| bit-field; (ii) a zero-sized bit-field will affect the alignment of |
| the whole enclosing structure, even if it is unnamed; except that |
| (iii) a zero-sized bit-field will be disregarded unless it follows |
| another bit-field of non-zero size. If this hook returns @code{true}, |
| other macros that control bit-field layout are ignored. |
| @end deftypefn |
| |
| @node Type Layout |
| @section Layout of Source Language Data Types |
| |
| These macros define the sizes and other characteristics of the standard |
| basic data types used in programs being compiled. Unlike the macros in |
| the previous section, these apply to specific features of C and related |
| languages, rather than to fundamental aspects of storage layout. |
| |
| @table @code |
| @findex INT_TYPE_SIZE |
| @item INT_TYPE_SIZE |
| A C expression for the size in bits of the type @code{int} on the |
| target machine. If you don't define this, the default is one word. |
| |
| @findex SHORT_TYPE_SIZE |
| @item SHORT_TYPE_SIZE |
| A C expression for the size in bits of the type @code{short} on the |
| target machine. If you don't define this, the default is half a word. |
| (If this would be less than one storage unit, it is rounded up to one |
| unit.) |
| |
| @findex LONG_TYPE_SIZE |
| @item LONG_TYPE_SIZE |
| A C expression for the size in bits of the type @code{long} on the |
| target machine. If you don't define this, the default is one word. |
| |
| @findex ADA_LONG_TYPE_SIZE |
| @item ADA_LONG_TYPE_SIZE |
| On some machines, the size used for the Ada equivalent of the type |
| @code{long} by a native Ada compiler differs from that used by C. In |
| that situation, define this macro to be a C expression to be used for |
| the size of that type. If you don't define this, the default is the |
| value of @code{LONG_TYPE_SIZE}. |
| |
| @findex MAX_LONG_TYPE_SIZE |
| @item MAX_LONG_TYPE_SIZE |
| Maximum number for the size in bits of the type @code{long} on the |
| target machine. If this is undefined, the default is |
| @code{LONG_TYPE_SIZE}. Otherwise, it is the constant value that is the |
| largest value that @code{LONG_TYPE_SIZE} can have at run-time. This is |
| used in @code{cpp}. |
| |
| @findex LONG_LONG_TYPE_SIZE |
| @item LONG_LONG_TYPE_SIZE |
| A C expression for the size in bits of the type @code{long long} on the |
| target machine. If you don't define this, the default is two |
| words. If you want to support GNU Ada on your machine, the value of this |
| macro must be at least 64. |
| |
| @findex CHAR_TYPE_SIZE |
| @item CHAR_TYPE_SIZE |
| A C expression for the size in bits of the type @code{char} on the |
| target machine. If you don't define this, the default is |
| @code{BITS_PER_UNIT}. |
| |
| @findex MAX_CHAR_TYPE_SIZE |
| @item MAX_CHAR_TYPE_SIZE |
| Maximum number for the size in bits of the type @code{char} on the |
| target machine. If this is undefined, the default is |
| @code{CHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the |
| largest value that @code{CHAR_TYPE_SIZE} can have at run-time. This is |
| used in @code{cpp}. |
| |
| @findex BOOL_TYPE_SIZE |
| @item BOOL_TYPE_SIZE |
| A C expression for the size in bits of the C++ type @code{bool} on the |
| target machine. If you don't define this, the default is |
| @code{CHAR_TYPE_SIZE}. |
| |
| @findex FLOAT_TYPE_SIZE |
| @item FLOAT_TYPE_SIZE |
| A C expression for the size in bits of the type @code{float} on the |
| target machine. If you don't define this, the default is one word. |
| |
| @findex DOUBLE_TYPE_SIZE |
| @item DOUBLE_TYPE_SIZE |
| A C expression for the size in bits of the type @code{double} on the |
| target machine. If you don't define this, the default is two |
| words. |
| |
| @findex LONG_DOUBLE_TYPE_SIZE |
| @item LONG_DOUBLE_TYPE_SIZE |
| A C expression for the size in bits of the type @code{long double} on |
| the target machine. If you don't define this, the default is two |
| words. |
| |
| @findex MAX_LONG_DOUBLE_TYPE_SIZE |
| Maximum number for the size in bits of the type @code{long double} on the |
| target machine. If this is undefined, the default is |
| @code{LONG_DOUBLE_TYPE_SIZE}. Otherwise, it is the constant value that is |
| the largest value that @code{LONG_DOUBLE_TYPE_SIZE} can have at run-time. |
| This is used in @code{cpp}. |
| |
| @findex INTEL_EXTENDED_IEEE_FORMAT |
| Define this macro to be 1 if the target machine uses 80-bit floating-point |
| values with 128-bit size and alignment. This is used in @file{real.c}. |
| |
| @findex WIDEST_HARDWARE_FP_SIZE |
| @item WIDEST_HARDWARE_FP_SIZE |
| A C expression for the size in bits of the widest floating-point format |
| supported by the hardware. If you define this macro, you must specify a |
| value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. |
| If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} |
| is the default. |
| |
| @findex DEFAULT_SIGNED_CHAR |
| @item DEFAULT_SIGNED_CHAR |
| An expression whose value is 1 or 0, according to whether the type |
| @code{char} should be signed or unsigned by default. The user can |
| always override this default with the options @option{-fsigned-char} |
| and @option{-funsigned-char}. |
| |
| @findex DEFAULT_SHORT_ENUMS |
| @item DEFAULT_SHORT_ENUMS |
| A C expression to determine whether to give an @code{enum} type |
| only as many bytes as it takes to represent the range of possible values |
| of that type. A nonzero value means to do that; a zero value means all |
| @code{enum} types should be allocated like @code{int}. |
| |
| If you don't define the macro, the default is 0. |
| |
| @findex SIZE_TYPE |
| @item SIZE_TYPE |
| A C expression for a string describing the name of the data type to use |
| for size values. The typedef name @code{size_t} is defined using the |
| contents of the string. |
| |
| The string can contain more than one keyword. If so, separate them with |
| spaces, and write first any length keyword, then @code{unsigned} if |
| appropriate, and finally @code{int}. The string must exactly match one |
| of the data type names defined in the function |
| @code{init_decl_processing} in the file @file{c-decl.c}. You may not |
| omit @code{int} or change the order---that would cause the compiler to |
| crash on startup. |
| |
| If you don't define this macro, the default is @code{"long unsigned |
| int"}. |
| |
| @findex PTRDIFF_TYPE |
| @item PTRDIFF_TYPE |
| A C expression for a string describing the name of the data type to use |
| for the result of subtracting two pointers. The typedef name |
| @code{ptrdiff_t} is defined using the contents of the string. See |
| @code{SIZE_TYPE} above for more information. |
| |
| If you don't define this macro, the default is @code{"long int"}. |
| |
| @findex WCHAR_TYPE |
| @item WCHAR_TYPE |
| A C expression for a string describing the name of the data type to use |
| for wide characters. The typedef name @code{wchar_t} is defined using |
| the contents of the string. See @code{SIZE_TYPE} above for more |
| information. |
| |
| If you don't define this macro, the default is @code{"int"}. |
| |
| @findex WCHAR_TYPE_SIZE |
| @item WCHAR_TYPE_SIZE |
| A C expression for the size in bits of the data type for wide |
| characters. This is used in @code{cpp}, which cannot make use of |
| @code{WCHAR_TYPE}. |
| |
| @findex MAX_WCHAR_TYPE_SIZE |
| @item MAX_WCHAR_TYPE_SIZE |
| Maximum number for the size in bits of the data type for wide |
| characters. If this is undefined, the default is |
| @code{WCHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the |
| largest value that @code{WCHAR_TYPE_SIZE} can have at run-time. This is |
| used in @code{cpp}. |
| |
| @findex GCOV_TYPE_SIZE |
| @item GCOV_TYPE_SIZE |
| A C expression for the size in bits of the type used for gcov counters on the |
| target machine. If you don't define this, the default is one |
| @code{LONG_TYPE_SIZE} in case it is greater or equal to 64-bit and |
| @code{LONG_LONG_TYPE_SIZE} otherwise. You may want to re-define the type to |
| ensure atomicity for counters in multithreaded programs. |
| |
| @findex WINT_TYPE |
| @item WINT_TYPE |
| A C expression for a string describing the name of the data type to |
| use for wide characters passed to @code{printf} and returned from |
| @code{getwc}. The typedef name @code{wint_t} is defined using the |
| contents of the string. See @code{SIZE_TYPE} above for more |
| information. |
| |
| If you don't define this macro, the default is @code{"unsigned int"}. |
| |
| @findex INTMAX_TYPE |
| @item INTMAX_TYPE |
| A C expression for a string describing the name of the data type that |
| can represent any value of any standard or extended signed integer type. |
| The typedef name @code{intmax_t} is defined using the contents of the |
| string. See @code{SIZE_TYPE} above for more information. |
| |
| If you don't define this macro, the default is the first of |
| @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as |
| much precision as @code{long long int}. |
| |
| @findex UINTMAX_TYPE |
| @item UINTMAX_TYPE |
| A C expression for a string describing the name of the data type that |
| can represent any value of any standard or extended unsigned integer |
| type. The typedef name @code{uintmax_t} is defined using the contents |
| of the string. See @code{SIZE_TYPE} above for more information. |
| |
| If you don't define this macro, the default is the first of |
| @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long |
| unsigned int"} that has as much precision as @code{long long unsigned |
| int}. |
| |
| @findex TARGET_PTRMEMFUNC_VBIT_LOCATION |
| @item TARGET_PTRMEMFUNC_VBIT_LOCATION |
| The C++ compiler represents a pointer-to-member-function with a struct |
| that looks like: |
| |
| @example |
| struct @{ |
| union @{ |
| void (*fn)(); |
| ptrdiff_t vtable_index; |
| @}; |
| ptrdiff_t delta; |
| @}; |
| @end example |
| |
| @noindent |
| The C++ compiler must use one bit to indicate whether the function that |
| will be called through a pointer-to-member-function is virtual. |
| Normally, we assume that the low-order bit of a function pointer must |
| always be zero. Then, by ensuring that the vtable_index is odd, we can |
| distinguish which variant of the union is in use. But, on some |
| platforms function pointers can be odd, and so this doesn't work. In |
| that case, we use the low-order bit of the @code{delta} field, and shift |
| the remainder of the @code{delta} field to the left. |
| |
| GCC will automatically make the right selection about where to store |
| this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. |
| However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} |
| set such that functions always start at even addresses, but the lowest |
| bit of pointers to functions indicate whether the function at that |
| address is in ARM or Thumb mode. If this is the case of your |
| architecture, you should define this macro to |
| @code{ptrmemfunc_vbit_in_delta}. |
| |
| In general, you should not have to define this macro. On architectures |
| in which function addresses are always even, according to |
| @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to |
| @code{ptrmemfunc_vbit_in_pfn}. |
| |
| @findex TARGET_VTABLE_USES_DESCRIPTORS |
| @item TARGET_VTABLE_USES_DESCRIPTORS |
| Normally, the C++ compiler uses function pointers in vtables. This |
| macro allows the target to change to use ``function descriptors'' |
| instead. Function descriptors are found on targets for whom a |
| function pointer is actually a small data structure. Normally the |
| data structure consists of the actual code address plus a data |
| pointer to which the function's data is relative. |
| |
| If vtables are used, the value of this macro should be the number |
| of words that the function descriptor occupies. |
| @end table |
| |
| @node Escape Sequences |
| @section Target Character Escape Sequences |
| @cindex escape sequences |
| |
| By default, GCC assumes that the C character escape sequences take on |
| their ASCII values for the target. If this is not correct, you must |
| explicitly define all of the macros below. |
| |
| @table @code |
| @findex TARGET_BELL |
| @item TARGET_BELL |
| A C constant expression for the integer value for escape sequence |
| @samp{\a}. |
| |
| @findex TARGET_ESC |
| @item TARGET_ESC |
| A C constant expression for the integer value of the target escape |
| character. As an extension, GCC evaluates the escape sequences |
| @samp{\e} and @samp{\E} to this. |
| |
| @findex TARGET_TAB |
| @findex TARGET_BS |
| @findex TARGET_NEWLINE |
| @item TARGET_BS |
| @itemx TARGET_TAB |
| @itemx TARGET_NEWLINE |
| C constant expressions for the integer values for escape sequences |
| @samp{\b}, @samp{\t} and @samp{\n}. |
| |
| @findex TARGET_VT |
| @findex TARGET_FF |
| @findex TARGET_CR |
| @item TARGET_VT |
| @itemx TARGET_FF |
| @itemx TARGET_CR |
| C constant expressions for the integer values for escape sequences |
| @samp{\v}, @samp{\f} and @samp{\r}. |
| @end table |
| |
| @node Registers |
| @section Register Usage |
| @cindex register usage |
| |
| This section explains how to describe what registers the target machine |
| has, and how (in general) they can be used. |
| |
| The description of which registers a specific instruction can use is |
| done with register classes; see @ref{Register Classes}. For information |
| on using registers to access a stack frame, see @ref{Frame Registers}. |
| For passing values in registers, see @ref{Register Arguments}. |
| For returning values in registers, see @ref{Scalar Return}. |
| |
| @menu |
| * Register Basics:: Number and kinds of registers. |
| * Allocation Order:: Order in which registers are allocated. |
| * Values in Registers:: What kinds of values each reg can hold. |
| * Leaf Functions:: Renumbering registers for leaf functions. |
| * Stack Registers:: Handling a register stack such as 80387. |
| @end menu |
| |
| @node Register Basics |
| @subsection Basic Characteristics of Registers |
| |
| @c prevent bad page break with this line |
| Registers have various characteristics. |
| |
| @table @code |
| @findex FIRST_PSEUDO_REGISTER |
| @item FIRST_PSEUDO_REGISTER |
| Number of hardware registers known to the compiler. They receive |
| numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first |
| pseudo register's number really is assigned the number |
| @code{FIRST_PSEUDO_REGISTER}. |
| |
| @item FIXED_REGISTERS |
| @findex FIXED_REGISTERS |
| @cindex fixed register |
| An initializer that says which registers are used for fixed purposes |
| all throughout the compiled code and are therefore not available for |
| general allocation. These would include the stack pointer, the frame |
| pointer (except on machines where that can be used as a general |
| register when no frame pointer is needed), the program counter on |
| machines where that is considered one of the addressable registers, |
| and any other numbered register with a standard use. |
| |
| This information is expressed as a sequence of numbers, separated by |
| commas and surrounded by braces. The @var{n}th number is 1 if |
| register @var{n} is fixed, 0 otherwise. |
| |
| The table initialized from this macro, and the table initialized by |
| the following one, may be overridden at run time either automatically, |
| by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by |
| the user with the command options @option{-ffixed-@var{reg}}, |
| @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. |
| |
| @findex CALL_USED_REGISTERS |
| @item CALL_USED_REGISTERS |
| @cindex call-used register |
| @cindex call-clobbered register |
| @cindex call-saved register |
| Like @code{FIXED_REGISTERS} but has 1 for each register that is |
| clobbered (in general) by function calls as well as for fixed |
| registers. This macro therefore identifies the registers that are not |
| available for general allocation of values that must live across |
| function calls. |
| |
| If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler |
| automatically saves it on function entry and restores it on function |
| exit, if the register is used within the function. |
| |
| @findex CALL_REALLY_USED_REGISTERS |
| @item CALL_REALLY_USED_REGISTERS |
| @cindex call-used register |
| @cindex call-clobbered register |
| @cindex call-saved register |
| Like @code{CALL_USED_REGISTERS} except this macro doesn't require |
| that the entire set of @code{FIXED_REGISTERS} be included. |
| (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). |
| This macro is optional. If not specified, it defaults to the value |
| of @code{CALL_USED_REGISTERS}. |
| |
| @findex HARD_REGNO_CALL_PART_CLOBBERED |
| @item HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode}) |
| @cindex call-used register |
| @cindex call-clobbered register |
| @cindex call-saved register |
| A C expression that is nonzero if it is not permissible to store a |
| value of mode @var{mode} in hard register number @var{regno} across a |
| call without some part of it being clobbered. For most machines this |
| macro need not be defined. It is only required for machines that do not |
| preserve the entire contents of a register across a call. |
| |
| @findex CONDITIONAL_REGISTER_USAGE |
| @findex fixed_regs |
| @findex call_used_regs |
| @item CONDITIONAL_REGISTER_USAGE |
| Zero or more C statements that may conditionally modify five variables |
| @code{fixed_regs}, @code{call_used_regs}, @code{global_regs}, |
| @code{reg_names}, and @code{reg_class_contents}, to take into account |
| any dependence of these register sets on target flags. The first three |
| of these are of type @code{char []} (interpreted as Boolean vectors). |
| @code{global_regs} is a @code{const char *[]}, and |
| @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is |
| called, @code{fixed_regs}, @code{call_used_regs}, |
| @code{reg_class_contents}, and @code{reg_names} have been initialized |
| from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS}, |
| @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively. |
| @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}}, |
| @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}} |
| command options have been applied. |
| |
| You need not define this macro if it has no work to do. |
| |
| @cindex disabling certain registers |
| @cindex controlling register usage |
| If the usage of an entire class of registers depends on the target |
| flags, you may indicate this to GCC by using this macro to modify |
| @code{fixed_regs} and @code{call_used_regs} to 1 for each of the |
| registers in the classes which should not be used by GCC@. Also define |
| the macro @code{REG_CLASS_FROM_LETTER} to return @code{NO_REGS} if it |
| is called with a letter for a class that shouldn't be used. |
| |
| (However, if this class is not included in @code{GENERAL_REGS} and all |
| of the insn patterns whose constraints permit this class are |
| controlled by target switches, then GCC will automatically avoid using |
| these registers when the target switches are opposed to them.) |
| |
| @findex NON_SAVING_SETJMP |
| @item NON_SAVING_SETJMP |
| If this macro is defined and has a nonzero value, it means that |
| @code{setjmp} and related functions fail to save the registers, or that |
| @code{longjmp} fails to restore them. To compensate, the compiler |
| avoids putting variables in registers in functions that use |
| @code{setjmp}. |
| |
| @findex INCOMING_REGNO |
| @item INCOMING_REGNO (@var{out}) |
| Define this macro if the target machine has register windows. This C |
| expression returns the register number as seen by the called function |
| corresponding to the register number @var{out} as seen by the calling |
| function. Return @var{out} if register number @var{out} is not an |
| outbound register. |
| |
| @findex OUTGOING_REGNO |
| @item OUTGOING_REGNO (@var{in}) |
| Define this macro if the target machine has register windows. This C |
| expression returns the register number as seen by the calling function |
| corresponding to the register number @var{in} as seen by the called |
| function. Return @var{in} if register number @var{in} is not an inbound |
| register. |
| |
| @findex LOCAL_REGNO |
| @item LOCAL_REGNO (@var{regno}) |
| Define this macro if the target machine has register windows. This C |
| expression returns true if the register is call-saved but is in the |
| register window. Unlike most call-saved registers, such registers |
| need not be explicitly restored on function exit or during non-local |
| gotos. |
| |
| @ignore |
| @findex PC_REGNUM |
| @item PC_REGNUM |
| If the program counter has a register number, define this as that |
| register number. Otherwise, do not define it. |
| @end ignore |
| @end table |
| |
| @node Allocation Order |
| @subsection Order of Allocation of Registers |
| @cindex order of register allocation |
| @cindex register allocation order |
| |
| @c prevent bad page break with this line |
| Registers are allocated in order. |
| |
| @table @code |
| @findex REG_ALLOC_ORDER |
| @item REG_ALLOC_ORDER |
| If defined, an initializer for a vector of integers, containing the |
| numbers of hard registers in the order in which GCC should prefer |
| to use them (from most preferred to least). |
| |
| If this macro is not defined, registers are used lowest numbered first |
| (all else being equal). |
| |
| One use of this macro is on machines where the highest numbered |
| registers must always be saved and the save-multiple-registers |
| instruction supports only sequences of consecutive registers. On such |
| machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists |
| the highest numbered allocable register first. |
| |
| @findex ORDER_REGS_FOR_LOCAL_ALLOC |
| @item ORDER_REGS_FOR_LOCAL_ALLOC |
| A C statement (sans semicolon) to choose the order in which to allocate |
| hard registers for pseudo-registers local to a basic block. |
| |
| Store the desired register order in the array @code{reg_alloc_order}. |
| Element 0 should be the register to allocate first; element 1, the next |
| register; and so on. |
| |
| The macro body should not assume anything about the contents of |
| @code{reg_alloc_order} before execution of the macro. |
| |
| On most machines, it is not necessary to define this macro. |
| @end table |
| |
| @node Values in Registers |
| @subsection How Values Fit in Registers |
| |
| This section discusses the macros that describe which kinds of values |
| (specifically, which machine modes) each register can hold, and how many |
| consecutive registers are needed for a given mode. |
| |
| @table @code |
| @findex HARD_REGNO_NREGS |
| @item HARD_REGNO_NREGS (@var{regno}, @var{mode}) |
| A C expression for the number of consecutive hard registers, starting |
| at register number @var{regno}, required to hold a value of mode |
| @var{mode}. |
| |
| On a machine where all registers are exactly one word, a suitable |
| definition of this macro is |
| |
| @smallexample |
| #define HARD_REGNO_NREGS(REGNO, MODE) \ |
| ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ |
| / UNITS_PER_WORD) |
| @end smallexample |
| |
| @findex HARD_REGNO_MODE_OK |
| @item HARD_REGNO_MODE_OK (@var{regno}, @var{mode}) |
| A C expression that is nonzero if it is permissible to store a value |
| of mode @var{mode} in hard register number @var{regno} (or in several |
| registers starting with that one). For a machine where all registers |
| are equivalent, a suitable definition is |
| |
| @smallexample |
| #define HARD_REGNO_MODE_OK(REGNO, MODE) 1 |
| @end smallexample |
| |
| You need not include code to check for the numbers of fixed registers, |
| because the allocation mechanism considers them to be always occupied. |
| |
| @cindex register pairs |
| On some machines, double-precision values must be kept in even/odd |
| register pairs. You can implement that by defining this macro to reject |
| odd register numbers for such modes. |
| |
| The minimum requirement for a mode to be OK in a register is that the |
| @samp{mov@var{mode}} instruction pattern support moves between the |
| register and other hard register in the same class and that moving a |
| value into the register and back out not alter it. |
| |
| Since the same instruction used to move @code{word_mode} will work for |
| all narrower integer modes, it is not necessary on any machine for |
| @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided |
| you define patterns @samp{movhi}, etc., to take advantage of this. This |
| is useful because of the interaction between @code{HARD_REGNO_MODE_OK} |
| and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes |
| to be tieable. |
| |
| Many machines have special registers for floating point arithmetic. |
| Often people assume that floating point machine modes are allowed only |
| in floating point registers. This is not true. Any registers that |
| can hold integers can safely @emph{hold} a floating point machine |
| mode, whether or not floating arithmetic can be done on it in those |
| registers. Integer move instructions can be used to move the values. |
| |
| On some machines, though, the converse is true: fixed-point machine |
| modes may not go in floating registers. This is true if the floating |
| registers normalize any value stored in them, because storing a |
| non-floating value there would garble it. In this case, |
| @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in |
| floating registers. But if the floating registers do not automatically |
| normalize, if you can store any bit pattern in one and retrieve it |
| unchanged without a trap, then any machine mode may go in a floating |
| register, so you can define this macro to say so. |
| |
| The primary significance of special floating registers is rather that |
| they are the registers acceptable in floating point arithmetic |
| instructions. However, this is of no concern to |
| @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper |
| constraints for those instructions. |
| |
| On some machines, the floating registers are especially slow to access, |
| so that it is better to store a value in a stack frame than in such a |
| register if floating point arithmetic is not being done. As long as the |
| floating registers are not in class @code{GENERAL_REGS}, they will not |
| be used unless some pattern's constraint asks for one. |
| |
| @findex MODES_TIEABLE_P |
| @item MODES_TIEABLE_P (@var{mode1}, @var{mode2}) |
| A C expression that is nonzero if a value of mode |
| @var{mode1} is accessible in mode @var{mode2} without copying. |
| |
| If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and |
| @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for |
| any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} |
| should be nonzero. If they differ for any @var{r}, you should define |
| this macro to return zero unless some other mechanism ensures the |
| accessibility of the value in a narrower mode. |
| |
| You should define this macro to return nonzero in as many cases as |
| possible since doing so will allow GCC to perform better register |
| allocation. |
| |
| @findex AVOID_CCMODE_COPIES |
| @item AVOID_CCMODE_COPIES |
| Define this macro if the compiler should avoid copies to/from @code{CCmode} |
| registers. You should only define this macro if support for copying to/from |
| @code{CCmode} is incomplete. |
| @end table |
| |
| @node Leaf Functions |
| @subsection Handling Leaf Functions |
| |
| @cindex leaf functions |
| @cindex functions, leaf |
| On some machines, a leaf function (i.e., one which makes no calls) can run |
| more efficiently if it does not make its own register window. Often this |
| means it is required to receive its arguments in the registers where they |
| are passed by the caller, instead of the registers where they would |
| normally arrive. |
| |
| The special treatment for leaf functions generally applies only when |
| other conditions are met; for example, often they may use only those |
| registers for its own variables and temporaries. We use the term ``leaf |
| function'' to mean a function that is suitable for this special |
| handling, so that functions with no calls are not necessarily ``leaf |
| functions''. |
| |
| GCC assigns register numbers before it knows whether the function is |
| suitable for leaf function treatment. So it needs to renumber the |
| registers in order to output a leaf function. The following macros |
| accomplish this. |
| |
| @table @code |
| @findex LEAF_REGISTERS |
| @item LEAF_REGISTERS |
| Name of a char vector, indexed by hard register number, which |
| contains 1 for a register that is allowable in a candidate for leaf |
| function treatment. |
| |
| If leaf function treatment involves renumbering the registers, then the |
| registers marked here should be the ones before renumbering---those that |
| GCC would ordinarily allocate. The registers which will actually be |
| used in the assembler code, after renumbering, should not be marked with 1 |
| in this vector. |
| |
| Define this macro only if the target machine offers a way to optimize |
| the treatment of leaf functions. |
| |
| @findex LEAF_REG_REMAP |
| @item LEAF_REG_REMAP (@var{regno}) |
| A C expression whose value is the register number to which @var{regno} |
| should be renumbered, when a function is treated as a leaf function. |
| |
| If @var{regno} is a register number which should not appear in a leaf |
| function before renumbering, then the expression should yield @minus{}1, which |
| will cause the compiler to abort. |
| |
| Define this macro only if the target machine offers a way to optimize the |
| treatment of leaf functions, and registers need to be renumbered to do |
| this. |
| @end table |
| |
| @findex current_function_is_leaf |
| @findex current_function_uses_only_leaf_regs |
| @code{TARGET_ASM_FUNCTION_PROLOGUE} and |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions |
| specially. They can test the C variable @code{current_function_is_leaf} |
| which is nonzero for leaf functions. @code{current_function_is_leaf} is |
| set prior to local register allocation and is valid for the remaining |
| compiler passes. They can also test the C variable |
| @code{current_function_uses_only_leaf_regs} which is nonzero for leaf |
| functions which only use leaf registers. |
| @code{current_function_uses_only_leaf_regs} is valid after reload and is |
| only useful if @code{LEAF_REGISTERS} is defined. |
| @c changed this to fix overfull. ALSO: why the "it" at the beginning |
| @c of the next paragraph?! --mew 2feb93 |
| |
| @node Stack Registers |
| @subsection Registers That Form a Stack |
| |
| There are special features to handle computers where some of the |
| ``registers'' form a stack, as in the 80387 coprocessor for the 80386. |
| Stack registers are normally written by pushing onto the stack, and are |
| numbered relative to the top of the stack. |
| |
| Currently, GCC can only handle one group of stack-like registers, and |
| they must be consecutively numbered. |
| |
| @table @code |
| @findex STACK_REGS |
| @item STACK_REGS |
| Define this if the machine has any stack-like registers. |
| |
| @findex FIRST_STACK_REG |
| @item FIRST_STACK_REG |
| The number of the first stack-like register. This one is the top |
| of the stack. |
| |
| @findex LAST_STACK_REG |
| @item LAST_STACK_REG |
| The number of the last stack-like register. This one is the bottom of |
| the stack. |
| @end table |
| |
| @node Register Classes |
| @section Register Classes |
| @cindex register class definitions |
| @cindex class definitions, register |
| |
| On many machines, the numbered registers are not all equivalent. |
| For example, certain registers may not be allowed for indexed addressing; |
| certain registers may not be allowed in some instructions. These machine |
| restrictions are described to the compiler using @dfn{register classes}. |
| |
| You define a number of register classes, giving each one a name and saying |
| which of the registers belong to it. Then you can specify register classes |
| that are allowed as operands to particular instruction patterns. |
| |
| @findex ALL_REGS |
| @findex NO_REGS |
| In general, each register will belong to several classes. In fact, one |
| class must be named @code{ALL_REGS} and contain all the registers. Another |
| class must be named @code{NO_REGS} and contain no registers. Often the |
| union of two classes will be another class; however, this is not required. |
| |
| @findex GENERAL_REGS |
| One of the classes must be named @code{GENERAL_REGS}. There is nothing |
| terribly special about the name, but the operand constraint letters |
| @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is |
| the same as @code{ALL_REGS}, just define it as a macro which expands |
| to @code{ALL_REGS}. |
| |
| Order the classes so that if class @var{x} is contained in class @var{y} |
| then @var{x} has a lower class number than @var{y}. |
| |
| The way classes other than @code{GENERAL_REGS} are specified in operand |
| constraints is through machine-dependent operand constraint letters. |
| You can define such letters to correspond to various classes, then use |
| them in operand constraints. |
| |
| You should define a class for the union of two classes whenever some |
| instruction allows both classes. For example, if an instruction allows |
| either a floating point (coprocessor) register or a general register for a |
| certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} |
| which includes both of them. Otherwise you will get suboptimal code. |
| |
| You must also specify certain redundant information about the register |
| classes: for each class, which classes contain it and which ones are |
| contained in it; for each pair of classes, the largest class contained |
| in their union. |
| |
| When a value occupying several consecutive registers is expected in a |
| certain class, all the registers used must belong to that class. |
| Therefore, register classes cannot be used to enforce a requirement for |
| a register pair to start with an even-numbered register. The way to |
| specify this requirement is with @code{HARD_REGNO_MODE_OK}. |
| |
| Register classes used for input-operands of bitwise-and or shift |
| instructions have a special requirement: each such class must have, for |
| each fixed-point machine mode, a subclass whose registers can transfer that |
| mode to or from memory. For example, on some machines, the operations for |
| single-byte values (@code{QImode}) are limited to certain registers. When |
| this is so, each register class that is used in a bitwise-and or shift |
| instruction must have a subclass consisting of registers from which |
| single-byte values can be loaded or stored. This is so that |
| @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. |
| |
| @table @code |
| @findex enum reg_class |
| @item enum reg_class |
| An enumeral type that must be defined with all the register class names |
| as enumeral values. @code{NO_REGS} must be first. @code{ALL_REGS} |
| must be the last register class, followed by one more enumeral value, |
| @code{LIM_REG_CLASSES}, which is not a register class but rather |
| tells how many classes there are. |
| |
| Each register class has a number, which is the value of casting |
| the class name to type @code{int}. The number serves as an index |
| in many of the tables described below. |
| |
| @findex N_REG_CLASSES |
| @item N_REG_CLASSES |
| The number of distinct register classes, defined as follows: |
| |
| @example |
| #define N_REG_CLASSES (int) LIM_REG_CLASSES |
| @end example |
| |
| @findex REG_CLASS_NAMES |
| @item REG_CLASS_NAMES |
| An initializer containing the names of the register classes as C string |
| constants. These names are used in writing some of the debugging dumps. |
| |
| @findex REG_CLASS_CONTENTS |
| @item REG_CLASS_CONTENTS |
| An initializer containing the contents of the register classes, as integers |
| which are bit masks. The @var{n}th integer specifies the contents of class |
| @var{n}. The way the integer @var{mask} is interpreted is that |
| register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. |
| |
| When the machine has more than 32 registers, an integer does not suffice. |
| Then the integers are replaced by sub-initializers, braced groupings containing |
| several integers. Each sub-initializer must be suitable as an initializer |
| for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. |
| In this situation, the first integer in each sub-initializer corresponds to |
| registers 0 through 31, the second integer to registers 32 through 63, and |
| so on. |
| |
| @findex REGNO_REG_CLASS |
| @item REGNO_REG_CLASS (@var{regno}) |
| A C expression whose value is a register class containing hard register |
| @var{regno}. In general there is more than one such class; choose a class |
| which is @dfn{minimal}, meaning that no smaller class also contains the |
| register. |
| |
| @findex BASE_REG_CLASS |
| @item BASE_REG_CLASS |
| A macro whose definition is the name of the class to which a valid |
| base register must belong. A base register is one used in an address |
| which is the register value plus a displacement. |
| |
| @findex MODE_BASE_REG_CLASS |
| @item MODE_BASE_REG_CLASS (@var{mode}) |
| This is a variation of the @code{BASE_REG_CLASS} macro which allows |
| the selection of a base register in a mode depenedent manner. If |
| @var{mode} is VOIDmode then it should return the same value as |
| @code{BASE_REG_CLASS}. |
| |
| @findex INDEX_REG_CLASS |
| @item INDEX_REG_CLASS |
| A macro whose definition is the name of the class to which a valid |
| index register must belong. An index register is one used in an |
| address where its value is either multiplied by a scale factor or |
| added to another register (as well as added to a displacement). |
| |
| @findex REG_CLASS_FROM_LETTER |
| @item REG_CLASS_FROM_LETTER (@var{char}) |
| A C expression which defines the machine-dependent operand constraint |
| letters for register classes. If @var{char} is such a letter, the |
| value should be the register class corresponding to it. Otherwise, |
| the value should be @code{NO_REGS}. The register letter @samp{r}, |
| corresponding to class @code{GENERAL_REGS}, will not be passed |
| to this macro; you do not need to handle it. |
| |
| @findex REGNO_OK_FOR_BASE_P |
| @item REGNO_OK_FOR_BASE_P (@var{num}) |
| A C expression which is nonzero if register number @var{num} is |
| suitable for use as a base register in operand addresses. It may be |
| either a suitable hard register or a pseudo register that has been |
| allocated such a hard register. |
| |
| @findex REGNO_MODE_OK_FOR_BASE_P |
| @item REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) |
| A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that |
| that expression may examine the mode of the memory reference in |
| @var{mode}. You should define this macro if the mode of the memory |
| reference affects whether a register may be used as a base register. If |
| you define this macro, the compiler will use it instead of |
| @code{REGNO_OK_FOR_BASE_P}. |
| |
| @findex REGNO_OK_FOR_INDEX_P |
| @item REGNO_OK_FOR_INDEX_P (@var{num}) |
| A C expression which is nonzero if register number @var{num} is |
| suitable for use as an index register in operand addresses. It may be |
| either a suitable hard register or a pseudo register that has been |
| allocated such a hard register. |
| |
| The difference between an index register and a base register is that |
| the index register may be scaled. If an address involves the sum of |
| two registers, neither one of them scaled, then either one may be |
| labeled the ``base'' and the other the ``index''; but whichever |
| labeling is used must fit the machine's constraints of which registers |
| may serve in each capacity. The compiler will try both labelings, |
| looking for one that is valid, and will reload one or both registers |
| only if neither labeling works. |
| |
| @findex PREFERRED_RELOAD_CLASS |
| @item PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) |
| A C expression that places additional restrictions on the register class |
| to use when it is necessary to copy value @var{x} into a register in class |
| @var{class}. The value is a register class; perhaps @var{class}, or perhaps |
| another, smaller class. On many machines, the following definition is |
| safe: |
| |
| @example |
| #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS |
| @end example |
| |
| Sometimes returning a more restrictive class makes better code. For |
| example, on the 68000, when @var{x} is an integer constant that is in range |
| for a @samp{moveq} instruction, the value of this macro is always |
| @code{DATA_REGS} as long as @var{class} includes the data registers. |
| Requiring a data register guarantees that a @samp{moveq} will be used. |
| |
| If @var{x} is a @code{const_double}, by returning @code{NO_REGS} |
| you can force @var{x} into a memory constant. This is useful on |
| certain machines where immediate floating values cannot be loaded into |
| certain kinds of registers. |
| |
| @findex PREFERRED_OUTPUT_RELOAD_CLASS |
| @item PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class}) |
| Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of |
| input reloads. If you don't define this macro, the default is to use |
| @var{class}, unchanged. |
| |
| @findex LIMIT_RELOAD_CLASS |
| @item LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) |
| A C expression that places additional restrictions on the register class |
| to use when it is necessary to be able to hold a value of mode |
| @var{mode} in a reload register for which class @var{class} would |
| ordinarily be used. |
| |
| Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when |
| there are certain modes that simply can't go in certain reload classes. |
| |
| The value is a register class; perhaps @var{class}, or perhaps another, |
| smaller class. |
| |
| Don't define this macro unless the target machine has limitations which |
| require the macro to do something nontrivial. |
| |
| @findex SECONDARY_RELOAD_CLASS |
| @findex SECONDARY_INPUT_RELOAD_CLASS |
| @findex SECONDARY_OUTPUT_RELOAD_CLASS |
| @item SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) |
| @itemx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) |
| @itemx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) |
| Many machines have some registers that cannot be copied directly to or |
| from memory or even from other types of registers. An example is the |
| @samp{MQ} register, which on most machines, can only be copied to or |
| from general registers, but not memory. Some machines allow copying all |
| registers to and from memory, but require a scratch register for stores |
| to some memory locations (e.g., those with symbolic address on the RT, |
| and those with certain symbolic address on the Sparc when compiling |
| PIC)@. In some cases, both an intermediate and a scratch register are |
| required. |
| |
| You should define these macros to indicate to the reload phase that it may |
| need to allocate at least one register for a reload in addition to the |
| register to contain the data. Specifically, if copying @var{x} to a |
| register @var{class} in @var{mode} requires an intermediate register, |
| you should define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the |
| largest register class all of whose registers can be used as |
| intermediate registers or scratch registers. |
| |
| If copying a register @var{class} in @var{mode} to @var{x} requires an |
| intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} |
| should be defined to return the largest register class required. If the |
| requirements for input and output reloads are the same, the macro |
| @code{SECONDARY_RELOAD_CLASS} should be used instead of defining both |
| macros identically. |
| |
| The values returned by these macros are often @code{GENERAL_REGS}. |
| Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} |
| can be directly copied to or from a register of @var{class} in |
| @var{mode} without requiring a scratch register. Do not define this |
| macro if it would always return @code{NO_REGS}. |
| |
| If a scratch register is required (either with or without an |
| intermediate register), you should define patterns for |
| @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required |
| (@pxref{Standard Names}. These patterns, which will normally be |
| implemented with a @code{define_expand}, should be similar to the |
| @samp{mov@var{m}} patterns, except that operand 2 is the scratch |
| register. |
| |
| Define constraints for the reload register and scratch register that |
| contain a single register class. If the original reload register (whose |
| class is @var{class}) can meet the constraint given in the pattern, the |
| value returned by these macros is used for the class of the scratch |
| register. Otherwise, two additional reload registers are required. |
| Their classes are obtained from the constraints in the insn pattern. |
| |
| @var{x} might be a pseudo-register or a @code{subreg} of a |
| pseudo-register, which could either be in a hard register or in memory. |
| Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is |
| in memory and the hard register number if it is in a register. |
| |
| These macros should not be used in the case where a particular class of |
| registers can only be copied to memory and not to another class of |
| registers. In that case, secondary reload registers are not needed and |
| would not be helpful. Instead, a stack location must be used to perform |
| the copy and the @code{mov@var{m}} pattern should use memory as an |
| intermediate storage. This case often occurs between floating-point and |
| general registers. |
| |
| @findex SECONDARY_MEMORY_NEEDED |
| @item SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m}) |
| Certain machines have the property that some registers cannot be copied |
| to some other registers without using memory. Define this macro on |
| those machines to be a C expression that is nonzero if objects of mode |
| @var{m} in registers of @var{class1} can only be copied to registers of |
| class @var{class2} by storing a register of @var{class1} into memory |
| and loading that memory location into a register of @var{class2}. |
| |
| Do not define this macro if its value would always be zero. |
| |
| @findex SECONDARY_MEMORY_NEEDED_RTX |
| @item SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) |
| Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler |
| allocates a stack slot for a memory location needed for register copies. |
| If this macro is defined, the compiler instead uses the memory location |
| defined by this macro. |
| |
| Do not define this macro if you do not define |
| @code{SECONDARY_MEMORY_NEEDED}. |
| |
| @findex SECONDARY_MEMORY_NEEDED_MODE |
| @item SECONDARY_MEMORY_NEEDED_MODE (@var{mode}) |
| When the compiler needs a secondary memory location to copy between two |
| registers of mode @var{mode}, it normally allocates sufficient memory to |
| hold a quantity of @code{BITS_PER_WORD} bits and performs the store and |
| load operations in a mode that many bits wide and whose class is the |
| same as that of @var{mode}. |
| |
| This is right thing to do on most machines because it ensures that all |
| bits of the register are copied and prevents accesses to the registers |
| in a narrower mode, which some machines prohibit for floating-point |
| registers. |
| |
| However, this default behavior is not correct on some machines, such as |
| the DEC Alpha, that store short integers in floating-point registers |
| differently than in integer registers. On those machines, the default |
| widening will not work correctly and you must define this macro to |
| suppress that widening in some cases. See the file @file{alpha.h} for |
| details. |
| |
| Do not define this macro if you do not define |
| @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that |
| is @code{BITS_PER_WORD} bits wide is correct for your machine. |
| |
| @findex SMALL_REGISTER_CLASSES |
| @item SMALL_REGISTER_CLASSES |
| On some machines, it is risky to let hard registers live across arbitrary |
| insns. Typically, these machines have instructions that require values |
| to be in specific registers (like an accumulator), and reload will fail |
| if the required hard register is used for another purpose across such an |
| insn. |
| |
| Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero |
| value on these machines. When this macro has a nonzero value, the |
| compiler will try to minimize the lifetime of hard registers. |
| |
| It is always safe to define this macro with a nonzero value, but if you |
| unnecessarily define it, you will reduce the amount of optimizations |
| that can be performed in some cases. If you do not define this macro |
| with a nonzero value when it is required, the compiler will run out of |
| spill registers and print a fatal error message. For most machines, you |
| should not define this macro at all. |
| |
| @findex CLASS_LIKELY_SPILLED_P |
| @item CLASS_LIKELY_SPILLED_P (@var{class}) |
| A C expression whose value is nonzero if pseudos that have been assigned |
| to registers of class @var{class} would likely be spilled because |
| registers of @var{class} are needed for spill registers. |
| |
| The default value of this macro returns 1 if @var{class} has exactly one |
| register and zero otherwise. On most machines, this default should be |
| used. Only define this macro to some other expression if pseudos |
| allocated by @file{local-alloc.c} end up in memory because their hard |
| registers were needed for spill registers. If this macro returns nonzero |
| for those classes, those pseudos will only be allocated by |
| @file{global.c}, which knows how to reallocate the pseudo to another |
| register. If there would not be another register available for |
| reallocation, you should not change the definition of this macro since |
| the only effect of such a definition would be to slow down register |
| allocation. |
| |
| @findex CLASS_MAX_NREGS |
| @item CLASS_MAX_NREGS (@var{class}, @var{mode}) |
| A C expression for the maximum number of consecutive registers |
| of class @var{class} needed to hold a value of mode @var{mode}. |
| |
| This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact, |
| the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} |
| should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, |
| @var{mode})} for all @var{regno} values in the class @var{class}. |
| |
| This macro helps control the handling of multiple-word values |
| in the reload pass. |
| |
| @item CLASS_CANNOT_CHANGE_MODE |
| If defined, a C expression for a class that contains registers for |
| which the compiler may not change modes arbitrarily. |
| |
| @item CLASS_CANNOT_CHANGE_MODE_P(@var{from}, @var{to}) |
| A C expression that is true if, for a register in |
| @code{CLASS_CANNOT_CHANGE_MODE}, the requested mode punning is invalid. |
| |
| For the example, loading 32-bit integer or floating-point objects into |
| floating-point registers on the Alpha extends them to 64-bits. |
| Therefore loading a 64-bit object and then storing it as a 32-bit object |
| does not store the low-order 32-bits, as would be the case for a normal |
| register. Therefore, @file{alpha.h} defines @code{CLASS_CANNOT_CHANGE_MODE} |
| as @code{FLOAT_REGS} and @code{CLASS_CANNOT_CHANGE_MODE_P} restricts |
| mode changes to same-size modes. |
| |
| Compare this to IA-64, which extends floating-point values to 82-bits, |
| and stores 64-bit integers in a different format than 64-bit doubles. |
| Therefore @code{CLASS_CANNOT_CHANGE_MODE_P} is always true. |
| @end table |
| |
| Three other special macros describe which operands fit which constraint |
| letters. |
| |
| @table @code |
| @findex CONST_OK_FOR_LETTER_P |
| @item CONST_OK_FOR_LETTER_P (@var{value}, @var{c}) |
| A C expression that defines the machine-dependent operand constraint |
| letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify |
| particular ranges of integer values. If @var{c} is one of those |
| letters, the expression should check that @var{value}, an integer, is in |
| the appropriate range and return 1 if so, 0 otherwise. If @var{c} is |
| not one of those letters, the value should be 0 regardless of |
| @var{value}. |
| |
| @findex CONST_DOUBLE_OK_FOR_LETTER_P |
| @item CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c}) |
| A C expression that defines the machine-dependent operand constraint |
| letters that specify particular ranges of @code{const_double} values |
| (@samp{G} or @samp{H}). |
| |
| If @var{c} is one of those letters, the expression should check that |
| @var{value}, an RTX of code @code{const_double}, is in the appropriate |
| range and return 1 if so, 0 otherwise. If @var{c} is not one of those |
| letters, the value should be 0 regardless of @var{value}. |
| |
| @code{const_double} is used for all floating-point constants and for |
| @code{DImode} fixed-point constants. A given letter can accept either |
| or both kinds of values. It can use @code{GET_MODE} to distinguish |
| between these kinds. |
| |
| @findex EXTRA_CONSTRAINT |
| @item EXTRA_CONSTRAINT (@var{value}, @var{c}) |
| A C expression that defines the optional machine-dependent constraint |
| letters that can be used to segregate specific types of operands, usually |
| memory references, for the target machine. Any letter that is not |
| elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} |
| may be used. Normally this macro will not be defined. |
| |
| If it is required for a particular target machine, it should return 1 |
| if @var{value} corresponds to the operand type represented by the |
| constraint letter @var{c}. If @var{c} is not defined as an extra |
| constraint, the value returned should be 0 regardless of @var{value}. |
| |
| For example, on the ROMP, load instructions cannot have their output |
| in r0 if the memory reference contains a symbolic address. Constraint |
| letter @samp{Q} is defined as representing a memory address that does |
| @emph{not} contain a symbolic address. An alternative is specified with |
| a @samp{Q} constraint on the input and @samp{r} on the output. The next |
| alternative specifies @samp{m} on the input and a register class that |
| does not include r0 on the output. |
| @end table |
| |
| @node Stack and Calling |
| @section Stack Layout and Calling Conventions |
| @cindex calling conventions |
| |
| @c prevent bad page break with this line |
| This describes the stack layout and calling conventions. |
| |
| @menu |
| * Frame Layout:: |
| * Exception Handling:: |
| * Stack Checking:: |
| * Frame Registers:: |
| * Elimination:: |
| * Stack Arguments:: |
| * Register Arguments:: |
| * Scalar Return:: |
| * Aggregate Return:: |
| * Caller Saves:: |
| * Function Entry:: |
| * Profiling:: |
| * Tail Calls:: |
| @end menu |
| |
| @node Frame Layout |
| @subsection Basic Stack Layout |
| @cindex stack frame layout |
| @cindex frame layout |
| |
| @c prevent bad page break with this line |
| Here is the basic stack layout. |
| |
| @table @code |
| @findex STACK_GROWS_DOWNWARD |
| @item STACK_GROWS_DOWNWARD |
| Define this macro if pushing a word onto the stack moves the stack |
| pointer to a smaller address. |
| |
| When we say, ``define this macro if @dots{},'' it means that the |
| compiler checks this macro only with @code{#ifdef} so the precise |
| definition used does not matter. |
| |
| @findex STACK_PUSH_CODE |
| @item STACK_PUSH_CODE |
| |
| This macro defines the operation used when something is pushed |
| on the stack. In RTL, a push operation will be |
| @code{(set (mem (STACK_PUSH_CODE (reg sp))) ...)} |
| |
| The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, |
| and @code{POST_INC}. Which of these is correct depends on |
| the stack direction and on whether the stack pointer points |
| to the last item on the stack or whether it points to the |
| space for the next item on the stack. |
| |
| The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is |
| defined, which is almost always right, and @code{PRE_INC} otherwise, |
| which is often wrong. |
| |
| @findex FRAME_GROWS_DOWNWARD |
| @item FRAME_GROWS_DOWNWARD |
| Define this macro if the addresses of local variable slots are at negative |
| offsets from the frame pointer. |
| |
| @findex ARGS_GROW_DOWNWARD |
| @item ARGS_GROW_DOWNWARD |
| Define this macro if successive arguments to a function occupy decreasing |
| addresses on the stack. |
| |
| @findex STARTING_FRAME_OFFSET |
| @item STARTING_FRAME_OFFSET |
| Offset from the frame pointer to the first local variable slot to be allocated. |
| |
| If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by |
| subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}. |
| Otherwise, it is found by adding the length of the first slot to the |
| value @code{STARTING_FRAME_OFFSET}. |
| @c i'm not sure if the above is still correct.. had to change it to get |
| @c rid of an overfull. --mew 2feb93 |
| |
| @findex STACK_POINTER_OFFSET |
| @item STACK_POINTER_OFFSET |
| Offset from the stack pointer register to the first location at which |
| outgoing arguments are placed. If not specified, the default value of |
| zero is used. This is the proper value for most machines. |
| |
| If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above |
| the first location at which outgoing arguments are placed. |
| |
| @findex FIRST_PARM_OFFSET |
| @item FIRST_PARM_OFFSET (@var{fundecl}) |
| Offset from the argument pointer register to the first argument's |
| address. On some machines it may depend on the data type of the |
| function. |
| |
| If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above |
| the first argument's address. |
| |
| @findex STACK_DYNAMIC_OFFSET |
| @item STACK_DYNAMIC_OFFSET (@var{fundecl}) |
| Offset from the stack pointer register to an item dynamically allocated |
| on the stack, e.g., by @code{alloca}. |
| |
| The default value for this macro is @code{STACK_POINTER_OFFSET} plus the |
| length of the outgoing arguments. The default is correct for most |
| machines. See @file{function.c} for details. |
| |
| @findex DYNAMIC_CHAIN_ADDRESS |
| @item DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) |
| A C expression whose value is RTL representing the address in a stack |
| frame where the pointer to the caller's frame is stored. Assume that |
| @var{frameaddr} is an RTL expression for the address of the stack frame |
| itself. |
| |
| If you don't define this macro, the default is to return the value |
| of @var{frameaddr}---that is, the stack frame address is also the |
| address of the stack word that points to the previous frame. |
| |
| @findex SETUP_FRAME_ADDRESSES |
| @item SETUP_FRAME_ADDRESSES |
| If defined, a C expression that produces the machine-specific code to |
| setup the stack so that arbitrary frames can be accessed. For example, |
| on the Sparc, we must flush all of the register windows to the stack |
| before we can access arbitrary stack frames. You will seldom need to |
| define this macro. |
| |
| @findex BUILTIN_SETJMP_FRAME_VALUE |
| @item BUILTIN_SETJMP_FRAME_VALUE |
| If defined, a C expression that contains an rtx that is used to store |
| the address of the current frame into the built in @code{setjmp} buffer. |
| The default value, @code{virtual_stack_vars_rtx}, is correct for most |
| machines. One reason you may need to define this macro is if |
| @code{hard_frame_pointer_rtx} is the appropriate value on your machine. |
| |
| @findex RETURN_ADDR_RTX |
| @item RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) |
| A C expression whose value is RTL representing the value of the return |
| address for the frame @var{count} steps up from the current frame, after |
| the prologue. @var{frameaddr} is the frame pointer of the @var{count} |
| frame, or the frame pointer of the @var{count} @minus{} 1 frame if |
| @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined. |
| |
| The value of the expression must always be the correct address when |
| @var{count} is zero, but may be @code{NULL_RTX} if there is not way to |
| determine the return address of other frames. |
| |
| @findex RETURN_ADDR_IN_PREVIOUS_FRAME |
| @item RETURN_ADDR_IN_PREVIOUS_FRAME |
| Define this if the return address of a particular stack frame is accessed |
| from the frame pointer of the previous stack frame. |
| |
| @findex INCOMING_RETURN_ADDR_RTX |
| @item INCOMING_RETURN_ADDR_RTX |
| A C expression whose value is RTL representing the location of the |
| incoming return address at the beginning of any function, before the |
| prologue. This RTL is either a @code{REG}, indicating that the return |
| value is saved in @samp{REG}, or a @code{MEM} representing a location in |
| the stack. |
| |
| You only need to define this macro if you want to support call frame |
| debugging information like that provided by DWARF 2. |
| |
| If this RTL is a @code{REG}, you should also define |
| @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. |
| |
| @findex INCOMING_FRAME_SP_OFFSET |
| @item INCOMING_FRAME_SP_OFFSET |
| A C expression whose value is an integer giving the offset, in bytes, |
| from the value of the stack pointer register to the top of the stack |
| frame at the beginning of any function, before the prologue. The top of |
| the frame is defined to be the value of the stack pointer in the |
| previous frame, just before the call instruction. |
| |
| You only need to define this macro if you want to support call frame |
| debugging information like that provided by DWARF 2. |
| |
| @findex ARG_POINTER_CFA_OFFSET |
| @item ARG_POINTER_CFA_OFFSET (@var{fundecl}) |
| A C expression whose value is an integer giving the offset, in bytes, |
| from the argument pointer to the canonical frame address (cfa). The |
| final value should coincide with that calculated by |
| @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable |
| during virtual register instantiation. |
| |
| The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)}, |
| which is correct for most machines; in general, the arguments are found |
| immediately before the stack frame. Note that this is not the case on |
| some targets that save registers into the caller's frame, such as SPARC |
| and rs6000, and so such targets need to define this macro. |
| |
| You only need to define this macro if the default is incorrect, and you |
| want to support call frame debugging information like that provided by |
| DWARF 2. |
| |
| @findex SMALL_STACK |
| @item SMALL_STACK |
| Define this macro if the stack size for the target is very small. This |
| has the effect of disabling gcc's built-in @samp{alloca}, though |
| @samp{__builtin_alloca} is not affected. |
| @end table |
| |
| @node Exception Handling |
| @subsection Exception Handling Support |
| @cindex exception handling |
| |
| @table @code |
| @findex EH_RETURN_DATA_REGNO |
| @item EH_RETURN_DATA_REGNO (@var{N}) |
| A C expression whose value is the @var{N}th register number used for |
| data by exception handlers, or @code{INVALID_REGNUM} if fewer than |
| @var{N} registers are usable. |
| |
| The exception handling library routines communicate with the exception |
| handlers via a set of agreed upon registers. Ideally these registers |
| should be call-clobbered; it is possible to use call-saved registers, |
| but may negatively impact code size. The target must support at least |
| 2 data registers, but should define 4 if there are enough free registers. |
| |
| You must define this macro if you want to support call frame exception |
| handling like that provided by DWARF 2. |
| |
| @findex EH_RETURN_STACKADJ_RTX |
| @item EH_RETURN_STACKADJ_RTX |
| A C expression whose value is RTL representing a location in which |
| to store a stack adjustment to be applied before function return. |
| This is used to unwind the stack to an exception handler's call frame. |
| It will be assigned zero on code paths that return normally. |
| |
| Typically this is a call-clobbered hard register that is otherwise |
| untouched by the epilogue, but could also be a stack slot. |
| |
| You must define this macro if you want to support call frame exception |
| handling like that provided by DWARF 2. |
| |
| @findex EH_RETURN_HANDLER_RTX |
| @item EH_RETURN_HANDLER_RTX |
| A C expression whose value is RTL representing a location in which |
| to store the address of an exception handler to which we should |
| return. It will not be assigned on code paths that return normally. |
| |
| Typically this is the location in the call frame at which the normal |
| return address is stored. For targets that return by popping an |
| address off the stack, this might be a memory address just below |
| the @emph{target} call frame rather than inside the current call |
| frame. @code{EH_RETURN_STACKADJ_RTX} will have already been assigned, |
| so it may be used to calculate the location of the target call frame. |
| |
| Some targets have more complex requirements than storing to an |
| address calculable during initial code generation. In that case |
| the @code{eh_return} instruction pattern should be used instead. |
| |
| If you want to support call frame exception handling, you must |
| define either this macro or the @code{eh_return} instruction pattern. |
| |
| @findex ASM_PREFERRED_EH_DATA_FORMAT |
| @item ASM_PREFERRED_EH_DATA_FORMAT(@var{code}, @var{global}) |
| This macro chooses the encoding of pointers embedded in the exception |
| handling sections. If at all possible, this should be defined such |
| that the exception handling section will not require dynamic relocations, |
| and so may be read-only. |
| |
| @var{code} is 0 for data, 1 for code labels, 2 for function pointers. |
| @var{global} is true if the symbol may be affected by dynamic relocations. |
| The macro should return a combination of the @code{DW_EH_PE_*} defines |
| as found in @file{dwarf2.h}. |
| |
| If this macro is not defined, pointers will not be encoded but |
| represented directly. |
| |
| @findex ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX |
| @item ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX(@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) |
| This macro allows the target to emit whatever special magic is required |
| to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. |
| Generic code takes care of pc-relative and indirect encodings; this must |
| be defined if the target uses text-relative or data-relative encodings. |
| |
| This is a C statement that branches to @var{done} if the format was |
| handled. @var{encoding} is the format chosen, @var{size} is the number |
| of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} |
| to be emitted. |
| |
| @findex MD_FALLBACK_FRAME_STATE_FOR |
| @item MD_FALLBACK_FRAME_STATE_FOR(@var{context}, @var{fs}, @var{success}) |
| This macro allows the target to add cpu and operating system specific |
| code to the call-frame unwinder for use when there is no unwind data |
| available. The most common reason to implement this macro is to unwind |
| through signal frames. |
| |
| This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c} |
| and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; |
| @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} |
| for the address of the code being executed and @code{context->cfa} for |
| the stack pointer value. If the frame can be decoded, the register save |
| addresses should be updated in @var{fs} and the macro should branch to |
| @var{success}. If the frame cannot be decoded, the macro should do |
| nothing. |
| @end table |
| |
| @node Stack Checking |
| @subsection Specifying How Stack Checking is Done |
| |
| GCC will check that stack references are within the boundaries of |
| the stack, if the @option{-fstack-check} is specified, in one of three ways: |
| |
| @enumerate |
| @item |
| If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC |
| will assume that you have arranged for stack checking to be done at |
| appropriate places in the configuration files, e.g., in |
| @code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special |
| processing. |
| |
| @item |
| If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern |
| called @code{check_stack} in your @file{md} file, GCC will call that |
| pattern with one argument which is the address to compare the stack |
| value against. You must arrange for this pattern to report an error if |
| the stack pointer is out of range. |
| |
| @item |
| If neither of the above are true, GCC will generate code to periodically |
| ``probe'' the stack pointer using the values of the macros defined below. |
| @end enumerate |
| |
| Normally, you will use the default values of these macros, so GCC |
| will use the third approach. |
| |
| @table @code |
| @findex STACK_CHECK_BUILTIN |
| @item STACK_CHECK_BUILTIN |
| A nonzero value if stack checking is done by the configuration files in a |
| machine-dependent manner. You should define this macro if stack checking |
| is require by the ABI of your machine or if you would like to have to stack |
| checking in some more efficient way than GCC's portable approach. |
| The default value of this macro is zero. |
| |
| @findex STACK_CHECK_PROBE_INTERVAL |
| @item STACK_CHECK_PROBE_INTERVAL |
| An integer representing the interval at which GCC must generate stack |
| probe instructions. You will normally define this macro to be no larger |
| than the size of the ``guard pages'' at the end of a stack area. The |
| default value of 4096 is suitable for most systems. |
| |
| @findex STACK_CHECK_PROBE_LOAD |
| @item STACK_CHECK_PROBE_LOAD |
| A integer which is nonzero if GCC should perform the stack probe |
| as a load instruction and zero if GCC should use a store instruction. |
| The default is zero, which is the most efficient choice on most systems. |
| |
| @findex STACK_CHECK_PROTECT |
| @item STACK_CHECK_PROTECT |
| The number of bytes of stack needed to recover from a stack overflow, |
| for languages where such a recovery is supported. The default value of |
| 75 words should be adequate for most machines. |
| |
| @findex STACK_CHECK_MAX_FRAME_SIZE |
| @item STACK_CHECK_MAX_FRAME_SIZE |
| The maximum size of a stack frame, in bytes. GCC will generate probe |
| instructions in non-leaf functions to ensure at least this many bytes of |
| stack are available. If a stack frame is larger than this size, stack |
| checking will not be reliable and GCC will issue a warning. The |
| default is chosen so that GCC only generates one instruction on most |
| systems. You should normally not change the default value of this macro. |
| |
| @findex STACK_CHECK_FIXED_FRAME_SIZE |
| @item STACK_CHECK_FIXED_FRAME_SIZE |
| GCC uses this value to generate the above warning message. It |
| represents the amount of fixed frame used by a function, not including |
| space for any callee-saved registers, temporaries and user variables. |
| You need only specify an upper bound for this amount and will normally |
| use the default of four words. |
| |
| @findex STACK_CHECK_MAX_VAR_SIZE |
| @item STACK_CHECK_MAX_VAR_SIZE |
| The maximum size, in bytes, of an object that GCC will place in the |
| fixed area of the stack frame when the user specifies |
| @option{-fstack-check}. |
| GCC computed the default from the values of the above macros and you will |
| normally not need to override that default. |
| @end table |
| |
| @need 2000 |
| @node Frame Registers |
| @subsection Registers That Address the Stack Frame |
| |
| @c prevent bad page break with this line |
| This discusses registers that address the stack frame. |
| |
| @table @code |
| @findex STACK_POINTER_REGNUM |
| @item STACK_POINTER_REGNUM |
| The register number of the stack pointer register, which must also be a |
| fixed register according to @code{FIXED_REGISTERS}. On most machines, |
| the hardware determines which register this is. |
| |
| @findex FRAME_POINTER_REGNUM |
| @item FRAME_POINTER_REGNUM |
| The register number of the frame pointer register, which is used to |
| access automatic variables in the stack frame. On some machines, the |
| hardware determines which register this is. On other machines, you can |
| choose any register you wish for this purpose. |
| |
| @findex HARD_FRAME_POINTER_REGNUM |
| @item HARD_FRAME_POINTER_REGNUM |
| On some machines the offset between the frame pointer and starting |
| offset of the automatic variables is not known until after register |
| allocation has been done (for example, because the saved registers are |
| between these two locations). On those machines, define |
| @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to |
| be used internally until the offset is known, and define |
| @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number |
| used for the frame pointer. |
| |
| You should define this macro only in the very rare circumstances when it |
| is not possible to calculate the offset between the frame pointer and |
| the automatic variables until after register allocation has been |
| completed. When this macro is defined, you must also indicate in your |
| definition of @code{ELIMINABLE_REGS} how to eliminate |
| @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} |
| or @code{STACK_POINTER_REGNUM}. |
| |
| Do not define this macro if it would be the same as |
| @code{FRAME_POINTER_REGNUM}. |
| |
| @findex ARG_POINTER_REGNUM |
| @item ARG_POINTER_REGNUM |
| The register number of the arg pointer register, which is used to access |
| the function's argument list. On some machines, this is the same as the |
| frame pointer register. On some machines, the hardware determines which |
| register this is. On other machines, you can choose any register you |
| wish for this purpose. If this is not the same register as the frame |
| pointer register, then you must mark it as a fixed register according to |
| @code{FIXED_REGISTERS}, or arrange to be able to eliminate it |
| (@pxref{Elimination}). |
| |
| @findex RETURN_ADDRESS_POINTER_REGNUM |
| @item RETURN_ADDRESS_POINTER_REGNUM |
| The register number of the return address pointer register, which is used to |
| access the current function's return address from the stack. On some |
| machines, the return address is not at a fixed offset from the frame |
| pointer or stack pointer or argument pointer. This register can be defined |
| to point to the return address on the stack, and then be converted by |
| @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. |
| |
| Do not define this macro unless there is no other way to get the return |
| address from the stack. |
| |
| @findex STATIC_CHAIN_REGNUM |
| @findex STATIC_CHAIN_INCOMING_REGNUM |
| @item STATIC_CHAIN_REGNUM |
| @itemx STATIC_CHAIN_INCOMING_REGNUM |
| Register numbers used for passing a function's static chain pointer. If |
| register windows are used, the register number as seen by the called |
| function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register |
| number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If |
| these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need |
| not be defined. |
| |
| The static chain register need not be a fixed register. |
| |
| If the static chain is passed in memory, these macros should not be |
| defined; instead, the next two macros should be defined. |
| |
| @findex STATIC_CHAIN |
| @findex STATIC_CHAIN_INCOMING |
| @item STATIC_CHAIN |
| @itemx STATIC_CHAIN_INCOMING |
| If the static chain is passed in memory, these macros provide rtx giving |
| @code{mem} expressions that denote where they are stored. |
| @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations |
| as seen by the calling and called functions, respectively. Often the former |
| will be at an offset from the stack pointer and the latter at an offset from |
| the frame pointer. |
| |
| @findex stack_pointer_rtx |
| @findex frame_pointer_rtx |
| @findex arg_pointer_rtx |
| The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and |
| @code{arg_pointer_rtx} will have been initialized prior to the use of these |
| macros and should be used to refer to those items. |
| |
| If the static chain is passed in a register, the two previous macros should |
| be defined instead. |
| |
| @findex DWARF_FRAME_REGISTERS |
| @item DWARF_FRAME_REGISTERS |
| This macro specifies the maximum number of hard registers that can be |
| saved in a call frame. This is used to size data structures used in |
| DWARF2 exception handling. |
| |
| Prior to GCC 3.0, this macro was needed in order to establish a stable |
| exception handling ABI in the face of adding new hard registers for ISA |
| extensions. In GCC 3.0 and later, the EH ABI is insulated from changes |
| in the number of hard registers. Nevertheless, this macro can still be |
| used to reduce the runtime memory requirements of the exception handling |
| routines, which can be substantial if the ISA contains a lot of |
| registers that are not call-saved. |
| |
| If this macro is not defined, it defaults to |
| @code{FIRST_PSEUDO_REGISTER}. |
| |
| @findex PRE_GCC3_DWARF_FRAME_REGISTERS |
| @item PRE_GCC3_DWARF_FRAME_REGISTERS |
| |
| This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided |
| for backward compatibility in pre GCC 3.0 compiled code. |
| |
| If this macro is not defined, it defaults to |
| @code{DWARF_FRAME_REGISTERS}. |
| |
| @end table |
| |
| @node Elimination |
| @subsection Eliminating Frame Pointer and Arg Pointer |
| |
| @c prevent bad page break with this line |
| This is about eliminating the frame pointer and arg pointer. |
| |
| @table @code |
| @findex FRAME_POINTER_REQUIRED |
| @item FRAME_POINTER_REQUIRED |
| A C expression which is nonzero if a function must have and use a frame |
| pointer. This expression is evaluated in the reload pass. If its value is |
| nonzero the function will have a frame pointer. |
| |
| The expression can in principle examine the current function and decide |
| according to the facts, but on most machines the constant 0 or the |
| constant 1 suffices. Use 0 when the machine allows code to be generated |
| with no frame pointer, and doing so saves some time or space. Use 1 |
| when there is no possible advantage to avoiding a frame pointer. |
| |
| In certain cases, the compiler does not know how to produce valid code |
| without a frame pointer. The compiler recognizes those cases and |
| automatically gives the function a frame pointer regardless of what |
| @code{FRAME_POINTER_REQUIRED} says. You don't need to worry about |
| them. |
| |
| In a function that does not require a frame pointer, the frame pointer |
| register can be allocated for ordinary usage, unless you mark it as a |
| fixed register. See @code{FIXED_REGISTERS} for more information. |
| |
| @findex INITIAL_FRAME_POINTER_OFFSET |
| @findex get_frame_size |
| @item INITIAL_FRAME_POINTER_OFFSET (@var{depth-var}) |
| A C statement to store in the variable @var{depth-var} the difference |
| between the frame pointer and the stack pointer values immediately after |
| the function prologue. The value would be computed from information |
| such as the result of @code{get_frame_size ()} and the tables of |
| registers @code{regs_ever_live} and @code{call_used_regs}. |
| |
| If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and |
| need not be defined. Otherwise, it must be defined even if |
| @code{FRAME_POINTER_REQUIRED} is defined to always be true; in that |
| case, you may set @var{depth-var} to anything. |
| |
| @findex ELIMINABLE_REGS |
| @item ELIMINABLE_REGS |
| If defined, this macro specifies a table of register pairs used to |
| eliminate unneeded registers that point into the stack frame. If it is not |
| defined, the only elimination attempted by the compiler is to replace |
| references to the frame pointer with references to the stack pointer. |
| |
| The definition of this macro is a list of structure initializations, each |
| of which specifies an original and replacement register. |
| |
| On some machines, the position of the argument pointer is not known until |
| the compilation is completed. In such a case, a separate hard register |
| must be used for the argument pointer. This register can be eliminated by |
| replacing it with either the frame pointer or the argument pointer, |
| depending on whether or not the frame pointer has been eliminated. |
| |
| In this case, you might specify: |
| @example |
| #define ELIMINABLE_REGS \ |
| @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ |
| @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ |
| @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} |
| @end example |
| |
| Note that the elimination of the argument pointer with the stack pointer is |
| specified first since that is the preferred elimination. |
| |
| @findex CAN_ELIMINATE |
| @item CAN_ELIMINATE (@var{from-reg}, @var{to-reg}) |
| A C expression that returns nonzero if the compiler is allowed to try |
| to replace register number @var{from-reg} with register number |
| @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS} |
| is defined, and will usually be the constant 1, since most of the cases |
| preventing register elimination are things that the compiler already |
| knows about. |
| |
| @findex INITIAL_ELIMINATION_OFFSET |
| @item INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) |
| This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It |
| specifies the initial difference between the specified pair of |
| registers. This macro must be defined if @code{ELIMINABLE_REGS} is |
| defined. |
| @end table |
| |
| @node Stack Arguments |
| @subsection Passing Function Arguments on the Stack |
| @cindex arguments on stack |
| @cindex stack arguments |
| |
| The macros in this section control how arguments are passed |
| on the stack. See the following section for other macros that |
| control passing certain arguments in registers. |
| |
| @table @code |
| @findex PROMOTE_PROTOTYPES |
| @item PROMOTE_PROTOTYPES |
| A C expression whose value is nonzero if an argument declared in |
| a prototype as an integral type smaller than @code{int} should |
| actually be passed as an @code{int}. In addition to avoiding |
| errors in certain cases of mismatch, it also makes for better |
| code on certain machines. If the macro is not defined in target |
| header files, it defaults to 0. |
| |
| @findex PUSH_ARGS |
| @item PUSH_ARGS |
| A C expression. If nonzero, push insns will be used to pass |
| outgoing arguments. |
| If the target machine does not have a push instruction, set it to zero. |
| That directs GCC to use an alternate strategy: to |
| allocate the entire argument block and then store the arguments into |
| it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too. |
| On some machines, the definition |
| |
| @findex PUSH_ROUNDING |
| @item PUSH_ROUNDING (@var{npushed}) |
| A C expression that is the number of bytes actually pushed onto the |
| stack when an instruction attempts to push @var{npushed} bytes. |
| |
| On some machines, the definition |
| |
| @example |
| #define PUSH_ROUNDING(BYTES) (BYTES) |
| @end example |
| |
| @noindent |
| will suffice. But on other machines, instructions that appear |
| to push one byte actually push two bytes in an attempt to maintain |
| alignment. Then the definition should be |
| |
| @example |
| #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) |
| @end example |
| |
| @findex ACCUMULATE_OUTGOING_ARGS |
| @findex current_function_outgoing_args_size |
| @item ACCUMULATE_OUTGOING_ARGS |
| A C expression. If nonzero, the maximum amount of space required for outgoing arguments |
| will be computed and placed into the variable |
| @code{current_function_outgoing_args_size}. No space will be pushed |
| onto the stack for each call; instead, the function prologue should |
| increase the stack frame size by this amount. |
| |
| Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} |
| is not proper. |
| |
| @findex REG_PARM_STACK_SPACE |
| @item REG_PARM_STACK_SPACE (@var{fndecl}) |
| Define this macro if functions should assume that stack space has been |
| allocated for arguments even when their values are passed in |
| registers. |
| |
| The value of this macro is the size, in bytes, of the area reserved for |
| arguments passed in registers for the function represented by @var{fndecl}, |
| which can be zero if GCC is calling a library function. |
| |
| This space can be allocated by the caller, or be a part of the |
| machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says |
| which. |
| @c above is overfull. not sure what to do. --mew 5feb93 did |
| @c something, not sure if it looks good. --mew 10feb93 |
| |
| @findex MAYBE_REG_PARM_STACK_SPACE |
| @findex FINAL_REG_PARM_STACK_SPACE |
| @item MAYBE_REG_PARM_STACK_SPACE |
| @itemx FINAL_REG_PARM_STACK_SPACE (@var{const_size}, @var{var_size}) |
| Define these macros in addition to the one above if functions might |
| allocate stack space for arguments even when their values are passed |
| in registers. These should be used when the stack space allocated |
| for arguments in registers is not a simple constant independent of the |
| function declaration. |
| |
| The value of the first macro is the size, in bytes, of the area that |
| we should initially assume would be reserved for arguments passed in registers. |
| |
| The value of the second macro is the actual size, in bytes, of the area |
| that will be reserved for arguments passed in registers. This takes two |
| arguments: an integer representing the number of bytes of fixed sized |
| arguments on the stack, and a tree representing the number of bytes of |
| variable sized arguments on the stack. |
| |
| When these macros are defined, @code{REG_PARM_STACK_SPACE} will only be |
| called for libcall functions, the current function, or for a function |
| being called when it is known that such stack space must be allocated. |
| In each case this value can be easily computed. |
| |
| When deciding whether a called function needs such stack space, and how |
| much space to reserve, GCC uses these two macros instead of |
| @code{REG_PARM_STACK_SPACE}. |
| |
| @findex OUTGOING_REG_PARM_STACK_SPACE |
| @item OUTGOING_REG_PARM_STACK_SPACE |
| Define this if it is the responsibility of the caller to allocate the area |
| reserved for arguments passed in registers. |
| |
| If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls |
| whether the space for these arguments counts in the value of |
| @code{current_function_outgoing_args_size}. |
| |
| @findex STACK_PARMS_IN_REG_PARM_AREA |
| @item STACK_PARMS_IN_REG_PARM_AREA |
| Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the |
| stack parameters don't skip the area specified by it. |
| @c i changed this, makes more sens and it should have taken care of the |
| @c overfull.. not as specific, tho. --mew 5feb93 |
| |
| Normally, when a parameter is not passed in registers, it is placed on the |
| stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro |
| suppresses this behavior and causes the parameter to be passed on the |
| stack in its natural location. |
| |
| @findex RETURN_POPS_ARGS |
| @item RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size}) |
| A C expression that should indicate the number of bytes of its own |
| arguments that a function pops on returning, or 0 if the |
| function pops no arguments and the caller must therefore pop them all |
| after the function returns. |
| |
| @var{fundecl} is a C variable whose value is a tree node that describes |
| the function in question. Normally it is a node of type |
| @code{FUNCTION_DECL} that describes the declaration of the function. |
| From this you can obtain the @code{DECL_ATTRIBUTES} of the function. |
| |
| @var{funtype} is a C variable whose value is a tree node that |
| describes the function in question. Normally it is a node of type |
| @code{FUNCTION_TYPE} that describes the data type of the function. |
| From this it is possible to obtain the data types of the value and |
| arguments (if known). |
| |
| When a call to a library function is being considered, @var{fundecl} |
| will contain an identifier node for the library function. Thus, if |
| you need to distinguish among various library functions, you can do so |
| by their names. Note that ``library function'' in this context means |
| a function used to perform arithmetic, whose name is known specially |
| in the compiler and was not mentioned in the C code being compiled. |
| |
| @var{stack-size} is the number of bytes of arguments passed on the |
| stack. If a variable number of bytes is passed, it is zero, and |
| argument popping will always be the responsibility of the calling function. |
| |
| On the VAX, all functions always pop their arguments, so the definition |
| of this macro is @var{stack-size}. On the 68000, using the standard |
| calling convention, no functions pop their arguments, so the value of |
| the macro is always 0 in this case. But an alternative calling |
| convention is available in which functions that take a fixed number of |
| arguments pop them but other functions (such as @code{printf}) pop |
| nothing (the caller pops all). When this convention is in use, |
| @var{funtype} is examined to determine whether a function takes a fixed |
| number of arguments. |
| |
| @findex CALL_POPS_ARGS |
| @item CALL_POPS_ARGS (@var{cum}) |
| A C expression that should indicate the number of bytes a call sequence |
| pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} |
| when compiling a function call. |
| |
| @var{cum} is the variable in which all arguments to the called function |
| have been accumulated. |
| |
| On certain architectures, such as the SH5, a call trampoline is used |
| that pops certain registers off the stack, depending on the arguments |
| that have been passed to the function. Since this is a property of the |
| call site, not of the called function, @code{RETURN_POPS_ARGS} is not |
| appropriate. |
| |
| @end table |
| |
| @node Register Arguments |
| @subsection Passing Arguments in Registers |
| @cindex arguments in registers |
| @cindex registers arguments |
| |
| This section describes the macros which let you control how various |
| types of arguments are passed in registers or how they are arranged in |
| the stack. |
| |
| @table @code |
| @findex FUNCTION_ARG |
| @item FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| A C expression that controls whether a function argument is passed |
| in a register, and which register. |
| |
| The arguments are @var{cum}, which summarizes all the previous |
| arguments; @var{mode}, the machine mode of the argument; @var{type}, |
| the data type of the argument as a tree node or 0 if that is not known |
| (which happens for C support library functions); and @var{named}, |
| which is 1 for an ordinary argument and 0 for nameless arguments that |
| correspond to @samp{@dots{}} in the called function's prototype. |
| @var{type} can be an incomplete type if a syntax error has previously |
| occurred. |
| |
| The value of the expression is usually either a @code{reg} RTX for the |
| hard register in which to pass the argument, or zero to pass the |
| argument on the stack. |
| |
| For machines like the VAX and 68000, where normally all arguments are |
| pushed, zero suffices as a definition. |
| |
| The value of the expression can also be a @code{parallel} RTX@. This is |
| used when an argument is passed in multiple locations. The mode of the |
| of the @code{parallel} should be the mode of the entire argument. The |
| @code{parallel} holds any number of @code{expr_list} pairs; each one |
| describes where part of the argument is passed. In each |
| @code{expr_list} the first operand must be a @code{reg} RTX for the hard |
| register in which to pass this part of the argument, and the mode of the |
| register RTX indicates how large this part of the argument is. The |
| second operand of the @code{expr_list} is a @code{const_int} which gives |
| the offset in bytes into the entire argument of where this part starts. |
| As a special exception the first @code{expr_list} in the @code{parallel} |
| RTX may have a first operand of zero. This indicates that the entire |
| argument is also stored on the stack. |
| |
| The last time this macro is called, it is called with @code{MODE == |
| VOIDmode}, and its result is passed to the @code{call} or @code{call_value} |
| pattern as operands 2 and 3 respectively. |
| |
| @cindex @file{stdarg.h} and register arguments |
| The usual way to make the ISO library @file{stdarg.h} work on a machine |
| where some arguments are usually passed in registers, is to cause |
| nameless arguments to be passed on the stack instead. This is done |
| by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0. |
| |
| @cindex @code{MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG} |
| @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG} |
| You may use the macro @code{MUST_PASS_IN_STACK (@var{mode}, @var{type})} |
| in the definition of this macro to determine if this argument is of a |
| type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} |
| is not defined and @code{FUNCTION_ARG} returns nonzero for such an |
| argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is |
| defined, the argument will be computed in the stack and then loaded into |
| a register. |
| |
| @findex MUST_PASS_IN_STACK |
| @item MUST_PASS_IN_STACK (@var{mode}, @var{type}) |
| Define as a C expression that evaluates to nonzero if we do not know how |
| to pass TYPE solely in registers. The file @file{expr.h} defines a |
| definition that is usually appropriate, refer to @file{expr.h} for additional |
| documentation. |
| |
| @findex FUNCTION_INCOMING_ARG |
| @item FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| Define this macro if the target machine has ``register windows'', so |
| that the register in which a function sees an arguments is not |
| necessarily the same as the one in which the caller passed the |
| argument. |
| |
| For such machines, @code{FUNCTION_ARG} computes the register in which |
| the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should |
| be defined in a similar fashion to tell the function being called |
| where the arguments will arrive. |
| |
| If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG} |
| serves both purposes. |
| |
| @findex FUNCTION_ARG_PARTIAL_NREGS |
| @item FUNCTION_ARG_PARTIAL_NREGS (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| A C expression for the number of words, at the beginning of an |
| argument, that must be put in registers. The value must be zero for |
| arguments that are passed entirely in registers or that are entirely |
| pushed on the stack. |
| |
| On some machines, certain arguments must be passed partially in |
| registers and partially in memory. On these machines, typically the |
| first @var{n} words of arguments are passed in registers, and the rest |
| on the stack. If a multi-word argument (a @code{double} or a |
| structure) crosses that boundary, its first few words must be passed |
| in registers and the rest must be pushed. This macro tells the |
| compiler when this occurs, and how many of the words should go in |
| registers. |
| |
| @code{FUNCTION_ARG} for these arguments should return the first |
| register to be used by the caller for this argument; likewise |
| @code{FUNCTION_INCOMING_ARG}, for the called function. |
| |
| @findex FUNCTION_ARG_PASS_BY_REFERENCE |
| @item FUNCTION_ARG_PASS_BY_REFERENCE (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| A C expression that indicates when an argument must be passed by reference. |
| If nonzero for an argument, a copy of that argument is made in memory and a |
| pointer to the argument is passed instead of the argument itself. |
| The pointer is passed in whatever way is appropriate for passing a pointer |
| to that type. |
| |
| On machines where @code{REG_PARM_STACK_SPACE} is not defined, a suitable |
| definition of this macro might be |
| @smallexample |
| #define FUNCTION_ARG_PASS_BY_REFERENCE\ |
| (CUM, MODE, TYPE, NAMED) \ |
| MUST_PASS_IN_STACK (MODE, TYPE) |
| @end smallexample |
| @c this is *still* too long. --mew 5feb93 |
| |
| @findex FUNCTION_ARG_CALLEE_COPIES |
| @item FUNCTION_ARG_CALLEE_COPIES (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| If defined, a C expression that indicates when it is the called function's |
| responsibility to make a copy of arguments passed by invisible reference. |
| Normally, the caller makes a copy and passes the address of the copy to the |
| routine being called. When @code{FUNCTION_ARG_CALLEE_COPIES} is defined and is |
| nonzero, the caller does not make a copy. Instead, it passes a pointer to the |
| ``live'' value. The called function must not modify this value. If it can be |
| determined that the value won't be modified, it need not make a copy; |
| otherwise a copy must be made. |
| |
| @findex FUNCTION_ARG_REG_LITTLE_ENDIAN |
| @item FUNCTION_ARG_REG_LITTLE_ENDIAN |
| If defined TRUE on a big-endian system then structure arguments passed |
| (and returned) in registers are passed in a little-endian manner instead of |
| the big-endian manner. On the HP-UX IA64 and PA64 platforms structures are |
| aligned differently then integral values and setting this value to true will |
| allow for the special handling of structure arguments and return values. |
| |
| @findex CUMULATIVE_ARGS |
| @item CUMULATIVE_ARGS |
| A C type for declaring a variable that is used as the first argument of |
| @code{FUNCTION_ARG} and other related values. For some target machines, |
| the type @code{int} suffices and can hold the number of bytes of |
| argument so far. |
| |
| There is no need to record in @code{CUMULATIVE_ARGS} anything about the |
| arguments that have been passed on the stack. The compiler has other |
| variables to keep track of that. For target machines on which all |
| arguments are passed on the stack, there is no need to store anything in |
| @code{CUMULATIVE_ARGS}; however, the data structure must exist and |
| should not be empty, so use @code{int}. |
| |
| @findex INIT_CUMULATIVE_ARGS |
| @item INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{indirect}) |
| A C statement (sans semicolon) for initializing the variable @var{cum} |
| for the state at the beginning of the argument list. The variable has |
| type @code{CUMULATIVE_ARGS}. The value of @var{fntype} is the tree node |
| for the data type of the function which will receive the args, or 0 |
| if the args are to a compiler support library function. The value of |
| @var{indirect} is nonzero when processing an indirect call, for example |
| a call through a function pointer. The value of @var{indirect} is zero |
| for a call to an explicitly named function, a library function call, or when |
| @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function |
| being compiled. |
| |
| When processing a call to a compiler support library function, |
| @var{libname} identifies which one. It is a @code{symbol_ref} rtx which |
| contains the name of the function, as a string. @var{libname} is 0 when |
| an ordinary C function call is being processed. Thus, each time this |
| macro is called, either @var{libname} or @var{fntype} is nonzero, but |
| never both of them at once. |
| |
| @findex INIT_CUMULATIVE_LIBCALL_ARGS |
| @item INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) |
| Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, |
| it gets a @code{MODE} argument instead of @var{fntype}, that would be |
| @code{NULL}. @var{indirect} would always be zero, too. If this macro |
| is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, |
| 0)} is used instead. |
| |
| @findex INIT_CUMULATIVE_INCOMING_ARGS |
| @item INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) |
| Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of |
| finding the arguments for the function being compiled. If this macro is |
| undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. |
| |
| The value passed for @var{libname} is always 0, since library routines |
| with special calling conventions are never compiled with GCC@. The |
| argument @var{libname} exists for symmetry with |
| @code{INIT_CUMULATIVE_ARGS}. |
| @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. |
| @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 |
| |
| @findex FUNCTION_ARG_ADVANCE |
| @item FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| A C statement (sans semicolon) to update the summarizer variable |
| @var{cum} to advance past an argument in the argument list. The |
| values @var{mode}, @var{type} and @var{named} describe that argument. |
| Once this is done, the variable @var{cum} is suitable for analyzing |
| the @emph{following} argument with @code{FUNCTION_ARG}, etc. |
| |
| This macro need not do anything if the argument in question was passed |
| on the stack. The compiler knows how to track the amount of stack space |
| used for arguments without any special help. |
| |
| @findex FUNCTION_ARG_PADDING |
| @item FUNCTION_ARG_PADDING (@var{mode}, @var{type}) |
| If defined, a C expression which determines whether, and in which direction, |
| to pad out an argument with extra space. The value should be of type |
| @code{enum direction}: either @code{upward} to pad above the argument, |
| @code{downward} to pad below, or @code{none} to inhibit padding. |
| |
| The @emph{amount} of padding is always just enough to reach the next |
| multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control |
| it. |
| |
| This macro has a default definition which is right for most systems. |
| For little-endian machines, the default is to pad upward. For |
| big-endian machines, the default is to pad downward for an argument of |
| constant size shorter than an @code{int}, and upward otherwise. |
| |
| @findex PAD_VARARGS_DOWN |
| @item PAD_VARARGS_DOWN |
| If defined, a C expression which determines whether the default |
| implementation of va_arg will attempt to pad down before reading the |
| next argument, if that argument is smaller than its aligned space as |
| controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such |
| arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. |
| |
| @findex FUNCTION_ARG_BOUNDARY |
| @item FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type}) |
| If defined, a C expression that gives the alignment boundary, in bits, |
| of an argument with the specified mode and type. If it is not defined, |
| @code{PARM_BOUNDARY} is used for all arguments. |
| |
| @findex FUNCTION_ARG_REGNO_P |
| @item FUNCTION_ARG_REGNO_P (@var{regno}) |
| A C expression that is nonzero if @var{regno} is the number of a hard |
| register in which function arguments are sometimes passed. This does |
| @emph{not} include implicit arguments such as the static chain and |
| the structure-value address. On many machines, no registers can be |
| used for this purpose since all function arguments are pushed on the |
| stack. |
| |
| @findex LOAD_ARGS_REVERSED |
| @item LOAD_ARGS_REVERSED |
| If defined, the order in which arguments are loaded into their |
| respective argument registers is reversed so that the last |
| argument is loaded first. This macro only affects arguments |
| passed in registers. |
| |
| @end table |
| |
| @node Scalar Return |
| @subsection How Scalar Function Values Are Returned |
| @cindex return values in registers |
| @cindex values, returned by functions |
| @cindex scalars, returned as values |
| |
| This section discusses the macros that control returning scalars as |
| values---values that can fit in registers. |
| |
| @table @code |
| @findex FUNCTION_VALUE |
| @item FUNCTION_VALUE (@var{valtype}, @var{func}) |
| A C expression to create an RTX representing the place where a |
| function returns a value of data type @var{valtype}. @var{valtype} is |
| a tree node representing a data type. Write @code{TYPE_MODE |
| (@var{valtype})} to get the machine mode used to represent that type. |
| On many machines, only the mode is relevant. (Actually, on most |
| machines, scalar values are returned in the same place regardless of |
| mode). |
| |
| The value of the expression is usually a @code{reg} RTX for the hard |
| register where the return value is stored. The value can also be a |
| @code{parallel} RTX, if the return value is in multiple places. See |
| @code{FUNCTION_ARG} for an explanation of the @code{parallel} form. |
| |
| If @code{PROMOTE_FUNCTION_RETURN} is defined, you must apply the same |
| promotion rules specified in @code{PROMOTE_MODE} if @var{valtype} is a |
| scalar type. |
| |
| If the precise function being called is known, @var{func} is a tree |
| node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null |
| pointer. This makes it possible to use a different value-returning |
| convention for specific functions when all their calls are |
| known. |
| |
| @code{FUNCTION_VALUE} is not used for return vales with aggregate data |
| types, because these are returned in another way. See |
| @code{STRUCT_VALUE_REGNUM} and related macros, below. |
| |
| @findex FUNCTION_OUTGOING_VALUE |
| @item FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func}) |
| Define this macro if the target machine has ``register windows'' |
| so that the register in which a function returns its value is not |
| the same as the one in which the caller sees the value. |
| |
| For such machines, @code{FUNCTION_VALUE} computes the register in which |
| the caller will see the value. @code{FUNCTION_OUTGOING_VALUE} should be |
| defined in a similar fashion to tell the function where to put the |
| value. |
| |
| If @code{FUNCTION_OUTGOING_VALUE} is not defined, |
| @code{FUNCTION_VALUE} serves both purposes. |
| |
| @code{FUNCTION_OUTGOING_VALUE} is not used for return vales with |
| aggregate data types, because these are returned in another way. See |
| @code{STRUCT_VALUE_REGNUM} and related macros, below. |
| |
| @findex LIBCALL_VALUE |
| @item LIBCALL_VALUE (@var{mode}) |
| A C expression to create an RTX representing the place where a library |
| function returns a value of mode @var{mode}. If the precise function |
| being called is known, @var{func} is a tree node |
| (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null |
| pointer. This makes it possible to use a different value-returning |
| convention for specific functions when all their calls are |
| known. |
| |
| Note that ``library function'' in this context means a compiler |
| support routine, used to perform arithmetic, whose name is known |
| specially by the compiler and was not mentioned in the C code being |
| compiled. |
| |
| The definition of @code{LIBRARY_VALUE} need not be concerned aggregate |
| data types, because none of the library functions returns such types. |
| |
| @findex FUNCTION_VALUE_REGNO_P |
| @item FUNCTION_VALUE_REGNO_P (@var{regno}) |
| A C expression that is nonzero if @var{regno} is the number of a hard |
| register in which the values of called function may come back. |
| |
| A register whose use for returning values is limited to serving as the |
| second of a pair (for a value of type @code{double}, say) need not be |
| recognized by this macro. So for most machines, this definition |
| suffices: |
| |
| @example |
| #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) |
| @end example |
| |
| If the machine has register windows, so that the caller and the called |
| function use different registers for the return value, this macro |
| should recognize only the caller's register numbers. |
| |
| @findex APPLY_RESULT_SIZE |
| @item APPLY_RESULT_SIZE |
| Define this macro if @samp{untyped_call} and @samp{untyped_return} |
| need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for |
| saving and restoring an arbitrary return value. |
| @end table |
| |
| @node Aggregate Return |
| @subsection How Large Values Are Returned |
| @cindex aggregates as return values |
| @cindex large return values |
| @cindex returning aggregate values |
| @cindex structure value address |
| |
| When a function value's mode is @code{BLKmode} (and in some other |
| cases), the value is not returned according to @code{FUNCTION_VALUE} |
| (@pxref{Scalar Return}). Instead, the caller passes the address of a |
| block of memory in which the value should be stored. This address |
| is called the @dfn{structure value address}. |
| |
| This section describes how to control returning structure values in |
| memory. |
| |
| @table @code |
| @findex RETURN_IN_MEMORY |
| @item RETURN_IN_MEMORY (@var{type}) |
| A C expression which can inhibit the returning of certain function |
| values in registers, based on the type of value. A nonzero value says |
| to return the function value in memory, just as large structures are |
| always returned. Here @var{type} will be a C expression of type |
| @code{tree}, representing the data type of the value. |
| |
| Note that values of mode @code{BLKmode} must be explicitly handled |
| by this macro. Also, the option @option{-fpcc-struct-return} |
| takes effect regardless of this macro. On most systems, it is |
| possible to leave the macro undefined; this causes a default |
| definition to be used, whose value is the constant 1 for @code{BLKmode} |
| values, and 0 otherwise. |
| |
| Do not use this macro to indicate that structures and unions should always |
| be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} |
| to indicate this. |
| |
| @findex DEFAULT_PCC_STRUCT_RETURN |
| @item DEFAULT_PCC_STRUCT_RETURN |
| Define this macro to be 1 if all structure and union return values must be |
| in memory. Since this results in slower code, this should be defined |
| only if needed for compatibility with other compilers or with an ABI@. |
| If you define this macro to be 0, then the conventions used for structure |
| and union return values are decided by the @code{RETURN_IN_MEMORY} macro. |
| |
| If not defined, this defaults to the value 1. |
| |
| @findex STRUCT_VALUE_REGNUM |
| @item STRUCT_VALUE_REGNUM |
| If the structure value address is passed in a register, then |
| @code{STRUCT_VALUE_REGNUM} should be the number of that register. |
| |
| @findex STRUCT_VALUE |
| @item STRUCT_VALUE |
| If the structure value address is not passed in a register, define |
| @code{STRUCT_VALUE} as an expression returning an RTX for the place |
| where the address is passed. If it returns 0, the address is passed as |
| an ``invisible'' first argument. |
| |
| @findex STRUCT_VALUE_INCOMING_REGNUM |
| @item STRUCT_VALUE_INCOMING_REGNUM |
| On some architectures the place where the structure value address |
| is found by the called function is not the same place that the |
| caller put it. This can be due to register windows, or it could |
| be because the function prologue moves it to a different place. |
| |
| If the incoming location of the structure value address is in a |
| register, define this macro as the register number. |
| |
| @findex STRUCT_VALUE_INCOMING |
| @item STRUCT_VALUE_INCOMING |
| If the incoming location is not a register, then you should define |
| @code{STRUCT_VALUE_INCOMING} as an expression for an RTX for where the |
| called function should find the value. If it should find the value on |
| the stack, define this to create a @code{mem} which refers to the frame |
| pointer. A definition of 0 means that the address is passed as an |
| ``invisible'' first argument. |
| |
| @findex PCC_STATIC_STRUCT_RETURN |
| @item PCC_STATIC_STRUCT_RETURN |
| Define this macro if the usual system convention on the target machine |
| for returning structures and unions is for the called function to return |
| the address of a static variable containing the value. |
| |
| Do not define this if the usual system convention is for the caller to |
| pass an address to the subroutine. |
| |
| This macro has effect in @option{-fpcc-struct-return} mode, but it does |
| nothing when you use @option{-freg-struct-return} mode. |
| @end table |
| |
| @node Caller Saves |
| @subsection Caller-Saves Register Allocation |
| |
| If you enable it, GCC can save registers around function calls. This |
| makes it possible to use call-clobbered registers to hold variables that |
| must live across calls. |
| |
| @table @code |
| @findex DEFAULT_CALLER_SAVES |
| @item DEFAULT_CALLER_SAVES |
| Define this macro if function calls on the target machine do not preserve |
| any registers; in other words, if @code{CALL_USED_REGISTERS} has 1 |
| for all registers. When defined, this macro enables @option{-fcaller-saves} |
| by default for all optimization levels. It has no effect for optimization |
| levels 2 and higher, where @option{-fcaller-saves} is the default. |
| |
| @findex CALLER_SAVE_PROFITABLE |
| @item CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls}) |
| A C expression to determine whether it is worthwhile to consider placing |
| a pseudo-register in a call-clobbered hard register and saving and |
| restoring it around each function call. The expression should be 1 when |
| this is worth doing, and 0 otherwise. |
| |
| If you don't define this macro, a default is used which is good on most |
| machines: @code{4 * @var{calls} < @var{refs}}. |
| |
| @findex HARD_REGNO_CALLER_SAVE_MODE |
| @item HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) |
| A C expression specifying which mode is required for saving @var{nregs} |
| of a pseudo-register in call-clobbered hard register @var{regno}. If |
| @var{regno} is unsuitable for caller save, @code{VOIDmode} should be |
| returned. For most machines this macro need not be defined since GCC |
| will select the smallest suitable mode. |
| @end table |
| |
| @node Function Entry |
| @subsection Function Entry and Exit |
| @cindex function entry and exit |
| @cindex prologue |
| @cindex epilogue |
| |
| This section describes the macros that output function entry |
| (@dfn{prologue}) and exit (@dfn{epilogue}) code. |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) |
| If defined, a function that outputs the assembler code for entry to a |
| function. The prologue is responsible for setting up the stack frame, |
| initializing the frame pointer register, saving registers that must be |
| saved, and allocating @var{size} additional bytes of storage for the |
| local variables. @var{size} is an integer. @var{file} is a stdio |
| stream to which the assembler code should be output. |
| |
| The label for the beginning of the function need not be output by this |
| macro. That has already been done when the macro is run. |
| |
| @findex regs_ever_live |
| To determine which registers to save, the macro can refer to the array |
| @code{regs_ever_live}: element @var{r} is nonzero if hard register |
| @var{r} is used anywhere within the function. This implies the function |
| prologue should save register @var{r}, provided it is not one of the |
| call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use |
| @code{regs_ever_live}.) |
| |
| On machines that have ``register windows'', the function entry code does |
| not save on the stack the registers that are in the windows, even if |
| they are supposed to be preserved by function calls; instead it takes |
| appropriate steps to ``push'' the register stack, if any non-call-used |
| registers are used in the function. |
| |
| @findex frame_pointer_needed |
| On machines where functions may or may not have frame-pointers, the |
| function entry code must vary accordingly; it must set up the frame |
| pointer if one is wanted, and not otherwise. To determine whether a |
| frame pointer is in wanted, the macro can refer to the variable |
| @code{frame_pointer_needed}. The variable's value will be 1 at run |
| time in a function that needs a frame pointer. @xref{Elimination}. |
| |
| The function entry code is responsible for allocating any stack space |
| required for the function. This stack space consists of the regions |
| listed below. In most cases, these regions are allocated in the |
| order listed, with the last listed region closest to the top of the |
| stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and |
| the highest address if it is not defined). You can use a different order |
| for a machine if doing so is more convenient or required for |
| compatibility reasons. Except in cases where required by standard |
| or by a debugger, there is no reason why the stack layout used by GCC |
| need agree with that used by other compilers for a machine. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file}) |
| If defined, a function that outputs assembler code at the end of a |
| prologue. This should be used when the function prologue is being |
| emitted as RTL, and you have some extra assembler that needs to be |
| emitted. @xref{prologue instruction pattern}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file}) |
| If defined, a function that outputs assembler code at the start of an |
| epilogue. This should be used when the function epilogue is being |
| emitted as RTL, and you have some extra assembler that needs to be |
| emitted. @xref{epilogue instruction pattern}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) |
| If defined, a function that outputs the assembler code for exit from a |
| function. The epilogue is responsible for restoring the saved |
| registers and stack pointer to their values when the function was |
| called, and returning control to the caller. This macro takes the |
| same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the |
| registers to restore are determined from @code{regs_ever_live} and |
| @code{CALL_USED_REGISTERS} in the same way. |
| |
| On some machines, there is a single instruction that does all the work |
| of returning from the function. On these machines, give that |
| instruction the name @samp{return} and do not define the macro |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} at all. |
| |
| Do not define a pattern named @samp{return} if you want the |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target |
| switches to control whether return instructions or epilogues are used, |
| define a @samp{return} pattern with a validity condition that tests the |
| target switches appropriately. If the @samp{return} pattern's validity |
| condition is false, epilogues will be used. |
| |
| On machines where functions may or may not have frame-pointers, the |
| function exit code must vary accordingly. Sometimes the code for these |
| two cases is completely different. To determine whether a frame pointer |
| is wanted, the macro can refer to the variable |
| @code{frame_pointer_needed}. The variable's value will be 1 when compiling |
| a function that needs a frame pointer. |
| |
| Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. |
| The C variable @code{current_function_is_leaf} is nonzero for such a |
| function. @xref{Leaf Functions}. |
| |
| On some machines, some functions pop their arguments on exit while |
| others leave that for the caller to do. For example, the 68020 when |
| given @option{-mrtd} pops arguments in functions that take a fixed |
| number of arguments. |
| |
| @findex current_function_pops_args |
| Your definition of the macro @code{RETURN_POPS_ARGS} decides which |
| functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} |
| needs to know what was decided. The variable that is called |
| @code{current_function_pops_args} is the number of bytes of its |
| arguments that a function should pop. @xref{Scalar Return}. |
| @c what is the "its arguments" in the above sentence referring to, pray |
| @c tell? --mew 5feb93 |
| @end deftypefn |
| |
| @table @code |
| |
| @itemize @bullet |
| @item |
| @findex current_function_pretend_args_size |
| A region of @code{current_function_pretend_args_size} bytes of |
| uninitialized space just underneath the first argument arriving on the |
| stack. (This may not be at the very start of the allocated stack region |
| if the calling sequence has pushed anything else since pushing the stack |
| arguments. But usually, on such machines, nothing else has been pushed |
| yet, because the function prologue itself does all the pushing.) This |
| region is used on machines where an argument may be passed partly in |
| registers and partly in memory, and, in some cases to support the |
| features in @code{<varargs.h>} and @code{<stdarg.h>}. |
| |
| @item |
| An area of memory used to save certain registers used by the function. |
| The size of this area, which may also include space for such things as |
| the return address and pointers to previous stack frames, is |
| machine-specific and usually depends on which registers have been used |
| in the function. Machines with register windows often do not require |
| a save area. |
| |
| @item |
| A region of at least @var{size} bytes, possibly rounded up to an allocation |
| boundary, to contain the local variables of the function. On some machines, |
| this region and the save area may occur in the opposite order, with the |
| save area closer to the top of the stack. |
| |
| @item |
| @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames |
| Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of |
| @code{current_function_outgoing_args_size} bytes to be used for outgoing |
| argument lists of the function. @xref{Stack Arguments}. |
| @end itemize |
| |
| Normally, it is necessary for the macros |
| @code{TARGET_ASM_FUNCTION_PROLOGUE} and |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} to treat leaf functions specially. |
| The C variable @code{current_function_is_leaf} is nonzero for such a |
| function. |
| |
| @findex EXIT_IGNORE_STACK |
| @item EXIT_IGNORE_STACK |
| Define this macro as a C expression that is nonzero if the return |
| instruction or the function epilogue ignores the value of the stack |
| pointer; in other words, if it is safe to delete an instruction to |
| adjust the stack pointer before a return from the function. |
| |
| Note that this macro's value is relevant only for functions for which |
| frame pointers are maintained. It is never safe to delete a final |
| stack adjustment in a function that has no frame pointer, and the |
| compiler knows this regardless of @code{EXIT_IGNORE_STACK}. |
| |
| @findex EPILOGUE_USES |
| @item EPILOGUE_USES (@var{regno}) |
| Define this macro as a C expression that is nonzero for registers that are |
| used by the epilogue or the @samp{return} pattern. The stack and frame |
| pointer registers are already be assumed to be used as needed. |
| |
| @findex DELAY_SLOTS_FOR_EPILOGUE |
| @item DELAY_SLOTS_FOR_EPILOGUE |
| Define this macro if the function epilogue contains delay slots to which |
| instructions from the rest of the function can be ``moved''. The |
| definition should be a C expression whose value is an integer |
| representing the number of delay slots there. |
| |
| @findex ELIGIBLE_FOR_EPILOGUE_DELAY |
| @item ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n}) |
| A C expression that returns 1 if @var{insn} can be placed in delay |
| slot number @var{n} of the epilogue. |
| |
| The argument @var{n} is an integer which identifies the delay slot now |
| being considered (since different slots may have different rules of |
| eligibility). It is never negative and is always less than the number |
| of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns). |
| If you reject a particular insn for a given delay slot, in principle, it |
| may be reconsidered for a subsequent delay slot. Also, other insns may |
| (at least in principle) be considered for the so far unfilled delay |
| slot. |
| |
| @findex current_function_epilogue_delay_list |
| @findex final_scan_insn |
| The insns accepted to fill the epilogue delay slots are put in an RTL |
| list made with @code{insn_list} objects, stored in the variable |
| @code{current_function_epilogue_delay_list}. The insn for the first |
| delay slot comes first in the list. Your definition of the macro |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by |
| outputting the insns in this list, usually by calling |
| @code{final_scan_insn}. |
| |
| You need not define this macro if you did not define |
| @code{DELAY_SLOTS_FOR_EPILOGUE}. |
| |
| @findex ASM_OUTPUT_MI_THUNK |
| @item ASM_OUTPUT_MI_THUNK (@var{file}, @var{thunk_fndecl}, @var{delta}, @var{function}) |
| A C compound statement that outputs the assembler code for a thunk |
| function, used to implement C++ virtual function calls with multiple |
| inheritance. The thunk acts as a wrapper around a virtual function, |
| adjusting the implicit object parameter before handing control off to |
| the real function. |
| |
| First, emit code to add the integer @var{delta} to the location that |
| contains the incoming first argument. Assume that this argument |
| contains a pointer, and is the one used to pass the @code{this} pointer |
| in C++. This is the incoming argument @emph{before} the function prologue, |
| e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of |
| all other incoming arguments. |
| |
| After the addition, emit code to jump to @var{function}, which is a |
| @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does |
| not touch the return address. Hence returning from @var{FUNCTION} will |
| return to whoever called the current @samp{thunk}. |
| |
| The effect must be as if @var{function} had been called directly with |
| the adjusted first argument. This macro is responsible for emitting all |
| of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} |
| and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. |
| |
| The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} |
| have already been extracted from it.) It might possibly be useful on |
| some targets, but probably not. |
| |
| If you do not define this macro, the target-independent code in the C++ |
| front end will generate a less efficient heavyweight thunk that calls |
| @var{function} instead of jumping to it. The generic approach does |
| not support varargs. |
| @end table |
| |
| @node Profiling |
| @subsection Generating Code for Profiling |
| @cindex profiling, code generation |
| |
| These macros will help you generate code for profiling. |
| |
| @table @code |
| @findex FUNCTION_PROFILER |
| @item FUNCTION_PROFILER (@var{file}, @var{labelno}) |
| A C statement or compound statement to output to @var{file} some |
| assembler code to call the profiling subroutine @code{mcount}. |
| |
| @findex mcount |
| The details of how @code{mcount} expects to be called are determined by |
| your operating system environment, not by GCC@. To figure them out, |
| compile a small program for profiling using the system's installed C |
| compiler and look at the assembler code that results. |
| |
| Older implementations of @code{mcount} expect the address of a counter |
| variable to be loaded into some register. The name of this variable is |
| @samp{LP} followed by the number @var{labelno}, so you would generate |
| the name using @samp{LP%d} in a @code{fprintf}. |
| |
| @findex PROFILE_HOOK |
| @item PROFILE_HOOK |
| A C statement or compound statement to output to @var{file} some assembly |
| code to call the profiling subroutine @code{mcount} even the target does |
| not support profiling. |
| |
| @findex NO_PROFILE_COUNTERS |
| @item NO_PROFILE_COUNTERS |
| Define this macro if the @code{mcount} subroutine on your system does |
| not need a counter variable allocated for each function. This is true |
| for almost all modern implementations. If you define this macro, you |
| must not use the @var{labelno} argument to @code{FUNCTION_PROFILER}. |
| |
| @findex PROFILE_BEFORE_PROLOGUE |
| @item PROFILE_BEFORE_PROLOGUE |
| Define this macro if the code for function profiling should come before |
| the function prologue. Normally, the profiling code comes after. |
| |
| |
| @findex TARGET_ALLOWS_PROFILING_WITHOUT_FRAME_POINTER |
| @item TARGET_ALLOWS_PROFILING_WITHOUT_FRAME_POINTER |
| On some targets, it is impossible to use profiling when the frame |
| pointer has been omitted. For example, on x86 GNU/Linux systems, |
| the @code{mcount} routine provided by the GNU C Library finds the |
| address of the routine that called the routine that called @code{mcount} |
| by looking in the immediate caller's stack frame. If the immediate |
| caller has no frame pointer, this lookup will fail. |
| |
| By default, GCC assumes that the target does allow profiling when the |
| frame pointer is omitted. This macro should be defined to a C |
| expression that evaluates to @code{false} if the target does not allow |
| profiling when the frame pointer is omitted. |
| |
| @end table |
| |
| @node Tail Calls |
| @subsection Permitting tail calls |
| @cindex tail calls |
| |
| @table @code |
| @findex FUNCTION_OK_FOR_SIBCALL |
| @item FUNCTION_OK_FOR_SIBCALL (@var{decl}) |
| A C expression that evaluates to true if it is ok to perform a sibling |
| call to @var{decl} from the current function. |
| |
| It is not uncommon for limitations of calling conventions to prevent |
| tail calls to functions outside the current unit of translation, or |
| during PIC compilation. Use this macro to enforce these restrictions, |
| as the @code{sibcall} md pattern can not fail, or fall over to a |
| ``normal'' call. |
| @end table |
| |
| @node Varargs |
| @section Implementing the Varargs Macros |
| @cindex varargs implementation |
| |
| GCC comes with an implementation of @code{<varargs.h>} and |
| @code{<stdarg.h>} that work without change on machines that pass arguments |
| on the stack. Other machines require their own implementations of |
| varargs, and the two machine independent header files must have |
| conditionals to include it. |
| |
| ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in |
| the calling convention for @code{va_start}. The traditional |
| implementation takes just one argument, which is the variable in which |
| to store the argument pointer. The ISO implementation of |
| @code{va_start} takes an additional second argument. The user is |
| supposed to write the last named argument of the function here. |
| |
| However, @code{va_start} should not use this argument. The way to find |
| the end of the named arguments is with the built-in functions described |
| below. |
| |
| @table @code |
| @findex __builtin_saveregs |
| @item __builtin_saveregs () |
| Use this built-in function to save the argument registers in memory so |
| that the varargs mechanism can access them. Both ISO and traditional |
| versions of @code{va_start} must use @code{__builtin_saveregs}, unless |
| you use @code{SETUP_INCOMING_VARARGS} (see below) instead. |
| |
| On some machines, @code{__builtin_saveregs} is open-coded under the |
| control of the macro @code{EXPAND_BUILTIN_SAVEREGS}. On other machines, |
| it calls a routine written in assembler language, found in |
| @file{libgcc2.c}. |
| |
| Code generated for the call to @code{__builtin_saveregs} appears at the |
| beginning of the function, as opposed to where the call to |
| @code{__builtin_saveregs} is written, regardless of what the code is. |
| This is because the registers must be saved before the function starts |
| to use them for its own purposes. |
| @c i rewrote the first sentence above to fix an overfull hbox. --mew |
| @c 10feb93 |
| |
| @findex __builtin_args_info |
| @item __builtin_args_info (@var{category}) |
| Use this built-in function to find the first anonymous arguments in |
| registers. |
| |
| In general, a machine may have several categories of registers used for |
| arguments, each for a particular category of data types. (For example, |
| on some machines, floating-point registers are used for floating-point |
| arguments while other arguments are passed in the general registers.) |
| To make non-varargs functions use the proper calling convention, you |
| have defined the @code{CUMULATIVE_ARGS} data type to record how many |
| registers in each category have been used so far |
| |
| @code{__builtin_args_info} accesses the same data structure of type |
| @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished |
| with it, with @var{category} specifying which word to access. Thus, the |
| value indicates the first unused register in a given category. |
| |
| Normally, you would use @code{__builtin_args_info} in the implementation |
| of @code{va_start}, accessing each category just once and storing the |
| value in the @code{va_list} object. This is because @code{va_list} will |
| have to update the values, and there is no way to alter the |
| values accessed by @code{__builtin_args_info}. |
| |
| @findex __builtin_next_arg |
| @item __builtin_next_arg (@var{lastarg}) |
| This is the equivalent of @code{__builtin_args_info}, for stack |
| arguments. It returns the address of the first anonymous stack |
| argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it |
| returns the address of the location above the first anonymous stack |
| argument. Use it in @code{va_start} to initialize the pointer for |
| fetching arguments from the stack. Also use it in @code{va_start} to |
| verify that the second parameter @var{lastarg} is the last named argument |
| of the current function. |
| |
| @findex __builtin_classify_type |
| @item __builtin_classify_type (@var{object}) |
| Since each machine has its own conventions for which data types are |
| passed in which kind of register, your implementation of @code{va_arg} |
| has to embody these conventions. The easiest way to categorize the |
| specified data type is to use @code{__builtin_classify_type} together |
| with @code{sizeof} and @code{__alignof__}. |
| |
| @code{__builtin_classify_type} ignores the value of @var{object}, |
| considering only its data type. It returns an integer describing what |
| kind of type that is---integer, floating, pointer, structure, and so on. |
| |
| The file @file{typeclass.h} defines an enumeration that you can use to |
| interpret the values of @code{__builtin_classify_type}. |
| @end table |
| |
| These machine description macros help implement varargs: |
| |
| @table @code |
| @findex EXPAND_BUILTIN_SAVEREGS |
| @item EXPAND_BUILTIN_SAVEREGS () |
| If defined, is a C expression that produces the machine-specific code |
| for a call to @code{__builtin_saveregs}. This code will be moved to the |
| very beginning of the function, before any parameter access are made. |
| The return value of this function should be an RTX that contains the |
| value to use as the return of @code{__builtin_saveregs}. |
| |
| @findex SETUP_INCOMING_VARARGS |
| @item SETUP_INCOMING_VARARGS (@var{args_so_far}, @var{mode}, @var{type}, @var{pretend_args_size}, @var{second_time}) |
| This macro offers an alternative to using @code{__builtin_saveregs} and |
| defining the macro @code{EXPAND_BUILTIN_SAVEREGS}. Use it to store the |
| anonymous register arguments into the stack so that all the arguments |
| appear to have been passed consecutively on the stack. Once this is |
| done, you can use the standard implementation of varargs that works for |
| machines that pass all their arguments on the stack. |
| |
| The argument @var{args_so_far} is the @code{CUMULATIVE_ARGS} data |
| structure, containing the values that are obtained after processing the |
| named arguments. The arguments @var{mode} and @var{type} describe the |
| last named argument---its machine mode and its data type as a tree node. |
| |
| The macro implementation should do two things: first, push onto the |
| stack all the argument registers @emph{not} used for the named |
| arguments, and second, store the size of the data thus pushed into the |
| @code{int}-valued variable whose name is supplied as the argument |
| @var{pretend_args_size}. The value that you store here will serve as |
| additional offset for setting up the stack frame. |
| |
| Because you must generate code to push the anonymous arguments at |
| compile time without knowing their data types, |
| @code{SETUP_INCOMING_VARARGS} is only useful on machines that have just |
| a single category of argument register and use it uniformly for all data |
| types. |
| |
| If the argument @var{second_time} is nonzero, it means that the |
| arguments of the function are being analyzed for the second time. This |
| happens for an inline function, which is not actually compiled until the |
| end of the source file. The macro @code{SETUP_INCOMING_VARARGS} should |
| not generate any instructions in this case. |
| |
| @findex STRICT_ARGUMENT_NAMING |
| @item STRICT_ARGUMENT_NAMING |
| Define this macro to be a nonzero value if the location where a function |
| argument is passed depends on whether or not it is a named argument. |
| |
| This macro controls how the @var{named} argument to @code{FUNCTION_ARG} |
| is set for varargs and stdarg functions. If this macro returns a |
| nonzero value, the @var{named} argument is always true for named |
| arguments, and false for unnamed arguments. If it returns a value of |
| zero, but @code{SETUP_INCOMING_VARARGS} is defined, then all arguments |
| are treated as named. Otherwise, all named arguments except the last |
| are treated as named. |
| |
| You need not define this macro if it always returns zero. |
| |
| @findex PRETEND_OUTGOING_VARARGS_NAMED |
| @item PRETEND_OUTGOING_VARARGS_NAMED |
| If you need to conditionally change ABIs so that one works with |
| @code{SETUP_INCOMING_VARARGS}, but the other works like neither |
| @code{SETUP_INCOMING_VARARGS} nor @code{STRICT_ARGUMENT_NAMING} was |
| defined, then define this macro to return nonzero if |
| @code{SETUP_INCOMING_VARARGS} is used, zero otherwise. |
| Otherwise, you should not define this macro. |
| @end table |
| |
| @node Trampolines |
| @section Trampolines for Nested Functions |
| @cindex trampolines for nested functions |
| @cindex nested functions, trampolines for |
| |
| A @dfn{trampoline} is a small piece of code that is created at run time |
| when the address of a nested function is taken. It normally resides on |
| the stack, in the stack frame of the containing function. These macros |
| tell GCC how to generate code to allocate and initialize a |
| trampoline. |
| |
| The instructions in the trampoline must do two things: load a constant |
| address into the static chain register, and jump to the real address of |
| the nested function. On CISC machines such as the m68k, this requires |
| two instructions, a move immediate and a jump. Then the two addresses |
| exist in the trampoline as word-long immediate operands. On RISC |
| machines, it is often necessary to load each address into a register in |
| two parts. Then pieces of each address form separate immediate |
| operands. |
| |
| The code generated to initialize the trampoline must store the variable |
| parts---the static chain value and the function address---into the |
| immediate operands of the instructions. On a CISC machine, this is |
| simply a matter of copying each address to a memory reference at the |
| proper offset from the start of the trampoline. On a RISC machine, it |
| may be necessary to take out pieces of the address and store them |
| separately. |
| |
| @table @code |
| @findex TRAMPOLINE_TEMPLATE |
| @item TRAMPOLINE_TEMPLATE (@var{file}) |
| A C statement to output, on the stream @var{file}, assembler code for a |
| block of data that contains the constant parts of a trampoline. This |
| code should not include a label---the label is taken care of |
| automatically. |
| |
| If you do not define this macro, it means no template is needed |
| for the target. Do not define this macro on systems where the block move |
| code to copy the trampoline into place would be larger than the code |
| to generate it on the spot. |
| |
| @findex TRAMPOLINE_SECTION |
| @item TRAMPOLINE_SECTION |
| The name of a subroutine to switch to the section in which the |
| trampoline template is to be placed (@pxref{Sections}). The default is |
| a value of @samp{readonly_data_section}, which places the trampoline in |
| the section containing read-only data. |
| |
| @findex TRAMPOLINE_SIZE |
| @item TRAMPOLINE_SIZE |
| A C expression for the size in bytes of the trampoline, as an integer. |
| |
| @findex TRAMPOLINE_ALIGNMENT |
| @item TRAMPOLINE_ALIGNMENT |
| Alignment required for trampolines, in bits. |
| |
| If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT} |
| is used for aligning trampolines. |
| |
| @findex INITIALIZE_TRAMPOLINE |
| @item INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain}) |
| A C statement to initialize the variable parts of a trampoline. |
| @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is |
| an RTX for the address of the nested function; @var{static_chain} is an |
| RTX for the static chain value that should be passed to the function |
| when it is called. |
| |
| @findex TRAMPOLINE_ADJUST_ADDRESS |
| @item TRAMPOLINE_ADJUST_ADDRESS (@var{addr}) |
| A C statement that should perform any machine-specific adjustment in |
| the address of the trampoline. Its argument contains the address that |
| was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be |
| used for a function call should be different from the address in which |
| the template was stored, the different address should be assigned to |
| @var{addr}. If this macro is not defined, @var{addr} will be used for |
| function calls. |
| |
| @findex ALLOCATE_TRAMPOLINE |
| @item ALLOCATE_TRAMPOLINE (@var{fp}) |
| A C expression to allocate run-time space for a trampoline. The |
| expression value should be an RTX representing a memory reference to the |
| space for the trampoline. |
| |
| @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines |
| @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines |
| If this macro is not defined, by default the trampoline is allocated as |
| a stack slot. This default is right for most machines. The exceptions |
| are machines where it is impossible to execute instructions in the stack |
| area. On such machines, you may have to implement a separate stack, |
| using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE} |
| and @code{TARGET_ASM_FUNCTION_EPILOGUE}. |
| |
| @var{fp} points to a data structure, a @code{struct function}, which |
| describes the compilation status of the immediate containing function of |
| the function which the trampoline is for. Normally (when |
| @code{ALLOCATE_TRAMPOLINE} is not defined), the stack slot for the |
| trampoline is in the stack frame of this containing function. Other |
| allocation strategies probably must do something analogous with this |
| information. |
| @end table |
| |
| Implementing trampolines is difficult on many machines because they have |
| separate instruction and data caches. Writing into a stack location |
| fails to clear the memory in the instruction cache, so when the program |
| jumps to that location, it executes the old contents. |
| |
| Here are two possible solutions. One is to clear the relevant parts of |
| the instruction cache whenever a trampoline is set up. The other is to |
| make all trampolines identical, by having them jump to a standard |
| subroutine. The former technique makes trampoline execution faster; the |
| latter makes initialization faster. |
| |
| To clear the instruction cache when a trampoline is initialized, define |
| the following macros which describe the shape of the cache. |
| |
| @table @code |
| @findex INSN_CACHE_SIZE |
| @item INSN_CACHE_SIZE |
| The total size in bytes of the cache. |
| |
| @findex INSN_CACHE_LINE_WIDTH |
| @item INSN_CACHE_LINE_WIDTH |
| The length in bytes of each cache line. The cache is divided into cache |
| lines which are disjoint slots, each holding a contiguous chunk of data |
| fetched from memory. Each time data is brought into the cache, an |
| entire line is read at once. The data loaded into a cache line is |
| always aligned on a boundary equal to the line size. |
| |
| @findex INSN_CACHE_DEPTH |
| @item INSN_CACHE_DEPTH |
| The number of alternative cache lines that can hold any particular memory |
| location. |
| @end table |
| |
| Alternatively, if the machine has system calls or instructions to clear |
| the instruction cache directly, you can define the following macro. |
| |
| @table @code |
| @findex CLEAR_INSN_CACHE |
| @item CLEAR_INSN_CACHE (@var{beg}, @var{end}) |
| If defined, expands to a C expression clearing the @emph{instruction |
| cache} in the specified interval. If it is not defined, and the macro |
| @code{INSN_CACHE_SIZE} is defined, some generic code is generated to clear the |
| cache. The definition of this macro would typically be a series of |
| @code{asm} statements. Both @var{beg} and @var{end} are both pointer |
| expressions. |
| @end table |
| |
| To use a standard subroutine, define the following macro. In addition, |
| you must make sure that the instructions in a trampoline fill an entire |
| cache line with identical instructions, or else ensure that the |
| beginning of the trampoline code is always aligned at the same point in |
| its cache line. Look in @file{m68k.h} as a guide. |
| |
| @table @code |
| @findex TRANSFER_FROM_TRAMPOLINE |
| @item TRANSFER_FROM_TRAMPOLINE |
| Define this macro if trampolines need a special subroutine to do their |
| work. The macro should expand to a series of @code{asm} statements |
| which will be compiled with GCC@. They go in a library function named |
| @code{__transfer_from_trampoline}. |
| |
| If you need to avoid executing the ordinary prologue code of a compiled |
| C function when you jump to the subroutine, you can do so by placing a |
| special label of your own in the assembler code. Use one @code{asm} |
| statement to generate an assembler label, and another to make the label |
| global. Then trampolines can use that label to jump directly to your |
| special assembler code. |
| @end table |
| |
| @node Library Calls |
| @section Implicit Calls to Library Routines |
| @cindex library subroutine names |
| @cindex @file{libgcc.a} |
| |
| @c prevent bad page break with this line |
| Here is an explanation of implicit calls to library routines. |
| |
| @table @code |
| @findex MULSI3_LIBCALL |
| @item MULSI3_LIBCALL |
| A C string constant giving the name of the function to call for |
| multiplication of one signed full-word by another. If you do not |
| define this macro, the default name is used, which is @code{__mulsi3}, |
| a function defined in @file{libgcc.a}. |
| |
| @findex DIVSI3_LIBCALL |
| @item DIVSI3_LIBCALL |
| A C string constant giving the name of the function to call for |
| division of one signed full-word by another. If you do not define |
| this macro, the default name is used, which is @code{__divsi3}, a |
| function defined in @file{libgcc.a}. |
| |
| @findex UDIVSI3_LIBCALL |
| @item UDIVSI3_LIBCALL |
| A C string constant giving the name of the function to call for |
| division of one unsigned full-word by another. If you do not define |
| this macro, the default name is used, which is @code{__udivsi3}, a |
| function defined in @file{libgcc.a}. |
| |
| @findex MODSI3_LIBCALL |
| @item MODSI3_LIBCALL |
| A C string constant giving the name of the function to call for the |
| remainder in division of one signed full-word by another. If you do |
| not define this macro, the default name is used, which is |
| @code{__modsi3}, a function defined in @file{libgcc.a}. |
| |
| @findex UMODSI3_LIBCALL |
| @item UMODSI3_LIBCALL |
| A C string constant giving the name of the function to call for the |
| remainder in division of one unsigned full-word by another. If you do |
| not define this macro, the default name is used, which is |
| @code{__umodsi3}, a function defined in @file{libgcc.a}. |
| |
| @findex MULDI3_LIBCALL |
| @item MULDI3_LIBCALL |
| A C string constant giving the name of the function to call for |
| multiplication of one signed double-word by another. If you do not |
| define this macro, the default name is used, which is @code{__muldi3}, |
| a function defined in @file{libgcc.a}. |
| |
| @findex DIVDI3_LIBCALL |
| @item DIVDI3_LIBCALL |
| A C string constant giving the name of the function to call for |
| division of one signed double-word by another. If you do not define |
| this macro, the default name is used, which is @code{__divdi3}, a |
| function defined in @file{libgcc.a}. |
| |
| @findex UDIVDI3_LIBCALL |
| @item UDIVDI3_LIBCALL |
| A C string constant giving the name of the function to call for |
| division of one unsigned full-word by another. If you do not define |
| this macro, the default name is used, which is @code{__udivdi3}, a |
| function defined in @file{libgcc.a}. |
| |
| @findex MODDI3_LIBCALL |
| @item MODDI3_LIBCALL |
| A C string constant giving the name of the function to call for the |
| remainder in division of one signed double-word by another. If you do |
| not define this macro, the default name is used, which is |
| @code{__moddi3}, a function defined in @file{libgcc.a}. |
| |
| @findex UMODDI3_LIBCALL |
| @item UMODDI3_LIBCALL |
| A C string constant giving the name of the function to call for the |
| remainder in division of one unsigned full-word by another. If you do |
| not define this macro, the default name is used, which is |
| @code{__umoddi3}, a function defined in @file{libgcc.a}. |
| |
| @findex INIT_TARGET_OPTABS |
| @item INIT_TARGET_OPTABS |
| Define this macro as a C statement that declares additional library |
| routines renames existing ones. @code{init_optabs} calls this macro after |
| initializing all the normal library routines. |
| |
| @findex FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) |
| @item FLOAT_LIB_COMPARE_RETURNS_BOOL |
| Define this macro as a C statement that returns nonzero if a call to |
| the floating point comparison library function will return a boolean |
| value that indicates the result of the comparison. It should return |
| zero if one of gcc's own libgcc functions is called. |
| |
| Most ports don't need to define this macro. |
| |
| @findex TARGET_EDOM |
| @cindex @code{EDOM}, implicit usage |
| @item TARGET_EDOM |
| The value of @code{EDOM} on the target machine, as a C integer constant |
| expression. If you don't define this macro, GCC does not attempt to |
| deposit the value of @code{EDOM} into @code{errno} directly. Look in |
| @file{/usr/include/errno.h} to find the value of @code{EDOM} on your |
| system. |
| |
| If you do not define @code{TARGET_EDOM}, then compiled code reports |
| domain errors by calling the library function and letting it report the |
| error. If mathematical functions on your system use @code{matherr} when |
| there is an error, then you should leave @code{TARGET_EDOM} undefined so |
| that @code{matherr} is used normally. |
| |
| @findex GEN_ERRNO_RTX |
| @cindex @code{errno}, implicit usage |
| @item GEN_ERRNO_RTX |
| Define this macro as a C expression to create an rtl expression that |
| refers to the global ``variable'' @code{errno}. (On certain systems, |
| @code{errno} may not actually be a variable.) If you don't define this |
| macro, a reasonable default is used. |
| |
| @findex TARGET_MEM_FUNCTIONS |
| @cindex @code{bcopy}, implicit usage |
| @cindex @code{memcpy}, implicit usage |
| @cindex @code{memmove}, implicit usage |
| @cindex @code{bzero}, implicit usage |
| @cindex @code{memset}, implicit usage |
| @item TARGET_MEM_FUNCTIONS |
| Define this macro if GCC should generate calls to the ISO C |
| (and System V) library functions @code{memcpy}, @code{memmove} and |
| @code{memset} rather than the BSD functions @code{bcopy} and @code{bzero}. |
| |
| @findex LIBGCC_NEEDS_DOUBLE |
| @item LIBGCC_NEEDS_DOUBLE |
| Define this macro if @code{float} arguments cannot be passed to library |
| routines (so they must be converted to @code{double}). This macro |
| affects both how library calls are generated and how the library |
| routines in @file{libgcc.a} accept their arguments. It is useful on |
| machines where floating and fixed point arguments are passed |
| differently, such as the i860. |
| |
| @findex NEXT_OBJC_RUNTIME |
| @item NEXT_OBJC_RUNTIME |
| Define this macro to generate code for Objective-C message sending using |
| the calling convention of the NeXT system. This calling convention |
| involves passing the object, the selector and the method arguments all |
| at once to the method-lookup library function. |
| |
| The default calling convention passes just the object and the selector |
| to the lookup function, which returns a pointer to the method. |
| @end table |
| |
| @node Addressing Modes |
| @section Addressing Modes |
| @cindex addressing modes |
| |
| @c prevent bad page break with this line |
| This is about addressing modes. |
| |
| @table @code |
| @findex HAVE_PRE_INCREMENT |
| @findex HAVE_PRE_DECREMENT |
| @findex HAVE_POST_INCREMENT |
| @findex HAVE_POST_DECREMENT |
| @item HAVE_PRE_INCREMENT |
| @itemx HAVE_PRE_DECREMENT |
| @itemx HAVE_POST_INCREMENT |
| @itemx HAVE_POST_DECREMENT |
| A C expression that is nonzero if the machine supports pre-increment, |
| pre-decrement, post-increment, or post-decrement addressing respectively. |
| |
| @findex HAVE_POST_MODIFY_DISP |
| @findex HAVE_PRE_MODIFY_DISP |
| @item HAVE_PRE_MODIFY_DISP |
| @itemx HAVE_POST_MODIFY_DISP |
| A C expression that is nonzero if the machine supports pre- or |
| post-address side-effect generation involving constants other than |
| the size of the memory operand. |
| |
| @findex HAVE_POST_MODIFY_REG |
| @findex HAVE_PRE_MODIFY_REG |
| @item HAVE_PRE_MODIFY_REG |
| @itemx HAVE_POST_MODIFY_REG |
| A C expression that is nonzero if the machine supports pre- or |
| post-address side-effect generation involving a register displacement. |
| |
| @findex CONSTANT_ADDRESS_P |
| @item CONSTANT_ADDRESS_P (@var{x}) |
| A C expression that is 1 if the RTX @var{x} is a constant which |
| is a valid address. On most machines, this can be defined as |
| @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive |
| in which constant addresses are supported. |
| |
| @findex CONSTANT_P |
| @code{CONSTANT_P} accepts integer-values expressions whose values are |
| not explicitly known, such as @code{symbol_ref}, @code{label_ref}, and |
| @code{high} expressions and @code{const} arithmetic expressions, in |
| addition to @code{const_int} and @code{const_double} expressions. |
| |
| @findex MAX_REGS_PER_ADDRESS |
| @item MAX_REGS_PER_ADDRESS |
| A number, the maximum number of registers that can appear in a valid |
| memory address. Note that it is up to you to specify a value equal to |
| the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever |
| accept. |
| |
| @findex GO_IF_LEGITIMATE_ADDRESS |
| @item GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) |
| A C compound statement with a conditional @code{goto @var{label};} |
| executed if @var{x} (an RTX) is a legitimate memory address on the |
| target machine for a memory operand of mode @var{mode}. |
| |
| It usually pays to define several simpler macros to serve as |
| subroutines for this one. Otherwise it may be too complicated to |
| understand. |
| |
| This macro must exist in two variants: a strict variant and a |
| non-strict one. The strict variant is used in the reload pass. It |
| must be defined so that any pseudo-register that has not been |
| allocated a hard register is considered a memory reference. In |
| contexts where some kind of register is required, a pseudo-register |
| with no hard register must be rejected. |
| |
| The non-strict variant is used in other passes. It must be defined to |
| accept all pseudo-registers in every context where some kind of |
| register is required. |
| |
| @findex REG_OK_STRICT |
| Compiler source files that want to use the strict variant of this |
| macro define the macro @code{REG_OK_STRICT}. You should use an |
| @code{#ifdef REG_OK_STRICT} conditional to define the strict variant |
| in that case and the non-strict variant otherwise. |
| |
| Subroutines to check for acceptable registers for various purposes (one |
| for base registers, one for index registers, and so on) are typically |
| among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}. |
| Then only these subroutine macros need have two variants; the higher |
| levels of macros may be the same whether strict or not. |
| |
| Normally, constant addresses which are the sum of a @code{symbol_ref} |
| and an integer are stored inside a @code{const} RTX to mark them as |
| constant. Therefore, there is no need to recognize such sums |
| specifically as legitimate addresses. Normally you would simply |
| recognize any @code{const} as legitimate. |
| |
| Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant |
| sums that are not marked with @code{const}. It assumes that a naked |
| @code{plus} indicates indexing. If so, then you @emph{must} reject such |
| naked constant sums as illegitimate addresses, so that none of them will |
| be given to @code{PRINT_OPERAND_ADDRESS}. |
| |
| @cindex @code{ENCODE_SECTION_INFO} and address validation |
| On some machines, whether a symbolic address is legitimate depends on |
| the section that the address refers to. On these machines, define the |
| macro @code{ENCODE_SECTION_INFO} to store the information into the |
| @code{symbol_ref}, and then check for it here. When you see a |
| @code{const}, you will have to look inside it to find the |
| @code{symbol_ref} in order to determine the section. @xref{Assembler |
| Format}. |
| |
| @findex saveable_obstack |
| The best way to modify the name string is by adding text to the |
| beginning, with suitable punctuation to prevent any ambiguity. Allocate |
| the new name in @code{saveable_obstack}. You will have to modify |
| @code{ASM_OUTPUT_LABELREF} to remove and decode the added text and |
| output the name accordingly, and define @code{STRIP_NAME_ENCODING} to |
| access the original name string. |
| |
| You can check the information stored here into the @code{symbol_ref} in |
| the definitions of the macros @code{GO_IF_LEGITIMATE_ADDRESS} and |
| @code{PRINT_OPERAND_ADDRESS}. |
| |
| @findex REG_OK_FOR_BASE_P |
| @item REG_OK_FOR_BASE_P (@var{x}) |
| A C expression that is nonzero if @var{x} (assumed to be a @code{reg} |
| RTX) is valid for use as a base register. For hard registers, it |
| should always accept those which the hardware permits and reject the |
| others. Whether the macro accepts or rejects pseudo registers must be |
| controlled by @code{REG_OK_STRICT} as described above. This usually |
| requires two variant definitions, of which @code{REG_OK_STRICT} |
| controls the one actually used. |
| |
| @findex REG_MODE_OK_FOR_BASE_P |
| @item REG_MODE_OK_FOR_BASE_P (@var{x}, @var{mode}) |
| A C expression that is just like @code{REG_OK_FOR_BASE_P}, except that |
| that expression may examine the mode of the memory reference in |
| @var{mode}. You should define this macro if the mode of the memory |
| reference affects whether a register may be used as a base register. If |
| you define this macro, the compiler will use it instead of |
| @code{REG_OK_FOR_BASE_P}. |
| |
| @findex REG_OK_FOR_INDEX_P |
| @item REG_OK_FOR_INDEX_P (@var{x}) |
| A C expression that is nonzero if @var{x} (assumed to be a @code{reg} |
| RTX) is valid for use as an index register. |
| |
| The difference between an index register and a base register is that |
| the index register may be scaled. If an address involves the sum of |
| two registers, neither one of them scaled, then either one may be |
| labeled the ``base'' and the other the ``index''; but whichever |
| labeling is used must fit the machine's constraints of which registers |
| may serve in each capacity. The compiler will try both labelings, |
| looking for one that is valid, and will reload one or both registers |
| only if neither labeling works. |
| |
| @findex FIND_BASE_TERM |
| @item FIND_BASE_TERM (@var{x}) |
| A C expression to determine the base term of address @var{x}. |
| This macro is used in only one place: `find_base_term' in alias.c. |
| |
| It is always safe for this macro to not be defined. It exists so |
| that alias analysis can understand machine-dependent addresses. |
| |
| The typical use of this macro is to handle addresses containing |
| a label_ref or symbol_ref within an UNSPEC@. |
| |
| @findex LEGITIMIZE_ADDRESS |
| @item LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win}) |
| A C compound statement that attempts to replace @var{x} with a valid |
| memory address for an operand of mode @var{mode}. @var{win} will be a |
| C statement label elsewhere in the code; the macro definition may use |
| |
| @example |
| GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win}); |
| @end example |
| |
| @noindent |
| to avoid further processing if the address has become legitimate. |
| |
| @findex break_out_memory_refs |
| @var{x} will always be the result of a call to @code{break_out_memory_refs}, |
| and @var{oldx} will be the operand that was given to that function to produce |
| @var{x}. |
| |
| The code generated by this macro should not alter the substructure of |
| @var{x}. If it transforms @var{x} into a more legitimate form, it |
| should assign @var{x} (which will always be a C variable) a new value. |
| |
| It is not necessary for this macro to come up with a legitimate |
| address. The compiler has standard ways of doing so in all cases. In |
| fact, it is safe for this macro to do nothing. But often a |
| machine-dependent strategy can generate better code. |
| |
| @findex LEGITIMIZE_RELOAD_ADDRESS |
| @item LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) |
| A C compound statement that attempts to replace @var{x}, which is an address |
| that needs reloading, with a valid memory address for an operand of mode |
| @var{mode}. @var{win} will be a C statement label elsewhere in the code. |
| It is not necessary to define this macro, but it might be useful for |
| performance reasons. |
| |
| For example, on the i386, it is sometimes possible to use a single |
| reload register instead of two by reloading a sum of two pseudo |
| registers into a register. On the other hand, for number of RISC |
| processors offsets are limited so that often an intermediate address |
| needs to be generated in order to address a stack slot. By defining |
| @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses |
| generated for adjacent some stack slots can be made identical, and thus |
| be shared. |
| |
| @emph{Note}: This macro should be used with caution. It is necessary |
| to know something of how reload works in order to effectively use this, |
| and it is quite easy to produce macros that build in too much knowledge |
| of reload internals. |
| |
| @emph{Note}: This macro must be able to reload an address created by a |
| previous invocation of this macro. If it fails to handle such addresses |
| then the compiler may generate incorrect code or abort. |
| |
| @findex push_reload |
| The macro definition should use @code{push_reload} to indicate parts that |
| need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually |
| suitable to be passed unaltered to @code{push_reload}. |
| |
| The code generated by this macro must not alter the substructure of |
| @var{x}. If it transforms @var{x} into a more legitimate form, it |
| should assign @var{x} (which will always be a C variable) a new value. |
| This also applies to parts that you change indirectly by calling |
| @code{push_reload}. |
| |
| @findex strict_memory_address_p |
| The macro definition may use @code{strict_memory_address_p} to test if |
| the address has become legitimate. |
| |
| @findex copy_rtx |
| If you want to change only a part of @var{x}, one standard way of doing |
| this is to use @code{copy_rtx}. Note, however, that is unshares only a |
| single level of rtl. Thus, if the part to be changed is not at the |
| top level, you'll need to replace first the top level. |
| It is not necessary for this macro to come up with a legitimate |
| address; but often a machine-dependent strategy can generate better code. |
| |
| @findex GO_IF_MODE_DEPENDENT_ADDRESS |
| @item GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) |
| A C statement or compound statement with a conditional @code{goto |
| @var{label};} executed if memory address @var{x} (an RTX) can have |
| different meanings depending on the machine mode of the memory |
| reference it is used for or if the address is valid for some modes |
| but not others. |
| |
| Autoincrement and autodecrement addresses typically have mode-dependent |
| effects because the amount of the increment or decrement is the size |
| of the operand being addressed. Some machines have other mode-dependent |
| addresses. Many RISC machines have no mode-dependent addresses. |
| |
| You may assume that @var{addr} is a valid address for the machine. |
| |
| @findex LEGITIMATE_CONSTANT_P |
| @item LEGITIMATE_CONSTANT_P (@var{x}) |
| A C expression that is nonzero if @var{x} is a legitimate constant for |
| an immediate operand on the target machine. You can assume that |
| @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact, |
| @samp{1} is a suitable definition for this macro on machines where |
| anything @code{CONSTANT_P} is valid. |
| @end table |
| |
| @node Condition Code |
| @section Condition Code Status |
| @cindex condition code status |
| |
| @c prevent bad page break with this line |
| This describes the condition code status. |
| |
| @findex cc_status |
| The file @file{conditions.h} defines a variable @code{cc_status} to |
| describe how the condition code was computed (in case the interpretation of |
| the condition code depends on the instruction that it was set by). This |
| variable contains the RTL expressions on which the condition code is |
| currently based, and several standard flags. |
| |
| Sometimes additional machine-specific flags must be defined in the machine |
| description header file. It can also add additional machine-specific |
| information by defining @code{CC_STATUS_MDEP}. |
| |
| @table @code |
| @findex CC_STATUS_MDEP |
| @item CC_STATUS_MDEP |
| C code for a data type which is used for declaring the @code{mdep} |
| component of @code{cc_status}. It defaults to @code{int}. |
| |
| This macro is not used on machines that do not use @code{cc0}. |
| |
| @findex CC_STATUS_MDEP_INIT |
| @item CC_STATUS_MDEP_INIT |
| A C expression to initialize the @code{mdep} field to ``empty''. |
| The default definition does nothing, since most machines don't use |
| the field anyway. If you want to use the field, you should probably |
| define this macro to initialize it. |
| |
| This macro is not used on machines that do not use @code{cc0}. |
| |
| @findex NOTICE_UPDATE_CC |
| @item NOTICE_UPDATE_CC (@var{exp}, @var{insn}) |
| A C compound statement to set the components of @code{cc_status} |
| appropriately for an insn @var{insn} whose body is @var{exp}. It is |
| this macro's responsibility to recognize insns that set the condition |
| code as a byproduct of other activity as well as those that explicitly |
| set @code{(cc0)}. |
| |
| This macro is not used on machines that do not use @code{cc0}. |
| |
| If there are insns that do not set the condition code but do alter |
| other machine registers, this macro must check to see whether they |
| invalidate the expressions that the condition code is recorded as |
| reflecting. For example, on the 68000, insns that store in address |
| registers do not set the condition code, which means that usually |
| @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such |
| insns. But suppose that the previous insn set the condition code |
| based on location @samp{a4@@(102)} and the current insn stores a new |
| value in @samp{a4}. Although the condition code is not changed by |
| this, it will no longer be true that it reflects the contents of |
| @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter |
| @code{cc_status} in this case to say that nothing is known about the |
| condition code value. |
| |
| The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal |
| with the results of peephole optimization: insns whose patterns are |
| @code{parallel} RTXs containing various @code{reg}, @code{mem} or |
| constants which are just the operands. The RTL structure of these |
| insns is not sufficient to indicate what the insns actually do. What |
| @code{NOTICE_UPDATE_CC} should do when it sees one is just to run |
| @code{CC_STATUS_INIT}. |
| |
| A possible definition of @code{NOTICE_UPDATE_CC} is to call a function |
| that looks at an attribute (@pxref{Insn Attributes}) named, for example, |
| @samp{cc}. This avoids having detailed information about patterns in |
| two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}. |
| |
| @findex EXTRA_CC_MODES |
| @item EXTRA_CC_MODES |
| A list of additional modes for condition code values in registers |
| (@pxref{Jump Patterns}). This macro should expand to a sequence of |
| calls of the macro @code{CC} separated by white space. @code{CC} takes |
| two arguments. The first is the enumeration name of the mode, which |
| should begin with @samp{CC} and end with @samp{mode}. The second is a C |
| string giving the printable name of the mode; it should be the same as |
| the first argument, but with the trailing @samp{mode} removed. |
| |
| You should only define this macro if additional modes are required. |
| |
| A sample definition of @code{EXTRA_CC_MODES} is: |
| @smallexample |
| #define EXTRA_CC_MODES \ |
| CC(CC_NOOVmode, "CC_NOOV") \ |
| CC(CCFPmode, "CCFP") \ |
| CC(CCFPEmode, "CCFPE") |
| @end smallexample |
| |
| @findex SELECT_CC_MODE |
| @item SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) |
| Returns a mode from class @code{MODE_CC} to be used when comparison |
| operation code @var{op} is applied to rtx @var{x} and @var{y}. For |
| example, on the Sparc, @code{SELECT_CC_MODE} is defined as (see |
| @pxref{Jump Patterns} for a description of the reason for this |
| definition) |
| |
| @smallexample |
| #define SELECT_CC_MODE(OP,X,Y) \ |
| (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ |
| ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ |
| : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ |
| || GET_CODE (X) == NEG) \ |
| ? CC_NOOVmode : CCmode)) |
| @end smallexample |
| |
| You need not define this macro if @code{EXTRA_CC_MODES} is not defined. |
| |
| @findex CANONICALIZE_COMPARISON |
| @item CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1}) |
| On some machines not all possible comparisons are defined, but you can |
| convert an invalid comparison into a valid one. For example, the Alpha |
| does not have a @code{GT} comparison, but you can use an @code{LT} |
| comparison instead and swap the order of the operands. |
| |
| On such machines, define this macro to be a C statement to do any |
| required conversions. @var{code} is the initial comparison code |
| and @var{op0} and @var{op1} are the left and right operands of the |
| comparison, respectively. You should modify @var{code}, @var{op0}, and |
| @var{op1} as required. |
| |
| GCC will not assume that the comparison resulting from this macro is |
| valid but will see if the resulting insn matches a pattern in the |
| @file{md} file. |
| |
| You need not define this macro if it would never change the comparison |
| code or operands. |
| |
| @findex REVERSIBLE_CC_MODE |
| @item REVERSIBLE_CC_MODE (@var{mode}) |
| A C expression whose value is one if it is always safe to reverse a |
| comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} |
| can ever return @var{mode} for a floating-point inequality comparison, |
| then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. |
| |
| You need not define this macro if it would always returns zero or if the |
| floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. |
| For example, here is the definition used on the Sparc, where floating-point |
| inequality comparisons are always given @code{CCFPEmode}: |
| |
| @smallexample |
| #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) |
| @end smallexample |
| |
| @findex REVERSE_CONDITION (@var{code}, @var{mode}) |
| A C expression whose value is reversed condition code of the @var{code} for |
| comparison done in CC_MODE @var{mode}. The macro is used only in case |
| @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case |
| machine has some non-standard way how to reverse certain conditionals. For |
| instance in case all floating point conditions are non-trapping, compiler may |
| freely convert unordered compares to ordered one. Then definition may look |
| like: |
| |
| @smallexample |
| #define REVERSE_CONDITION(CODE, MODE) \ |
| ((MODE) != CCFPmode ? reverse_condition (CODE) \ |
| : reverse_condition_maybe_unordered (CODE)) |
| @end smallexample |
| |
| @findex REVERSE_CONDEXEC_PREDICATES_P |
| @item REVERSE_CONDEXEC_PREDICATES_P (@var{code1}, @var{code2}) |
| A C expression that returns true if the conditional execution predicate |
| @var{code1} is the inverse of @var{code2} and vice versa. Define this to |
| return 0 if the target has conditional execution predicates that cannot be |
| reversed safely. If no expansion is specified, this macro is defined as |
| follows: |
| |
| @smallexample |
| #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \ |
| ((x) == reverse_condition (y)) |
| @end smallexample |
| |
| @end table |
| |
| @node Costs |
| @section Describing Relative Costs of Operations |
| @cindex costs of instructions |
| @cindex relative costs |
| @cindex speed of instructions |
| |
| These macros let you describe the relative speed of various operations |
| on the target machine. |
| |
| @table @code |
| @findex CONST_COSTS |
| @item CONST_COSTS (@var{x}, @var{code}, @var{outer_code}) |
| A part of a C @code{switch} statement that describes the relative costs |
| of constant RTL expressions. It must contain @code{case} labels for |
| expression codes @code{const_int}, @code{const}, @code{symbol_ref}, |
| @code{label_ref} and @code{const_double}. Each case must ultimately |
| reach a @code{return} statement to return the relative cost of the use |
| of that kind of constant value in an expression. The cost may depend on |
| the precise value of the constant, which is available for examination in |
| @var{x}, and the rtx code of the expression in which it is contained, |
| found in @var{outer_code}. |
| |
| @var{code} is the expression code---redundant, since it can be |
| obtained with @code{GET_CODE (@var{x})}. |
| |
| @findex RTX_COSTS |
| @findex COSTS_N_INSNS |
| @item RTX_COSTS (@var{x}, @var{code}, @var{outer_code}) |
| Like @code{CONST_COSTS} but applies to nonconstant RTL expressions. |
| This can be used, for example, to indicate how costly a multiply |
| instruction is. In writing this macro, you can use the construct |
| @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast |
| instructions. @var{outer_code} is the code of the expression in which |
| @var{x} is contained. |
| |
| This macro is optional; do not define it if the default cost assumptions |
| are adequate for the target machine. |
| |
| @findex DEFAULT_RTX_COSTS |
| @item DEFAULT_RTX_COSTS (@var{x}, @var{code}, @var{outer_code}) |
| This macro, if defined, is called for any case not handled by the |
| @code{RTX_COSTS} or @code{CONST_COSTS} macros. This eliminates the need |
| to put case labels into the macro, but the code, or any functions it |
| calls, must assume that the RTL in @var{x} could be of any type that has |
| not already been handled. The arguments are the same as for |
| @code{RTX_COSTS}, and the macro should execute a return statement giving |
| the cost of any RTL expressions that it can handle. The default cost |
| calculation is used for any RTL for which this macro does not return a |
| value. |
| |
| This macro is optional; do not define it if the default cost assumptions |
| are adequate for the target machine. |
| |
| @findex ADDRESS_COST |
| @item ADDRESS_COST (@var{address}) |
| An expression giving the cost of an addressing mode that contains |
| @var{address}. If not defined, the cost is computed from |
| the @var{address} expression and the @code{CONST_COSTS} values. |
| |
| For most CISC machines, the default cost is a good approximation of the |
| true cost of the addressing mode. However, on RISC machines, all |
| instructions normally have the same length and execution time. Hence |
| all addresses will have equal costs. |
| |
| In cases where more than one form of an address is known, the form with |
| the lowest cost will be used. If multiple forms have the same, lowest, |
| cost, the one that is the most complex will be used. |
| |
| For example, suppose an address that is equal to the sum of a register |
| and a constant is used twice in the same basic block. When this macro |
| is not defined, the address will be computed in a register and memory |
| references will be indirect through that register. On machines where |
| the cost of the addressing mode containing the sum is no higher than |
| that of a simple indirect reference, this will produce an additional |
| instruction and possibly require an additional register. Proper |
| specification of this macro eliminates this overhead for such machines. |
| |
| Similar use of this macro is made in strength reduction of loops. |
| |
| @var{address} need not be valid as an address. In such a case, the cost |
| is not relevant and can be any value; invalid addresses need not be |
| assigned a different cost. |
| |
| On machines where an address involving more than one register is as |
| cheap as an address computation involving only one register, defining |
| @code{ADDRESS_COST} to reflect this can cause two registers to be live |
| over a region of code where only one would have been if |
| @code{ADDRESS_COST} were not defined in that manner. This effect should |
| be considered in the definition of this macro. Equivalent costs should |
| probably only be given to addresses with different numbers of registers |
| on machines with lots of registers. |
| |
| This macro will normally either not be defined or be defined as a |
| constant. |
| |
| @findex REGISTER_MOVE_COST |
| @item REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) |
| A C expression for the cost of moving data of mode @var{mode} from a |
| register in class @var{from} to one in class @var{to}. The classes are |
| expressed using the enumeration values such as @code{GENERAL_REGS}. A |
| value of 2 is the default; other values are interpreted relative to |
| that. |
| |
| It is not required that the cost always equal 2 when @var{from} is the |
| same as @var{to}; on some machines it is expensive to move between |
| registers if they are not general registers. |
| |
| If reload sees an insn consisting of a single @code{set} between two |
| hard registers, and if @code{REGISTER_MOVE_COST} applied to their |
| classes returns a value of 2, reload does not check to ensure that the |
| constraints of the insn are met. Setting a cost of other than 2 will |
| allow reload to verify that the constraints are met. You should do this |
| if the @samp{mov@var{m}} pattern's constraints do not allow such copying. |
| |
| @findex MEMORY_MOVE_COST |
| @item MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) |
| A C expression for the cost of moving data of mode @var{mode} between a |
| register of class @var{class} and memory; @var{in} is zero if the value |
| is to be written to memory, nonzero if it is to be read in. This cost |
| is relative to those in @code{REGISTER_MOVE_COST}. If moving between |
| registers and memory is more expensive than between two registers, you |
| should define this macro to express the relative cost. |
| |
| If you do not define this macro, GCC uses a default cost of 4 plus |
| the cost of copying via a secondary reload register, if one is |
| needed. If your machine requires a secondary reload register to copy |
| between memory and a register of @var{class} but the reload mechanism is |
| more complex than copying via an intermediate, define this macro to |
| reflect the actual cost of the move. |
| |
| GCC defines the function @code{memory_move_secondary_cost} if |
| secondary reloads are needed. It computes the costs due to copying via |
| a secondary register. If your machine copies from memory using a |
| secondary register in the conventional way but the default base value of |
| 4 is not correct for your machine, define this macro to add some other |
| value to the result of that function. The arguments to that function |
| are the same as to this macro. |
| |
| @findex BRANCH_COST |
| @item BRANCH_COST |
| A C expression for the cost of a branch instruction. A value of 1 is |
| the default; other values are interpreted relative to that. |
| @end table |
| |
| Here are additional macros which do not specify precise relative costs, |
| but only that certain actions are more expensive than GCC would |
| ordinarily expect. |
| |
| @table @code |
| @findex SLOW_BYTE_ACCESS |
| @item SLOW_BYTE_ACCESS |
| Define this macro as a C expression which is nonzero if accessing less |
| than a word of memory (i.e.@: a @code{char} or a @code{short}) is no |
| faster than accessing a word of memory, i.e., if such access |
| require more than one instruction or if there is no difference in cost |
| between byte and (aligned) word loads. |
| |
| When this macro is not defined, the compiler will access a field by |
| finding the smallest containing object; when it is defined, a fullword |
| load will be used if alignment permits. Unless bytes accesses are |
| faster than word accesses, using word accesses is preferable since it |
| may eliminate subsequent memory access if subsequent accesses occur to |
| other fields in the same word of the structure, but to different bytes. |
| |
| @findex SLOW_UNALIGNED_ACCESS |
| @item SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) |
| Define this macro to be the value 1 if memory accesses described by the |
| @var{mode} and @var{alignment} parameters have a cost many times greater |
| than aligned accesses, for example if they are emulated in a trap |
| handler. |
| |
| When this macro is nonzero, the compiler will act as if |
| @code{STRICT_ALIGNMENT} were nonzero when generating code for block |
| moves. This can cause significantly more instructions to be produced. |
| Therefore, do not set this macro nonzero if unaligned accesses only add a |
| cycle or two to the time for a memory access. |
| |
| If the value of this macro is always zero, it need not be defined. If |
| this macro is defined, it should produce a nonzero value when |
| @code{STRICT_ALIGNMENT} is nonzero. |
| |
| @findex DONT_REDUCE_ADDR |
| @item DONT_REDUCE_ADDR |
| Define this macro to inhibit strength reduction of memory addresses. |
| (On some machines, such strength reduction seems to do harm rather |
| than good.) |
| |
| @findex MOVE_RATIO |
| @item MOVE_RATIO |
| The threshold of number of scalar memory-to-memory move insns, @emph{below} |
| which a sequence of insns should be generated instead of a |
| string move insn or a library call. Increasing the value will always |
| make code faster, but eventually incurs high cost in increased code size. |
| |
| Note that on machines where the corresponding move insn is a |
| @code{define_expand} that emits a sequence of insns, this macro counts |
| the number of such sequences. |
| |
| If you don't define this, a reasonable default is used. |
| |
| @findex MOVE_BY_PIECES_P |
| @item MOVE_BY_PIECES_P (@var{size}, @var{alignment}) |
| A C expression used to determine whether @code{move_by_pieces} will be used to |
| copy a chunk of memory, or whether some other block move mechanism |
| will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less |
| than @code{MOVE_RATIO}. |
| |
| @findex MOVE_MAX_PIECES |
| @item MOVE_MAX_PIECES |
| A C expression used by @code{move_by_pieces} to determine the largest unit |
| a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. |
| |
| @findex USE_LOAD_POST_INCREMENT |
| @item USE_LOAD_POST_INCREMENT (@var{mode}) |
| A C expression used to determine whether a load postincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_INCREMENT}. |
| |
| @findex USE_LOAD_POST_DECREMENT |
| @item USE_LOAD_POST_DECREMENT (@var{mode}) |
| A C expression used to determine whether a load postdecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_DECREMENT}. |
| |
| @findex USE_LOAD_PRE_INCREMENT |
| @item USE_LOAD_PRE_INCREMENT (@var{mode}) |
| A C expression used to determine whether a load preincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_INCREMENT}. |
| |
| @findex USE_LOAD_PRE_DECREMENT |
| @item USE_LOAD_PRE_DECREMENT (@var{mode}) |
| A C expression used to determine whether a load predecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_DECREMENT}. |
| |
| @findex USE_STORE_POST_INCREMENT |
| @item USE_STORE_POST_INCREMENT (@var{mode}) |
| A C expression used to determine whether a store postincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_INCREMENT}. |
| |
| @findex USE_STORE_POST_DECREMENT |
| @item USE_STORE_POST_DECREMENT (@var{mode}) |
| A C expression used to determine whether a store postdecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_DECREMENT}. |
| |
| @findex USE_STORE_PRE_INCREMENT |
| @item USE_STORE_PRE_INCREMENT (@var{mode}) |
| This macro is used to determine whether a store preincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_INCREMENT}. |
| |
| @findex USE_STORE_PRE_DECREMENT |
| @item USE_STORE_PRE_DECREMENT (@var{mode}) |
| This macro is used to determine whether a store predecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_DECREMENT}. |
| |
| @findex NO_FUNCTION_CSE |
| @item NO_FUNCTION_CSE |
| Define this macro if it is as good or better to call a constant |
| function address than to call an address kept in a register. |
| |
| @findex NO_RECURSIVE_FUNCTION_CSE |
| @item NO_RECURSIVE_FUNCTION_CSE |
| Define this macro if it is as good or better for a function to call |
| itself with an explicit address than to call an address kept in a |
| register. |
| @end table |
| |
| @node Scheduling |
| @section Adjusting the Instruction Scheduler |
| |
| The instruction scheduler may need a fair amount of machine-specific |
| adjustment in order to produce good code. GCC provides several target |
| hooks for this purpose. It is usually enough to define just a few of |
| them: try the first ones in this list first. |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void) |
| This hook returns the maximum number of instructions that can ever issue |
| at the same time on the target machine. The default is one. This value |
| must be constant over the entire compilation. If you need it to vary |
| depending on what the instructions are, you must use |
| @samp{TARGET_SCHED_VARIABLE_ISSUE}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more}) |
| This hook is executed by the scheduler after it has scheduled an insn |
| from the ready list. It should return the number of insns which can |
| still be issued in the current cycle. Normally this is |
| @samp{@w{@var{more} - 1}}. You should define this hook if some insns |
| take more machine resources than others, so that fewer insns can follow |
| them in the same cycle. @var{file} is either a null pointer, or a stdio |
| stream to write any debug output to. @var{verbose} is the verbose level |
| provided by @option{-fsched-verbose-@var{n}}. @var{insn} is the |
| instruction that was scheduled. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost}) |
| This function corrects the value of @var{cost} based on the relationship |
| between @var{insn} and @var{dep_insn} through the dependence @var{link}. |
| It should return the new value. The default is to make no adjustment to |
| @var{cost}. This can be used for example to specify to the scheduler |
| that an output- or anti-dependence does not incur the same cost as a |
| data-dependence. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority}) |
| This hook adjusts the integer scheduling priority @var{priority} of |
| @var{insn}. It should return the new priority. Reduce the priority to |
| execute @var{insn} earlier, increase the priority to execute @var{insn} |
| later. Do not define this hook if you do not need to adjust the |
| scheduling priorities of insns. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock}) |
| This hook is executed by the scheduler after it has scheduled the ready |
| list, to allow the machine description to reorder it (for example to |
| combine two small instructions together on @samp{VLIW} machines). |
| @var{file} is either a null pointer, or a stdio stream to write any |
| debug output to. @var{verbose} is the verbose level provided by |
| @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready |
| list of instructions that are ready to be scheduled. @var{n_readyp} is |
| a pointer to the number of elements in the ready list. The scheduler |
| reads the ready list in reverse order, starting with |
| @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock} |
| is the timer tick of the scheduler. You may modify the ready list and |
| the number of ready insns. The return value is the number of insns that |
| can issue this cycle; normally this is just @code{issue_rate}. See also |
| @samp{TARGET_SCHED_REORDER2}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock}) |
| Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That |
| function is called whenever the scheduler starts a new cycle. This one |
| is called once per iteration over a cycle, immediately after |
| @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and |
| return the number of insns to be scheduled in the same cycle. Defining |
| this hook can be useful if there are frequent situations where |
| scheduling one insn causes other insns to become ready in the same |
| cycle. These other insns can then be taken into account properly. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready}) |
| This hook is executed by the scheduler at the beginning of each block of |
| instructions that are to be scheduled. @var{file} is either a null |
| pointer, or a stdio stream to write any debug output to. @var{verbose} |
| is the verbose level provided by @option{-fsched-verbose-@var{n}}. |
| @var{max_ready} is the maximum number of insns in the current scheduling |
| region that can be live at the same time. This can be used to allocate |
| scratch space if it is needed, e.g. by @samp{TARGET_SCHED_REORDER}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose}) |
| This hook is executed by the scheduler at the end of each block of |
| instructions that are to be scheduled. It can be used to perform |
| cleanup of any actions done by the other scheduling hooks. @var{file} |
| is either a null pointer, or a stdio stream to write any debug output |
| to. @var{verbose} is the verbose level provided by |
| @option{-fsched-verbose-@var{n}}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} rtx TARGET_SCHED_CYCLE_DISPLAY (int @var{clock}, rtx @var{last}) |
| This hook is called in verbose mode only, at the beginning of each pass |
| over a basic block. It should insert an insn into the chain after |
| @var{last}, which has no effect, but records the value @var{clock} in |
| RTL dumps and assembly output. Define this hook only if you need this |
| level of detail about what the scheduler is doing. |
| @end deftypefn |
| |
| @node Sections |
| @section Dividing the Output into Sections (Texts, Data, @dots{}) |
| @c the above section title is WAY too long. maybe cut the part between |
| @c the (...)? --mew 10feb93 |
| |
| An object file is divided into sections containing different types of |
| data. In the most common case, there are three sections: the @dfn{text |
| section}, which holds instructions and read-only data; the @dfn{data |
| section}, which holds initialized writable data; and the @dfn{bss |
| section}, which holds uninitialized data. Some systems have other kinds |
| of sections. |
| |
| The compiler must tell the assembler when to switch sections. These |
| macros control what commands to output to tell the assembler this. You |
| can also define additional sections. |
| |
| @table @code |
| @findex TEXT_SECTION_ASM_OP |
| @item TEXT_SECTION_ASM_OP |
| A C expression whose value is a string, including spacing, containing the |
| assembler operation that should precede instructions and read-only data. |
| Normally @code{"\t.text"} is right. |
| |
| @findex TEXT_SECTION |
| @item TEXT_SECTION |
| A C statement that switches to the default section containing instructions. |
| Normally this is not needed, as simply defining @code{TEXT_SECTION_ASM_OP} |
| is enough. The MIPS port uses this to sort all functions after all data |
| declarations. |
| |
| @findex DATA_SECTION_ASM_OP |
| @item DATA_SECTION_ASM_OP |
| A C expression whose value is a string, including spacing, containing the |
| assembler operation to identify the following data as writable initialized |
| data. Normally @code{"\t.data"} is right. |
| |
| @findex SHARED_SECTION_ASM_OP |
| @item SHARED_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| shared data. If not defined, @code{DATA_SECTION_ASM_OP} will be used. |
| |
| @findex BSS_SECTION_ASM_OP |
| @item BSS_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| uninitialized global data. If not defined, and neither |
| @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined, |
| uninitialized global data will be output in the data section if |
| @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be |
| used. |
| |
| @findex SHARED_BSS_SECTION_ASM_OP |
| @item SHARED_BSS_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| uninitialized global shared data. If not defined, and |
| @code{BSS_SECTION_ASM_OP} is, the latter will be used. |
| |
| @findex INIT_SECTION_ASM_OP |
| @item INIT_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| initialization code. If not defined, GCC will assume such a section does |
| not exist. |
| |
| @findex FINI_SECTION_ASM_OP |
| @item FINI_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| finalization code. If not defined, GCC will assume such a section does |
| not exist. |
| |
| @findex CRT_CALL_STATIC_FUNCTION |
| @item CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) |
| If defined, an ASM statement that switches to a different section |
| via @var{section_op}, calls @var{function}, and switches back to |
| the text section. This is used in @file{crtstuff.c} if |
| @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls |
| to initialization and finalization functions from the init and fini |
| sections. By default, this macro uses a simple function call. Some |
| ports need hand-crafted assembly code to avoid dependencies on |
| registers initialized in the function prologue or to ensure that |
| constant pools don't end up too far way in the text section. |
| |
| @findex FORCE_CODE_SECTION_ALIGN |
| @item FORCE_CODE_SECTION_ALIGN |
| If defined, an ASM statement that aligns a code section to some |
| arbitrary boundary. This is used to force all fragments of the |
| @code{.init} and @code{.fini} sections to have to same alignment |
| and thus prevent the linker from having to add any padding. |
| |
| @findex EXTRA_SECTIONS |
| @findex in_text |
| @findex in_data |
| @item EXTRA_SECTIONS |
| A list of names for sections other than the standard two, which are |
| @code{in_text} and @code{in_data}. You need not define this macro |
| on a system with no other sections (that GCC needs to use). |
| |
| @findex EXTRA_SECTION_FUNCTIONS |
| @findex text_section |
| @findex data_section |
| @item EXTRA_SECTION_FUNCTIONS |
| One or more functions to be defined in @file{varasm.c}. These |
| functions should do jobs analogous to those of @code{text_section} and |
| @code{data_section}, for your additional sections. Do not define this |
| macro if you do not define @code{EXTRA_SECTIONS}. |
| |
| @findex READONLY_DATA_SECTION |
| @item READONLY_DATA_SECTION |
| On most machines, read-only variables, constants, and jump tables are |
| placed in the text section. If this is not the case on your machine, |
| this macro should be defined to be the name of a function (either |
| @code{data_section} or a function defined in @code{EXTRA_SECTIONS}) that |
| switches to the section to be used for read-only items. |
| |
| If these items should be placed in the text section, this macro should |
| not be defined. |
| |
| @findex SELECT_SECTION |
| @item SELECT_SECTION (@var{exp}, @var{reloc}, @var{align}) |
| A C statement or statements to switch to the appropriate section for |
| output of @var{exp}. You can assume that @var{exp} is either a |
| @code{VAR_DECL} node or a constant of some sort. @var{reloc} |
| indicates whether the initial value of @var{exp} requires link-time |
| relocations. Bit 1 is set when variable contains local relocations |
| only, while bit 2 is set for global relocations. |
| Select the section by calling @code{text_section} or one |
| of the alternatives for other sections. @var{align} is the constant |
| alignment in bits. |
| |
| Do not define this macro if you put all read-only variables and |
| constants in the read-only data section (usually the text section). |
| |
| @findex SELECT_RTX_SECTION |
| @item SELECT_RTX_SECTION (@var{mode}, @var{rtx}, @var{align}) |
| A C statement or statements to switch to the appropriate section for |
| output of @var{rtx} in mode @var{mode}. You can assume that @var{rtx} |
| is some kind of constant in RTL@. The argument @var{mode} is redundant |
| except in the case of a @code{const_int} rtx. Select the section by |
| calling @code{text_section} or one of the alternatives for other |
| sections. @var{align} is the constant alignment in bits. |
| |
| Do not define this macro if you put all constants in the read-only |
| data section. |
| |
| @findex JUMP_TABLES_IN_TEXT_SECTION |
| @item JUMP_TABLES_IN_TEXT_SECTION |
| Define this macro to be an expression with a nonzero value if jump |
| tables (for @code{tablejump} insns) should be output in the text |
| section, along with the assembler instructions. Otherwise, the |
| readonly data section is used. |
| |
| This macro is irrelevant if there is no separate readonly data section. |
| |
| @findex ENCODE_SECTION_INFO |
| @item ENCODE_SECTION_INFO (@var{decl}, @var{new_decl_p}) |
| Define this macro if references to a symbol or a constant must be |
| treated differently depending on something about the variable or |
| function named by the symbol (such as what section it is in). |
| |
| The macro definition, if any, is executed under two circumstances. One |
| is immediately after the rtl for @var{decl} that represents a variable |
| or a function has been created and stored in @code{DECL_RTL(@var{decl})}. |
| The value of the rtl will be a @code{mem} whose address is a @code{symbol_ref}. |
| The other is immediately after the rtl for @var{decl} that represents a |
| constant has been created and stored in @code{TREE_CST_RTL (@var{decl})}. |
| The macro is called once for each distinct constant in a source file. |
| |
| The @var{new_decl_p} argument will be true if this is the first time that |
| @code{ENCODE_SECTION_INFO} has been invoked on this decl. It will |
| be false for subsequent invocations, which will happen for duplicate |
| declarations. Whether or not anything must be done for the duplicate |
| declaration depends on whether @code{ENCODE_SECTION_INFO} examines |
| @code{DECL_ATTRIBUTES}. |
| |
| @cindex @code{SYMBOL_REF_FLAG}, in @code{ENCODE_SECTION_INFO} |
| The usual thing for this macro to do is to record a flag in the |
| @code{symbol_ref} (such as @code{SYMBOL_REF_FLAG}) or to store a |
| modified name string in the @code{symbol_ref} (if one bit is not |
| enough information). |
| |
| @findex STRIP_NAME_ENCODING |
| @item STRIP_NAME_ENCODING (@var{var}, @var{sym_name}) |
| Decode @var{sym_name} and store the real name part in @var{var}, sans |
| the characters that encode section info. Define this macro if |
| @code{ENCODE_SECTION_INFO} alters the symbol's name string. |
| |
| @findex UNIQUE_SECTION |
| @item UNIQUE_SECTION (@var{decl}, @var{reloc}) |
| A C statement to build up a unique section name, expressed as a |
| @code{STRING_CST} node, and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. |
| @var{reloc} indicates whether the initial value of @var{exp} requires |
| link-time relocations. If you do not define this macro, GCC will use |
| the symbol name prefixed by @samp{.} as the section name. Note - this |
| macro can now be called for uninitialized data items as well as |
| initialized data and functions. |
| @end table |
| |
| @node PIC |
| @section Position Independent Code |
| @cindex position independent code |
| @cindex PIC |
| |
| This section describes macros that help implement generation of position |
| independent code. Simply defining these macros is not enough to |
| generate valid PIC; you must also add support to the macros |
| @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as |
| well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of |
| @samp{movsi} to do something appropriate when the source operand |
| contains a symbolic address. You may also need to alter the handling of |
| switch statements so that they use relative addresses. |
| @c i rearranged the order of the macros above to try to force one of |
| @c them to the next line, to eliminate an overfull hbox. --mew 10feb93 |
| |
| @table @code |
| @findex PIC_OFFSET_TABLE_REGNUM |
| @item PIC_OFFSET_TABLE_REGNUM |
| The register number of the register used to address a table of static |
| data addresses in memory. In some cases this register is defined by a |
| processor's ``application binary interface'' (ABI)@. When this macro |
| is defined, RTL is generated for this register once, as with the stack |
| pointer and frame pointer registers. If this macro is not defined, it |
| is up to the machine-dependent files to allocate such a register (if |
| necessary). Note that this register must be fixed when in use (e.g.@: |
| when @code{flag_pic} is true). |
| |
| @findex PIC_OFFSET_TABLE_REG_CALL_CLOBBERED |
| @item PIC_OFFSET_TABLE_REG_CALL_CLOBBERED |
| Define this macro if the register defined by |
| @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define |
| this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. |
| |
| @findex FINALIZE_PIC |
| @item FINALIZE_PIC |
| By generating position-independent code, when two different programs (A |
| and B) share a common library (libC.a), the text of the library can be |
| shared whether or not the library is linked at the same address for both |
| programs. In some of these environments, position-independent code |
| requires not only the use of different addressing modes, but also |
| special code to enable the use of these addressing modes. |
| |
| The @code{FINALIZE_PIC} macro serves as a hook to emit these special |
| codes once the function is being compiled into assembly code, but not |
| before. (It is not done before, because in the case of compiling an |
| inline function, it would lead to multiple PIC prologues being |
| included in functions which used inline functions and were compiled to |
| assembly language.) |
| |
| @findex LEGITIMATE_PIC_OPERAND_P |
| @item LEGITIMATE_PIC_OPERAND_P (@var{x}) |
| A C expression that is nonzero if @var{x} is a legitimate immediate |
| operand on the target machine when generating position independent code. |
| You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not |
| check this. You can also assume @var{flag_pic} is true, so you need not |
| check it either. You need not define this macro if all constants |
| (including @code{SYMBOL_REF}) can be immediate operands when generating |
| position independent code. |
| @end table |
| |
| @node Assembler Format |
| @section Defining the Output Assembler Language |
| |
| This section describes macros whose principal purpose is to describe how |
| to write instructions in assembler language---rather than what the |
| instructions do. |
| |
| @menu |
| * File Framework:: Structural information for the assembler file. |
| * Data Output:: Output of constants (numbers, strings, addresses). |
| * Uninitialized Data:: Output of uninitialized variables. |
| * Label Output:: Output and generation of labels. |
| * Initialization:: General principles of initialization |
| and termination routines. |
| * Macros for Initialization:: |
| Specific macros that control the handling of |
| initialization and termination routines. |
| * Instruction Output:: Output of actual instructions. |
| * Dispatch Tables:: Output of jump tables. |
| * Exception Region Output:: Output of exception region code. |
| * Alignment Output:: Pseudo ops for alignment and skipping data. |
| @end menu |
| |
| @node File Framework |
| @subsection The Overall Framework of an Assembler File |
| @cindex assembler format |
| @cindex output of assembler code |
| |
| @c prevent bad page break with this line |
| This describes the overall framework of an assembler file. |
| |
| @table @code |
| @findex ASM_FILE_START |
| @item ASM_FILE_START (@var{stream}) |
| A C expression which outputs to the stdio stream @var{stream} |
| some appropriate text to go at the start of an assembler file. |
| |
| Normally this macro is defined to output a line containing |
| @samp{#NO_APP}, which is a comment that has no effect on most |
| assemblers but tells the GNU assembler that it can save time by not |
| checking for certain assembler constructs. |
| |
| On systems that use SDB, it is necessary to output certain commands; |
| see @file{attasm.h}. |
| |
| @findex ASM_FILE_END |
| @item ASM_FILE_END (@var{stream}) |
| A C expression which outputs to the stdio stream @var{stream} |
| some appropriate text to go at the end of an assembler file. |
| |
| If this macro is not defined, the default is to output nothing |
| special at the end of the file. Most systems don't require any |
| definition. |
| |
| On systems that use SDB, it is necessary to output certain commands; |
| see @file{attasm.h}. |
| |
| @findex ASM_COMMENT_START |
| @item ASM_COMMENT_START |
| A C string constant describing how to begin a comment in the target |
| assembler language. The compiler assumes that the comment will end at |
| the end of the line. |
| |
| @findex ASM_APP_ON |
| @item ASM_APP_ON |
| A C string constant for text to be output before each @code{asm} |
| statement or group of consecutive ones. Normally this is |
| @code{"#APP"}, which is a comment that has no effect on most |
| assemblers but tells the GNU assembler that it must check the lines |
| that follow for all valid assembler constructs. |
| |
| @findex ASM_APP_OFF |
| @item ASM_APP_OFF |
| A C string constant for text to be output after each @code{asm} |
| statement or group of consecutive ones. Normally this is |
| @code{"#NO_APP"}, which tells the GNU assembler to resume making the |
| time-saving assumptions that are valid for ordinary compiler output. |
| |
| @findex ASM_OUTPUT_SOURCE_FILENAME |
| @item ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) |
| A C statement to output COFF information or DWARF debugging information |
| which indicates that filename @var{name} is the current source file to |
| the stdio stream @var{stream}. |
| |
| This macro need not be defined if the standard form of output |
| for the file format in use is appropriate. |
| |
| @findex OUTPUT_QUOTED_STRING |
| @item OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) |
| A C statement to output the string @var{string} to the stdio stream |
| @var{stream}. If you do not call the function @code{output_quoted_string} |
| in your config files, GCC will only call it to output filenames to |
| the assembler source. So you can use it to canonicalize the format |
| of the filename using this macro. |
| |
| @findex ASM_OUTPUT_SOURCE_LINE |
| @item ASM_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}) |
| A C statement to output DBX or SDB debugging information before code |
| for line number @var{line} of the current source file to the |
| stdio stream @var{stream}. |
| |
| This macro need not be defined if the standard form of debugging |
| information for the debugger in use is appropriate. |
| |
| @findex ASM_OUTPUT_IDENT |
| @item ASM_OUTPUT_IDENT (@var{stream}, @var{string}) |
| A C statement to output something to the assembler file to handle a |
| @samp{#ident} directive containing the text @var{string}. If this |
| macro is not defined, nothing is output for a @samp{#ident} directive. |
| |
| @findex OBJC_PROLOGUE |
| @item OBJC_PROLOGUE |
| A C statement to output any assembler statements which are required to |
| precede any Objective-C object definitions or message sending. The |
| statement is executed only when compiling an Objective-C program. |
| @end table |
| |
| @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align}) |
| Output assembly directives to switch to section @var{name}. The section |
| should have attributes as specified by @var{flags}, which is a bit mask |
| of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align} |
| is nonzero, it contains an alignment in bytes to be used for the section, |
| otherwise some target default should be used. Only targets that must |
| specify an alignment within the section directive need pay attention to |
| @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS |
| This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) |
| Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} |
| based on a variable or function decl, a section name, and whether or not the |
| declaration's initializer may contain runtime relocations. @var{decl} may be |
| null, in which case read-write data should be assumed. |
| |
| The default version if this function handles choosing code vs data, |
| read-only vs read-write data, and @code{flag_pic}. You should only |
| need to override this if your target has special flags that might be |
| set via @code{__attribute__}. |
| @end deftypefn |
| |
| @need 2000 |
| @node Data Output |
| @subsection Output of Data |
| |
| |
| @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP |
| These hooks specify assembly directives for creating certain kinds |
| of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a |
| byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an |
| aligned two-byte object, and so on. Any of the hooks may be |
| @code{NULL}, indicating that no suitable directive is available. |
| |
| The compiler will print these strings at the start of a new line, |
| followed immediately by the object's initial value. In most cases, |
| the string should contain a tab, a pseudo-op, and then another tab. |
| @end deftypevr |
| |
| @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p}) |
| The @code{assemble_integer} function uses this hook to output an |
| integer object. @var{x} is the object's value, @var{size} is its size |
| in bytes and @var{aligned_p} indicates whether it is aligned. The |
| function should return @code{true} if it was able to output the |
| object. If it returns false, @code{assemble_integer} will try to |
| split the object into smaller parts. |
| |
| The default implementation of this hook will use the |
| @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} |
| when the relevant string is @code{NULL}. |
| @end deftypefn |
| |
| @table @code |
| @findex OUTPUT_ADDR_CONST_EXTRA |
| @item OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail}) |
| A C statement to recognize @var{rtx} patterns that |
| @code{output_addr_const} can't deal with, and output assembly code to |
| @var{stream} corresponding to the pattern @var{x}. This may be used to |
| allow machine-dependent @code{UNSPEC}s to appear within constants. |
| |
| If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must |
| @code{goto fail}, so that a standard error message is printed. If it |
| prints an error message itself, by calling, for example, |
| @code{output_operand_lossage}, it may just complete normally. |
| |
| @findex ASM_OUTPUT_ASCII |
| @item ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| instruction to assemble a string constant containing the @var{len} |
| bytes at @var{ptr}. @var{ptr} will be a C expression of type |
| @code{char *} and @var{len} a C expression of type @code{int}. |
| |
| If the assembler has a @code{.ascii} pseudo-op as found in the |
| Berkeley Unix assembler, do not define the macro |
| @code{ASM_OUTPUT_ASCII}. |
| |
| @findex ASM_OUTPUT_FDESC |
| @item ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) |
| A C statement to output word @var{n} of a function descriptor for |
| @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} |
| is defined, and is otherwise unused. |
| |
| @findex CONSTANT_POOL_BEFORE_FUNCTION |
| @item CONSTANT_POOL_BEFORE_FUNCTION |
| You may define this macro as a C expression. You should define the |
| expression to have a nonzero value if GCC should output the constant |
| pool for a function before the code for the function, or a zero value if |
| GCC should output the constant pool after the function. If you do |
| not define this macro, the usual case, GCC will output the constant |
| pool before the function. |
| |
| @findex ASM_OUTPUT_POOL_PROLOGUE |
| @item ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) |
| A C statement to output assembler commands to define the start of the |
| constant pool for a function. @var{funname} is a string giving |
| the name of the function. Should the return type of the function |
| be required, it can be obtained via @var{fundecl}. @var{size} |
| is the size, in bytes, of the constant pool that will be written |
| immediately after this call. |
| |
| If no constant-pool prefix is required, the usual case, this macro need |
| not be defined. |
| |
| @findex ASM_OUTPUT_SPECIAL_POOL_ENTRY |
| @item ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) |
| A C statement (with or without semicolon) to output a constant in the |
| constant pool, if it needs special treatment. (This macro need not do |
| anything for RTL expressions that can be output normally.) |
| |
| The argument @var{file} is the standard I/O stream to output the |
| assembler code on. @var{x} is the RTL expression for the constant to |
| output, and @var{mode} is the machine mode (in case @var{x} is a |
| @samp{const_int}). @var{align} is the required alignment for the value |
| @var{x}; you should output an assembler directive to force this much |
| alignment. |
| |
| The argument @var{labelno} is a number to use in an internal label for |
| the address of this pool entry. The definition of this macro is |
| responsible for outputting the label definition at the proper place. |
| Here is how to do this: |
| |
| @example |
| ASM_OUTPUT_INTERNAL_LABEL (@var{file}, "LC", @var{labelno}); |
| @end example |
| |
| When you output a pool entry specially, you should end with a |
| @code{goto} to the label @var{jumpto}. This will prevent the same pool |
| entry from being output a second time in the usual manner. |
| |
| You need not define this macro if it would do nothing. |
| |
| @findex CONSTANT_AFTER_FUNCTION_P |
| @item CONSTANT_AFTER_FUNCTION_P (@var{exp}) |
| Define this macro as a C expression which is nonzero if the constant |
| @var{exp}, of type @code{tree}, should be output after the code for a |
| function. The compiler will normally output all constants before the |
| function; you need not define this macro if this is OK@. |
| |
| @findex ASM_OUTPUT_POOL_EPILOGUE |
| @item ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) |
| A C statement to output assembler commands to at the end of the constant |
| pool for a function. @var{funname} is a string giving the name of the |
| function. Should the return type of the function be required, you can |
| obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the |
| constant pool that GCC wrote immediately before this call. |
| |
| If no constant-pool epilogue is required, the usual case, you need not |
| define this macro. |
| |
| @findex IS_ASM_LOGICAL_LINE_SEPARATOR |
| @item IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}) |
| Define this macro as a C expression which is nonzero if @var{C} is |
| used as a logical line separator by the assembler. |
| |
| If you do not define this macro, the default is that only |
| the character @samp{;} is treated as a logical line separator. |
| @end table |
| |
| @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN |
| These target hooks are C string constants, describing the syntax in the |
| assembler for grouping arithmetic expressions. If not overridden, they |
| default to normal parentheses, which is correct for most assemblers. |
| @end deftypevr |
| |
| These macros are provided by @file{real.h} for writing the definitions |
| of @code{ASM_OUTPUT_DOUBLE} and the like: |
| |
| @table @code |
| @item REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) |
| @itemx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) |
| @itemx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) |
| @findex REAL_VALUE_TO_TARGET_SINGLE |
| @findex REAL_VALUE_TO_TARGET_DOUBLE |
| @findex REAL_VALUE_TO_TARGET_LONG_DOUBLE |
| These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the target's |
| floating point representation, and store its bit pattern in the array of |
| @code{long int} whose address is @var{l}. The number of elements in the |
| output array is determined by the size of the desired target floating |
| point data type: 32 bits of it go in each @code{long int} array |
| element. Each array element holds 32 bits of the result, even if |
| @code{long int} is wider than 32 bits on the host machine. |
| |
| The array element values are designed so that you can print them out |
| using @code{fprintf} in the order they should appear in the target |
| machine's memory. |
| |
| @item REAL_VALUE_TO_DECIMAL (@var{x}, @var{format}, @var{string}) |
| @findex REAL_VALUE_TO_DECIMAL |
| This macro converts @var{x}, of type @code{REAL_VALUE_TYPE}, to a |
| decimal number and stores it as a string into @var{string}. |
| You must pass, as @var{string}, the address of a long enough block |
| of space to hold the result. |
| |
| The argument @var{format} is a @code{printf}-specification that serves |
| as a suggestion for how to format the output string. |
| @end table |
| |
| @node Uninitialized Data |
| @subsection Output of Uninitialized Variables |
| |
| Each of the macros in this section is used to do the whole job of |
| outputting a single uninitialized variable. |
| |
| @table @code |
| @findex ASM_OUTPUT_COMMON |
| @item ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of a common-label named |
| @var{name} whose size is @var{size} bytes. The variable @var{rounded} |
| is the size rounded up to whatever alignment the caller wants. |
| |
| Use the expression @code{assemble_name (@var{stream}, @var{name})} to |
| output the name itself; before and after that, output the additional |
| assembler syntax for defining the name, and a newline. |
| |
| This macro controls how the assembler definitions of uninitialized |
| common global variables are output. |
| |
| @findex ASM_OUTPUT_ALIGNED_COMMON |
| @item ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a |
| separate, explicit argument. If you define this macro, it is used in |
| place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in |
| handling the required alignment of the variable. The alignment is specified |
| as the number of bits. |
| |
| @findex ASM_OUTPUT_ALIGNED_DECL_COMMON |
| @item ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the |
| variable to be output, if there is one, or @code{NULL_TREE} if there |
| is no corresponding variable. If you define this macro, GCC will use it |
| in place of both @code{ASM_OUTPUT_COMMON} and |
| @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see |
| the variable's decl in order to chose what to output. |
| |
| @findex ASM_OUTPUT_SHARED_COMMON |
| @item ASM_OUTPUT_SHARED_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) |
| If defined, it is similar to @code{ASM_OUTPUT_COMMON}, except that it |
| is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_COMMON} |
| will be used. |
| |
| @findex ASM_OUTPUT_BSS |
| @item ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of uninitialized global @var{decl} named |
| @var{name} whose size is @var{size} bytes. The variable @var{rounded} |
| is the size rounded up to whatever alignment the caller wants. |
| |
| Try to use function @code{asm_output_bss} defined in @file{varasm.c} when |
| defining this macro. If unable, use the expression |
| @code{assemble_name (@var{stream}, @var{name})} to output the name itself; |
| before and after that, output the additional assembler syntax for defining |
| the name, and a newline. |
| |
| This macro controls how the assembler definitions of uninitialized global |
| variables are output. This macro exists to properly support languages like |
| C++ which do not have @code{common} data. However, this macro currently |
| is not defined for all targets. If this macro and |
| @code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON} |
| or @code{ASM_OUTPUT_ALIGNED_COMMON} or |
| @code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used. |
| |
| @findex ASM_OUTPUT_ALIGNED_BSS |
| @item ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a |
| separate, explicit argument. If you define this macro, it is used in |
| place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in |
| handling the required alignment of the variable. The alignment is specified |
| as the number of bits. |
| |
| Try to use function @code{asm_output_aligned_bss} defined in file |
| @file{varasm.c} when defining this macro. |
| |
| @findex ASM_OUTPUT_SHARED_BSS |
| @item ASM_OUTPUT_SHARED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) |
| If defined, it is similar to @code{ASM_OUTPUT_BSS}, except that it |
| is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_BSS} |
| will be used. |
| |
| @findex ASM_OUTPUT_LOCAL |
| @item ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of a local-common-label named |
| @var{name} whose size is @var{size} bytes. The variable @var{rounded} |
| is the size rounded up to whatever alignment the caller wants. |
| |
| Use the expression @code{assemble_name (@var{stream}, @var{name})} to |
| output the name itself; before and after that, output the additional |
| assembler syntax for defining the name, and a newline. |
| |
| This macro controls how the assembler definitions of uninitialized |
| static variables are output. |
| |
| @findex ASM_OUTPUT_ALIGNED_LOCAL |
| @item ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a |
| separate, explicit argument. If you define this macro, it is used in |
| place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in |
| handling the required alignment of the variable. The alignment is specified |
| as the number of bits. |
| |
| @findex ASM_OUTPUT_ALIGNED_DECL_LOCAL |
| @item ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the |
| variable to be output, if there is one, or @code{NULL_TREE} if there |
| is no corresponding variable. If you define this macro, GCC will use it |
| in place of both @code{ASM_OUTPUT_DECL} and |
| @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see |
| the variable's decl in order to chose what to output. |
| |
| @findex ASM_OUTPUT_SHARED_LOCAL |
| @item ASM_OUTPUT_SHARED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) |
| If defined, it is similar to @code{ASM_OUTPUT_LOCAL}, except that it |
| is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_LOCAL} |
| will be used. |
| @end table |
| |
| @node Label Output |
| @subsection Output and Generation of Labels |
| |
| @c prevent bad page break with this line |
| This is about outputting labels. |
| |
| @table @code |
| @findex ASM_OUTPUT_LABEL |
| @findex assemble_name |
| @item ASM_OUTPUT_LABEL (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of a label named @var{name}. |
| Use the expression @code{assemble_name (@var{stream}, @var{name})} to |
| output the name itself; before and after that, output the additional |
| assembler syntax for defining the name, and a newline. |
| |
| @findex ASM_DECLARE_FUNCTION_NAME |
| @item ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name @var{name} of a |
| function which is being defined. This macro is responsible for |
| outputting the label definition (perhaps using |
| @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the |
| @code{FUNCTION_DECL} tree node representing the function. |
| |
| If this macro is not defined, then the function name is defined in the |
| usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). |
| |
| @findex ASM_DECLARE_FUNCTION_SIZE |
| @item ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the size of a function |
| which is being defined. The argument @var{name} is the name of the |
| function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node |
| representing the function. |
| |
| If this macro is not defined, then the function size is not defined. |
| |
| @findex ASM_DECLARE_OBJECT_NAME |
| @item ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name @var{name} of an |
| initialized variable which is being defined. This macro must output the |
| label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument |
| @var{decl} is the @code{VAR_DECL} tree node representing the variable. |
| |
| If this macro is not defined, then the variable name is defined in the |
| usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). |
| |
| @findex ASM_DECLARE_REGISTER_GLOBAL |
| @item ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for claiming a register @var{regno} |
| for a global variable @var{decl} with name @var{name}. |
| |
| If you don't define this macro, that is equivalent to defining it to do |
| nothing. |
| |
| @findex ASM_FINISH_DECLARE_OBJECT |
| @item ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) |
| A C statement (sans semicolon) to finish up declaring a variable name |
| once the compiler has processed its initializer fully and thus has had a |
| chance to determine the size of an array when controlled by an |
| initializer. This is used on systems where it's necessary to declare |
| something about the size of the object. |
| |
| If you don't define this macro, that is equivalent to defining it to do |
| nothing. |
| |
| @findex ASM_GLOBALIZE_LABEL |
| @item ASM_GLOBALIZE_LABEL (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} some commands that will make the label @var{name} global; |
| that is, available for reference from other files. Use the expression |
| @code{assemble_name (@var{stream}, @var{name})} to output the name |
| itself; before and after that, output the additional assembler syntax |
| for making that name global, and a newline. |
| |
| @findex ASM_WEAKEN_LABEL |
| @item ASM_WEAKEN_LABEL (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} some commands that will make the label @var{name} weak; |
| that is, available for reference from other files but only used if |
| no other definition is available. Use the expression |
| @code{assemble_name (@var{stream}, @var{name})} to output the name |
| itself; before and after that, output the additional assembler syntax |
| for making that name weak, and a newline. |
| |
| If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not |
| support weak symbols and you should not define the @code{SUPPORTS_WEAK} |
| macro. |
| |
| @findex ASM_WEAKEN_DECL |
| @item ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) |
| Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and |
| @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function |
| or variable decl. If @var{value} is not @code{NULL}, this C statement |
| should output to the stdio stream @var{stream} assembler code which |
| defines (equates) the weak symbol @var{name} to have the value |
| @var{value}. If @var{value} is @code{NULL}, it should output commands |
| to make @var{name} weak. |
| |
| @findex SUPPORTS_WEAK |
| @item SUPPORTS_WEAK |
| A C expression which evaluates to true if the target supports weak symbols. |
| |
| If you don't define this macro, @file{defaults.h} provides a default |
| definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} |
| is defined, the default definition is @samp{1}; otherwise, it is |
| @samp{0}. Define this macro if you want to control weak symbol support |
| with a compiler flag such as @option{-melf}. |
| |
| @findex MAKE_DECL_ONE_ONLY (@var{decl}) |
| @item MAKE_DECL_ONE_ONLY |
| A C statement (sans semicolon) to mark @var{decl} to be emitted as a |
| public symbol such that extra copies in multiple translation units will |
| be discarded by the linker. Define this macro if your object file |
| format provides support for this concept, such as the @samp{COMDAT} |
| section flags in the Microsoft Windows PE/COFF format, and this support |
| requires changes to @var{decl}, such as putting it in a separate section. |
| |
| @findex SUPPORTS_ONE_ONLY |
| @item SUPPORTS_ONE_ONLY |
| A C expression which evaluates to true if the target supports one-only |
| semantics. |
| |
| If you don't define this macro, @file{varasm.c} provides a default |
| definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default |
| definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if |
| you want to control one-only symbol support with a compiler flag, or if |
| setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to |
| be emitted as one-only. |
| |
| @findex ASM_OUTPUT_EXTERNAL |
| @item ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name of an external |
| symbol named @var{name} which is referenced in this compilation but |
| not defined. The value of @var{decl} is the tree node for the |
| declaration. |
| |
| This macro need not be defined if it does not need to output anything. |
| The GNU assembler and most Unix assemblers don't require anything. |
| |
| @findex ASM_OUTPUT_EXTERNAL_LIBCALL |
| @item ASM_OUTPUT_EXTERNAL_LIBCALL (@var{stream}, @var{symref}) |
| A C statement (sans semicolon) to output on @var{stream} an assembler |
| pseudo-op to declare a library function name external. The name of the |
| library function is given by @var{symref}, which has type @code{rtx} and |
| is a @code{symbol_ref}. |
| |
| This macro need not be defined if it does not need to output anything. |
| The GNU assembler and most Unix assemblers don't require anything. |
| |
| @findex ASM_OUTPUT_LABELREF |
| @item ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} a reference in assembler syntax to a label named |
| @var{name}. This should add @samp{_} to the front of the name, if that |
| is customary on your operating system, as it is in most Berkeley Unix |
| systems. This macro is used in @code{assemble_name}. |
| |
| @findex ASM_OUTPUT_SYMBOL_REF |
| @item ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) |
| A C statement (sans semicolon) to output a reference to |
| @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} |
| will be used to output the name of the symbol. This macro may be used |
| to modify the way a symbol is referenced depending on information |
| encoded by @code{ENCODE_SECTION_INFO}. |
| |
| @findex ASM_OUTPUT_LABEL_REF |
| @item ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) |
| A C statement (sans semicolon) to output a reference to @var{buf}, the |
| result of ASM_GENERATE_INTERNAL_LABEL. If not defined, |
| @code{assemble_name} will be used to output the name of the symbol. |
| This macro is not used by @code{output_asm_label}, or the @code{%l} |
| specifier that calls it; the intention is that this macro should be set |
| when it is necessary to output a label differently when its address |
| is being taken. |
| |
| @findex ASM_OUTPUT_INTERNAL_LABEL |
| @item ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{prefix}, @var{num}) |
| A C statement to output to the stdio stream @var{stream} a label whose |
| name is made from the string @var{prefix} and the number @var{num}. |
| |
| It is absolutely essential that these labels be distinct from the labels |
| used for user-level functions and variables. Otherwise, certain programs |
| will have name conflicts with internal labels. |
| |
| It is desirable to exclude internal labels from the symbol table of the |
| object file. Most assemblers have a naming convention for labels that |
| should be excluded; on many systems, the letter @samp{L} at the |
| beginning of a label has this effect. You should find out what |
| convention your system uses, and follow it. |
| |
| The usual definition of this macro is as follows: |
| |
| @example |
| fprintf (@var{stream}, "L%s%d:\n", @var{prefix}, @var{num}) |
| @end example |
| |
| @findex ASM_OUTPUT_DEBUG_LABEL |
| @item ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) |
| A C statement to output to the stdio stream @var{stream} a debug info |
| label whose name is made from the string @var{prefix} and the number |
| @var{num}. This is useful for VLIW targets, where debug info labels |
| may need to be treated differently than branch target labels. On some |
| systems, branch target labels must be at the beginning of instruction |
| bundles, but debug info labels can occur in the middle of instruction |
| bundles. |
| |
| If this macro is not defined, then @code{ASM_OUTPUT_INTERNAL_LABEL} will be |
| used. |
| |
| @findex ASM_OUTPUT_ALTERNATE_LABEL_NAME |
| @item ASM_OUTPUT_ALTERNATE_LABEL_NAME (@var{stream}, @var{string}) |
| A C statement to output to the stdio stream @var{stream} the string |
| @var{string}. |
| |
| The default definition of this macro is as follows: |
| |
| @example |
| fprintf (@var{stream}, "%s:\n", LABEL_ALTERNATE_NAME (INSN)) |
| @end example |
| |
| @findex ASM_GENERATE_INTERNAL_LABEL |
| @item ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) |
| A C statement to store into the string @var{string} a label whose name |
| is made from the string @var{prefix} and the number @var{num}. |
| |
| This string, when output subsequently by @code{assemble_name}, should |
| produce the output that @code{ASM_OUTPUT_INTERNAL_LABEL} would produce |
| with the same @var{prefix} and @var{num}. |
| |
| If the string begins with @samp{*}, then @code{assemble_name} will |
| output the rest of the string unchanged. It is often convenient for |
| @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the |
| string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets |
| to output the string, and may change it. (Of course, |
| @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so |
| you should know what it does on your machine.) |
| |
| @findex ASM_FORMAT_PRIVATE_NAME |
| @item ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) |
| A C expression to assign to @var{outvar} (which is a variable of type |
| @code{char *}) a newly allocated string made from the string |
| @var{name} and the number @var{number}, with some suitable punctuation |
| added. Use @code{alloca} to get space for the string. |
| |
| The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to |
| produce an assembler label for an internal static variable whose name is |
| @var{name}. Therefore, the string must be such as to result in valid |
| assembler code. The argument @var{number} is different each time this |
| macro is executed; it prevents conflicts between similarly-named |
| internal static variables in different scopes. |
| |
| Ideally this string should not be a valid C identifier, to prevent any |
| conflict with the user's own symbols. Most assemblers allow periods |
| or percent signs in assembler symbols; putting at least one of these |
| between the name and the number will suffice. |
| |
| @findex ASM_OUTPUT_DEF |
| @item ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the symbol @var{name} to have the value @var{value}. |
| |
| @findex SET_ASM_OP |
| If @code{SET_ASM_OP} is defined, a default definition is provided which is |
| correct for most systems. |
| |
| @findex ASM_OUTPUT_DEF_FROM_DECLS |
| @item ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the symbol whose tree node is @var{decl_of_name} |
| to have the value of the tree node @var{decl_of_value}. This macro will |
| be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if |
| the tree nodes are available. |
| |
| @findex ASM_OUTPUT_DEFINE_LABEL_DIFFERENCE_SYMBOL |
| @item ASM_OUTPUT_DEFINE_LABEL_DIFFERENCE_SYMBOL (@var{stream}, @var{symbol}, @var{high}, @var{low}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the symbol @var{symbol} to have a value equal to |
| the difference of the two symbols @var{high} and @var{low}, |
| i.e.@: @var{high} minus @var{low}. GCC guarantees that the symbols @var{high} |
| and @var{low} are already known by the assembler so that the difference |
| resolves into a constant. |
| |
| @findex SET_ASM_OP |
| If @code{SET_ASM_OP} is defined, a default definition is provided which is |
| correct for most systems. |
| |
| @findex ASM_OUTPUT_WEAK_ALIAS |
| @item ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the weak symbol @var{name} to have the value |
| @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as |
| an undefined weak symbol. |
| |
| Define this macro if the target only supports weak aliases; define |
| @code{ASM_OUTPUT_DEF} instead if possible. |
| |
| @findex OBJC_GEN_METHOD_LABEL |
| @item OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) |
| Define this macro to override the default assembler names used for |
| Objective-C methods. |
| |
| The default name is a unique method number followed by the name of the |
| class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of |
| the category is also included in the assembler name (e.g.@: |
| @samp{_1_Foo_Bar}). |
| |
| These names are safe on most systems, but make debugging difficult since |
| the method's selector is not present in the name. Therefore, particular |
| systems define other ways of computing names. |
| |
| @var{buf} is an expression of type @code{char *} which gives you a |
| buffer in which to store the name; its length is as long as |
| @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus |
| 50 characters extra. |
| |
| The argument @var{is_inst} specifies whether the method is an instance |
| method or a class method; @var{class_name} is the name of the class; |
| @var{cat_name} is the name of the category (or @code{NULL} if the method is not |
| in a category); and @var{sel_name} is the name of the selector. |
| |
| On systems where the assembler can handle quoted names, you can use this |
| macro to provide more human-readable names. |
| |
| @findex ASM_DECLARE_CLASS_REFERENCE |
| @item ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} commands to declare that the label @var{name} is an |
| Objective-C class reference. This is only needed for targets whose |
| linkers have special support for NeXT-style runtimes. |
| |
| @findex ASM_DECLARE_UNRESOLVED_REFERENCE |
| @item ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} commands to declare that the label @var{name} is an |
| unresolved Objective-C class reference. This is only needed for targets |
| whose linkers have special support for NeXT-style runtimes. |
| @end table |
| |
| @node Initialization |
| @subsection How Initialization Functions Are Handled |
| @cindex initialization routines |
| @cindex termination routines |
| @cindex constructors, output of |
| @cindex destructors, output of |
| |
| The compiled code for certain languages includes @dfn{constructors} |
| (also called @dfn{initialization routines})---functions to initialize |
| data in the program when the program is started. These functions need |
| to be called before the program is ``started''---that is to say, before |
| @code{main} is called. |
| |
| Compiling some languages generates @dfn{destructors} (also called |
| @dfn{termination routines}) that should be called when the program |
| terminates. |
| |
| To make the initialization and termination functions work, the compiler |
| must output something in the assembler code to cause those functions to |
| be called at the appropriate time. When you port the compiler to a new |
| system, you need to specify how to do this. |
| |
| There are two major ways that GCC currently supports the execution of |
| initialization and termination functions. Each way has two variants. |
| Much of the structure is common to all four variations. |
| |
| @findex __CTOR_LIST__ |
| @findex __DTOR_LIST__ |
| The linker must build two lists of these functions---a list of |
| initialization functions, called @code{__CTOR_LIST__}, and a list of |
| termination functions, called @code{__DTOR_LIST__}. |
| |
| Each list always begins with an ignored function pointer (which may hold |
| 0, @minus{}1, or a count of the function pointers after it, depending on |
| the environment). This is followed by a series of zero or more function |
| pointers to constructors (or destructors), followed by a function |
| pointer containing zero. |
| |
| Depending on the operating system and its executable file format, either |
| @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup |
| time and exit time. Constructors are called in reverse order of the |
| list; destructors in forward order. |
| |
| The best way to handle static constructors works only for object file |
| formats which provide arbitrarily-named sections. A section is set |
| aside for a list of constructors, and another for a list of destructors. |
| Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each |
| object file that defines an initialization function also puts a word in |
| the constructor section to point to that function. The linker |
| accumulates all these words into one contiguous @samp{.ctors} section. |
| Termination functions are handled similarly. |
| |
| This method will be chosen as the default by @file{target-def.h} if |
| @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not |
| support arbitrary sections, but does support special designated |
| constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} |
| and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. |
| |
| When arbitrary sections are available, there are two variants, depending |
| upon how the code in @file{crtstuff.c} is called. On systems that |
| support a @dfn{.init} section which is executed at program startup, |
| parts of @file{crtstuff.c} are compiled into that section. The |
| program is linked by the @code{gcc} driver like this: |
| |
| @example |
| ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o |
| @end example |
| |
| The prologue of a function (@code{__init}) appears in the @code{.init} |
| section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise |
| for the function @code{__fini} in the @dfn{.fini} section. Normally these |
| files are provided by the operating system or by the GNU C library, but |
| are provided by GCC for a few targets. |
| |
| The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) |
| compiled from @file{crtstuff.c}. They contain, among other things, code |
| fragments within the @code{.init} and @code{.fini} sections that branch |
| to routines in the @code{.text} section. The linker will pull all parts |
| of a section together, which results in a complete @code{__init} function |
| that invokes the routines we need at startup. |
| |
| To use this variant, you must define the @code{INIT_SECTION_ASM_OP} |
| macro properly. |
| |
| If no init section is available, when GCC compiles any function called |
| @code{main} (or more accurately, any function designated as a program |
| entry point by the language front end calling @code{expand_main_function}), |
| it inserts a procedure call to @code{__main} as the first executable code |
| after the function prologue. The @code{__main} function is defined |
| in @file{libgcc2.c} and runs the global constructors. |
| |
| In file formats that don't support arbitrary sections, there are again |
| two variants. In the simplest variant, the GNU linker (GNU @code{ld}) |
| and an `a.out' format must be used. In this case, |
| @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} |
| entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, |
| and with the address of the void function containing the initialization |
| code as its value. The GNU linker recognizes this as a request to add |
| the value to a @dfn{set}; the values are accumulated, and are eventually |
| placed in the executable as a vector in the format described above, with |
| a leading (ignored) count and a trailing zero element. |
| @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init |
| section is available, the absence of @code{INIT_SECTION_ASM_OP} causes |
| the compilation of @code{main} to call @code{__main} as above, starting |
| the initialization process. |
| |
| The last variant uses neither arbitrary sections nor the GNU linker. |
| This is preferable when you want to do dynamic linking and when using |
| file formats which the GNU linker does not support, such as `ECOFF'@. In |
| this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and |
| termination functions are recognized simply by their names. This requires |
| an extra program in the linkage step, called @command{collect2}. This program |
| pretends to be the linker, for use with GCC; it does its job by running |
| the ordinary linker, but also arranges to include the vectors of |
| initialization and termination functions. These functions are called |
| via @code{__main} as described above. In order to use this method, |
| @code{use_collect2} must be defined in the target in @file{config.gcc}. |
| |
| @ifinfo |
| The following section describes the specific macros that control and |
| customize the handling of initialization and termination functions. |
| @end ifinfo |
| |
| @node Macros for Initialization |
| @subsection Macros Controlling Initialization Routines |
| |
| Here are the macros that control how the compiler handles initialization |
| and termination functions: |
| |
| @table @code |
| @findex INIT_SECTION_ASM_OP |
| @item INIT_SECTION_ASM_OP |
| If defined, a C string constant, including spacing, for the assembler |
| operation to identify the following data as initialization code. If not |
| defined, GCC will assume such a section does not exist. When you are |
| using special sections for initialization and termination functions, this |
| macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to |
| run the initialization functions. |
| |
| @item HAS_INIT_SECTION |
| @findex HAS_INIT_SECTION |
| If defined, @code{main} will not call @code{__main} as described above. |
| This macro should be defined for systems that control start-up code |
| on a symbol-by-symbol basis, such as OSF/1, and should not |
| be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. |
| |
| @item LD_INIT_SWITCH |
| @findex LD_INIT_SWITCH |
| If defined, a C string constant for a switch that tells the linker that |
| the following symbol is an initialization routine. |
| |
| @item LD_FINI_SWITCH |
| @findex LD_FINI_SWITCH |
| If defined, a C string constant for a switch that tells the linker that |
| the following symbol is a finalization routine. |
| |
| @item COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) |
| If defined, a C statement that will write a function that can be |
| automatically called when a shared library is loaded. The function |
| should call @var{func}, which takes no arguments. If not defined, and |
| the object format requires an explicit initialization function, then a |
| function called @code{_GLOBAL__DI} will be generated. |
| |
| This function and the following one are used by collect2 when linking a |
| shared library that needs constructors or destructors, or has DWARF2 |
| exception tables embedded in the code. |
| |
| @item COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) |
| If defined, a C statement that will write a function that can be |
| automatically called when a shared library is unloaded. The function |
| should call @var{func}, which takes no arguments. If not defined, and |
| the object format requires an explicit finalization function, then a |
| function called @code{_GLOBAL__DD} will be generated. |
| |
| @item INVOKE__main |
| @findex INVOKE__main |
| If defined, @code{main} will call @code{__main} despite the presence of |
| @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems |
| where the init section is not actually run automatically, but is still |
| useful for collecting the lists of constructors and destructors. |
| |
| @item SUPPORTS_INIT_PRIORITY |
| @findex SUPPORTS_INIT_PRIORITY |
| If nonzero, the C++ @code{init_priority} attribute is supported and the |
| compiler should emit instructions to control the order of initialization |
| of objects. If zero, the compiler will issue an error message upon |
| encountering an @code{init_priority} attribute. |
| @end table |
| |
| @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS |
| This value is true if the target supports some ``native'' method of |
| collecting constructors and destructors to be run at startup and exit. |
| It is false if we must use @command{collect2}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority}) |
| If defined, a function that outputs assembler code to arrange to call |
| the function referenced by @var{symbol} at initialization time. |
| |
| Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking |
| no arguments and with no return value. If the target supports initialization |
| priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; |
| otherwise it must be @code{DEFAULT_INIT_PRIORITY}. |
| |
| If this macro is not defined by the target, a suitable default will |
| be chosen if (1) the target supports arbitrary section names, (2) the |
| target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} |
| is not defined. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority}) |
| This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination |
| functions rather than initialization functions. |
| @end deftypefn |
| |
| If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine |
| generated for the generated object file will have static linkage. |
| |
| If your system uses @command{collect2} as the means of processing |
| constructors, then that program normally uses @command{nm} to scan |
| an object file for constructor functions to be called. |
| |
| On certain kinds of systems, you can define these macros to make |
| @command{collect2} work faster (and, in some cases, make it work at all): |
| |
| @table @code |
| @findex OBJECT_FORMAT_COFF |
| @item OBJECT_FORMAT_COFF |
| Define this macro if the system uses COFF (Common Object File Format) |
| object files, so that @command{collect2} can assume this format and scan |
| object files directly for dynamic constructor/destructor functions. |
| |
| @findex OBJECT_FORMAT_ROSE |
| @item OBJECT_FORMAT_ROSE |
| Define this macro if the system uses ROSE format object files, so that |
| @command{collect2} can assume this format and scan object files directly |
| for dynamic constructor/destructor functions. |
| |
| These macros are effective only in a native compiler; @command{collect2} as |
| part of a cross compiler always uses @command{nm} for the target machine. |
| |
| @findex REAL_NM_FILE_NAME |
| @item REAL_NM_FILE_NAME |
| Define this macro as a C string constant containing the file name to use |
| to execute @command{nm}. The default is to search the path normally for |
| @command{nm}. |
| |
| If your system supports shared libraries and has a program to list the |
| dynamic dependencies of a given library or executable, you can define |
| these macros to enable support for running initialization and |
| termination functions in shared libraries: |
| |
| @findex LDD_SUFFIX |
| @item LDD_SUFFIX |
| Define this macro to a C string constant containing the name of the program |
| which lists dynamic dependencies, like @command{"ldd"} under SunOS 4. |
| |
| @findex PARSE_LDD_OUTPUT |
| @item PARSE_LDD_OUTPUT (@var{ptr}) |
| Define this macro to be C code that extracts filenames from the output |
| of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable |
| of type @code{char *} that points to the beginning of a line of output |
| from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the |
| code must advance @var{ptr} to the beginning of the filename on that |
| line. Otherwise, it must set @var{ptr} to @code{NULL}. |
| @end table |
| |
| @node Instruction Output |
| @subsection Output of Assembler Instructions |
| |
| @c prevent bad page break with this line |
| This describes assembler instruction output. |
| |
| @table @code |
| @findex REGISTER_NAMES |
| @item REGISTER_NAMES |
| A C initializer containing the assembler's names for the machine |
| registers, each one as a C string constant. This is what translates |
| register numbers in the compiler into assembler language. |
| |
| @findex ADDITIONAL_REGISTER_NAMES |
| @item ADDITIONAL_REGISTER_NAMES |
| If defined, a C initializer for an array of structures containing a name |
| and a register number. This macro defines additional names for hard |
| registers, thus allowing the @code{asm} option in declarations to refer |
| to registers using alternate names. |
| |
| @findex ASM_OUTPUT_OPCODE |
| @item ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) |
| Define this macro if you are using an unusual assembler that |
| requires different names for the machine instructions. |
| |
| The definition is a C statement or statements which output an |
| assembler instruction opcode to the stdio stream @var{stream}. The |
| macro-operand @var{ptr} is a variable of type @code{char *} which |
| points to the opcode name in its ``internal'' form---the form that is |
| written in the machine description. The definition should output the |
| opcode name to @var{stream}, performing any translation you desire, and |
| increment the variable @var{ptr} to point at the end of the opcode |
| so that it will not be output twice. |
| |
| In fact, your macro definition may process less than the entire opcode |
| name, or more than the opcode name; but if you want to process text |
| that includes @samp{%}-sequences to substitute operands, you must take |
| care of the substitution yourself. Just be sure to increment |
| @var{ptr} over whatever text should not be output normally. |
| |
| @findex recog_data.operand |
| If you need to look at the operand values, they can be found as the |
| elements of @code{recog_data.operand}. |
| |
| If the macro definition does nothing, the instruction is output |
| in the usual way. |
| |
| @findex FINAL_PRESCAN_INSN |
| @item FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) |
| If defined, a C statement to be executed just prior to the output of |
| assembler code for @var{insn}, to modify the extracted operands so |
| they will be output differently. |
| |
| Here the argument @var{opvec} is the vector containing the operands |
| extracted from @var{insn}, and @var{noperands} is the number of |
| elements of the vector which contain meaningful data for this insn. |
| The contents of this vector are what will be used to convert the insn |
| template into assembler code, so you can change the assembler output |
| by changing the contents of the vector. |
| |
| This macro is useful when various assembler syntaxes share a single |
| file of instruction patterns; by defining this macro differently, you |
| can cause a large class of instructions to be output differently (such |
| as with rearranged operands). Naturally, variations in assembler |
| syntax affecting individual insn patterns ought to be handled by |
| writing conditional output routines in those patterns. |
| |
| If this macro is not defined, it is equivalent to a null statement. |
| |
| @findex FINAL_PRESCAN_LABEL |
| @item FINAL_PRESCAN_LABEL |
| If defined, @code{FINAL_PRESCAN_INSN} will be called on each |
| @code{CODE_LABEL}. In that case, @var{opvec} will be a null pointer and |
| @var{noperands} will be zero. |
| |
| @findex PRINT_OPERAND |
| @item PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) |
| A C compound statement to output to stdio stream @var{stream} the |
| assembler syntax for an instruction operand @var{x}. @var{x} is an |
| RTL expression. |
| |
| @var{code} is a value that can be used to specify one of several ways |
| of printing the operand. It is used when identical operands must be |
| printed differently depending on the context. @var{code} comes from |
| the @samp{%} specification that was used to request printing of the |
| operand. If the specification was just @samp{%@var{digit}} then |
| @var{code} is 0; if the specification was @samp{%@var{ltr} |
| @var{digit}} then @var{code} is the ASCII code for @var{ltr}. |
| |
| @findex reg_names |
| If @var{x} is a register, this macro should print the register's name. |
| The names can be found in an array @code{reg_names} whose type is |
| @code{char *[]}. @code{reg_names} is initialized from |
| @code{REGISTER_NAMES}. |
| |
| When the machine description has a specification @samp{%@var{punct}} |
| (a @samp{%} followed by a punctuation character), this macro is called |
| with a null pointer for @var{x} and the punctuation character for |
| @var{code}. |
| |
| @findex PRINT_OPERAND_PUNCT_VALID_P |
| @item PRINT_OPERAND_PUNCT_VALID_P (@var{code}) |
| A C expression which evaluates to true if @var{code} is a valid |
| punctuation character for use in the @code{PRINT_OPERAND} macro. If |
| @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no |
| punctuation characters (except for the standard one, @samp{%}) are used |
| in this way. |
| |
| @findex PRINT_OPERAND_ADDRESS |
| @item PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) |
| A C compound statement to output to stdio stream @var{stream} the |
| assembler syntax for an instruction operand that is a memory reference |
| whose address is @var{x}. @var{x} is an RTL expression. |
| |
| @cindex @code{ENCODE_SECTION_INFO} usage |
| On some machines, the syntax for a symbolic address depends on the |
| section that the address refers to. On these machines, define the macro |
| @code{ENCODE_SECTION_INFO} to store the information into the |
| @code{symbol_ref}, and then check for it here. @xref{Assembler Format}. |
| |
| @findex DBR_OUTPUT_SEQEND |
| @findex dbr_sequence_length |
| @item DBR_OUTPUT_SEQEND(@var{file}) |
| A C statement, to be executed after all slot-filler instructions have |
| been output. If necessary, call @code{dbr_sequence_length} to |
| determine the number of slots filled in a sequence (zero if not |
| currently outputting a sequence), to decide how many no-ops to output, |
| or whatever. |
| |
| Don't define this macro if it has nothing to do, but it is helpful in |
| reading assembly output if the extent of the delay sequence is made |
| explicit (e.g.@: with white space). |
| |
| @findex final_sequence |
| Note that output routines for instructions with delay slots must be |
| prepared to deal with not being output as part of a sequence |
| (i.e.@: when the scheduling pass is not run, or when no slot fillers could be |
| found.) The variable @code{final_sequence} is null when not |
| processing a sequence, otherwise it contains the @code{sequence} rtx |
| being output. |
| |
| @findex REGISTER_PREFIX |
| @findex LOCAL_LABEL_PREFIX |
| @findex USER_LABEL_PREFIX |
| @findex IMMEDIATE_PREFIX |
| @findex asm_fprintf |
| @item REGISTER_PREFIX |
| @itemx LOCAL_LABEL_PREFIX |
| @itemx USER_LABEL_PREFIX |
| @itemx IMMEDIATE_PREFIX |
| If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, |
| @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see |
| @file{final.c}). These are useful when a single @file{md} file must |
| support multiple assembler formats. In that case, the various @file{tm.h} |
| files can define these macros differently. |
| |
| @item ASM_FPRINTF_EXTENSIONS(@var{file}, @var{argptr}, @var{format}) |
| @findex ASM_FPRINTF_EXTENSIONS |
| If defined this macro should expand to a series of @code{case} |
| statements which will be parsed inside the @code{switch} statement of |
| the @code{asm_fprintf} function. This allows targets to define extra |
| printf formats which may useful when generating their assembler |
| statements. Note that upper case letters are reserved for future |
| generic extensions to asm_fprintf, and so are not available to target |
| specific code. The output file is given by the parameter @var{file}. |
| The varargs input pointer is @var{argptr} and the rest of the format |
| string, starting the character after the one that is being switched |
| upon, is pointed to by @var{format}. |
| |
| @findex ASSEMBLER_DIALECT |
| @item ASSEMBLER_DIALECT |
| If your target supports multiple dialects of assembler language (such as |
| different opcodes), define this macro as a C expression that gives the |
| numeric index of the assembler language dialect to use, with zero as the |
| first variant. |
| |
| If this macro is defined, you may use constructs of the form |
| @smallexample |
| @samp{@{option0|option1|option2@dots{}@}} |
| @end smallexample |
| @noindent |
| in the output templates of patterns (@pxref{Output Template}) or in the |
| first argument of @code{asm_fprintf}. This construct outputs |
| @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of |
| @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters |
| within these strings retain their usual meaning. If there are fewer |
| alternatives within the braces than the value of |
| @code{ASSEMBLER_DIALECT}, the construct outputs nothing. |
| |
| If you do not define this macro, the characters @samp{@{}, @samp{|} and |
| @samp{@}} do not have any special meaning when used in templates or |
| operands to @code{asm_fprintf}. |
| |
| Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, |
| @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express |
| the variations in assembler language syntax with that mechanism. Define |
| @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax |
| if the syntax variant are larger and involve such things as different |
| opcodes or operand order. |
| |
| @findex ASM_OUTPUT_REG_PUSH |
| @item ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) |
| A C expression to output to @var{stream} some assembler code |
| which will push hard register number @var{regno} onto the stack. |
| The code need not be optimal, since this macro is used only when |
| profiling. |
| |
| @findex ASM_OUTPUT_REG_POP |
| @item ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) |
| A C expression to output to @var{stream} some assembler code |
| which will pop hard register number @var{regno} off of the stack. |
| The code need not be optimal, since this macro is used only when |
| profiling. |
| @end table |
| |
| @node Dispatch Tables |
| @subsection Output of Dispatch Tables |
| |
| @c prevent bad page break with this line |
| This concerns dispatch tables. |
| |
| @table @code |
| @cindex dispatch table |
| @findex ASM_OUTPUT_ADDR_DIFF_ELT |
| @item ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| pseudo-instruction to generate a difference between two labels. |
| @var{value} and @var{rel} are the numbers of two internal labels. The |
| definitions of these labels are output using |
| @code{ASM_OUTPUT_INTERNAL_LABEL}, and they must be printed in the same |
| way here. For example, |
| |
| @example |
| fprintf (@var{stream}, "\t.word L%d-L%d\n", |
| @var{value}, @var{rel}) |
| @end example |
| |
| You must provide this macro on machines where the addresses in a |
| dispatch table are relative to the table's own address. If defined, GCC |
| will also use this macro on all machines when producing PIC@. |
| @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the |
| mode and flags can be read. |
| |
| @findex ASM_OUTPUT_ADDR_VEC_ELT |
| @item ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) |
| This macro should be provided on machines where the addresses |
| in a dispatch table are absolute. |
| |
| The definition should be a C statement to output to the stdio stream |
| @var{stream} an assembler pseudo-instruction to generate a reference to |
| a label. @var{value} is the number of an internal label whose |
| definition is output using @code{ASM_OUTPUT_INTERNAL_LABEL}. |
| For example, |
| |
| @example |
| fprintf (@var{stream}, "\t.word L%d\n", @var{value}) |
| @end example |
| |
| @findex ASM_OUTPUT_CASE_LABEL |
| @item ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) |
| Define this if the label before a jump-table needs to be output |
| specially. The first three arguments are the same as for |
| @code{ASM_OUTPUT_INTERNAL_LABEL}; the fourth argument is the |
| jump-table which follows (a @code{jump_insn} containing an |
| @code{addr_vec} or @code{addr_diff_vec}). |
| |
| This feature is used on system V to output a @code{swbeg} statement |
| for the table. |
| |
| If this macro is not defined, these labels are output with |
| @code{ASM_OUTPUT_INTERNAL_LABEL}. |
| |
| @findex ASM_OUTPUT_CASE_END |
| @item ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) |
| Define this if something special must be output at the end of a |
| jump-table. The definition should be a C statement to be executed |
| after the assembler code for the table is written. It should write |
| the appropriate code to stdio stream @var{stream}. The argument |
| @var{table} is the jump-table insn, and @var{num} is the label-number |
| of the preceding label. |
| |
| If this macro is not defined, nothing special is output at the end of |
| the jump-table. |
| @end table |
| |
| @node Exception Region Output |
| @subsection Assembler Commands for Exception Regions |
| |
| @c prevent bad page break with this line |
| |
| This describes commands marking the start and the end of an exception |
| region. |
| |
| @table @code |
| @findex EH_FRAME_SECTION_NAME |
| @item EH_FRAME_SECTION_NAME |
| If defined, a C string constant for the name of the section containing |
| exception handling frame unwind information. If not defined, GCC will |
| provide a default definition if the target supports named sections. |
| @file{crtstuff.c} uses this macro to switch to the appropriate section. |
| |
| You should define this symbol if your target supports DWARF 2 frame |
| unwind information and the default definition does not work. |
| |
| @findex EH_FRAME_IN_DATA_SECTION |
| @item EH_FRAME_IN_DATA_SECTION |
| If defined, DWARF 2 frame unwind information will be placed in the |
| data section even though the target supports named sections. This |
| might be necessary, for instance, if the system linker does garbage |
| collection and sections cannot be marked as not to be collected. |
| |
| Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is |
| also defined. |
| |
| @findex MASK_RETURN_ADDR |
| @item MASK_RETURN_ADDR |
| An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so |
| that it does not contain any extraneous set bits in it. |
| |
| @findex DWARF2_UNWIND_INFO |
| @item DWARF2_UNWIND_INFO |
| Define this macro to 0 if your target supports DWARF 2 frame unwind |
| information, but it does not yet work with exception handling. |
| Otherwise, if your target supports this information (if it defines |
| @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP} |
| or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of |
| 1. |
| |
| If this macro is defined to 1, the DWARF 2 unwinder will be the default |
| exception handling mechanism; otherwise, @code{setjmp}/@code{longjmp} will be used by |
| default. |
| |
| If this macro is defined to anything, the DWARF 2 unwinder will be used |
| instead of inline unwinders and @code{__unwind_function} in the non-@code{setjmp} case. |
| |
| @findex DWARF_CIE_DATA_ALIGNMENT |
| @item DWARF_CIE_DATA_ALIGNMENT |
| This macro need only be defined if the target might save registers in the |
| function prologue at an offset to the stack pointer that is not aligned to |
| @code{UNITS_PER_WORD}. The definition should be the negative minimum |
| alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive |
| minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if |
| the target supports DWARF 2 frame unwind information. |
| |
| @end table |
| |
| @deftypefn {Target Hook} void TARGET_ASM_EXCEPTION_SECTION () |
| If defined, a function that switches to the section in which the main |
| exception table is to be placed (@pxref{Sections}). The default is a |
| function that switches to a section named @code{.gcc_except_table} on |
| machines that support named sections via |
| @code{TARGET_ASM_NAMED_SECTION}, otherwise if @option{-fpic} or |
| @option{-fPIC} is in effect, the @code{data_section}, otherwise the |
| @code{readonly_data_section}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_EH_FRAME_SECTION () |
| If defined, a function that switches to the section in which the DWARF 2 |
| frame unwind information to be placed (@pxref{Sections}). The default |
| is a function that outputs a standard GAS section directive, if |
| @code{EH_FRAME_SECTION_NAME} is defined, or else a data section |
| directive followed by a synthetic label. |
| @end deftypefn |
| |
| @node Alignment Output |
| @subsection Assembler Commands for Alignment |
| |
| @c prevent bad page break with this line |
| This describes commands for alignment. |
| |
| @table @code |
| @findex JUMP_ALIGN |
| @item JUMP_ALIGN (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}, which is |
| a common destination of jumps and has no fallthru incoming edge. |
| |
| This macro need not be defined if you don't want any special alignment |
| to be done at such a time. Most machine descriptions do not currently |
| define the macro. |
| |
| Unless it's necessary to inspect the @var{label} parameter, it is better |
| to set the variable @var{align_jumps} in the target's |
| @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's |
| selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. |
| |
| @findex LABEL_ALIGN_AFTER_BARRIER |
| @item LABEL_ALIGN_AFTER_BARRIER (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}, which follows |
| a @code{BARRIER}. |
| |
| This macro need not be defined if you don't want any special alignment |
| to be done at such a time. Most machine descriptions do not currently |
| define the macro. |
| |
| @findex LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP |
| @item LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP |
| The maximum number of bytes to skip when applying |
| @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if |
| @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. |
| |
| @findex LOOP_ALIGN |
| @item LOOP_ALIGN (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}, which follows |
| a @code{NOTE_INSN_LOOP_BEG} note. |
| |
| This macro need not be defined if you don't want any special alignment |
| to be done at such a time. Most machine descriptions do not currently |
| define the macro. |
| |
| Unless it's necessary to inspect the @var{label} parameter, it is better |
| to set the variable @code{align_loops} in the target's |
| @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's |
| selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. |
| |
| @findex LOOP_ALIGN_MAX_SKIP |
| @item LOOP_ALIGN_MAX_SKIP |
| The maximum number of bytes to skip when applying @code{LOOP_ALIGN}. |
| This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. |
| |
| @findex LABEL_ALIGN |
| @item LABEL_ALIGN (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}. |
| If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, |
| the maximum of the specified values is used. |
| |
| Unless it's necessary to inspect the @var{label} parameter, it is better |
| to set the variable @code{align_labels} in the target's |
| @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's |
| selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. |
| |
| @findex LABEL_ALIGN_MAX_SKIP |
| @item LABEL_ALIGN_MAX_SKIP |
| The maximum number of bytes to skip when applying @code{LABEL_ALIGN}. |
| This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. |
| |
| @findex ASM_OUTPUT_SKIP |
| @item ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| instruction to advance the location counter by @var{nbytes} bytes. |
| Those bytes should be zero when loaded. @var{nbytes} will be a C |
| expression of type @code{int}. |
| |
| @findex ASM_NO_SKIP_IN_TEXT |
| @item ASM_NO_SKIP_IN_TEXT |
| Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the |
| text section because it fails to put zeros in the bytes that are skipped. |
| This is true on many Unix systems, where the pseudo--op to skip bytes |
| produces no-op instructions rather than zeros when used in the text |
| section. |
| |
| @findex ASM_OUTPUT_ALIGN |
| @item ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| command to advance the location counter to a multiple of 2 to the |
| @var{power} bytes. @var{power} will be a C expression of type @code{int}. |
| |
| @findex ASM_OUTPUT_MAX_SKIP_ALIGN |
| @item ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| command to advance the location counter to a multiple of 2 to the |
| @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to |
| satisfy the alignment request. @var{power} and @var{max_skip} will be |
| a C expression of type @code{int}. |
| @end table |
| |
| @need 3000 |
| @node Debugging Info |
| @section Controlling Debugging Information Format |
| |
| @c prevent bad page break with this line |
| This describes how to specify debugging information. |
| |
| @menu |
| * All Debuggers:: Macros that affect all debugging formats uniformly. |
| * DBX Options:: Macros enabling specific options in DBX format. |
| * DBX Hooks:: Hook macros for varying DBX format. |
| * File Names and DBX:: Macros controlling output of file names in DBX format. |
| * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. |
| * VMS Debug:: Macros for VMS debug format. |
| @end menu |
| |
| @node All Debuggers |
| @subsection Macros Affecting All Debugging Formats |
| |
| @c prevent bad page break with this line |
| These macros affect all debugging formats. |
| |
| @table @code |
| @findex DBX_REGISTER_NUMBER |
| @item DBX_REGISTER_NUMBER (@var{regno}) |
| A C expression that returns the DBX register number for the compiler |
| register number @var{regno}. In the default macro provided, the value |
| of this expression will be @var{regno} itself. But sometimes there are |
| some registers that the compiler knows about and DBX does not, or vice |
| versa. In such cases, some register may need to have one number in the |
| compiler and another for DBX@. |
| |
| If two registers have consecutive numbers inside GCC, and they can be |
| used as a pair to hold a multiword value, then they @emph{must} have |
| consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}. |
| Otherwise, debuggers will be unable to access such a pair, because they |
| expect register pairs to be consecutive in their own numbering scheme. |
| |
| If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that |
| does not preserve register pairs, then what you must do instead is |
| redefine the actual register numbering scheme. |
| |
| @findex DEBUGGER_AUTO_OFFSET |
| @item DEBUGGER_AUTO_OFFSET (@var{x}) |
| A C expression that returns the integer offset value for an automatic |
| variable having address @var{x} (an RTL expression). The default |
| computation assumes that @var{x} is based on the frame-pointer and |
| gives the offset from the frame-pointer. This is required for targets |
| that produce debugging output for DBX or COFF-style debugging output |
| for SDB and allow the frame-pointer to be eliminated when the |
| @option{-g} options is used. |
| |
| @findex DEBUGGER_ARG_OFFSET |
| @item DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) |
| A C expression that returns the integer offset value for an argument |
| having address @var{x} (an RTL expression). The nominal offset is |
| @var{offset}. |
| |
| @findex PREFERRED_DEBUGGING_TYPE |
| @item PREFERRED_DEBUGGING_TYPE |
| A C expression that returns the type of debugging output GCC should |
| produce when the user specifies just @option{-g}. Define |
| this if you have arranged for GCC to support more than one format of |
| debugging output. Currently, the allowable values are @code{DBX_DEBUG}, |
| @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG}, |
| @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}. |
| |
| When the user specifies @option{-ggdb}, GCC normally also uses the |
| value of this macro to select the debugging output format, but with two |
| exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined and |
| @code{LINKER_DOES_NOT_WORK_WITH_DWARF2} is not defined, GCC uses the |
| value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is |
| defined, GCC uses @code{DBX_DEBUG}. |
| |
| The value of this macro only affects the default debugging output; the |
| user can always get a specific type of output by using @option{-gstabs}, |
| @option{-gcoff}, @option{-gdwarf-1}, @option{-gdwarf-2}, @option{-gxcoff}, |
| or @option{-gvms}. |
| @end table |
| |
| @node DBX Options |
| @subsection Specific Options for DBX Output |
| |
| @c prevent bad page break with this line |
| These are specific options for DBX output. |
| |
| @table @code |
| @findex DBX_DEBUGGING_INFO |
| @item DBX_DEBUGGING_INFO |
| Define this macro if GCC should produce debugging output for DBX |
| in response to the @option{-g} option. |
| |
| @findex XCOFF_DEBUGGING_INFO |
| @item XCOFF_DEBUGGING_INFO |
| Define this macro if GCC should produce XCOFF format debugging output |
| in response to the @option{-g} option. This is a variant of DBX format. |
| |
| @findex DEFAULT_GDB_EXTENSIONS |
| @item DEFAULT_GDB_EXTENSIONS |
| Define this macro to control whether GCC should by default generate |
| GDB's extended version of DBX debugging information (assuming DBX-format |
| debugging information is enabled at all). If you don't define the |
| macro, the default is 1: always generate the extended information |
| if there is any occasion to. |
| |
| @findex DEBUG_SYMS_TEXT |
| @item DEBUG_SYMS_TEXT |
| Define this macro if all @code{.stabs} commands should be output while |
| in the text section. |
| |
| @findex ASM_STABS_OP |
| @item ASM_STABS_OP |
| A C string constant, including spacing, naming the assembler pseudo op to |
| use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol. |
| If you don't define this macro, @code{"\t.stabs\t"} is used. This macro |
| applies only to DBX debugging information format. |
| |
| @findex ASM_STABD_OP |
| @item ASM_STABD_OP |
| A C string constant, including spacing, naming the assembler pseudo op to |
| use instead of @code{"\t.stabd\t"} to define a debugging symbol whose |
| value is the current location. If you don't define this macro, |
| @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging |
| information format. |
| |
| @findex ASM_STABN_OP |
| @item ASM_STABN_OP |
| A C string constant, including spacing, naming the assembler pseudo op to |
| use instead of @code{"\t.stabn\t"} to define a debugging symbol with no |
| name. If you don't define this macro, @code{"\t.stabn\t"} is used. This |
| macro applies only to DBX debugging information format. |
| |
| @findex DBX_NO_XREFS |
| @item DBX_NO_XREFS |
| Define this macro if DBX on your system does not support the construct |
| @samp{xs@var{tagname}}. On some systems, this construct is used to |
| describe a forward reference to a structure named @var{tagname}. |
| On other systems, this construct is not supported at all. |
| |
| @findex DBX_CONTIN_LENGTH |
| @item DBX_CONTIN_LENGTH |
| A symbol name in DBX-format debugging information is normally |
| continued (split into two separate @code{.stabs} directives) when it |
| exceeds a certain length (by default, 80 characters). On some |
| operating systems, DBX requires this splitting; on others, splitting |
| must not be done. You can inhibit splitting by defining this macro |
| with the value zero. You can override the default splitting-length by |
| defining this macro as an expression for the length you desire. |
| |
| @findex DBX_CONTIN_CHAR |
| @item DBX_CONTIN_CHAR |
| Normally continuation is indicated by adding a @samp{\} character to |
| the end of a @code{.stabs} string when a continuation follows. To use |
| a different character instead, define this macro as a character |
| constant for the character you want to use. Do not define this macro |
| if backslash is correct for your system. |
| |
| @findex DBX_STATIC_STAB_DATA_SECTION |
| @item DBX_STATIC_STAB_DATA_SECTION |
| Define this macro if it is necessary to go to the data section before |
| outputting the @samp{.stabs} pseudo-op for a non-global static |
| variable. |
| |
| @findex DBX_TYPE_DECL_STABS_CODE |
| @item DBX_TYPE_DECL_STABS_CODE |
| The value to use in the ``code'' field of the @code{.stabs} directive |
| for a typedef. The default is @code{N_LSYM}. |
| |
| @findex DBX_STATIC_CONST_VAR_CODE |
| @item DBX_STATIC_CONST_VAR_CODE |
| The value to use in the ``code'' field of the @code{.stabs} directive |
| for a static variable located in the text section. DBX format does not |
| provide any ``right'' way to do this. The default is @code{N_FUN}. |
| |
| @findex DBX_REGPARM_STABS_CODE |
| @item DBX_REGPARM_STABS_CODE |
| The value to use in the ``code'' field of the @code{.stabs} directive |
| for a parameter passed in registers. DBX format does not provide any |
| ``right'' way to do this. The default is @code{N_RSYM}. |
| |
| @findex DBX_REGPARM_STABS_LETTER |
| @item DBX_REGPARM_STABS_LETTER |
| The letter to use in DBX symbol data to identify a symbol as a parameter |
| passed in registers. DBX format does not customarily provide any way to |
| do this. The default is @code{'P'}. |
| |
| @findex DBX_MEMPARM_STABS_LETTER |
| @item DBX_MEMPARM_STABS_LETTER |
| The letter to use in DBX symbol data to identify a symbol as a stack |
| parameter. The default is @code{'p'}. |
| |
| @findex DBX_FUNCTION_FIRST |
| @item DBX_FUNCTION_FIRST |
| Define this macro if the DBX information for a function and its |
| arguments should precede the assembler code for the function. Normally, |
| in DBX format, the debugging information entirely follows the assembler |
| code. |
| |
| @findex DBX_LBRAC_FIRST |
| @item DBX_LBRAC_FIRST |
| Define this macro if the @code{N_LBRAC} symbol for a block should |
| precede the debugging information for variables and functions defined in |
| that block. Normally, in DBX format, the @code{N_LBRAC} symbol comes |
| first. |
| |
| @findex DBX_BLOCKS_FUNCTION_RELATIVE |
| @item DBX_BLOCKS_FUNCTION_RELATIVE |
| Define this macro if the value of a symbol describing the scope of a |
| block (@code{N_LBRAC} or @code{N_RBRAC}) should be relative to the start |
| of the enclosing function. Normally, GCC uses an absolute address. |
| |
| @findex DBX_USE_BINCL |
| @item DBX_USE_BINCL |
| Define this macro if GCC should generate @code{N_BINCL} and |
| @code{N_EINCL} stabs for included header files, as on Sun systems. This |
| macro also directs GCC to output a type number as a pair of a file |
| number and a type number within the file. Normally, GCC does not |
| generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single |
| number for a type number. |
| @end table |
| |
| @node DBX Hooks |
| @subsection Open-Ended Hooks for DBX Format |
| |
| @c prevent bad page break with this line |
| These are hooks for DBX format. |
| |
| @table @code |
| @findex DBX_OUTPUT_LBRAC |
| @item DBX_OUTPUT_LBRAC (@var{stream}, @var{name}) |
| Define this macro to say how to output to @var{stream} the debugging |
| information for the start of a scope level for variable names. The |
| argument @var{name} is the name of an assembler symbol (for use with |
| @code{assemble_name}) whose value is the address where the scope begins. |
| |
| @findex DBX_OUTPUT_RBRAC |
| @item DBX_OUTPUT_RBRAC (@var{stream}, @var{name}) |
| Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level. |
| |
| @findex DBX_OUTPUT_ENUM |
| @item DBX_OUTPUT_ENUM (@var{stream}, @var{type}) |
| Define this macro if the target machine requires special handling to |
| output an enumeration type. The definition should be a C statement |
| (sans semicolon) to output the appropriate information to @var{stream} |
| for the type @var{type}. |
| |
| @findex DBX_OUTPUT_FUNCTION_END |
| @item DBX_OUTPUT_FUNCTION_END (@var{stream}, @var{function}) |
| Define this macro if the target machine requires special output at the |
| end of the debugging information for a function. The definition should |
| be a C statement (sans semicolon) to output the appropriate information |
| to @var{stream}. @var{function} is the @code{FUNCTION_DECL} node for |
| the function. |
| |
| @findex DBX_OUTPUT_STANDARD_TYPES |
| @item DBX_OUTPUT_STANDARD_TYPES (@var{syms}) |
| Define this macro if you need to control the order of output of the |
| standard data types at the beginning of compilation. The argument |
| @var{syms} is a @code{tree} which is a chain of all the predefined |
| global symbols, including names of data types. |
| |
| Normally, DBX output starts with definitions of the types for integers |
| and characters, followed by all the other predefined types of the |
| particular language in no particular order. |
| |
| On some machines, it is necessary to output different particular types |
| first. To do this, define @code{DBX_OUTPUT_STANDARD_TYPES} to output |
| those symbols in the necessary order. Any predefined types that you |
| don't explicitly output will be output afterward in no particular order. |
| |
| Be careful not to define this macro so that it works only for C@. There |
| are no global variables to access most of the built-in types, because |
| another language may have another set of types. The way to output a |
| particular type is to look through @var{syms} to see if you can find it. |
| Here is an example: |
| |
| @smallexample |
| @{ |
| tree decl; |
| for (decl = syms; decl; decl = TREE_CHAIN (decl)) |
| if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)), |
| "long int")) |
| dbxout_symbol (decl); |
| @dots{} |
| @} |
| @end smallexample |
| |
| @noindent |
| This does nothing if the expected type does not exist. |
| |
| See the function @code{init_decl_processing} in @file{c-decl.c} to find |
| the names to use for all the built-in C types. |
| |
| Here is another way of finding a particular type: |
| |
| @c this is still overfull. --mew 10feb93 |
| @smallexample |
| @{ |
| tree decl; |
| for (decl = syms; decl; decl = TREE_CHAIN (decl)) |
| if (TREE_CODE (decl) == TYPE_DECL |
| && (TREE_CODE (TREE_TYPE (decl)) |
| == INTEGER_CST) |
| && TYPE_PRECISION (TREE_TYPE (decl)) == 16 |
| && TYPE_UNSIGNED (TREE_TYPE (decl))) |
| @group |
| /* @r{This must be @code{unsigned short}.} */ |
| dbxout_symbol (decl); |
| @dots{} |
| @} |
| @end group |
| @end smallexample |
| |
| @findex NO_DBX_FUNCTION_END |
| @item NO_DBX_FUNCTION_END |
| Some stabs encapsulation formats (in particular ECOFF), cannot handle the |
| @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct. |
| On those machines, define this macro to turn this feature off without |
| disturbing the rest of the gdb extensions. |
| |
| @end table |
| |
| @node File Names and DBX |
| @subsection File Names in DBX Format |
| |
| @c prevent bad page break with this line |
| This describes file names in DBX format. |
| |
| @table @code |
| @findex DBX_WORKING_DIRECTORY |
| @item DBX_WORKING_DIRECTORY |
| Define this if DBX wants to have the current directory recorded in each |
| object file. |
| |
| Note that the working directory is always recorded if GDB extensions are |
| enabled. |
| |
| @findex DBX_OUTPUT_MAIN_SOURCE_FILENAME |
| @item DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name}) |
| A C statement to output DBX debugging information to the stdio stream |
| @var{stream} which indicates that file @var{name} is the main source |
| file---the file specified as the input file for compilation. |
| This macro is called only once, at the beginning of compilation. |
| |
| This macro need not be defined if the standard form of output |
| for DBX debugging information is appropriate. |
| |
| @findex DBX_OUTPUT_MAIN_SOURCE_DIRECTORY |
| @item DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (@var{stream}, @var{name}) |
| A C statement to output DBX debugging information to the stdio stream |
| @var{stream} which indicates that the current directory during |
| compilation is named @var{name}. |
| |
| This macro need not be defined if the standard form of output |
| for DBX debugging information is appropriate. |
| |
| @findex DBX_OUTPUT_MAIN_SOURCE_FILE_END |
| @item DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name}) |
| A C statement to output DBX debugging information at the end of |
| compilation of the main source file @var{name}. |
| |
| If you don't define this macro, nothing special is output at the end |
| of compilation, which is correct for most machines. |
| |
| @findex DBX_OUTPUT_SOURCE_FILENAME |
| @item DBX_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) |
| A C statement to output DBX debugging information to the stdio stream |
| @var{stream} which indicates that file @var{name} is the current source |
| file. This output is generated each time input shifts to a different |
| source file as a result of @samp{#include}, the end of an included file, |
| or a @samp{#line} command. |
| |
| This macro need not be defined if the standard form of output |
| for DBX debugging information is appropriate. |
| @end table |
| |
| @need 2000 |
| @node SDB and DWARF |
| @subsection Macros for SDB and DWARF Output |
| |
| @c prevent bad page break with this line |
| Here are macros for SDB and DWARF output. |
| |
| @table @code |
| @findex SDB_DEBUGGING_INFO |
| @item SDB_DEBUGGING_INFO |
| Define this macro if GCC should produce COFF-style debugging output |
| for SDB in response to the @option{-g} option. |
| |
| @findex DWARF_DEBUGGING_INFO |
| @item DWARF_DEBUGGING_INFO |
| Define this macro if GCC should produce dwarf format debugging output |
| in response to the @option{-g} option. |
| |
| @findex DWARF2_DEBUGGING_INFO |
| @item DWARF2_DEBUGGING_INFO |
| Define this macro if GCC should produce dwarf version 2 format |
| debugging output in response to the @option{-g} option. |
| |
| To support optional call frame debugging information, you must also |
| define @code{INCOMING_RETURN_ADDR_RTX} and either set |
| @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the |
| prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} |
| as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. |
| |
| @findex DWARF2_FRAME_INFO |
| @item DWARF2_FRAME_INFO |
| Define this macro to a nonzero value if GCC should always output |
| Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO} |
| (@pxref{Exception Region Output} is nonzero, GCC will output this |
| information not matter how you define @code{DWARF2_FRAME_INFO}. |
| |
| @findex LINKER_DOES_NOT_WORK_WITH_DWARF2 |
| @item LINKER_DOES_NOT_WORK_WITH_DWARF2 |
| Define this macro if the linker does not work with Dwarf version 2. |
| Normally, if the user specifies only @option{-ggdb} GCC will use Dwarf |
| version 2 if available; this macro disables this. See the description |
| of the @code{PREFERRED_DEBUGGING_TYPE} macro for more details. |
| |
| @findex DWARF2_GENERATE_TEXT_SECTION_LABEL |
| @item DWARF2_GENERATE_TEXT_SECTION_LABEL |
| By default, the Dwarf 2 debugging information generator will generate a |
| label to mark the beginning of the text section. If it is better simply |
| to use the name of the text section itself, rather than an explicit label, |
| to indicate the beginning of the text section, define this macro to zero. |
| |
| @findex DWARF2_ASM_LINE_DEBUG_INFO |
| @item DWARF2_ASM_LINE_DEBUG_INFO |
| Define this macro to be a nonzero value if the assembler can generate Dwarf 2 |
| line debug info sections. This will result in much more compact line number |
| tables, and hence is desirable if it works. |
| |
| @findex PUT_SDB_@dots{} |
| @item PUT_SDB_@dots{} |
| Define these macros to override the assembler syntax for the special |
| SDB assembler directives. See @file{sdbout.c} for a list of these |
| macros and their arguments. If the standard syntax is used, you need |
| not define them yourself. |
| |
| @findex SDB_DELIM |
| @item SDB_DELIM |
| Some assemblers do not support a semicolon as a delimiter, even between |
| SDB assembler directives. In that case, define this macro to be the |
| delimiter to use (usually @samp{\n}). It is not necessary to define |
| a new set of @code{PUT_SDB_@var{op}} macros if this is the only change |
| required. |
| |
| @findex SDB_GENERATE_FAKE |
| @item SDB_GENERATE_FAKE |
| Define this macro to override the usual method of constructing a dummy |
| name for anonymous structure and union types. See @file{sdbout.c} for |
| more information. |
| |
| @findex SDB_ALLOW_UNKNOWN_REFERENCES |
| @item SDB_ALLOW_UNKNOWN_REFERENCES |
| Define this macro to allow references to unknown structure, |
| union, or enumeration tags to be emitted. Standard COFF does not |
| allow handling of unknown references, MIPS ECOFF has support for |
| it. |
| |
| @findex SDB_ALLOW_FORWARD_REFERENCES |
| @item SDB_ALLOW_FORWARD_REFERENCES |
| Define this macro to allow references to structure, union, or |
| enumeration tags that have not yet been seen to be handled. Some |
| assemblers choke if forward tags are used, while some require it. |
| @end table |
| |
| @need 2000 |
| @node VMS Debug |
| @subsection Macros for VMS Debug Format |
| |
| @c prevent bad page break with this line |
| Here are macros for VMS debug format. |
| |
| @table @code |
| @findex VMS_DEBUGGING_INFO |
| @item VMS_DEBUGGING_INFO |
| Define this macro if GCC should produce debugging output for VMS |
| in response to the @option{-g} option. The default behavior for VMS |
| is to generate minimal debug info for a traceback in the absence of |
| @option{-g} unless explicitly overridden with @option{-g0}. This |
| behavior is controlled by @code{OPTIMIZATION_OPTIONS} and |
| @code{OVERRIDE_OPTIONS}. |
| @end table |
| |
| @node Cross-compilation |
| @section Cross Compilation and Floating Point |
| @cindex cross compilation and floating point |
| @cindex floating point and cross compilation |
| |
| While all modern machines use 2's complement representation for integers, |
| there are a variety of representations for floating point numbers. This |
| means that in a cross-compiler the representation of floating point numbers |
| in the compiled program may be different from that used in the machine |
| doing the compilation. |
| |
| @findex atof |
| Because different representation systems may offer different amounts of |
| range and precision, the cross compiler cannot safely use the host |
| machine's floating point arithmetic. Therefore, floating point constants |
| must be represented in the target machine's format. This means that the |
| cross compiler cannot use @code{atof} to parse a floating point constant; |
| it must have its own special routine to use instead. Also, constant |
| folding must emulate the target machine's arithmetic (or must not be done |
| at all). |
| |
| The macros in the following table are provided by @file{real.h} for the |
| compiler to use. All parts of the compiler which generate or optimize |
| floating-point calculations must use these macros. They may evaluate |
| their operands more than once, so operands must not have side effects. |
| |
| @table @code |
| @findex REAL_VALUE_TYPE |
| @item REAL_VALUE_TYPE |
| A macro for the C data type to be used to hold a floating point value |
| in the target machine's format. Typically this would be a |
| @code{struct} containing an array of @code{int}. |
| |
| @findex REAL_VALUES_EQUAL |
| @item REAL_VALUES_EQUAL (@var{x}, @var{y}) |
| A macro for a C expression which compares for equality the two values, |
| @var{x} and @var{y}, both of type @code{REAL_VALUE_TYPE}. |
| |
| @findex REAL_VALUES_LESS |
| @item REAL_VALUES_LESS (@var{x}, @var{y}) |
| A macro for a C expression which tests whether @var{x} is less than |
| @var{y}, both values being of type @code{REAL_VALUE_TYPE} and |
| interpreted as floating point numbers in the target machine's |
| representation. |
| |
| @findex REAL_VALUE_LDEXP |
| @findex ldexp |
| @item REAL_VALUE_LDEXP (@var{x}, @var{scale}) |
| A macro for a C expression which performs the standard library |
| function @code{ldexp}, but using the target machine's floating point |
| representation. Both @var{x} and the value of the expression have |
| type @code{REAL_VALUE_TYPE}. The second argument, @var{scale}, is an |
| integer. |
| |
| @findex REAL_VALUE_FIX |
| @item REAL_VALUE_FIX (@var{x}) |
| A macro whose definition is a C expression to convert the target-machine |
| floating point value @var{x} to a signed integer. @var{x} has type |
| @code{REAL_VALUE_TYPE}. |
| |
| @findex REAL_VALUE_UNSIGNED_FIX |
| @item REAL_VALUE_UNSIGNED_FIX (@var{x}) |
| A macro whose definition is a C expression to convert the target-machine |
| floating point value @var{x} to an unsigned integer. @var{x} has type |
| @code{REAL_VALUE_TYPE}. |
| |
| @findex REAL_VALUE_RNDZINT |
| @item REAL_VALUE_RNDZINT (@var{x}) |
| A macro whose definition is a C expression to round the target-machine |
| floating point value @var{x} towards zero to an integer value (but still |
| as a floating point number). @var{x} has type @code{REAL_VALUE_TYPE}, |
| and so does the value. |
| |
| @findex REAL_VALUE_UNSIGNED_RNDZINT |
| @item REAL_VALUE_UNSIGNED_RNDZINT (@var{x}) |
| A macro whose definition is a C expression to round the target-machine |
| floating point value @var{x} towards zero to an unsigned integer value |
| (but still represented as a floating point number). @var{x} has type |
| @code{REAL_VALUE_TYPE}, and so does the value. |
| |
| @findex REAL_VALUE_ATOF |
| @item REAL_VALUE_ATOF (@var{string}, @var{mode}) |
| A macro for a C expression which converts @var{string}, an expression of |
| type @code{char *}, into a floating point number in the target machine's |
| representation for mode @var{mode}. The value has type |
| @code{REAL_VALUE_TYPE}. |
| |
| @findex REAL_INFINITY |
| @item REAL_INFINITY |
| Define this macro if infinity is a possible floating point value, and |
| therefore division by 0 is legitimate. |
| |
| @findex REAL_VALUE_ISINF |
| @findex isinf |
| @item REAL_VALUE_ISINF (@var{x}) |
| A macro for a C expression which determines whether @var{x}, a floating |
| point value, is infinity. The value has type @code{int}. |
| By default, this is defined to call @code{isinf}. |
| |
| @findex REAL_VALUE_ISNAN |
| @findex isnan |
| @item REAL_VALUE_ISNAN (@var{x}) |
| A macro for a C expression which determines whether @var{x}, a floating |
| point value, is a ``nan'' (not-a-number). The value has type |
| @code{int}. By default, this is defined to call @code{isnan}. |
| |
| @findex REAL_ARITHMETIC |
| @item REAL_ARITHMETIC (@var{output}, @var{code}, @var{x}, @var{y}) |
| A macro for a C statement which calculates an arithmetic operation of |
| the two floating point values @var{x} and @var{y}, both of type |
| @code{REAL_VALUE_TYPE} in the target machine's representation, to |
| produce a result of the same type and representation which is stored |
| in @var{output} (which will be a variable). |
| |
| The operation to be performed is specified by @var{code}, a tree code |
| which will always be one of the following: @code{PLUS_EXPR}, |
| @code{MINUS_EXPR}, @code{MULT_EXPR}, @code{RDIV_EXPR}, |
| @code{MAX_EXPR}, @code{MIN_EXPR}. |
| |
| @cindex overflow while constant folding |
| If overflow happens, the macro expansion executes the statement |
| @code{return 0;}, which indicates the inability to perform the |
| arithmetic operation requested. |
| |
| @findex REAL_VALUE_NEGATE |
| @item REAL_VALUE_NEGATE (@var{x}) |
| A macro for a C expression which returns the negative of the floating |
| point value @var{x}. Both @var{x} and the value of the expression |
| have type @code{REAL_VALUE_TYPE} and are in the target machine's |
| floating point representation. |
| |
| There is no way for this macro to report overflow, since overflow |
| can't happen in the negation operation. |
| |
| @findex REAL_VALUE_TRUNCATE |
| @item REAL_VALUE_TRUNCATE (@var{mode}, @var{x}) |
| A macro for a C expression which converts the floating point value |
| @var{x} to mode @var{mode}. |
| |
| Both @var{x} and the value of the expression are in the target machine's |
| floating point representation and have type @code{REAL_VALUE_TYPE}. |
| However, the value should have an appropriate bit pattern to be output |
| properly as a floating constant whose precision accords with mode |
| @var{mode}. |
| |
| There is no way for this macro to report overflow. |
| |
| @findex REAL_VALUE_TO_INT |
| @item REAL_VALUE_TO_INT (@var{low}, @var{high}, @var{x}) |
| A macro for a C expression which converts a floating point value |
| @var{x} into a double-precision integer which is then stored into |
| @var{low} and @var{high}, two variables of type @var{int}. |
| |
| @item REAL_VALUE_FROM_INT (@var{x}, @var{low}, @var{high}, @var{mode}) |
| @findex REAL_VALUE_FROM_INT |
| A macro for a C expression which converts a double-precision integer |
| found in @var{low} and @var{high}, two variables of type @var{int}, |
| into a floating point value which is then stored into @var{x}. |
| The value is in the target machine's representation for mode @var{mode} |
| and has the type @code{REAL_VALUE_TYPE}. |
| @end table |
| |
| @node Mode Switching |
| @section Mode Switching Instructions |
| @cindex mode switching |
| The following macros control mode switching optimizations: |
| |
| @table @code |
| @findex OPTIMIZE_MODE_SWITCHING |
| @item OPTIMIZE_MODE_SWITCHING (@var{entity}) |
| Define this macro if the port needs extra instructions inserted for mode |
| switching in an optimizing compilation. |
| |
| For an example, the SH4 can perform both single and double precision |
| floating point operations, but to perform a single precision operation, |
| the FPSCR PR bit has to be cleared, while for a double precision |
| operation, this bit has to be set. Changing the PR bit requires a general |
| purpose register as a scratch register, hence these FPSCR sets have to |
| be inserted before reload, i.e.@: you can't put this into instruction emitting |
| or @code{MACHINE_DEPENDENT_REORG}. |
| |
| You can have multiple entities that are mode-switched, and select at run time |
| which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should |
| return nonzero for any @var{entity} that needs mode-switching. |
| If you define this macro, you also have to define |
| @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED}, |
| @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}. |
| @code{NORMAL_MODE} is optional. |
| |
| @findex NUM_MODES_FOR_MODE_SWITCHING |
| @item NUM_MODES_FOR_MODE_SWITCHING |
| If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as |
| initializer for an array of integers. Each initializer element |
| N refers to an entity that needs mode switching, and specifies the number |
| of different modes that might need to be set for this entity. |
| The position of the initializer in the initializer - starting counting at |
| zero - determines the integer that is used to refer to the mode-switched |
| entity in question. |
| In macros that take mode arguments / yield a mode result, modes are |
| represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode |
| switch is needed / supplied. |
| |
| @findex MODE_NEEDED |
| @item MODE_NEEDED (@var{entity}, @var{insn}) |
| @var{entity} is an integer specifying a mode-switched entity. If |
| @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to |
| return an integer value not larger than the corresponding element in |
| @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must |
| be switched into prior to the execution of @var{insn}. |
| |
| @findex NORMAL_MODE |
| @item NORMAL_MODE (@var{entity}) |
| If this macro is defined, it is evaluated for every @var{entity} that needs |
| mode switching. It should evaluate to an integer, which is a mode that |
| @var{entity} is assumed to be switched to at function entry and exit. |
| |
| @findex MODE_PRIORITY_TO_MODE |
| @item MODE_PRIORITY_TO_MODE (@var{entity}, @var{n}) |
| This macro specifies the order in which modes for @var{entity} are processed. |
| 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the |
| lowest. The value of the macro should be an integer designating a mode |
| for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode} |
| (@var{entity}, @var{n}) shall be a bijection in 0 @dots{} |
| @code{num_modes_for_mode_switching[@var{entity}] - 1}. |
| |
| @findex EMIT_MODE_SET |
| @item EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live}) |
| Generate one or more insns to set @var{entity} to @var{mode}. |
| @var{hard_reg_live} is the set of hard registers live at the point where |
| the insn(s) are to be inserted. |
| @end table |
| |
| @node Target Attributes |
| @section Defining target-specific uses of @code{__attribute__} |
| @cindex target attributes |
| @cindex machine attributes |
| @cindex attributes, target-specific |
| |
| Target-specific attributes may be defined for functions, data and types. |
| These are described using the following target hooks; they also need to |
| be documented in @file{extend.texi}. |
| |
| @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE |
| If defined, this target hook points to an array of @samp{struct |
| attribute_spec} (defined in @file{tree.h}) specifying the machine |
| specific attributes for this target and some of the restrictions on the |
| entities to which these attributes are applied and the arguments they |
| take. |
| @end deftypevr |
| |
| @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) |
| If defined, this target hook is a function which returns zero if the attributes on |
| @var{type1} and @var{type2} are incompatible, one if they are compatible, |
| and two if they are nearly compatible (which causes a warning to be |
| generated). If this is not defined, machine-specific attributes are |
| supposed always to be compatible. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type}) |
| If defined, this target hook is a function which assigns default attributes to |
| newly defined @var{type}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) |
| Define this target hook if the merging of type attributes needs special |
| handling. If defined, the result is a list of the combined |
| @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed |
| that @code{comptypes} has already been called and returned 1. This |
| function may call @code{merge_attributes} to handle machine-independent |
| merging. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl}) |
| Define this target hook if the merging of decl attributes needs special |
| handling. If defined, the result is a list of the combined |
| @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. |
| @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of |
| when this is needed are when one attribute overrides another, or when an |
| attribute is nullified by a subsequent definition. This function may |
| call @code{merge_attributes} to handle machine-independent merging. |
| |
| @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES |
| If the only target-specific handling you require is @samp{dllimport} for |
| Windows targets, you should define the macro |
| @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. This links in a function |
| called @code{merge_dllimport_decl_attributes} which can then be defined |
| as the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. This is done |
| in @file{i386/cygwin.h} and @file{i386/i386.c}, for example. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr}) |
| Define this target hook if you want to be able to add attributes to a decl |
| when it is being created. This is normally useful for back ends which |
| wish to implement a pragma by using the attributes which correspond to |
| the pragma's effect. The @var{node} argument is the decl which is being |
| created. The @var{attr_ptr} argument is a pointer to the attribute list |
| for this decl. The list itself should not be modified, since it may be |
| shared with other decls, but attributes may be chained on the head of |
| the list and @code{*@var{attr_ptr}} modified to point to the new |
| attributes, or a copy of the list may be made if further changes are |
| needed. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl}) |
| @cindex inlining |
| This target hook returns @code{true} if it is ok to inline @var{fndecl} |
| into the current function, despite its having target-specific |
| attributes, @code{false} otherwise. By default, if a function has a |
| target specific attribute attached to it, it will not be inlined. |
| @end deftypefn |
| |
| @node Misc |
| @section Miscellaneous Parameters |
| @cindex parameters, miscellaneous |
| |
| @c prevent bad page break with this line |
| Here are several miscellaneous parameters. |
| |
| @table @code |
| @item PREDICATE_CODES |
| @findex PREDICATE_CODES |
| Define this if you have defined special-purpose predicates in the file |
| @file{@var{machine}.c}. This macro is called within an initializer of an |
| array of structures. The first field in the structure is the name of a |
| predicate and the second field is an array of rtl codes. For each |
| predicate, list all rtl codes that can be in expressions matched by the |
| predicate. The list should have a trailing comma. Here is an example |
| of two entries in the list for a typical RISC machine: |
| |
| @smallexample |
| #define PREDICATE_CODES \ |
| @{"gen_reg_rtx_operand", @{SUBREG, REG@}@}, \ |
| @{"reg_or_short_cint_operand", @{SUBREG, REG, CONST_INT@}@}, |
| @end smallexample |
| |
| Defining this macro does not affect the generated code (however, |
| incorrect definitions that omit an rtl code that may be matched by the |
| predicate can cause the compiler to malfunction). Instead, it allows |
| the table built by @file{genrecog} to be more compact and efficient, |
| thus speeding up the compiler. The most important predicates to include |
| in the list specified by this macro are those used in the most insn |
| patterns. |
| |
| For each predicate function named in @code{PREDICATE_CODES}, a |
| declaration will be generated in @file{insn-codes.h}. |
| |
| @item SPECIAL_MODE_PREDICATES |
| @findex SPECIAL_MODE_PREDICATES |
| Define this if you have special predicates that know special things |
| about modes. Genrecog will warn about certain forms of |
| @code{match_operand} without a mode; if the operand predicate is |
| listed in @code{SPECIAL_MODE_PREDICATES}, the warning will be |
| suppressed. |
| |
| Here is an example from the IA-32 port (@code{ext_register_operand} |
| specially checks for @code{HImode} or @code{SImode} in preparation |
| for a byte extraction from @code{%ah} etc.). |
| |
| @smallexample |
| #define SPECIAL_MODE_PREDICATES \ |
| "ext_register_operand", |
| @end smallexample |
| |
| @findex CASE_VECTOR_MODE |
| @item CASE_VECTOR_MODE |
| An alias for a machine mode name. This is the machine mode that |
| elements of a jump-table should have. |
| |
| @findex CASE_VECTOR_SHORTEN_MODE |
| @item CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) |
| Optional: return the preferred mode for an @code{addr_diff_vec} |
| when the minimum and maximum offset are known. If you define this, |
| it enables extra code in branch shortening to deal with @code{addr_diff_vec}. |
| To make this work, you also have to define INSN_ALIGN and |
| make the alignment for @code{addr_diff_vec} explicit. |
| The @var{body} argument is provided so that the offset_unsigned and scale |
| flags can be updated. |
| |
| @findex CASE_VECTOR_PC_RELATIVE |
| @item CASE_VECTOR_PC_RELATIVE |
| Define this macro to be a C expression to indicate when jump-tables |
| should contain relative addresses. If jump-tables never contain |
| relative addresses, then you need not define this macro. |
| |
| @findex CASE_DROPS_THROUGH |
| @item CASE_DROPS_THROUGH |
| Define this if control falls through a @code{case} insn when the index |
| value is out of range. This means the specified default-label is |
| actually ignored by the @code{case} insn proper. |
| |
| @findex CASE_VALUES_THRESHOLD |
| @item CASE_VALUES_THRESHOLD |
| Define this to be the smallest number of different values for which it |
| is best to use a jump-table instead of a tree of conditional branches. |
| The default is four for machines with a @code{casesi} instruction and |
| five otherwise. This is best for most machines. |
| |
| @findex WORD_REGISTER_OPERATIONS |
| @item WORD_REGISTER_OPERATIONS |
| Define this macro if operations between registers with integral mode |
| smaller than a word are always performed on the entire register. |
| Most RISC machines have this property and most CISC machines do not. |
| |
| @findex LOAD_EXTEND_OP |
| @item LOAD_EXTEND_OP (@var{mode}) |
| Define this macro to be a C expression indicating when insns that read |
| memory in @var{mode}, an integral mode narrower than a word, set the |
| bits outside of @var{mode} to be either the sign-extension or the |
| zero-extension of the data read. Return @code{SIGN_EXTEND} for values |
| of @var{mode} for which the |
| insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and |
| @code{NIL} for other modes. |
| |
| This macro is not called with @var{mode} non-integral or with a width |
| greater than or equal to @code{BITS_PER_WORD}, so you may return any |
| value in this case. Do not define this macro if it would always return |
| @code{NIL}. On machines where this macro is defined, you will normally |
| define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. |
| |
| @findex SHORT_IMMEDIATES_SIGN_EXTEND |
| @item SHORT_IMMEDIATES_SIGN_EXTEND |
| Define this macro if loading short immediate values into registers sign |
| extends. |
| |
| @findex FIXUNS_TRUNC_LIKE_FIX_TRUNC |
| @item FIXUNS_TRUNC_LIKE_FIX_TRUNC |
| Define this macro if the same instructions that convert a floating |
| point number to a signed fixed point number also convert validly to an |
| unsigned one. |
| |
| @findex MOVE_MAX |
| @item MOVE_MAX |
| The maximum number of bytes that a single instruction can move quickly |
| between memory and registers or between two memory locations. |
| |
| @findex MAX_MOVE_MAX |
| @item MAX_MOVE_MAX |
| The maximum number of bytes that a single instruction can move quickly |
| between memory and registers or between two memory locations. If this |
| is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the |
| constant value that is the largest value that @code{MOVE_MAX} can have |
| at run-time. |
| |
| @findex SHIFT_COUNT_TRUNCATED |
| @item SHIFT_COUNT_TRUNCATED |
| A C expression that is nonzero if on this machine the number of bits |
| actually used for the count of a shift operation is equal to the number |
| of bits needed to represent the size of the object being shifted. When |
| this macro is nonzero, the compiler will assume that it is safe to omit |
| a sign-extend, zero-extend, and certain bitwise `and' instructions that |
| truncates the count of a shift operation. On machines that have |
| instructions that act on bit-fields at variable positions, which may |
| include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} |
| also enables deletion of truncations of the values that serve as |
| arguments to bit-field instructions. |
| |
| If both types of instructions truncate the count (for shifts) and |
| position (for bit-field operations), or if no variable-position bit-field |
| instructions exist, you should define this macro. |
| |
| However, on some machines, such as the 80386 and the 680x0, truncation |
| only applies to shift operations and not the (real or pretended) |
| bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on |
| such machines. Instead, add patterns to the @file{md} file that include |
| the implied truncation of the shift instructions. |
| |
| You need not define this macro if it would always have the value of zero. |
| |
| @findex TRULY_NOOP_TRUNCATION |
| @item TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec}) |
| A C expression which is nonzero if on this machine it is safe to |
| ``convert'' an integer of @var{inprec} bits to one of @var{outprec} |
| bits (where @var{outprec} is smaller than @var{inprec}) by merely |
| operating on it as if it had only @var{outprec} bits. |
| |
| On many machines, this expression can be 1. |
| |
| @c rearranged this, removed the phrase "it is reported that". this was |
| @c to fix an overfull hbox. --mew 10feb93 |
| When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for |
| modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result. |
| If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in |
| such cases may improve things. |
| |
| @findex STORE_FLAG_VALUE |
| @item STORE_FLAG_VALUE |
| A C expression describing the value returned by a comparison operator |
| with an integral mode and stored by a store-flag instruction |
| (@samp{s@var{cond}}) when the condition is true. This description must |
| apply to @emph{all} the @samp{s@var{cond}} patterns and all the |
| comparison operators whose results have a @code{MODE_INT} mode. |
| |
| A value of 1 or @minus{}1 means that the instruction implementing the |
| comparison operator returns exactly 1 or @minus{}1 when the comparison is true |
| and 0 when the comparison is false. Otherwise, the value indicates |
| which bits of the result are guaranteed to be 1 when the comparison is |
| true. This value is interpreted in the mode of the comparison |
| operation, which is given by the mode of the first operand in the |
| @samp{s@var{cond}} pattern. Either the low bit or the sign bit of |
| @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by |
| the compiler. |
| |
| If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will |
| generate code that depends only on the specified bits. It can also |
| replace comparison operators with equivalent operations if they cause |
| the required bits to be set, even if the remaining bits are undefined. |
| For example, on a machine whose comparison operators return an |
| @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as |
| @samp{0x80000000}, saying that just the sign bit is relevant, the |
| expression |
| |
| @smallexample |
| (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) |
| @end smallexample |
| |
| @noindent |
| can be converted to |
| |
| @smallexample |
| (ashift:SI @var{x} (const_int @var{n})) |
| @end smallexample |
| |
| @noindent |
| where @var{n} is the appropriate shift count to move the bit being |
| tested into the sign bit. |
| |
| There is no way to describe a machine that always sets the low-order bit |
| for a true value, but does not guarantee the value of any other bits, |
| but we do not know of any machine that has such an instruction. If you |
| are trying to port GCC to such a machine, include an instruction to |
| perform a logical-and of the result with 1 in the pattern for the |
| comparison operators and let us know at @email{gcc@@gcc.gnu.org}. |
| |
| Often, a machine will have multiple instructions that obtain a value |
| from a comparison (or the condition codes). Here are rules to guide the |
| choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions |
| to be used: |
| |
| @itemize @bullet |
| @item |
| Use the shortest sequence that yields a valid definition for |
| @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to |
| ``normalize'' the value (convert it to, e.g., 1 or 0) than for the |
| comparison operators to do so because there may be opportunities to |
| combine the normalization with other operations. |
| |
| @item |
| For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being |
| slightly preferred on machines with expensive jumps and 1 preferred on |
| other machines. |
| |
| @item |
| As a second choice, choose a value of @samp{0x80000001} if instructions |
| exist that set both the sign and low-order bits but do not define the |
| others. |
| |
| @item |
| Otherwise, use a value of @samp{0x80000000}. |
| @end itemize |
| |
| Many machines can produce both the value chosen for |
| @code{STORE_FLAG_VALUE} and its negation in the same number of |
| instructions. On those machines, you should also define a pattern for |
| those cases, e.g., one matching |
| |
| @smallexample |
| (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) |
| @end smallexample |
| |
| Some machines can also perform @code{and} or @code{plus} operations on |
| condition code values with less instructions than the corresponding |
| @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those |
| machines, define the appropriate patterns. Use the names @code{incscc} |
| and @code{decscc}, respectively, for the patterns which perform |
| @code{plus} or @code{minus} operations on condition code values. See |
| @file{rs6000.md} for some examples. The GNU Superoptizer can be used to |
| find such instruction sequences on other machines. |
| |
| You need not define @code{STORE_FLAG_VALUE} if the machine has no store-flag |
| instructions. |
| |
| @findex FLOAT_STORE_FLAG_VALUE |
| @item FLOAT_STORE_FLAG_VALUE (@var{mode}) |
| A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is |
| returned when comparison operators with floating-point results are true. |
| Define this macro on machine that have comparison operations that return |
| floating-point values. If there are no such operations, do not define |
| this macro. |
| |
| @findex Pmode |
| @item Pmode |
| An alias for the machine mode for pointers. On most machines, define |
| this to be the integer mode corresponding to the width of a hardware |
| pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. |
| On some machines you must define this to be one of the partial integer |
| modes, such as @code{PSImode}. |
| |
| The width of @code{Pmode} must be at least as large as the value of |
| @code{POINTER_SIZE}. If it is not equal, you must define the macro |
| @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended |
| to @code{Pmode}. |
| |
| @findex FUNCTION_MODE |
| @item FUNCTION_MODE |
| An alias for the machine mode used for memory references to functions |
| being called, in @code{call} RTL expressions. On most machines this |
| should be @code{QImode}. |
| |
| @findex INTEGRATE_THRESHOLD |
| @item INTEGRATE_THRESHOLD (@var{decl}) |
| A C expression for the maximum number of instructions above which the |
| function @var{decl} should not be inlined. @var{decl} is a |
| @code{FUNCTION_DECL} node. |
| |
| The default definition of this macro is 64 plus 8 times the number of |
| arguments that the function accepts. Some people think a larger |
| threshold should be used on RISC machines. |
| |
| @findex STDC_0_IN_SYSTEM_HEADERS |
| @item STDC_0_IN_SYSTEM_HEADERS |
| In normal operation, the preprocessor expands @code{__STDC__} to the |
| constant 1, to signify that GCC conforms to ISO Standard C@. On some |
| hosts, like Solaris, the system compiler uses a different convention, |
| where @code{__STDC__} is normally 0, but is 1 if the user specifies |
| strict conformance to the C Standard. |
| |
| Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host |
| convention when processing system header files, but when processing user |
| files @code{__STDC__} will always expand to 1. |
| |
| @findex SCCS_DIRECTIVE |
| @item SCCS_DIRECTIVE |
| Define this if the preprocessor should ignore @code{#sccs} directives |
| and print no error message. |
| |
| @findex NO_IMPLICIT_EXTERN_C |
| @item NO_IMPLICIT_EXTERN_C |
| Define this macro if the system header files support C++ as well as C@. |
| This macro inhibits the usual method of using system header files in |
| C++, which is to pretend that the file's contents are enclosed in |
| @samp{extern "C" @{@dots{}@}}. |
| |
| @findex HANDLE_PRAGMA |
| @item HANDLE_PRAGMA (@var{getc}, @var{ungetc}, @var{name}) |
| This macro is no longer supported. You must use |
| @code{REGISTER_TARGET_PRAGMAS} instead. |
| |
| @findex REGISTER_TARGET_PRAGMAS |
| @findex #pragma |
| @findex pragma |
| @item REGISTER_TARGET_PRAGMAS (@var{pfile}) |
| Define this macro if you want to implement any target-specific pragmas. |
| If defined, it is a C expression which makes a series of calls to |
| @code{cpp_register_pragma} for each pragma, with @var{pfile} passed as |
| the first argument to to these functions. The macro may also do any |
| setup required for the pragmas. |
| |
| The primary reason to define this macro is to provide compatibility with |
| other compilers for the same target. In general, we discourage |
| definition of target-specific pragmas for GCC@. |
| |
| If the pragma can be implemented by attributes then you should consider |
| defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. |
| |
| Preprocessor macros that appear on pragma lines are not expanded. All |
| @samp{#pragma} directives that do not match any registered pragma are |
| silently ignored, unless the user specifies @option{-Wunknown-pragmas}. |
| |
| @deftypefun void cpp_register_pragma (cpp_reader *@var{pfile}, const char *@var{space}, const char *@var{name}, void (*@var{callback}) (cpp_reader *)) |
| |
| Each call to @code{cpp_register_pragma} establishes one pragma. The |
| @var{callback} routine will be called when the preprocessor encounters a |
| pragma of the form |
| |
| @smallexample |
| #pragma [@var{space}] @var{name} @dots{} |
| @end smallexample |
| |
| @var{space} is the case-sensitive namespace of the pragma, or |
| @code{NULL} to put the pragma in the global namespace. The callback |
| routine receives @var{pfile} as its first argument, which can be passed |
| on to cpplib's functions if necessary. You can lex tokens after the |
| @var{name} by calling @code{c_lex}. Tokens that are not read by the |
| callback will be silently ignored. The end of the line is indicated by |
| a token of type @code{CPP_EOF}. |
| |
| For an example use of this routine, see @file{c4x.h} and the callback |
| routines defined in @file{c4x-c.c}. |
| |
| Note that the use of @code{c_lex} is specific to the C and C++ |
| compilers. It will not work in the Java or Fortran compilers, or any |
| other language compilers for that matter. Thus if @code{c_lex} is going |
| to be called from target-specific code, it must only be done so when |
| building the C and C++ compilers. This can be done by defining the |
| variables @code{c_target_objs} and @code{cxx_target_objs} in the |
| target entry in the @file{config.gcc} file. These variables should name |
| the target-specific, language-specific object file which contains the |
| code that uses @code{c_lex}. Note it will also be necessary to add a |
| rule to the makefile fragment pointed to by @code{tmake_file} that shows |
| how to build this object file. |
| @end deftypefun |
| |
| @findex HANDLE_SYSV_PRAGMA |
| @findex #pragma |
| @findex pragma |
| @item HANDLE_SYSV_PRAGMA |
| Define this macro (to a value of 1) if you want the System V style |
| pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name> |
| [=<value>]} to be supported by gcc. |
| |
| The pack pragma specifies the maximum alignment (in bytes) of fields |
| within a structure, in much the same way as the @samp{__aligned__} and |
| @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets |
| the behavior to the default. |
| |
| The weak pragma only works if @code{SUPPORTS_WEAK} and |
| @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation |
| of specifically named weak labels, optionally with a value. |
| |
| @findex HANDLE_PRAGMA_PACK_PUSH_POP |
| @findex #pragma |
| @findex pragma |
| @item HANDLE_PRAGMA_PACK_PUSH_POP |
| Define this macro (to a value of 1) if you want to support the Win32 |
| style pragmas @samp{#pragma pack(push,@var{n})} and @samp{#pragma |
| pack(pop)}. The @samp{pack(push,@var{n})} pragma specifies the maximum alignment |
| (in bytes) of fields within a structure, in much the same way as the |
| @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A |
| pack value of zero resets the behavior to the default. Successive |
| invocations of this pragma cause the previous values to be stacked, so |
| that invocations of @samp{#pragma pack(pop)} will return to the previous |
| value. |
| |
| @findex DOLLARS_IN_IDENTIFIERS |
| @item DOLLARS_IN_IDENTIFIERS |
| Define this macro to control use of the character @samp{$} in identifier |
| names. 0 means @samp{$} is not allowed by default; 1 means it is allowed. |
| 1 is the default; there is no need to define this macro in that case. |
| This macro controls the compiler proper; it does not affect the preprocessor. |
| |
| @findex NO_DOLLAR_IN_LABEL |
| @item NO_DOLLAR_IN_LABEL |
| Define this macro if the assembler does not accept the character |
| @samp{$} in label names. By default constructors and destructors in |
| G++ have @samp{$} in the identifiers. If this macro is defined, |
| @samp{.} is used instead. |
| |
| @findex NO_DOT_IN_LABEL |
| @item NO_DOT_IN_LABEL |
| Define this macro if the assembler does not accept the character |
| @samp{.} in label names. By default constructors and destructors in G++ |
| have names that use @samp{.}. If this macro is defined, these names |
| are rewritten to avoid @samp{.}. |
| |
| @findex DEFAULT_MAIN_RETURN |
| @item DEFAULT_MAIN_RETURN |
| Define this macro if the target system expects every program's @code{main} |
| function to return a standard ``success'' value by default (if no other |
| value is explicitly returned). |
| |
| The definition should be a C statement (sans semicolon) to generate the |
| appropriate rtl instructions. It is used only when compiling the end of |
| @code{main}. |
| |
| @item NEED_ATEXIT |
| @findex NEED_ATEXIT |
| Define this if the target system lacks the function @code{atexit} |
| from the ISO C standard. If this macro is defined, a default definition |
| will be provided to support C++. If @code{ON_EXIT} is not defined, |
| a default @code{exit} function will also be provided. |
| |
| @item ON_EXIT |
| @findex ON_EXIT |
| Define this macro if the target has another way to implement atexit |
| functionality without replacing @code{exit}. For instance, SunOS 4 has |
| a similar @code{on_exit} library function. |
| |
| The definition should be a functional macro which can be used just like |
| the @code{atexit} function. |
| |
| @item EXIT_BODY |
| @findex EXIT_BODY |
| Define this if your @code{exit} function needs to do something |
| besides calling an external function @code{_cleanup} before |
| terminating with @code{_exit}. The @code{EXIT_BODY} macro is |
| only needed if @code{NEED_ATEXIT} is defined and @code{ON_EXIT} is not |
| defined. |
| |
| @findex INSN_SETS_ARE_DELAYED |
| @item INSN_SETS_ARE_DELAYED (@var{insn}) |
| Define this macro as a C expression that is nonzero if it is safe for the |
| delay slot scheduler to place instructions in the delay slot of @var{insn}, |
| even if they appear to use a resource set or clobbered in @var{insn}. |
| @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that |
| every @code{call_insn} has this behavior. On machines where some @code{insn} |
| or @code{jump_insn} is really a function call and hence has this behavior, |
| you should define this macro. |
| |
| You need not define this macro if it would always return zero. |
| |
| @findex INSN_REFERENCES_ARE_DELAYED |
| @item INSN_REFERENCES_ARE_DELAYED (@var{insn}) |
| Define this macro as a C expression that is nonzero if it is safe for the |
| delay slot scheduler to place instructions in the delay slot of @var{insn}, |
| even if they appear to set or clobber a resource referenced in @var{insn}. |
| @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where |
| some @code{insn} or @code{jump_insn} is really a function call and its operands |
| are registers whose use is actually in the subroutine it calls, you should |
| define this macro. Doing so allows the delay slot scheduler to move |
| instructions which copy arguments into the argument registers into the delay |
| slot of @var{insn}. |
| |
| You need not define this macro if it would always return zero. |
| |
| @findex MACHINE_DEPENDENT_REORG |
| @item MACHINE_DEPENDENT_REORG (@var{insn}) |
| In rare cases, correct code generation requires extra machine |
| dependent processing between the second jump optimization pass and |
| delayed branch scheduling. On those machines, define this macro as a C |
| statement to act on the code starting at @var{insn}. |
| |
| @findex MULTIPLE_SYMBOL_SPACES |
| @item MULTIPLE_SYMBOL_SPACES |
| Define this macro if in some cases global symbols from one translation |
| unit may not be bound to undefined symbols in another translation unit |
| without user intervention. For instance, under Microsoft Windows |
| symbols must be explicitly imported from shared libraries (DLLs). |
| |
| @findex MD_ASM_CLOBBERS |
| @item MD_ASM_CLOBBERS (@var{clobbers}) |
| A C statement that adds to @var{clobbers} @code{STRING_CST} trees for |
| any hard regs the port wishes to automatically clobber for all asms. |
| |
| @findex MAX_INTEGER_COMPUTATION_MODE |
| @item MAX_INTEGER_COMPUTATION_MODE |
| Define this to the largest integer machine mode which can be used for |
| operations other than load, store and copy operations. |
| |
| You need only define this macro if the target holds values larger than |
| @code{word_mode} in general purpose registers. Most targets should not define |
| this macro. |
| |
| @findex MATH_LIBRARY |
| @item MATH_LIBRARY |
| Define this macro as a C string constant for the linker argument to link |
| in the system math library, or @samp{""} if the target does not have a |
| separate math library. |
| |
| You need only define this macro if the default of @samp{"-lm"} is wrong. |
| |
| @findex LIBRARY_PATH_ENV |
| @item LIBRARY_PATH_ENV |
| Define this macro as a C string constant for the environment variable that |
| specifies where the linker should look for libraries. |
| |
| You need only define this macro if the default of @samp{"LIBRARY_PATH"} |
| is wrong. |
| |
| @findex TARGET_HAS_F_SETLKW |
| @item TARGET_HAS_F_SETLKW |
| Define this macro if the target supports file locking with fcntl / F_SETLKW@. |
| Note that this functionality is part of POSIX@. |
| Defining @code{TARGET_HAS_F_SETLKW} will enable the test coverage code |
| to use file locking when exiting a program, which avoids race conditions |
| if the program has forked. |
| |
| @findex MAX_CONDITIONAL_EXECUTE |
| @item MAX_CONDITIONAL_EXECUTE |
| |
| A C expression for the maximum number of instructions to execute via |
| conditional execution instructions instead of a branch. A value of |
| @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and |
| 1 if it does use cc0. |
| |
| @findex IFCVT_MODIFY_TESTS |
| @item IFCVT_MODIFY_TESTS |
| A C expression to modify the tests in @code{TRUE_EXPR}, and |
| @code{FALSE_EXPR} for use in converting insns in @code{TEST_BB}, |
| @code{THEN_BB}, @code{ELSE_BB}, and @code{JOIN_BB} basic blocks to |
| conditional execution. Set either @code{TRUE_EXPR} or @code{FALSE_EXPR} |
| to a null pointer if the tests cannot be converted. |
| |
| @findex IFCVT_MODIFY_INSN |
| @item IFCVT_MODIFY_INSN |
| A C expression to modify the @code{PATTERN} of an @code{INSN} that is to |
| be converted to conditional execution format. |
| |
| @findex IFCVT_MODIFY_FINAL |
| @item IFCVT_MODIFY_FINAL |
| A C expression to perform any final machine dependent modifications in |
| converting code to conditional execution in the basic blocks |
| @code{TEST_BB}, @code{THEN_BB}, @code{ELSE_BB}, and @code{JOIN_BB}. |
| |
| @findex IFCVT_MODIFY_CANCEL |
| @item IFCVT_MODIFY_CANCEL |
| A C expression to cancel any machine dependent modifications in |
| converting code to conditional execution in the basic blocks |
| @code{TEST_BB}, @code{THEN_BB}, @code{ELSE_BB}, and @code{JOIN_BB}. |
| @end table |
| |
| @deftypefn {Target Hook} void TARGET_INIT_BUILTINS () |
| Define this hook if you have any machine-specific built-in functions |
| that need to be defined. It should be a function that performs the |
| necessary setup. |
| |
| Machine specific built-in functions can be useful to expand special machine |
| instructions that would otherwise not normally be generated because |
| they have no equivalent in the source language (for example, SIMD vector |
| instructions or prefetch instructions). |
| |
| To create a built-in function, call the function @code{builtin_function} |
| which is defined by the language front end. You can use any type nodes set |
| up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2}; |
| only language front ends that use those two functions will call |
| @samp{TARGET_INIT_BUILTINS}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore}) |
| |
| Expand a call to a machine specific built-in function that was set up by |
| @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the |
| function call; the result should go to @var{target} if that is |
| convenient, and have mode @var{mode} if that is convenient. |
| @var{subtarget} may be used as the target for computing one of |
| @var{exp}'s operands. @var{ignore} is nonzero if the value is to be |
| ignored. This function should return the result of the call to the |
| built-in function. |
| @end deftypefn |
| |
| @table @code |
| @findex MD_CAN_REDIRECT_BRANCH |
| @item MD_CAN_REDIRECT_BRANCH(@var{branch1}, @var{branch2}) |
| |
| Take a branch insn in @var{branch1} and another in @var{branch2}. |
| Return true if redirecting @var{branch1} to the destination of |
| @var{branch2} is possible. |
| |
| On some targets, branches may have a limited range. Optimizing the |
| filling of delay slots can result in branches being redirected, and this |
| may in turn cause a branch offset to overflow. |
| |
| @findex ALLOCATE_INITIAL_VALUE |
| @item ALLOCATE_INITIAL_VALUE(@var{hard_reg}) |
| |
| When the initial value of a hard register has been copied in a pseudo |
| register, it is often not necessary to actually allocate another register |
| to this pseudo register, because the original hard register or a stack slot |
| it has been saved into can be used. @code{ALLOCATE_INITIAL_VALUE}, if |
| defined, is called at the start of register allocation once for each |
| hard register that had its initial value copied by using |
| @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. |
| Possible values are @code{NULL_RTX}, if you don't want |
| to do any special allocation, a @code{REG} rtx---that would typically be |
| the hard register itself, if it is known not to be clobbered---or a |
| @code{MEM}. |
| If you are returning a @code{MEM}, this is only a hint for the allocator; |
| it might decide to use another register anyways. |
| You may use @code{current_function_leaf_function} in the definition of the |
| macro, functions that use @code{REG_N_SETS}, to determine if the hard |
| register in question will not be clobbered. |
| |
| @findex TARGET_OBJECT_SUFFIX |
| @item TARGET_OBJECT_SUFFIX |
| Define this macro to be a C string representing the suffix for object |
| files on your target machine. If you do not define this macro, GCC will |
| use @samp{.o} as the suffix for object files. |
| |
| @findex TARGET_EXECUTABLE_SUFFIX |
| @item TARGET_EXECUTABLE_SUFFIX |
| Define this macro to be a C string representing the suffix to be |
| automatically added to executable files on your target machine. If you |
| do not define this macro, GCC will use the null string as the suffix for |
| executable files. |
| |
| @findex COLLECT_EXPORT_LIST |
| @item COLLECT_EXPORT_LIST |
| If defined, @code{collect2} will scan the individual object files |
| specified on its command line and create an export list for the linker. |
| Define this macro for systems like AIX, where the linker discards |
| object files that are not referenced from @code{main} and uses export |
| lists. |
| |
| @end table |
| |
| @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void) |
| This target hook returns @code{true} past the point in which new jump |
| instructions could be created. On machines that require a register for |
| every jump such as the SHmedia ISA of SH5, this point would typically be |
| reload, so this target hook should be defined to a function such as: |
| |
| @smallexample |
| static bool |
| cannot_modify_jumps_past_reload_p () |
| @{ |
| return (reload_completed || reload_in_progress); |
| @} |
| @end smallexample |
| @end deftypefn |