| %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% |
| % |
| % File: porting.texi |
| % Author: Mark Mitchell |
| % Date: 11/21/2000 |
| % |
| % Contents: |
| % |
| % Copyright (c) 2000 by Free Software Foundation, Inc. |
| % |
| %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% |
| |
| \input texinfo |
| |
| @c --------------------------------------------------------------------- |
| @c Prologue |
| @c --------------------------------------------------------------------- |
| |
| @setfilename porting.info |
| @settitle Porting libstdc++-v3 |
| @setchapternewpage odd |
| |
| @ifinfo |
| This file explains how to port libstdc++-v3 (the GNU C++ library) to |
| a new target. |
| |
| Copyright (c) 2000 Free Software Foundation, Inc. |
| @end ifinfo |
| |
| @c --------------------------------------------------------------------- |
| @c Titlepage |
| @c --------------------------------------------------------------------- |
| |
| @titlepage |
| @title Porting libstdc++-v3 |
| @author Mark Mitchell |
| @page |
| @vskip 0pt plus 1filll |
| Copyright @copyright{} 2000 Free Software Foundation, Inc. |
| @end titlepage |
| |
| @c --------------------------------------------------------------------- |
| @c Top |
| @c --------------------------------------------------------------------- |
| |
| @node Top |
| @top Porting libstdc++-v3 |
| |
| This document explains how to port libstdc++-v3 (the GNU C++ library) to |
| a new target. |
| |
| In order to make the GNU C++ library (libstdc++-v3) work with a new |
| target, you must edit some configuration files and provide some new |
| header files. |
| |
| Before you get started, make sure that you have a working C library on |
| your target. The C library need not precisely comply with any |
| particular standard, but should generally conform to the requirements |
| imposed by the ANSI/ISO standard. |
| |
| In addition, you should try to verify that the C++ compiler generally |
| works. It is difficult to test the C++ compiler without a working |
| library, but you should at least try some minimal test cases. |
| |
| Here are the primary steps required to port the library: |
| |
| @menu |
| * Operating system:: Configuring for your operating system. |
| * Character types:: Implementing character classification. |
| * Thread safety:: Implementing atomic operations. |
| * Libtool:: Using libtool. |
| @end menu |
| |
| @c --------------------------------------------------------------------- |
| @c Operating system |
| @c --------------------------------------------------------------------- |
| |
| @node Operating system |
| @chapter Operating system |
| |
| If you are porting to a new operating-system (as opposed to a new chip |
| using an existing operating system), you will need to create a new |
| directory in the @file{config/os} hierarchy. For example, the IRIX |
| configuration files are all in @file{config/os/irix}. There is no set |
| way to organize the OS configuration directory. For example, |
| @file{config/os/solaris/solaris-2.6} and |
| @file{config/os/solaris/solaris-2.7} are used as configuration |
| directories for these two versions of Solaris. On the other hand, both |
| Solaris 2.7 and Solaris 2.8 use the @file{config/os/solaris/solaris-2.7} |
| directory. The important information is that there needs to be a |
| directory under @file{config/os} to store the files for your operating |
| system. |
| |
| You'll have to change the @file{configure.target} file to ensure that |
| your new directory is activated. Look for the switch statement that |
| sets @code{os_include_dir}, and add a pattern to handle your operating |
| system. The switch statement switches on only the OS portion of the |
| standard target triplet; e.g., the @code{solaris2.8} in |
| @code{sparc-sun-solaris2.8}. |
| |
| The first file to create in this directory, should be called |
| @file{bits/os_defines.h}. This file contains basic macro definitions |
| that are required to allow the C++ library to work with your C library. |
| This file should provide macro definitions for @code{__off_t}, |
| @code{__off64_t}, and @code{__ssize_t}. Typically, this just looks |
| like: |
| |
| @example |
| #define __off_t off_t |
| #define __off64_t off64_t |
| #define __ssize_t ssize_t |
| @end example |
| |
| @noindent |
| You don't have to provide these definitions if your system library |
| already defines these types -- but the only library known to provide |
| these types is the GNU C Library, so you will almost certainly have to |
| provide these macros. Note that this file does not have to include a |
| header file that defines @code{off_t}, or the other types; you simply |
| have to provide the macros. |
| |
| In addition, several libstdc++-v3 source files unconditionally define the macro |
| @code{_POSIX_SOURCE}. On many systems, defining this macro causes large |
| portions of the C library header files to be eliminated at preprocessing |
| time. Therefore, you may have to @code{#undef} this macro, or define |
| other macros (like @code{_LARGEFILE_SOURCE} or @code{__EXTENSIONS__}). |
| You won't know what macros to define or undefine at this point; you'll |
| have to try compiling the library and seeing what goes wrong. If you |
| see errors about calling functions that have not been declared, look in |
| your C library headers to see if the functions are declared there, and |
| then figure out what macros you should but in @file{bits/os_defines.h} |
| to make these declarations available. |
| |
| Finally, you should bracket the entire file in an include-guard, like |
| this: |
| |
| @example |
| #ifndef _GLIBCPP_OS_DEFINES |
| #define _GLIBCPP_OS_DEFINES |
| ... |
| #endif |
| @end example |
| |
| We recommend copying an existing @file{bits/os_defines.h} to use as a |
| starting point. |
| |
| @c --------------------------------------------------------------------- |
| @c Character types |
| @c --------------------------------------------------------------------- |
| |
| @node Character types |
| @chapter Character types |
| |
| The library requires that you provide three header files to implement |
| character classification, analagous to that provided by the C libraries |
| @file{<ctype.h>} header. You can model these on the files provided in |
| @file{config/os/generic/bits}. However, these files will almost |
| certainly need some modification. |
| |
| The first file to write is @file{bits/ctype_base.h}. This file provides |
| some very basic information about character classification. The libstdc++-v3 |
| library assumes that your C library implements @file{<ctype.h>} by using |
| a table (indexed by character code) containing integers, where each of |
| these integers is a bit-mask indicating whether the charcter is |
| upper-case, lower-case, alphabetic, etc. The @file{bits/ctype_base.h} |
| file gives the type of the integer, and the values of the various bit |
| masks. You will have to peer at your own @file{<ctype.h>} to figure out |
| how to define the values required by this file. |
| |
| The @file{bits/ctype_base.h} header file does not need include guards. |
| It should contain a single @code{struct} definition called |
| @code{ctype_base}. This @code{struct} should contain two type |
| declarations, and one enumeration declaration, like this example, taken |
| from the IRIX configuration: |
| |
| @example |
| struct ctype_base |
| @{ |
| typedef unsigned int mask; |
| typedef int* __to_type; |
| |
| enum |
| @{ |
| space = _ISspace, |
| print = _ISprint, |
| cntrl = _IScntrl, |
| upper = _ISupper, |
| lower = _ISlower, |
| alpha = _ISalpha, |
| digit = _ISdigit, |
| punct = _ISpunct, |
| xdigit = _ISxdigit, |
| alnum = _ISalnum, |
| graph = _ISgraph |
| @}; |
| @}; |
| @end example |
| |
| @noindent |
| The @code{mask} type is the type of the elements in the table. If your |
| C library uses a table to map lower-case numbers to upper-case numbers, |
| and vice versa, you should define @code{__to_type} to be the type of the |
| elements in that table. If you don't mind taking a minor performance |
| penalty, or if your library doesn't implement @code{toupper} and |
| @code{tolower} in this way, you can pick any pointer-to-integer type, |
| but you must still define the type. |
| |
| The enumeration should give definitions for all the values in the above |
| example, using the values from your native @file{<ctype.h>}. They can |
| be given symbolically (as above), or numerically, if you prefer. You do |
| not have to include @file{<ctype.h>} in this header; it will always be |
| included before @file{bits/ctype_base.h} is included. |
| |
| The next file to write is @file{bits/ctype_noninline.h}, which also does |
| not require include guards. This file defines a few member functions |
| that will be included in @file{include/bits/locale_facets.h}. The first |
| function that must be written is the @code{ctype<char>::ctype} |
| constructor. Here is the IRIX example: |
| |
| @example |
| ctype<char>::ctype(const mask* __table = 0, bool __del = false, |
| size_t __refs = 0) |
| : _Ctype_nois<char>(__refs), _M_del(__table != 0 && __del), |
| _M_toupper(NULL), |
| _M_tolower(NULL), |
| _M_ctable(NULL), |
| _M_table(!__table |
| ? (const mask*) (__libc_attr._ctype_tbl->_class + 1) |
| : __table) |
| @{ @} |
| @end example |
| |
| @noindent |
| There are two parts of this that you might choose to alter. The first, |
| and most important, is the line involving @code{__libc_attr}. That is |
| IRIX system-dependent code that gets the base of the table mapping |
| character codes to attributes. You need to substitute code that obtains |
| the address of this table on your system. If you want to use your |
| operating system's tables to map upper-case letters to lower-case, and |
| vice versa, you should initialize @code{_M_toupper} and |
| @code{_M_tolower} with those tables, in similar fashion. |
| |
| Now, you have to write two functions to convert from upper-case to |
| lower-case, and vice versa. Here are the IRIX versions: |
| |
| @example |
| char |
| ctype<char>::do_toupper(char __c) const |
| @{ return _toupper(__c); @} |
| |
| char |
| ctype<char>::do_tolower(char __c) const |
| @{ return _tolower(__c); @} |
| @end example |
| |
| @noindent |
| Your C library provides equivalents to IRIX's @code{_toupper} and |
| @code{_tolower}. If you initialized @code{_M_toupper} and |
| @code{_M_tolower} above, then you could use those tables instead. |
| |
| Finally, you have to provide two utility functions that convert strings |
| of characters. The versions provided here will always work -- but you |
| could use specialized routines for greater performance if you have |
| machinery to do that on your system: |
| |
| @example |
| const char* |
| ctype<char>::do_toupper(char* __low, const char* __high) const |
| @{ |
| while (__low < __high) |
| @{ |
| *__low = do_toupper(*__low); |
| ++__low; |
| @} |
| return __high; |
| @} |
| |
| const char* |
| ctype<char>::do_tolower(char* __low, const char* __high) const |
| @{ |
| while (__low < __high) |
| @{ |
| *__low = do_tolower(*__low); |
| ++__low; |
| @} |
| return __high; |
| @} |
| @end example |
| |
| You must also provide the @file{bits/ctype_inline.h} file, which |
| contains a few more functions. On most systems, you can just copy |
| @file{config/os/generic/ctype_inline.h} and use it on your system. |
| |
| In detail, the functions provided test characters for particular |
| properties; they are analagous to the functions like @code{isalpha} and |
| @code{islower} provided by the C library. |
| |
| The first function is implemented like this on IRIX: |
| |
| @example |
| bool |
| ctype<char>:: |
| is(mask __m, char __c) const throw() |
| @{ return (_M_table)[(unsigned char)(__c)] & __m; @} |
| @end example |
| |
| @noindent |
| The @code{_M_table} is the table passed in above, in the constructor. |
| This is the table that contains the bitmasks for each character. The |
| implementation here should work on all systems. |
| |
| The next function is: |
| |
| @example |
| const char* |
| ctype<char>:: |
| is(const char* __low, const char* __high, mask* __vec) const throw() |
| @{ |
| while (__low < __high) |
| *__vec++ = (_M_table)[(unsigned char)(*__low++)]; |
| return __high; |
| @} |
| @end example |
| |
| @noindent |
| This function is similar; it copies the masks for all the characters |
| from @code{__low} up until @code{__high} into the vector given by |
| @code{__vec}. |
| |
| The last two functions again are entirely generic: |
| |
| @example |
| const char* |
| ctype<char>:: |
| scan_is(mask __m, const char* __low, const char* __high) const throw() |
| @{ |
| while (__low < __high && !this->is(__m, *__low)) |
| ++__low; |
| return __low; |
| @} |
| |
| const char* |
| ctype<char>:: |
| scan_not(mask __m, const char* __low, const char* __high) const throw() |
| @{ |
| while (__low < __high && this->is(__m, *__low)) |
| ++__low; |
| return __low; |
| @} |
| @end example |
| |
| @c --------------------------------------------------------------------- |
| @c Thread safety |
| @c --------------------------------------------------------------------- |
| |
| @node Thread safety |
| @chapter Thread safety |
| |
| The C++ library string functionality requires a couple of atomic |
| operations to provide thread-safety. If you don't take any special |
| action, the library will use stub versions of these functions that are |
| not thread-safe. They will work fine, unless your applications are |
| multi-threaded. |
| |
| If you want to provide custom, safe, versions of these functions, there |
| are two distinct approaches. One is to provide a version for your CPU, |
| using assembly language constructs. The other is to use the |
| thread-safety primitives in your operating system. In either case, you |
| make a file called @file{bits/atomicity.h}. |
| |
| If you are using the assembly-language approach, put this code in |
| @file{config/cpu/<chip>/bits/atomicity.h}, where chip is the name of |
| your processor. In that case, edit the switch statement in |
| @file{configure.target} to set the @code{cpu_include_dir}. In either |
| case, set the switch statement that sets @code{ATOMICITYH} to be the |
| directory containing @file{bits/atomicity.h}. |
| |
| With those bits out of the way, you have to actually write |
| @file{bits/atomicity.h} itself. This file should be wrapped in an |
| include guard named @code{_BITS_ATOMICITY_H}. It should define one |
| type, and two functions. |
| |
| The type is @code{_Atomic_word}. Here is the version used on IRIX: |
| |
| @example |
| typedef long _Atomic_word; |
| @end example |
| |
| @noindent |
| This type must be a signed integral type supporting atomic operations. |
| If you're using the OS approach, use the same type used by your system's |
| primitives. Otherwise, use the type for which your CPU provides atomic |
| primitives. |
| |
| Then, you must provide two functions. The bodies of these functions |
| must be equivalent to those provided here, but using atomic operations: |
| |
| @example |
| static inline _Atomic_word |
| __attribute__ ((__unused__)) |
| __exchange_and_add (_Atomic_word* __mem, int __val) |
| @{ |
| _Atomic_word __result = *__mem; |
| *__mem += __val; |
| return __result; |
| @} |
| |
| static inline void |
| __attribute__ ((__unused__)) |
| __atomic_add (_Atomic_word* __mem, int __val) |
| @{ |
| *__mem += __val; |
| @} |
| @end example |
| |
| @c --------------------------------------------------------------------- |
| @c Libtool |
| @c --------------------------------------------------------------------- |
| |
| @node Libtool |
| @chapter Libtool |
| |
| The C++ library is compiled, archived and linked with libtool. |
| Explaining the full workings of libtool is beyond the scope of this |
| document, but there are a few, particular bits that are necessary for |
| porting. |
| |
| Some parts of the libstdc++-v3 library are compiled with the libtool |
| @code{--tags CXX} option (the C++ definitions for libtool). Therefore, |
| @file{ltcf-cxx.sh} in the top-level directory needs to have the correct |
| logic to compile and archive objects equivalent to the C version of libtool, |
| @file{ltcf-c.sh}. Some libtool targets have definitions for C but not |
| for C++, or C++ definitions which have not been kept up to date. |
| |
| The C++ run-time library contains initialization code that needs to be |
| run as the library is loaded. Often, that requires linking in special |
| object files when the C++ library is built as a shared library, or |
| taking other system-specific actions. |
| |
| The libstdc++-v3 library is linked with the C version of libtool, even though it |
| is a C++ library. Therefore, the C version of libtool needs to ensure |
| that the run-time library initializers are run. The usual way to do |
| this is to build the library using @code{gcc -shared}. |
| |
| If you need to change how the library is linked, look at |
| @file{ltcf-c.sh} in the top-level directory. Find the switch statement |
| that sets @code{archive_cmds}. Here, adjust the setting for your |
| operating system. |
| |
| @c --------------------------------------------------------------------- |
| @c Epilogue |
| @c --------------------------------------------------------------------- |
| |
| @contents |
| @bye |