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This is as.info, produced by makeinfo version 4.0 from as.texinfo.
START-INFO-DIR-ENTRY
* As: (as). The GNU assembler.
END-INFO-DIR-ENTRY
This file documents the GNU Assembler "as".
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000 Free
Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions.

File: as.info, Node: ESA/390 Directives, Next: ESA/390 Opcodes, Prev: ESA/390 Floating Point, Up: ESA/390-Dependent
ESA/390 Assembler Directives
----------------------------
`as' for the ESA/390 supports all of the standard ELF/SVR4 assembler
directives that are documented in the main part of this documentation.
Several additional directives are supported in order to implement the
ESA/390 addressing model. The most important of these are `.using' and
`.ltorg'
These are the additional directives in `as' for the ESA/390:
`.dc'
A small subset of the usual DC directive is supported.
`.drop REGNO'
Stop using REGNO as the base register. The REGNO must have been
previously declared with a `.using' directive in the same section
as the current section.
`.ebcdic STRING'
Emit the EBCDIC equivalent of the indicated string. The emitted
string will be null terminated. Note that the directives
`.string' etc. emit ascii strings by default.
`EQU'
The standard HLASM-style EQU directive is not supported; however,
the standard `as' directive .equ can be used to the same effect.
`.ltorg'
Dump the literal pool accumulated so far; begin a new literal pool.
The literal pool will be written in the current section; in order
to generate correct assembly, a `.using' must have been previously
specified in the same section.
`.using EXPR,REGNO'
Use REGNO as the base register for all subsequent RX, RS, and SS
form instructions. The EXPR will be evaluated to obtain the base
address; usually, EXPR will merely be `*'.
This assembler allows two `.using' directives to be simultaneously
outstanding, one in the `.text' section, and one in another section
(typically, the `.data' section). This feature allows dynamically
loaded objects to be implemented in a relatively straightforward
way. A `.using' directive must always be specified in the `.text'
section; this will specify the base register that will be used for
branches in the `.text' section. A second `.using' may be
specified in another section; this will specify the base register
that is used for non-label address literals. When a second
`.using' is specified, then the subsequent `.ltorg' must be put in
the same section; otherwise an error will result.
Thus, for example, the following code uses `r3' to address branch
targets and `r4' to address the literal pool, which has been
written to the `.data' section. The is, the constants
`=A(some_routine)', `=H'42'' and `=E'3.1416'' will all appear in
the `.data' section.
.data
.using LITPOOL,r4
.text
BASR r3,0
.using *,r3
B START
.long LITPOOL
START:
L r4,4(,r3)
L r15,=A(some_routine)
LTR r15,r15
BNE LABEL
AH r0,=H'42'
LABEL:
ME r6,=E'3.1416'
.data
LITPOOL:
.ltorg
Note that this dual-`.using' directive semantics extends and is
not compatible with HLASM semantics. Note that this assembler
directive does not support the full range of HLASM semantics.

File: as.info, Node: ESA/390 Opcodes, Prev: ESA/390 Directives, Up: ESA/390-Dependent
Opcodes
-------
For detailed information on the ESA/390 machine instruction set, see
`ESA/390 Principles of Operation' (IBM Publication Number DZ9AR004).

File: as.info, Node: i386-Dependent, Next: i960-Dependent, Prev: ESA/390-Dependent, Up: Machine Dependencies
80386 Dependent Features
========================
* Menu:
* i386-Options:: Options
* i386-Syntax:: AT&T Syntax versus Intel Syntax
* i386-Mnemonics:: Instruction Naming
* i386-Regs:: Register Naming
* i386-Prefixes:: Instruction Prefixes
* i386-Memory:: Memory References
* i386-jumps:: Handling of Jump Instructions
* i386-Float:: Floating Point
* i386-SIMD:: Intel's MMX and AMD's 3DNow! SIMD Operations
* i386-16bit:: Writing 16-bit Code
* i386-Bugs:: AT&T Syntax bugs
* i386-Notes:: Notes

File: as.info, Node: i386-Options, Next: i386-Syntax, Up: i386-Dependent
Options
-------
The 80386 has no machine dependent options.

File: as.info, Node: i386-Syntax, Next: i386-Mnemonics, Prev: i386-Options, Up: i386-Dependent
AT&T Syntax versus Intel Syntax
-------------------------------
In order to maintain compatibility with the output of `gcc', `as'
supports AT&T System V/386 assembler syntax. This is quite different
from Intel syntax. We mention these differences because almost all
80386 documents use Intel syntax. Notable differences between the two
syntaxes are:
* AT&T immediate operands are preceded by `$'; Intel immediate
operands are undelimited (Intel `push 4' is AT&T `pushl $4').
AT&T register operands are preceded by `%'; Intel register operands
are undelimited. AT&T absolute (as opposed to PC relative)
jump/call operands are prefixed by `*'; they are undelimited in
Intel syntax.
* AT&T and Intel syntax use the opposite order for source and
destination operands. Intel `add eax, 4' is `addl $4, %eax'. The
`source, dest' convention is maintained for compatibility with
previous Unix assemblers. Note that instructions with more than
one source operand, such as the `enter' instruction, do _not_ have
reversed order. *Note i386-Bugs::.
* In AT&T syntax the size of memory operands is determined from the
last character of the instruction mnemonic. Mnemonic suffixes of
`b', `w', and `l' specify byte (8-bit), word (16-bit), and long
(32-bit) memory references. Intel syntax accomplishes this by
prefixing memory operands (_not_ the instruction mnemonics) with
`byte ptr', `word ptr', and `dword ptr'. Thus, Intel `mov al,
byte ptr FOO' is `movb FOO, %al' in AT&T syntax.
* Immediate form long jumps and calls are `lcall/ljmp $SECTION,
$OFFSET' in AT&T syntax; the Intel syntax is `call/jmp far
SECTION:OFFSET'. Also, the far return instruction is `lret
$STACK-ADJUST' in AT&T syntax; Intel syntax is `ret far
STACK-ADJUST'.
* The AT&T assembler does not provide support for multiple section
programs. Unix style systems expect all programs to be single
sections.

File: as.info, Node: i386-Mnemonics, Next: i386-Regs, Prev: i386-Syntax, Up: i386-Dependent
Instruction Naming
------------------
Instruction mnemonics are suffixed with one character modifiers which
specify the size of operands. The letters `b', `w', and `l' specify
byte, word, and long operands. If no suffix is specified by an
instruction then `as' tries to fill in the missing suffix based on the
destination register operand (the last one by convention). Thus, `mov
%ax, %bx' is equivalent to `movw %ax, %bx'; also, `mov $1, %bx' is
equivalent to `movw $1, %bx'. Note that this is incompatible with the
AT&T Unix assembler which assumes that a missing mnemonic suffix
implies long operand size. (This incompatibility does not affect
compiler output since compilers always explicitly specify the mnemonic
suffix.)
Almost all instructions have the same names in AT&T and Intel format.
There are a few exceptions. The sign extend and zero extend
instructions need two sizes to specify them. They need a size to
sign/zero extend _from_ and a size to zero extend _to_. This is
accomplished by using two instruction mnemonic suffixes in AT&T syntax.
Base names for sign extend and zero extend are `movs...' and `movz...'
in AT&T syntax (`movsx' and `movzx' in Intel syntax). The instruction
mnemonic suffixes are tacked on to this base name, the _from_ suffix
before the _to_ suffix. Thus, `movsbl %al, %edx' is AT&T syntax for
"move sign extend _from_ %al _to_ %edx." Possible suffixes, thus, are
`bl' (from byte to long), `bw' (from byte to word), and `wl' (from word
to long).
The Intel-syntax conversion instructions
* `cbw' -- sign-extend byte in `%al' to word in `%ax',
* `cwde' -- sign-extend word in `%ax' to long in `%eax',
* `cwd' -- sign-extend word in `%ax' to long in `%dx:%ax',
* `cdq' -- sign-extend dword in `%eax' to quad in `%edx:%eax',
are called `cbtw', `cwtl', `cwtd', and `cltd' in AT&T naming. `as'
accepts either naming for these instructions.
Far call/jump instructions are `lcall' and `ljmp' in AT&T syntax,
but are `call far' and `jump far' in Intel convention.

File: as.info, Node: i386-Regs, Next: i386-Prefixes, Prev: i386-Mnemonics, Up: i386-Dependent
Register Naming
---------------
Register operands are always prefixed with `%'. The 80386 registers
consist of
* the 8 32-bit registers `%eax' (the accumulator), `%ebx', `%ecx',
`%edx', `%edi', `%esi', `%ebp' (the frame pointer), and `%esp'
(the stack pointer).
* the 8 16-bit low-ends of these: `%ax', `%bx', `%cx', `%dx', `%di',
`%si', `%bp', and `%sp'.
* the 8 8-bit registers: `%ah', `%al', `%bh', `%bl', `%ch', `%cl',
`%dh', and `%dl' (These are the high-bytes and low-bytes of `%ax',
`%bx', `%cx', and `%dx')
* the 6 section registers `%cs' (code section), `%ds' (data
section), `%ss' (stack section), `%es', `%fs', and `%gs'.
* the 3 processor control registers `%cr0', `%cr2', and `%cr3'.
* the 6 debug registers `%db0', `%db1', `%db2', `%db3', `%db6', and
`%db7'.
* the 2 test registers `%tr6' and `%tr7'.
* the 8 floating point register stack `%st' or equivalently
`%st(0)', `%st(1)', `%st(2)', `%st(3)', `%st(4)', `%st(5)',
`%st(6)', and `%st(7)'.

File: as.info, Node: i386-Prefixes, Next: i386-Memory, Prev: i386-Regs, Up: i386-Dependent
Instruction Prefixes
--------------------
Instruction prefixes are used to modify the following instruction.
They are used to repeat string instructions, to provide section
overrides, to perform bus lock operations, and to change operand and
address sizes. (Most instructions that normally operate on 32-bit
operands will use 16-bit operands if the instruction has an "operand
size" prefix.) Instruction prefixes are best written on the same line
as the instruction they act upon. For example, the `scas' (scan string)
instruction is repeated with:
repne scas %es:(%edi),%al
You may also place prefixes on the lines immediately preceding the
instruction, but this circumvents checks that `as' does with prefixes,
and will not work with all prefixes.
Here is a list of instruction prefixes:
* Section override prefixes `cs', `ds', `ss', `es', `fs', `gs'.
These are automatically added by specifying using the
SECTION:MEMORY-OPERAND form for memory references.
* Operand/Address size prefixes `data16' and `addr16' change 32-bit
operands/addresses into 16-bit operands/addresses, while `data32'
and `addr32' change 16-bit ones (in a `.code16' section) into
32-bit operands/addresses. These prefixes _must_ appear on the
same line of code as the instruction they modify. For example, in
a 16-bit `.code16' section, you might write:
addr32 jmpl *(%ebx)
* The bus lock prefix `lock' inhibits interrupts during execution of
the instruction it precedes. (This is only valid with certain
instructions; see a 80386 manual for details).
* The wait for coprocessor prefix `wait' waits for the coprocessor to
complete the current instruction. This should never be needed for
the 80386/80387 combination.
* The `rep', `repe', and `repne' prefixes are added to string
instructions to make them repeat `%ecx' times (`%cx' times if the
current address size is 16-bits).

File: as.info, Node: i386-Memory, Next: i386-jumps, Prev: i386-Prefixes, Up: i386-Dependent
Memory References
-----------------
An Intel syntax indirect memory reference of the form
SECTION:[BASE + INDEX*SCALE + DISP]
is translated into the AT&T syntax
SECTION:DISP(BASE, INDEX, SCALE)
where BASE and INDEX are the optional 32-bit base and index registers,
DISP is the optional displacement, and SCALE, taking the values 1, 2,
4, and 8, multiplies INDEX to calculate the address of the operand. If
no SCALE is specified, SCALE is taken to be 1. SECTION specifies the
optional section register for the memory operand, and may override the
default section register (see a 80386 manual for section register
defaults). Note that section overrides in AT&T syntax _must_ be
preceded by a `%'. If you specify a section override which coincides
with the default section register, `as' does _not_ output any section
register override prefixes to assemble the given instruction. Thus,
section overrides can be specified to emphasize which section register
is used for a given memory operand.
Here are some examples of Intel and AT&T style memory references:
AT&T: `-4(%ebp)', Intel: `[ebp - 4]'
BASE is `%ebp'; DISP is `-4'. SECTION is missing, and the default
section is used (`%ss' for addressing with `%ebp' as the base
register). INDEX, SCALE are both missing.
AT&T: `foo(,%eax,4)', Intel: `[foo + eax*4]'
INDEX is `%eax' (scaled by a SCALE 4); DISP is `foo'. All other
fields are missing. The section register here defaults to `%ds'.
AT&T: `foo(,1)'; Intel `[foo]'
This uses the value pointed to by `foo' as a memory operand. Note
that BASE and INDEX are both missing, but there is only _one_ `,'.
This is a syntactic exception.
AT&T: `%gs:foo'; Intel `gs:foo'
This selects the contents of the variable `foo' with section
register SECTION being `%gs'.
Absolute (as opposed to PC relative) call and jump operands must be
prefixed with `*'. If no `*' is specified, `as' always chooses PC
relative addressing for jump/call labels.
Any instruction that has a memory operand, but no register operand,
_must_ specify its size (byte, word, or long) with an instruction
mnemonic suffix (`b', `w', or `l', respectively).

File: as.info, Node: i386-jumps, Next: i386-Float, Prev: i386-Memory, Up: i386-Dependent
Handling of Jump Instructions
-----------------------------
Jump instructions are always optimized to use the smallest possible
displacements. This is accomplished by using byte (8-bit) displacement
jumps whenever the target is sufficiently close. If a byte displacement
is insufficient a long (32-bit) displacement is used. We do not support
word (16-bit) displacement jumps in 32-bit mode (i.e. prefixing the jump
instruction with the `data16' instruction prefix), since the 80386
insists upon masking `%eip' to 16 bits after the word displacement is
added.
Note that the `jcxz', `jecxz', `loop', `loopz', `loope', `loopnz'
and `loopne' instructions only come in byte displacements, so that if
you use these instructions (`gcc' does not use them) you may get an
error message (and incorrect code). The AT&T 80386 assembler tries to
get around this problem by expanding `jcxz foo' to
jcxz cx_zero
jmp cx_nonzero
cx_zero: jmp foo
cx_nonzero:

File: as.info, Node: i386-Float, Next: i386-SIMD, Prev: i386-jumps, Up: i386-Dependent
Floating Point
--------------
All 80387 floating point types except packed BCD are supported.
(BCD support may be added without much difficulty). These data types
are 16-, 32-, and 64- bit integers, and single (32-bit), double
(64-bit), and extended (80-bit) precision floating point. Each
supported type has an instruction mnemonic suffix and a constructor
associated with it. Instruction mnemonic suffixes specify the operand's
data type. Constructors build these data types into memory.
* Floating point constructors are `.float' or `.single', `.double',
and `.tfloat' for 32-, 64-, and 80-bit formats. These correspond
to instruction mnemonic suffixes `s', `l', and `t'. `t' stands for
80-bit (ten byte) real. The 80387 only supports this format via
the `fldt' (load 80-bit real to stack top) and `fstpt' (store
80-bit real and pop stack) instructions.
* Integer constructors are `.word', `.long' or `.int', and `.quad'
for the 16-, 32-, and 64-bit integer formats. The corresponding
instruction mnemonic suffixes are `s' (single), `l' (long), and
`q' (quad). As with the 80-bit real format, the 64-bit `q' format
is only present in the `fildq' (load quad integer to stack top)
and `fistpq' (store quad integer and pop stack) instructions.
Register to register operations should not use instruction mnemonic
suffixes. `fstl %st, %st(1)' will give a warning, and be assembled as
if you wrote `fst %st, %st(1)', since all register to register
operations use 80-bit floating point operands. (Contrast this with
`fstl %st, mem', which converts `%st' from 80-bit to 64-bit floating
point format, then stores the result in the 4 byte location `mem')

File: as.info, Node: i386-SIMD, Next: i386-16bit, Prev: i386-Float, Up: i386-Dependent
Intel's MMX and AMD's 3DNow! SIMD Operations
--------------------------------------------
`as' supports Intel's MMX instruction set (SIMD instructions for
integer data), available on Intel's Pentium MMX processors and Pentium
II processors, AMD's K6 and K6-2 processors, Cyrix' M2 processor, and
probably others. It also supports AMD's 3DNow! instruction set (SIMD
instructions for 32-bit floating point data) available on AMD's K6-2
processor and possibly others in the future.
Currently, `as' does not support Intel's floating point SIMD, Katmai
(KNI).
The eight 64-bit MMX operands, also used by 3DNow!, are called
`%mm0', `%mm1', ... `%mm7'. They contain eight 8-bit integers, four
16-bit integers, two 32-bit integers, one 64-bit integer, or two 32-bit
floating point values. The MMX registers cannot be used at the same
time as the floating point stack.
See Intel and AMD documentation, keeping in mind that the operand
order in instructions is reversed from the Intel syntax.

File: as.info, Node: i386-16bit, Next: i386-Bugs, Prev: i386-SIMD, Up: i386-Dependent
Writing 16-bit Code
-------------------
While `as' normally writes only "pure" 32-bit i386 code, it also
supports writing code to run in real mode or in 16-bit protected mode
code segments. To do this, put a `.code16' or `.code16gcc' directive
before the assembly language instructions to be run in 16-bit mode.
You can switch `as' back to writing normal 32-bit code with the
`.code32' directive.
`.code16gcc' provides experimental support for generating 16-bit
code from gcc, and differs from `.code16' in that `call', `ret',
`enter', `leave', `push', `pop', `pusha', `popa', `pushf', and `popf'
instructions default to 32-bit size. This is so that the stack pointer
is manipulated in the same way over function calls, allowing access to
function parameters at the same stack offsets as in 32-bit mode.
`.code16gcc' also automatically adds address size prefixes where
necessary to use the 32-bit addressing modes that gcc generates.
The code which `as' generates in 16-bit mode will not necessarily
run on a 16-bit pre-80386 processor. To write code that runs on such a
processor, you must refrain from using _any_ 32-bit constructs which
require `as' to output address or operand size prefixes.
Note that writing 16-bit code instructions by explicitly specifying a
prefix or an instruction mnemonic suffix within a 32-bit code section
generates different machine instructions than those generated for a
16-bit code segment. In a 32-bit code section, the following code
generates the machine opcode bytes `66 6a 04', which pushes the value
`4' onto the stack, decrementing `%esp' by 2.
pushw $4
The same code in a 16-bit code section would generate the machine
opcode bytes `6a 04' (ie. without the operand size prefix), which is
correct since the processor default operand size is assumed to be 16
bits in a 16-bit code section.

File: as.info, Node: i386-Bugs, Next: i386-Notes, Prev: i386-16bit, Up: i386-Dependent
AT&T Syntax bugs
----------------
The UnixWare assembler, and probably other AT&T derived ix86 Unix
assemblers, generate floating point instructions with reversed source
and destination registers in certain cases. Unfortunately, gcc and
possibly many other programs use this reversed syntax, so we're stuck
with it.
For example
fsub %st,%st(3)
results in `%st(3)' being updated to `%st - %st(3)' rather than the
expected `%st(3) - %st'. This happens with all the non-commutative
arithmetic floating point operations with two register operands where
the source register is `%st' and the destination register is `%st(i)'.

File: as.info, Node: i386-Notes, Prev: i386-Bugs, Up: i386-Dependent
Notes
-----
There is some trickery concerning the `mul' and `imul' instructions
that deserves mention. The 16-, 32-, and 64-bit expanding multiplies
(base opcode `0xf6'; extension 4 for `mul' and 5 for `imul') can be
output only in the one operand form. Thus, `imul %ebx, %eax' does
_not_ select the expanding multiply; the expanding multiply would
clobber the `%edx' register, and this would confuse `gcc' output. Use
`imul %ebx' to get the 64-bit product in `%edx:%eax'.
We have added a two operand form of `imul' when the first operand is
an immediate mode expression and the second operand is a register.
This is just a shorthand, so that, multiplying `%eax' by 69, for
example, can be done with `imul $69, %eax' rather than `imul $69, %eax,
%eax'.

File: as.info, Node: i960-Dependent, Next: M68K-Dependent, Prev: i386-Dependent, Up: Machine Dependencies
Intel 80960 Dependent Features
==============================
* Menu:
* Options-i960:: i960 Command-line Options
* Floating Point-i960:: Floating Point
* Directives-i960:: i960 Machine Directives
* Opcodes for i960:: i960 Opcodes

File: as.info, Node: Options-i960, Next: Floating Point-i960, Up: i960-Dependent
i960 Command-line Options
-------------------------
`-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC'
Select the 80960 architecture. Instructions or features not
supported by the selected architecture cause fatal errors.
`-ACA' is equivalent to `-ACA_A'; `-AKC' is equivalent to `-AMC'.
Synonyms are provided for compatibility with other tools.
If you do not specify any of these options, `as' generates code
for any instruction or feature that is supported by _some_ version
of the 960 (even if this means mixing architectures!). In
principle, `as' attempts to deduce the minimal sufficient
processor type if none is specified; depending on the object code
format, the processor type may be recorded in the object file. If
it is critical that the `as' output match a specific architecture,
specify that architecture explicitly.
`-b'
Add code to collect information about conditional branches taken,
for later optimization using branch prediction bits. (The
conditional branch instructions have branch prediction bits in the
CA, CB, and CC architectures.) If BR represents a conditional
branch instruction, the following represents the code generated by
the assembler when `-b' is specified:
call INCREMENT ROUTINE
.word 0 # pre-counter
Label: BR
call INCREMENT ROUTINE
.word 0 # post-counter
The counter following a branch records the number of times that
branch was _not_ taken; the differenc between the two counters is
the number of times the branch _was_ taken.
A table of every such `Label' is also generated, so that the
external postprocessor `gbr960' (supplied by Intel) can locate all
the counters. This table is always labelled `__BRANCH_TABLE__';
this is a local symbol to permit collecting statistics for many
separate object files. The table is word aligned, and begins with
a two-word header. The first word, initialized to 0, is used in
maintaining linked lists of branch tables. The second word is a
count of the number of entries in the table, which follow
immediately: each is a word, pointing to one of the labels
illustrated above.
+------------+------------+------------+ ... +------------+
| | | | | |
| *NEXT | COUNT: N | *BRLAB 1 | | *BRLAB N |
| | | | | |
+------------+------------+------------+ ... +------------+
__BRANCH_TABLE__ layout
The first word of the header is used to locate multiple branch
tables, since each object file may contain one. Normally the links
are maintained with a call to an initialization routine, placed at
the beginning of each function in the file. The GNU C compiler
generates these calls automatically when you give it a `-b' option.
For further details, see the documentation of `gbr960'.
`-no-relax'
Normally, Compare-and-Branch instructions with targets that require
displacements greater than 13 bits (or that have external targets)
are replaced with the corresponding compare (or `chkbit') and
branch instructions. You can use the `-no-relax' option to
specify that `as' should generate errors instead, if the target
displacement is larger than 13 bits.
This option does not affect the Compare-and-Jump instructions; the
code emitted for them is _always_ adjusted when necessary
(depending on displacement size), regardless of whether you use
`-no-relax'.

File: as.info, Node: Floating Point-i960, Next: Directives-i960, Prev: Options-i960, Up: i960-Dependent
Floating Point
--------------
`as' generates IEEE floating-point numbers for the directives
`.float', `.double', `.extended', and `.single'.

File: as.info, Node: Directives-i960, Next: Opcodes for i960, Prev: Floating Point-i960, Up: i960-Dependent
i960 Machine Directives
-----------------------
`.bss SYMBOL, LENGTH, ALIGN'
Reserve LENGTH bytes in the bss section for a local SYMBOL,
aligned to the power of two specified by ALIGN. LENGTH and ALIGN
must be positive absolute expressions. This directive differs
from `.lcomm' only in that it permits you to specify an alignment.
*Note `.lcomm': Lcomm.
`.extended FLONUMS'
`.extended' expects zero or more flonums, separated by commas; for
each flonum, `.extended' emits an IEEE extended-format (80-bit)
floating-point number.
`.leafproc CALL-LAB, BAL-LAB'
You can use the `.leafproc' directive in conjunction with the
optimized `callj' instruction to enable faster calls of leaf
procedures. If a procedure is known to call no other procedures,
you may define an entry point that skips procedure prolog code
(and that does not depend on system-supplied saved context), and
declare it as the BAL-LAB using `.leafproc'. If the procedure
also has an entry point that goes through the normal prolog, you
can specify that entry point as CALL-LAB.
A `.leafproc' declaration is meant for use in conjunction with the
optimized call instruction `callj'; the directive records the data
needed later to choose between converting the `callj' into a `bal'
or a `call'.
CALL-LAB is optional; if only one argument is present, or if the
two arguments are identical, the single argument is assumed to be
the `bal' entry point.
`.sysproc NAME, INDEX'
The `.sysproc' directive defines a name for a system procedure.
After you define it using `.sysproc', you can use NAME to refer to
the system procedure identified by INDEX when calling procedures
with the optimized call instruction `callj'.
Both arguments are required; INDEX must be between 0 and 31
(inclusive).

File: as.info, Node: Opcodes for i960, Prev: Directives-i960, Up: i960-Dependent
i960 Opcodes
------------
All Intel 960 machine instructions are supported; *note i960
Command-line Options: Options-i960. for a discussion of selecting the
instruction subset for a particular 960 architecture.
Some opcodes are processed beyond simply emitting a single
corresponding instruction: `callj', and Compare-and-Branch or
Compare-and-Jump instructions with target displacements larger than 13
bits.
* Menu:
* callj-i960:: `callj'
* Compare-and-branch-i960:: Compare-and-Branch

File: as.info, Node: callj-i960, Next: Compare-and-branch-i960, Up: Opcodes for i960
`callj'
.......
You can write `callj' to have the assembler or the linker determine
the most appropriate form of subroutine call: `call', `bal', or
`calls'. If the assembly source contains enough information--a
`.leafproc' or `.sysproc' directive defining the operand--then `as'
translates the `callj'; if not, it simply emits the `callj', leaving it
for the linker to resolve.

File: as.info, Node: Compare-and-branch-i960, Prev: callj-i960, Up: Opcodes for i960
Compare-and-Branch
..................
The 960 architectures provide combined Compare-and-Branch
instructions that permit you to store the branch target in the lower 13
bits of the instruction word itself. However, if you specify a branch
target far enough away that its address won't fit in 13 bits, the
assembler can either issue an error, or convert your Compare-and-Branch
instruction into separate instructions to do the compare and the branch.
Whether `as' gives an error or expands the instruction depends on
two choices you can make: whether you use the `-no-relax' option, and
whether you use a "Compare and Branch" instruction or a "Compare and
Jump" instruction. The "Jump" instructions are _always_ expanded if
necessary; the "Branch" instructions are expanded when necessary
_unless_ you specify `-no-relax'--in which case `as' gives an error
instead.
These are the Compare-and-Branch instructions, their "Jump" variants,
and the instruction pairs they may expand into:
Compare and
Branch Jump Expanded to
------ ------ ------------
bbc chkbit; bno
bbs chkbit; bo
cmpibe cmpije cmpi; be
cmpibg cmpijg cmpi; bg
cmpibge cmpijge cmpi; bge
cmpibl cmpijl cmpi; bl
cmpible cmpijle cmpi; ble
cmpibno cmpijno cmpi; bno
cmpibne cmpijne cmpi; bne
cmpibo cmpijo cmpi; bo
cmpobe cmpoje cmpo; be
cmpobg cmpojg cmpo; bg
cmpobge cmpojge cmpo; bge
cmpobl cmpojl cmpo; bl
cmpoble cmpojle cmpo; ble
cmpobne cmpojne cmpo; bne

File: as.info, Node: M68K-Dependent, Next: MIPS-Dependent, Prev: i960-Dependent, Up: Machine Dependencies
M680x0 Dependent Features
=========================
* Menu:
* M68K-Opts:: M680x0 Options
* M68K-Syntax:: Syntax
* M68K-Moto-Syntax:: Motorola Syntax
* M68K-Float:: Floating Point
* M68K-Directives:: 680x0 Machine Directives
* M68K-opcodes:: Opcodes

File: as.info, Node: M68K-Opts, Next: M68K-Syntax, Up: M68K-Dependent
M680x0 Options
--------------
The Motorola 680x0 version of `as' has a few machine dependent
options.
You can use the `-l' option to shorten the size of references to
undefined symbols. If you do not use the `-l' option, references to
undefined symbols are wide enough for a full `long' (32 bits). (Since
`as' cannot know where these symbols end up, `as' can only allocate
space for the linker to fill in later. Since `as' does not know how
far away these symbols are, it allocates as much space as it can.) If
you use this option, the references are only one word wide (16 bits).
This may be useful if you want the object file to be as small as
possible, and you know that the relevant symbols are always less than
17 bits away.
For some configurations, especially those where the compiler normally
does not prepend an underscore to the names of user variables, the
assembler requires a `%' before any use of a register name. This is
intended to let the assembler distinguish between C variables and
functions named `a0' through `a7', and so on. The `%' is always
accepted, but is not required for certain configurations, notably
`sun3'. The `--register-prefix-optional' option may be used to permit
omitting the `%' even for configurations for which it is normally
required. If this is done, it will generally be impossible to refer to
C variables and functions with the same names as register names.
Normally the character `|' is treated as a comment character, which
means that it can not be used in expressions. The `--bitwise-or'
option turns `|' into a normal character. In this mode, you must
either use C style comments, or start comments with a `#' character at
the beginning of a line.
If you use an addressing mode with a base register without specifying
the size, `as' will normally use the full 32 bit value. For example,
the addressing mode `%a0@(%d0)' is equivalent to `%a0@(%d0:l)'. You
may use the `--base-size-default-16' option to tell `as' to default to
using the 16 bit value. In this case, `%a0@(%d0)' is equivalent to
`%a0@(%d0:w)'. You may use the `--base-size-default-32' option to
restore the default behaviour.
If you use an addressing mode with a displacement, and the value of
the displacement is not known, `as' will normally assume that the value
is 32 bits. For example, if the symbol `disp' has not been defined,
`as' will assemble the addressing mode `%a0@(disp,%d0)' as though
`disp' is a 32 bit value. You may use the `--disp-size-default-16'
option to tell `as' to instead assume that the displacement is 16 bits.
In this case, `as' will assemble `%a0@(disp,%d0)' as though `disp' is
a 16 bit value. You may use the `--disp-size-default-32' option to
restore the default behaviour.
`as' can assemble code for several different members of the Motorola
680x0 family. The default depends upon how `as' was configured when it
was built; normally, the default is to assemble code for the 68020
microprocessor. The following options may be used to change the
default. These options control which instructions and addressing modes
are permitted. The members of the 680x0 family are very similar. For
detailed information about the differences, see the Motorola manuals.
`-m68000'
`-m68ec000'
`-m68hc000'
`-m68hc001'
`-m68008'
`-m68302'
`-m68306'
`-m68307'
`-m68322'
`-m68356'
Assemble for the 68000. `-m68008', `-m68302', and so on are
synonyms for `-m68000', since the chips are the same from the
point of view of the assembler.
`-m68010'
Assemble for the 68010.
`-m68020'
`-m68ec020'
Assemble for the 68020. This is normally the default.
`-m68030'
`-m68ec030'
Assemble for the 68030.
`-m68040'
`-m68ec040'
Assemble for the 68040.
`-m68060'
`-m68ec060'
Assemble for the 68060.
`-mcpu32'
`-m68330'
`-m68331'
`-m68332'
`-m68333'
`-m68334'
`-m68336'
`-m68340'
`-m68341'
`-m68349'
`-m68360'
Assemble for the CPU32 family of chips.
`-m5200'
Assemble for the ColdFire family of chips.
`-m68881'
`-m68882'
Assemble 68881 floating point instructions. This is the default
for the 68020, 68030, and the CPU32. The 68040 and 68060 always
support floating point instructions.
`-mno-68881'
Do not assemble 68881 floating point instructions. This is the
default for 68000 and the 68010. The 68040 and 68060 always
support floating point instructions, even if this option is used.
`-m68851'
Assemble 68851 MMU instructions. This is the default for the
68020, 68030, and 68060. The 68040 accepts a somewhat different
set of MMU instructions; `-m68851' and `-m68040' should not be used
together.
`-mno-68851'
Do not assemble 68851 MMU instructions. This is the default for
the 68000, 68010, and the CPU32. The 68040 accepts a somewhat
different set of MMU instructions.

File: as.info, Node: M68K-Syntax, Next: M68K-Moto-Syntax, Prev: M68K-Opts, Up: M68K-Dependent
Syntax
------
This syntax for the Motorola 680x0 was developed at MIT.
The 680x0 version of `as' uses instructions names and syntax
compatible with the Sun assembler. Intervening periods are ignored;
for example, `movl' is equivalent to `mov.l'.
In the following table APC stands for any of the address registers
(`%a0' through `%a7'), the program counter (`%pc'), the zero-address
relative to the program counter (`%zpc'), a suppressed address register
(`%za0' through `%za7'), or it may be omitted entirely. The use of
SIZE means one of `w' or `l', and it may be omitted, along with the
leading colon, unless a scale is also specified. The use of SCALE
means one of `1', `2', `4', or `8', and it may always be omitted along
with the leading colon.
The following addressing modes are understood:
"Immediate"
`#NUMBER'
"Data Register"
`%d0' through `%d7'
"Address Register"
`%a0' through `%a7'
`%a7' is also known as `%sp', i.e. the Stack Pointer. `%a6' is
also known as `%fp', the Frame Pointer.
"Address Register Indirect"
`%a0@' through `%a7@'
"Address Register Postincrement"
`%a0@+' through `%a7@+'
"Address Register Predecrement"
`%a0@-' through `%a7@-'
"Indirect Plus Offset"
`APC@(NUMBER)'
"Index"
`APC@(NUMBER,REGISTER:SIZE:SCALE)'
The NUMBER may be omitted.
"Postindex"
`APC@(NUMBER)@(ONUMBER,REGISTER:SIZE:SCALE)'
The ONUMBER or the REGISTER, but not both, may be omitted.
"Preindex"
`APC@(NUMBER,REGISTER:SIZE:SCALE)@(ONUMBER)'
The NUMBER may be omitted. Omitting the REGISTER produces the
Postindex addressing mode.
"Absolute"
`SYMBOL', or `DIGITS', optionally followed by `:b', `:w', or `:l'.

File: as.info, Node: M68K-Moto-Syntax, Next: M68K-Float, Prev: M68K-Syntax, Up: M68K-Dependent
Motorola Syntax
---------------
The standard Motorola syntax for this chip differs from the syntax
already discussed (*note Syntax: M68K-Syntax.). `as' can accept
Motorola syntax for operands, even if MIT syntax is used for other
operands in the same instruction. The two kinds of syntax are fully
compatible.
In the following table APC stands for any of the address registers
(`%a0' through `%a7'), the program counter (`%pc'), the zero-address
relative to the program counter (`%zpc'), or a suppressed address
register (`%za0' through `%za7'). The use of SIZE means one of `w' or
`l', and it may always be omitted along with the leading dot. The use
of SCALE means one of `1', `2', `4', or `8', and it may always be
omitted along with the leading asterisk.
The following additional addressing modes are understood:
"Address Register Indirect"
`(%a0)' through `(%a7)'
`%a7' is also known as `%sp', i.e. the Stack Pointer. `%a6' is
also known as `%fp', the Frame Pointer.
"Address Register Postincrement"
`(%a0)+' through `(%a7)+'
"Address Register Predecrement"
`-(%a0)' through `-(%a7)'
"Indirect Plus Offset"
`NUMBER(%A0)' through `NUMBER(%A7)', or `NUMBER(%PC)'.
The NUMBER may also appear within the parentheses, as in
`(NUMBER,%A0)'. When used with the PC, the NUMBER may be omitted
(with an address register, omitting the NUMBER produces Address
Register Indirect mode).
"Index"
`NUMBER(APC,REGISTER.SIZE*SCALE)'
The NUMBER may be omitted, or it may appear within the
parentheses. The APC may be omitted. The REGISTER and the APC
may appear in either order. If both APC and REGISTER are address
registers, and the SIZE and SCALE are omitted, then the first
register is taken as the base register, and the second as the
index register.
"Postindex"
`([NUMBER,APC],REGISTER.SIZE*SCALE,ONUMBER)'
The ONUMBER, or the REGISTER, or both, may be omitted. Either the
NUMBER or the APC may be omitted, but not both.
"Preindex"
`([NUMBER,APC,REGISTER.SIZE*SCALE],ONUMBER)'
The NUMBER, or the APC, or the REGISTER, or any two of them, may
be omitted. The ONUMBER may be omitted. The REGISTER and the APC
may appear in either order. If both APC and REGISTER are address
registers, and the SIZE and SCALE are omitted, then the first
register is taken as the base register, and the second as the
index register.

File: as.info, Node: M68K-Float, Next: M68K-Directives, Prev: M68K-Moto-Syntax, Up: M68K-Dependent
Floating Point
--------------
Packed decimal (P) format floating literals are not supported. Feel
free to add the code!
The floating point formats generated by directives are these.
`.float'
`Single' precision floating point constants.
`.double'
`Double' precision floating point constants.
`.extend'
`.ldouble'
`Extended' precision (`long double') floating point constants.

File: as.info, Node: M68K-Directives, Next: M68K-opcodes, Prev: M68K-Float, Up: M68K-Dependent
680x0 Machine Directives
------------------------
In order to be compatible with the Sun assembler the 680x0 assembler
understands the following directives.
`.data1'
This directive is identical to a `.data 1' directive.
`.data2'
This directive is identical to a `.data 2' directive.
`.even'
This directive is a special case of the `.align' directive; it
aligns the output to an even byte boundary.
`.skip'
This directive is identical to a `.space' directive.

File: as.info, Node: M68K-opcodes, Prev: M68K-Directives, Up: M68K-Dependent
Opcodes
-------
* Menu:
* M68K-Branch:: Branch Improvement
* M68K-Chars:: Special Characters

File: as.info, Node: M68K-Branch, Next: M68K-Chars, Up: M68K-opcodes
Branch Improvement
..................
Certain pseudo opcodes are permitted for branch instructions. They
expand to the shortest branch instruction that reach the target.
Generally these mnemonics are made by substituting `j' for `b' at the
start of a Motorola mnemonic.
The following table summarizes the pseudo-operations. A `*' flags
cases that are more fully described after the table:
Displacement
+-------------------------------------------------
| 68020 68000/10
Pseudo-Op |BYTE WORD LONG LONG non-PC relative
+-------------------------------------------------
jbsr |bsrs bsr bsrl jsr jsr
jra |bras bra bral jmp jmp
* jXX |bXXs bXX bXXl bNXs;jmpl bNXs;jmp
* dbXX |dbXX dbXX dbXX; bra; jmpl
* fjXX |fbXXw fbXXw fbXXl fbNXw;jmp
XX: condition
NX: negative of condition XX
`*'--see full description below
`jbsr'
`jra'
These are the simplest jump pseudo-operations; they always map to
one particular machine instruction, depending on the displacement
to the branch target.
`jXX'
Here, `jXX' stands for an entire family of pseudo-operations,
where XX is a conditional branch or condition-code test. The full
list of pseudo-ops in this family is:
jhi jls jcc jcs jne jeq jvc
jvs jpl jmi jge jlt jgt jle
For the cases of non-PC relative displacements and long
displacements on the 68000 or 68010, `as' issues a longer code
fragment in terms of NX, the opposite condition to XX. For
example, for the non-PC relative case:
jXX foo
gives
bNXs oof
jmp foo
oof:
`dbXX'
The full family of pseudo-operations covered here is
dbhi dbls dbcc dbcs dbne dbeq dbvc
dbvs dbpl dbmi dbge dblt dbgt dble
dbf dbra dbt
Other than for word and byte displacements, when the source reads
`dbXX foo', `as' emits
dbXX oo1
bra oo2
oo1:jmpl foo
oo2:
`fjXX'
This family includes
fjne fjeq fjge fjlt fjgt fjle fjf
fjt fjgl fjgle fjnge fjngl fjngle fjngt
fjnle fjnlt fjoge fjogl fjogt fjole fjolt
fjor fjseq fjsf fjsne fjst fjueq fjuge
fjugt fjule fjult fjun
For branch targets that are not PC relative, `as' emits
fbNX oof
jmp foo
oof:
when it encounters `fjXX foo'.

File: as.info, Node: M68K-Chars, Prev: M68K-Branch, Up: M68K-opcodes
Special Characters
..................
The immediate character is `#' for Sun compatibility. The
line-comment character is `|' (unless the `--bitwise-or' option is
used). If a `#' appears at the beginning of a line, it is treated as a
comment unless it looks like `# line file', in which case it is treated
normally.

File: as.info, Node: MIPS-Dependent, Next: SH-Dependent, Prev: M68K-Dependent, Up: Machine Dependencies
MIPS Dependent Features
=======================
GNU `as' for MIPS architectures supports several different MIPS
processors, and MIPS ISA levels I through IV. For information about
the MIPS instruction set, see `MIPS RISC Architecture', by Kane and
Heindrich (Prentice-Hall). For an overview of MIPS assembly
conventions, see "Appendix D: Assembly Language Programming" in the
same work.
* Menu:
* MIPS Opts:: Assembler options
* MIPS Object:: ECOFF object code
* MIPS Stabs:: Directives for debugging information
* MIPS ISA:: Directives to override the ISA level
* MIPS autoextend:: Directives for extending MIPS 16 bit instructions
* MIPS insn:: Directive to mark data as an instruction
* MIPS option stack:: Directives to save and restore options