@c HPPA has no machine-dependent assembler options (yet).
@end ifset
@ifset SPARC
- [ -Av6 | -Av7 | -Av8 | -Asparclite | -bump ]
+ [ -Av6 | -Av7 | -Av8 | -Av9 | -Asparclite | -bump ]
@end ifset
@ifset Z8000
@c Z8000 has no machine-dependent assembler options
for the SPARC architecture:
@table @code
-@item -Av6 | -Av7 | -Av8 | -Asparclite
+@item -Av6 | -Av7 | -Av8 | -Av9 | -Asparclite
Explicitly select a variant of the SPARC architecture.
@item -bump
* App-File:: @code{.app-file @var{string}}
* Ascii:: @code{.ascii "@var{string}"}@dots{}
* Asciz:: @code{.asciz "@var{string}"}@dots{}
+* Balign:: @code{.balign @var{abs-expr} , @var{abs-expr}}
* Byte:: @code{.byte @var{expressions}}
* Comm:: @code{.comm @var{symbol} , @var{length} }
* Data:: @code{.data @var{subsection}}
* Nolist:: @code{.nolist}
* Octa:: @code{.octa @var{bignums}}
* Org:: @code{.org @var{new-lc} , @var{fill}}
+* P2align:: @code{.p2align @var{abs-expr} , @var{abs-expr}}
* Psize:: @code{.psize @var{lines}, @var{columns}}
* Quad:: @code{.quad @var{bignums}}
* Sbttl:: @code{.sbttl "@var{subheading}"}
@cindex @code{align} directive
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
-number of low-order zero bits the location counter must have after
-advancement. For example @samp{.align 3} advances the location
-counter until it a multiple of 8. If the location counter is already a
-multiple of 8, no change is needed.
+alignment required, as described below.
+The second expression (also absolute) gives the value to be stored in
+the padding bytes. It (and the comma) may be omitted. If it is
+omitted, the padding bytes are zero.
-@ifset HPPA
-For the HPPA, the first expression (which must be absolute) is the
+The way the required alignment is specified varies from system to system.
+For the a29k, HPPA, m86k, m88k, w65, sparc, and i386 using ELF format,
+the first expression is the
alignment request in bytes. For example @samp{.align 8} advances
the location counter until it is a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
-@end ifset
-The second expression (also absolute) gives the value to be stored in
-the padding bytes. It (and the comma) may be omitted. If it is
-omitted, the padding bytes are zero.
+For other systems, including the i386 using a.out format, it is the
+number of low-order zero bits the location counter must have after
+advancement. For example @samp{.align 3} advances the location
+counter until it a multiple of 8. If the location counter is already a
+multiple of 8, no change is needed.
+
+This inconsistency is due to the different behaviors of the various
+native assemblers for these systems which GAS must emulate.
+GAS also provides @code{.balign} and @code{.p2align} directives,
+described later, which have a consistent behavior across all
+architectures (but are specific to GAS).
@node App-File
@section @code{.app-file @var{string}}
@code{.asciz} is just like @code{.ascii}, but each string is followed by
a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''.
+@node Balign
+@section @code{.balign @var{abs-expr} , @var{abs-expr}}
+
+@cindex padding the location counter given number of bytes
+@cindex @code{balign} directive
+Pad the location counter (in the current subsection) to a particular
+storage boundary. The first expression (which must be absolute) is the
+alignment request in bytes. For example @samp{.balign 8} advances
+the location counter until it is a multiple of 8. If the location counter
+is already a multiple of 8, no change is needed.
+
+The second expression (also absolute) gives the value to be stored in
+the padding bytes. It (and the comma) may be omitted. If it is
+omitted, the padding bytes are zero.
+
@node Byte
@section @code{.byte @var{expressions}}
absolute expression. If the comma and @var{fill} are omitted,
@var{fill} defaults to zero.
+@node P2align
+@section @code{.p2align @var{abs-expr} , @var{abs-expr}}
+
+@cindex padding the location counter given a power of two
+@cindex @code{p2align} directive
+Pad the location counter (in the current subsection) to a particular
+storage boundary. The first expression (which must be absolute) is the
+number of low-order zero bits the location counter must have after
+advancement. For example @samp{.p2align 3} advances the location
+counter until it a multiple of 8. If the location counter is already a
+multiple of 8, no change is needed.
+
+The second expression (also absolute) gives the value to be stored in
+the padding bytes. It (and the comma) may be omitted. If it is
+omitted, the padding bytes are zero.
+
@node Psize
@section @code{.psize @var{lines} , @var{columns}}
@samp{#@var{digits}}
@item Data Register
-@samp{d0} through @samp{d7}
+@samp{%d0} through @samp{%d7}
@item Address Register
-@samp{a0} through @samp{a7}@*
-@samp{a7} is also known as @samp{sp}, i.e. the Stack Pointer. @code{a6}
-is also known as @samp{fp}, the Frame Pointer.
+@samp{%a0} through @samp{%a7}@*
+@samp{%a7} is also known as @samp{%sp}, i.e. the Stack Pointer. @code{%a6}
+is also known as @samp{%fp}, the Frame Pointer.
@item Address Register Indirect
-@samp{a0@@} through @samp{a7@@}
+@samp{%a0@@} through @samp{%a7@@}
@item Address Register Postincrement
-@samp{a0@@+} through @samp{a7@@+}
+@samp{%a0@@+} through @samp{%a7@@+}
@item Address Register Predecrement
-@samp{a0@@-} through @samp{a7@@-}
+@samp{%a0@@-} through @samp{%a7@@-}
@item Indirect Plus Offset
-@samp{@var{apc}@@(@var{digits})}
+@samp{%@var{apc}@@(@var{digits})}
@item Index
-@samp{@var{apc}@@(@var{digits},@var{register}:@var{size}:@var{scale})}
+@samp{%@var{apc}@@(@var{digits},%@var{register}:@var{size}:@var{scale})}
-or @samp{@var{apc}@@(@var{register}:@var{size}:@var{scale})}
+or @samp{%@var{apc}@@(%@var{register}:@var{size}:@var{scale})}
@item Postindex
-@samp{@var{apc}@@(@var{digits})@@(@var{digits},@var{register}:@var{size}:@var{scale})}
+@samp{%@var{apc}@@(@var{digits})@@(@var{digits},%@var{register}:@var{size}:@var{scale})}
-or @samp{@var{apc}@@(@var{digits})@@(@var{register}:@var{size}:@var{scale})}
+or @samp{%@var{apc}@@(@var{digits})@@(%@var{register}:@var{size}:@var{scale})}
@item Preindex
-@samp{@var{apc}@@(@var{digits},@var{register}:@var{size}:@var{scale})@@(@var{digits})}
+@samp{%@var{apc}@@(@var{digits},%@var{register}:@var{size}:@var{scale})@@(@var{digits})}
-or @samp{@var{apc}@@(@var{register}:@var{size}:@var{scale})@@(@var{digits})}
+or @samp{%@var{apc}@@(%@var{register}:@var{size}:@var{scale})@@(@var{digits})}
@item Memory Indirect
-@samp{@var{apc}@@(@var{digits})@@(@var{digits})}
+@samp{%@var{apc}@@(@var{digits})@@(@var{digits})}
@item Absolute
@samp{@var{symbol}}, or @samp{@var{digits}}
@end ignore
@end table
-For some configurations, especially those where the compiler normally
-does not prepend an underscore to the names of user variables, the
-assembler requires a @samp{%} before any use of a register name. This
-is intended to let the assembler distinguish between user variables and
-registers named @samp{a0} through @samp{a7}, and so on. The @samp{%} is
-always accepted, but is only required for some configurations, notably
-@samp{m68k-coff}.
+For some configurations, especially those where the compiler normally does not
+prepend an underscore to the names of user variables, the assembler requires a
+@samp{%} before any use of a register name. This is intended to let the
+assembler distinguish between C variables and registers named @samp{a0} through
+@samp{a7}, and so on. The @samp{%} is always accepted, but is not required for
+certain configurations, notably @samp{sun3}.
@node M68K-Moto-Syntax
@section Motorola Syntax
@cindex Motorola syntax for the 680x0
@cindex alternate syntax for the 680x0
-The standard Motorola syntax for this chip differs from the syntax
-already discussed (@pxref{M68K-Syntax,,Syntax}). @code{@value{AS}} can
-accept some forms of Motorola syntax for operands, even if @sc{mit} syntax is
-used for other operands in the same instruction. The
-two kinds of syntax are fully compatible; our support for Motorola syntax is
-simply incomplete at present.
-@ignore
-@c FIXME! I can't figure out what this means. Surely the "always" is in some
-@c restricted context, for instance. It's not necessary for the preceding text
-@c to explain this, so just ignore it for now; re-enable someday when someone
-@c has time to explain it better.
-, because the Motorola syntax never uses
-the @samp{@@} character and the @sc{mit} syntax always does, except in
-cases where the syntaxes are identical.
-@end ignore
+The standard Motorola syntax for this chip differs from the syntax already
+discussed (@pxref{M68K-Syntax,,Syntax}). @code{@value{AS}} can accept some
+forms of Motorola syntax for operands, even if @sc{mit} syntax is used for
+other operands in the same instruction. The two kinds of syntax are fully
+compatible; our support for Motorola syntax is simply incomplete at present.
@cindex M680x0 syntax
@cindex syntax, M680x0
In particular, you may write or generate M68K assembler with the
following conventions:
-(In the following table @dfn{apc} stands for any of the address
-registers (@samp{a0} through @samp{a7}), nothing, (@samp{}), the
-Program Counter (@samp{pc}), or the zero-address relative to the
-program counter (@samp{zpc}).)
+(In the following table @dfn{%apc} stands for any of the address registers
+(@samp{%a0} through @samp{%a7}), nothing (@samp{}), the Program Counter
+(@samp{%pc}), or the zero-address relative to the program counter
+(@samp{%zpc}).)
@cindex M680x0 addressing modes
@cindex addressing modes, M680x0
The following additional addressing modes are understood:
@table @dfn
@item Address Register Indirect
-@samp{a0} through @samp{a7}@*
-@samp{a7} is also known as @samp{sp}, i.e. the Stack Pointer. @code{a6}
-is also known as @samp{fp}, the Frame Pointer.
+@samp{%a0} through @samp{%a7}@*
+@samp{%a7} is also known as @samp{%sp}, i.e. the Stack Pointer. @code{%a6}
+is also known as @samp{%fp}, the Frame Pointer.
@item Address Register Postincrement
-@samp{(a0)+} through @samp{(a7)+}
+@samp{(%a0)+} through @samp{(%a7)+}
@item Address Register Predecrement
-@samp{-(a0)} through @samp{-(a7)}
+@samp{-(%a0)} through @samp{-(%a7)}
@item Indirect Plus Offset
-@samp{@var{digits}(@var{apc})}
+@samp{@var{digits}(%@var{apc})}
@item Index
-@samp{@var{digits}(@var{apc},(@var{register}.@var{size}*@var{scale}))}@*
-or @samp{(@var{apc},@var{register}.@var{size}*@var{scale})}@*
+@samp{@var{digits}(%@var{apc},(%@var{register}.@var{size}*@var{scale}))}@*
+or @samp{(%@var{apc},%@var{register}.@var{size}*@var{scale})}@*
In either case, @var{size} and @var{scale} are optional
(@var{scale} defaults to @samp{1}, @var{size} defaults to @samp{l}).
@var{scale} can be @samp{1}, @samp{2}, @samp{4}, or @samp{8}.
only exist in the higher levels.
@table @code
-@item -Av6 | -Av7 | -Av8 | -Asparclite
+@item -Av6 | -Av7 | -Av8 | -Av9 | -Asparclite
@kindex -Av6
@kindex Av7
@kindex -Av8
+@kindex -Av9
@kindex -Asparclite
Use one of the @samp{-A} options to select one of the SPARC
architectures explicitly. If you select an architecture explicitly,
machine directives:
@table @code
+@item .align
+@cindex @code{align} directive, SPARC
+This must be followed by the desired alignment in bytes.
+
@item .common
@cindex @code{common} directive, SPARC
This must be followed by a symbol name, a positive number, and
@item .word
@cindex @code{word} directive, SPARC
-On the Sparc, the .word directive produces 32 bit values,
+On the Sparc, the @code{.word} directive produces 32 bit values,
instead of the 16 bit values it produces on many other machines.
+
+@item .xword
+@cindex @code{xword} directive, SPARC
+On the Sparc V9 processor, the @code{.xword} directive produces
+64 bit values.
@end table
@end ifset
* i386-Memory:: Memory References
* i386-jumps:: Handling of Jump Instructions
* i386-Float:: Floating Point
+* i386-16bit:: Writing 16-bit Code
* i386-Notes:: Notes
@end menu
instructions are made equivalent to @samp{f@dots{}} instructions. If
@samp{fwait} is desired it must be explicitly coded.
+@node i386-16bit
+@section Writing 16-bit Code
+
+@cindex i386 16-bit code
+@cindex 16-bit code, i386
+@cindex real-mode code, i386
+@cindex @code{code16} directive, i386
+@cindex @code{code32} directive, i386
+While GAS normally writes only ``pure'' 32-bit i386 code, it has limited
+support for writing code to run in real mode or in 16-bit protected mode
+code segments. To do this, insert a @samp{.code16} directive before the
+assembly language instructions to be run in 16-bit mode. You can switch
+GAS back to writing normal 32-bit code with the @samp{.code32} directive.
+
+GAS understands exactly the same assembly language syntax in 16-bit mode as
+in 32-bit mode. The function of any given instruction is exactly the same
+regardless of mode, as long as the resulting object code is executed in the
+mode for which GAS wrote it. So, for example, the @samp{ret} mnemonic
+produces a 32-bit return instruction regardless of whether it is to be run
+in 16-bit or 32-bit mode. (If GAS is in 16-bit mode, it will add an
+operand size prefix to the instruction to force it to be a 32-bit return.)
+
+This means, for one thing, that you can use GNU CC to write code to be run
+in real mode or 16-bit protected mode. Just insert the statement
+@samp{asm(".code16");} at the beginning of your C source file, and while
+GNU CC will still be generating 32-bit code, GAS will automatically add all
+the necessary size prefixes to make that code run in 16-bit mode. Of
+course, since GNU CC only writes small-model code (it doesn't know how to
+attach segment selectors to pointers like native x86 compilers do), any
+16-bit code you write with GNU CC will essentially be limited to a 64K
+address space. Also, there will be a code size and performance penalty
+due to all the extra address and operand size prefixes GAS has to add to
+the instructions.
+
+Note that placing GAS in 16-bit mode does not mean that the resulting
+code will necessarily run on a 16-bit pre-80386 processor. To write code
+that runs on such a processor, you would have to refrain from using
+@emph{any} 32-bit constructs which require GAS to output address or
+operand size prefixes. At the moment this would be rather difficult,
+because GAS currently supports @emph{only} 32-bit addressing modes: when
+writing 16-bit code, it @emph{always} outputs address size prefixes for any
+instruction that uses a non-register addressing mode. So you can write
+code that runs on 16-bit processors, but only if that code never references
+memory.
+
@node i386-Notes
@section Notes
projects / binutils-gdb.git / commitdiff