diff options
Diffstat (limited to 'gas/doc')
| -rw-r--r-- | gas/doc/c-i386.texi | 48 |
1 files changed, 27 insertions, 21 deletions
diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi index c10d904..ec727db 100644 --- a/gas/doc/c-i386.texi +++ b/gas/doc/c-i386.texi @@ -77,7 +77,7 @@ reversed order. @ref{i386-Bugs}. In AT&T syntax the size of memory operands is determined from the last character of the opcode name. Opcode suffixes of @samp{b}, @samp{w}, and @samp{l} specify byte (8-bit), word (16-bit), and long (32-bit) -memory references. Intel syntax accomplishes this by prefixes memory +memory references. Intel syntax accomplishes this by prefixing memory operands (@emph{not} the opcodes themselves) with @samp{byte ptr}, @samp{word ptr}, and @samp{dword ptr}. Thus, Intel @samp{mov al, byte ptr @var{foo}} is @samp{movb @var{foo}, %al} in AT&T syntax. @@ -215,19 +215,18 @@ to repeat string instructions, to provide section overrides, to perform bus lock operations, and to give operand and address size (16-bit operands are specified in an instruction by prefixing what would normally be 32-bit operands with a ``operand size'' opcode prefix). -Opcode prefixes are usually given as single-line instructions with no -operands, and must directly precede the instruction they act upon. For -example, the @samp{scas} (scan string) instruction is repeated with: -@smallexample - repne - scas -@end smallexample -@noindent -or +Opcode prefixes are best written on the same line as the instruction +they act upon. For example, the @samp{scas} (scan string) instruction is +repeated with: + @smallexample - repne/scas + repne scas %es:(%edi),%al @end smallexample +You may also place prefixes on the lines immediately preceding the +opcode, but this circumvents checks that @code{@value{AS}} does with +prefixes, and will not work with all prefixes. + Here is a list of opcode prefixes: @cindex section override prefixes, i386 @@ -242,7 +241,13 @@ using the @var{section}:@var{memory-operand} form for memory references. Operand/Address size prefixes @samp{data16} and @samp{addr16} change 32-bit operands/addresses into 16-bit operands/addresses, while @samp{data32} and @samp{addr32} change 16-bit ones (in a -@code{.code16} section) into 32-bit operands/addresses. +@code{.code16} section) into 32-bit operands/addresses. These prefixes +@emph{must} appear on the same line of code as the opcode they modify. +For example, in a 16-bit @code{.code16} section, you might write: + +@smallexample + addr32 jmpl *(%ebx) +@end smallexample @cindex bus lock prefixes, i386 @cindex inhibiting interrupts, i386 @@ -289,7 +294,7 @@ to calculate the address of the operand. If no @var{scale} is specified, @var{scale} is taken to be 1. @var{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 @emph{must} have +defaults). Note that section overrides in AT&T syntax @emph{must} be preceded by a @samp{%}. If you specify a section override which coincides with the default section register, @code{@value{AS}} does @emph{not} output any section register override prefixes to assemble the given @@ -376,9 +381,9 @@ types. Constructors build these data types into memory. Floating point constructors are @samp{.float} or @samp{.single}, @samp{.double}, and @samp{.tfloat} for 32-, 64-, and 80-bit formats. These correspond to opcode suffixes @samp{s}, @samp{l}, and @samp{t}. -@samp{t} stands for temporary real, and that the 80387 only supports -this format via the @samp{fldt} (load temporary real to stack top) and -@samp{fstpt} (store temporary real and pop stack) instructions. +@samp{t} stands for 80-bit real. The 80387 only supports this format +via the @samp{fldt} (load 80-bit real to stack top) and @samp{fstpt} +(store 80-bit real and pop stack) instructions. @cindex @code{word} directive, i386 @cindex @code{long} directive, i386 @@ -386,11 +391,12 @@ this format via the @samp{fldt} (load temporary real to stack top) and @cindex @code{quad} directive, i386 @item Integer constructors are @samp{.word}, @samp{.long} or @samp{.int}, and -@samp{.quad} for the 16-, 32-, and 64-bit integer formats. The corresponding -opcode suffixes are @samp{s} (single), @samp{l} (long), and @samp{q} -(quad). As with the temporary real format the 64-bit @samp{q} format is -only present in the @samp{fildq} (load quad integer to stack top) and -@samp{fistpq} (store quad integer and pop stack) instructions. +@samp{.quad} for the 16-, 32-, and 64-bit integer formats. The +corresponding opcode suffixes are @samp{s} (single), @samp{l} (long), +and @samp{q} (quad). As with the 80-bit real format, the 64-bit +@samp{q} format is only present in the @samp{fildq} (load quad integer +to stack top) and @samp{fistpq} (store quad integer and pop stack) +instructions. @end itemize Register to register operations should not use opcode suffixes. |