@cindex i386 support
@cindex i80306 support
+@cindex x86-64 support
+
+The i386 version @code{@value{AS}} supports both the original Intel 386
+architecture in both 16 and 32-bit mode as well as AMD x86-64 architecture
+extending the Intel architecture to 64-bits.
+
@menu
* i386-Options:: Options
* i386-Syntax:: AT&T Syntax versus Intel Syntax
@node i386-Options
@section Options
-@cindex options for i386 (none)
-@cindex i386 options (none)
-The 80386 has no machine dependent options.
-
+@cindex options for i386
+@cindex options for x86-64
+@cindex i386 options
+@cindex x86-64 options
+
+The i386 version of @code{@value{AS}} has a few machine
+dependent options:
+
+@table @code
+@cindex @samp{--32} option, i386
+@cindex @samp{--32} option, x86-64
+@cindex @samp{--64} option, i386
+@cindex @samp{--64} option, x86-64
+@item --32 | --64
+Select the word size, either 32 bits or 64 bits. Selecting 32-bit
+implies Intel i386 architecture, while 64-bit implies AMD x86-64
+architecture.
+
+These options are only available with the ELF object file format, and
+require that the necessary BFD support has been included (on a 32-bit
+platform you have to add --enable-64-bit-bfd to configure enable 64-bit
+usage and use x86-64 as target platform).
+@end table
@node i386-Syntax
@section AT&T Syntax versus Intel Syntax
@cindex att_syntax pseudo op, i386
@cindex i386 syntax compatibility
@cindex syntax compatibility, i386
+@cindex x86-64 intel_syntax pseudo op
+@cindex intel_syntax pseudo op, x86-64
+@cindex x86-64 att_syntax pseudo op
+@cindex att_syntax pseudo op, x86-64
+@cindex x86-64 syntax compatibility
+@cindex syntax compatibility, x86-64
@code{@value{AS}} now supports assembly using Intel assembler syntax.
@code{.intel_syntax} selects Intel mode, and @code{.att_syntax} switches
@cindex jump/call operands, i386
@cindex i386 jump/call operands
@cindex operand delimiters, i386
+
+@cindex immediate operands, x86-64
+@cindex x86-64 immediate operands
+@cindex register operands, x86-64
+@cindex x86-64 register operands
+@cindex jump/call operands, x86-64
+@cindex x86-64 jump/call operands
+@cindex operand delimiters, x86-64
@itemize @bullet
@item
AT&T immediate operands are preceded by @samp{$}; Intel immediate
@cindex i386 source, destination operands
@cindex source, destination operands; i386
+@cindex x86-64 source, destination operands
+@cindex source, destination operands; x86-64
@item
AT&T and Intel syntax use the opposite order for source and destination
operands. Intel @samp{add eax, 4} is @samp{addl $4, %eax}. The
@cindex mnemonic suffixes, i386
@cindex sizes operands, i386
@cindex i386 size suffixes
+@cindex mnemonic suffixes, x86-64
+@cindex sizes operands, x86-64
+@cindex x86-64 size suffixes
@item
In AT&T syntax the size of memory operands is determined from the last
character of the instruction mnemonic. Mnemonic 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 prefixing
-memory operands (@emph{not} the instruction mnemonics) 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.
+@samp{w}, @samp{l} and @samp{q} specify byte (8-bit), word (16-bit), long
+(32-bit) and quadruple word (64-bit) memory references. Intel syntax accomplishes
+this by prefixing memory operands (@emph{not} the instruction mnemonics) with
+@samp{byte ptr}, @samp{word ptr}, @samp{dword ptr} and @samp{qword ptr}. Thus,
+Intel @samp{mov al, byte ptr @var{foo}} is @samp{movb @var{foo}, %al} in AT&T
+syntax.
@cindex return instructions, i386
@cindex i386 jump, call, return
+@cindex return instructions, x86-64
+@cindex x86-64 jump, call, return
@item
Immediate form long jumps and calls are
@samp{lcall/ljmp $@var{section}, $@var{offset}} in AT&T syntax; the
@cindex sections, i386
@cindex i386 sections
+@cindex sections, x86-64
+@cindex x86-64 sections
@item
The AT&T assembler does not provide support for multiple section
programs. Unix style systems expect all programs to be single sections.
@cindex i386 instruction naming
@cindex instruction naming, i386
+@cindex x86-64 instruction naming
+@cindex instruction naming, x86-64
+
Instruction mnemonics are suffixed with one character modifiers which
-specify the size of operands. The letters @samp{b}, @samp{w}, and
-@samp{l} specify byte, word, and long operands. If no suffix is
-specified by an instruction then @code{@value{AS}} tries to fill in the
-missing suffix based on the destination register operand (the last one
-by convention). Thus, @samp{mov %ax, %bx} is equivalent to @samp{movw
-%ax, %bx}; also, @samp{mov $1, %bx} is equivalent to @samp{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.)
+specify the size of operands. The letters @samp{b}, @samp{w}, @samp{l}
+and @samp{q} specify byte, word, long and quadruple word operands. If
+no suffix is specified by an instruction then @code{@value{AS}} tries to
+fill in the missing suffix based on the destination register operand
+(the last one by convention). Thus, @samp{mov %ax, %bx} is equivalent
+to @samp{movw %ax, %bx}; also, @samp{mov $1, %bx} is equivalent to
+@samp{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
@emph{to} suffix. Thus, @samp{movsbl %al, %edx} is AT&T syntax for
``move sign extend @emph{from} %al @emph{to} %edx.'' Possible suffixes,
thus, are @samp{bl} (from byte to long), @samp{bw} (from byte to word),
-and @samp{wl} (from word to long).
+@samp{wl} (from word to long), @samp{bq} (from byte to quadruple word),
+@samp{wq} (from word to quadruple word), and @samp{lq} (from long to
+quadruple word).
@cindex conversion instructions, i386
@cindex i386 conversion instructions
+@cindex conversion instructions, x86-64
+@cindex x86-64 conversion instructions
The Intel-syntax conversion instructions
@itemize @bullet
@item
@samp{cdq} --- sign-extend dword in @samp{%eax} to quad in @samp{%edx:%eax},
+
+@item
+@samp{cdqe} --- sign-extend dword in @samp{%eax} to quad in @samp{%rax}
+(x86-64 only),
+
+@item
+@samp{cdo} --- sign-extend quad in @samp{%rax} to octuple in
+@samp{%rdx:%rax} (x86-64 only),
@end itemize
@noindent
-are called @samp{cbtw}, @samp{cwtl}, @samp{cwtd}, and @samp{cltd} in
-AT&T naming. @code{@value{AS}} accepts either naming for these instructions.
+are called @samp{cbtw}, @samp{cwtl}, @samp{cwtd}, @samp{cltd}, @samp{cltq}, and
+@samp{cqto} in AT&T naming. @code{@value{AS}} accepts either naming for these
+instructions.
@cindex jump instructions, i386
@cindex call instructions, i386
+@cindex jump instructions, x86-64
+@cindex call instructions, x86-64
Far call/jump instructions are @samp{lcall} and @samp{ljmp} in
AT&T syntax, but are @samp{call far} and @samp{jump far} in Intel
convention.
@cindex i386 registers
@cindex registers, i386
+@cindex x86-64 registers
+@cindex registers, x86-64
Register operands are always prefixed with @samp{%}. The 80386 registers
consist of
the 8 floating point register stack @samp{%st} or equivalently
@samp{%st(0)}, @samp{%st(1)}, @samp{%st(2)}, @samp{%st(3)},
@samp{%st(4)}, @samp{%st(5)}, @samp{%st(6)}, and @samp{%st(7)}.
+These registers are overloaded by 8 MMX registers @samp{%mm0},
+@samp{%mm1}, @samp{%mm2}, @samp{%mm3}, @samp{%mm4}, @samp{%mm5},
+@samp{%mm6} and @samp{%mm7}.
+
+@item
+the 8 SSE registers registers @samp{%xmm0}, @samp{%xmm1}, @samp{%xmm2},
+@samp{%xmm3}, @samp{%xmm4}, @samp{%xmm5}, @samp{%xmm6} and @samp{%xmm7}.
+@end itemize
+
+The AMD x86-64 architecture extends the register set by:
+
+@itemize @bullet
+@item
+enhancing the 8 32-bit registers to 64-bit: @samp{%rax} (the
+accumulator), @samp{%rbx}, @samp{%rcx}, @samp{%rdx}, @samp{%rdi},
+@samp{%rsi}, @samp{%rbp} (the frame pointer), @samp{%rsp} (the stack
+pointer)
+
+@item
+the 8 extended registers @samp{%r8}--@samp{%r15}.
+
+@item
+the 8 32-bit low ends of the extended registers: @samp{%r8d}--@samp{%r15d}
+
+@item
+the 8 16-bit low ends of the extended registers: @samp{%r8w}--@samp{%r15w}
+
+@item
+the 8 8-bit low ends of the extended registers: @samp{%r8b}--@samp{%r15b}
+
+@item
+the 4 8-bit registers: @samp{%sil}, @samp{%dil}, @samp{%bpl}, @samp{%spl}.
+
+@item
+the 8 debug registers: @samp{%db8}--@samp{%db15}.
+
+@item
+the 8 SSE registers: @samp{%xmm8}--@samp{%xmm15}.
@end itemize
@node i386-Prefixes
The @samp{rep}, @samp{repe}, and @samp{repne} prefixes are added
to string instructions to make them repeat @samp{%ecx} times (@samp{%cx}
times if the current address size is 16-bits).
+@cindex REX prefixes, i386
+@item
+The @samp{rex} family of prefixes is used by x86-64 to encode
+extensions to i386 instruction set. The @samp{rex} prefix has four
+bits --- an operand size overwrite (@code{64}) used to change operand size
+from 32-bit to 64-bit and X, Y and Z extensions bits used to extend the
+register set.
+
+You may write the @samp{rex} prefixes directly. The @samp{rex64xyz}
+instruction emits @samp{rex} prefix with all the bits set. By omitting
+the @code{64}, @code{x}, @code{y} or @code{z} you may write other
+prefixes as well. Normally, there is no need to write the prefixes
+explicitly, since gas will automatically generate them based on the
+instruction operands.
@end itemize
@node i386-Memory
@cindex i386 memory references
@cindex memory references, i386
+@cindex x86-64 memory references
+@cindex memory references, x86-64
An Intel syntax indirect memory reference of the form
@smallexample
always chooses PC relative addressing for jump/call labels.
Any instruction that has a memory operand, but no register operand,
-@emph{must} specify its size (byte, word, or long) with an instruction
-mnemonic suffix (@samp{b}, @samp{w}, or @samp{l}, respectively).
+@emph{must} specify its size (byte, word, long, or quadruple) with an
+instruction mnemonic suffix (@samp{b}, @samp{w}, @samp{l} or @samp{q},
+respectively).
+
+The x86-64 architecture adds an RIP (instruction pointer relative)
+addressing. This addressing mode is specified by using @samp{rip} as a
+base register. Only constant offsets are valid. For example:
+
+@table @asis
+@item AT&T: @samp{1234(%rip)}, Intel: @samp{[rip + 1234]}
+Points to the address 1234 bytes past the end of the current
+instruction.
+
+@item AT&T: @samp{symbol(%rip)}, Intel: @samp{[rip + symbol]}
+Points to the @code{symbol} in RIP relative way, this is shorter than
+the default absolute addressing.
+@end table
+
+Other addressing modes remain unchanged in x86-64 architecture, except
+registers used are 64-bit instead of 32-bit.
@node i386-jumps
@section Handling of Jump Instructions
@cindex jump optimization, i386
@cindex i386 jump optimization
+@cindex jump optimization, x86-64
+@cindex x86-64 jump optimization
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
@cindex i386 floating point
@cindex floating point, i386
+@cindex x86-64 floating point
+@cindex floating point, x86-64
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),
@cindex @code{single} directive, i386
@cindex @code{double} directive, i386
@cindex @code{tfloat} directive, i386
+@cindex @code{float} directive, x86-64
+@cindex @code{single} directive, x86-64
+@cindex @code{double} directive, x86-64
+@cindex @code{tfloat} directive, x86-64
@itemize @bullet
@item
Floating point constructors are @samp{.float} or @samp{.single},
@cindex @code{long} directive, i386
@cindex @code{int} directive, i386
@cindex @code{quad} directive, i386
+@cindex @code{word} directive, x86-64
+@cindex @code{long} directive, x86-64
+@cindex @code{int} directive, x86-64
+@cindex @code{quad} directive, x86-64
@item
Integer constructors are @samp{.word}, @samp{.long} or @samp{.int}, and
@samp{.quad} for the 16-, 32-, and 64-bit integer formats. The
@cindex MMX, i386
@cindex 3DNow!, i386
@cindex SIMD, i386
+@cindex MMX, x86-64
+@cindex 3DNow!, x86-64
+@cindex SIMD, x86-64
@code{@value{AS}} supports Intel's MMX instruction set (SIMD
instructions for integer data), available on Intel's Pentium MMX
@cindex @code{code16gcc} directive, i386
@cindex @code{code16} directive, i386
@cindex @code{code32} directive, i386
-While @code{@value{AS}} normally writes only ``pure'' 32-bit i386 code,
+@cindex @code{code64} directive, i386
+@cindex @code{code64} directive, x86-64
+While @code{@value{AS}} normally writes only ``pure'' 32-bit i386 code
+or 64-bit x86-64 code depending on the default configuration,
it also supports writing code to run in real mode or in 16-bit protected
mode code segments. To do this, put a @samp{.code16} or
@samp{.code16gcc} directive before the assembly language instructions to
@cindex arch directive, i386
@cindex i386 arch directive
+@cindex arch directive, x86-64
+@cindex x86-64 arch directive
@code{@value{AS}} may be told to assemble for a particular CPU
architecture with the @code{.arch @var{cpu_type}} directive. This
@multitable @columnfractions .20 .20 .20 .20
@item @samp{i8086} @tab @samp{i186} @tab @samp{i286} @tab @samp{i386}
@item @samp{i486} @tab @samp{i586} @tab @samp{i686} @tab @samp{pentium}
-@item @samp{pentiumpro} @tab @samp{k6} @tab @samp{athlon}
+@item @samp{pentiumpro} @tab @samp {pentium4} @tab @samp {k6} @tab @samp {athlon}
+@item @samp{sledgehammer}
@end multitable
Apart from the warning, there is only one other effect on
@cindex i386 @code{mul}, @code{imul} instructions
@cindex @code{mul} instruction, i386
@cindex @code{imul} instruction, i386
+@cindex @code{mul} instruction, x86-64
+@cindex @code{imul} instruction, x86-64
There is some trickery concerning the @samp{mul} and @samp{imul}
-instructions that deserves mention. The 16-, 32-, and 64-bit expanding
+instructions that deserves mention. The 16-, 32-, 64- and 128-bit expanding
multiplies (base opcode @samp{0xf6}; extension 4 for @samp{mul} and 5
for @samp{imul}) can be output only in the one operand form. Thus,
@samp{imul %ebx, %eax} does @emph{not} select the expanding multiply;
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