This chapter documents the Backend for the 80x86 microprocessor family.

@section Legal

    This module is written in 2005-2006,2011,2015-2016 by Frank Wille and
    is covered by the vasm copyright without modifications.


@section Additional options for this module

This module provides the following additional options:

@table @option

    @item -cpudebug=<n>
        Enables debugging output.

    @item -m8086
        Generate code for the 8086 CPU.

    @item -mi186
        Generate code for the 80186 CPU.

    @item -mi286
        Generate code for the 80286 CPU.

    @item -mi386
        Generate code for the 80386 CPU.

    @item -mi486
        Generate code for the 80486 CPU.

    @item -mi586
        Generate code for the Pentium.

    @item -mi686
        Generate code for the PentiumPro.

    @item -mpentium
        Generate code for the Pentium.

    @item -mpentiumpro
        Generate code for the PentiumPro.

    @item -mk6
        Generate code for the AMD K6.

    @item -mathlon
        Generate code for the AMD Athlon.

    @item -msledgehammer
        Generate code for the Sledgehammer CPU.

    @item -m64
        Generate code for 64-bit architectures (x86_64).

@end table

@section General

This backend accepts 80x86 instructions as described in the
Intel Architecture Software Developer's Manual.

The target address type is 32 bits. It is 64 bits when the x86_64
architecture was selected (@option{-m64}).

Instructions do not need any alignment. Data is aligned to its natural
alignment by default.

The backend uses MIT-syntax! This means the left operands are always the
source and the right operand is the destination. Register names have to
be prefixed by a '%'.

The operation size is indicated by a 'b', 'w', 'l', etc. suffix directly
appended to the mnemonic. The assembler can also determine the operation
size from the size of the registers being used.

@section Extensions

Predefined register symbols in this backend:

@itemize @minus
@item 8-bit registers: @code{al cl dl bl ah ch dh bh axl cxl dxl spl bpl sil dil r8b r9b r10b r11b r12b r13b r14b r15b}
@item 16-bit registers: @code{ax cx dx bx sp bp si di r8w r9w r10w r11w r12w r13w r14w r15w}
@item 32-bit registers: @code{eax ecx edx ebx esp ebp esi edi r8d r9d r10d r11d r12d r13d r14d r15d}
@item 64-bit registers: @code{rax rcx rdx rbx rsp ebp rsi rdi r8 r9 r10 r11 r12 r13 r14 r15}
@item segment registers: @code{es cs ss ds fs gs}
@item control registers: @code{cr0 cr1 cr2 cr3 cr4 cr5 cr6 cr7 cr8 cr9 cr10 cr11 cr12 cr13 cr14 cr15}
@item debug registers: @code{dr0 dr1 dr2 dr3 dr4 dr5 dr6 dr7 dr8 dr9 dr10 dr11 dr12 dr13 dr14 dr15}
@item test registers: @code{tr0 tr1 tr2 tr3 tr4 tr5 tr6 tr7}
@item MMX and SIMD registers: @code{mm0 mm1 mm2 mm3 mm4 mm5 mm6 mm7 xmm0 xmm1 xmm2 xmm3 xmm4 xmm5 xmm6 xmm7 xmm8 xmm9 xmm10 xmm11 xmm12 xmm13 xmm14 xmm15}
@item FPU registers: @code{st st(0) st(1) st(2) st(3) st(4) st(5) st(6) st(7)}
@end itemize

This backend extends the selected syntax module by the following
directives:

@table @code
@item .code16
 Sets the assembler to 16-bit addressing mode.

@item .code32
 Sets the assembler to 32-bit addressing mode, which is the default.

@item .code64
 Sets the assembler to 64-bit addressing mode.

@end table


@section Optimizations

This backend performs the following optimizations:

@itemize @minus

@item Immediate operands are optimized to the smallest size which can
 still represent the absolute value.

@item Displacement operands are optimized to the smallest size which
 can still represent the absolute value.

@item Jump instructions are optimized to 8-bit displacements, when possible.

@end itemize

@section Known Problems

    Some known problems of this module at the moment:

@itemize @minus

@item 64-bit operations are incomplete and experimental.

@end itemize

@section Error Messages

This module has the following error messages:

@itemize @minus
@item 2001: instruction not supported on selected architecture
@item 2002: trailing garbage in operand
@item 2003: same type of prefix used twice
@item 2004: immediate operand illegal with absolute jump
@item 2005: base register expected
@item 2006: scale factor without index register
@item 2007: missing ')' in baseindex addressing mode
@item 2008: redundant %s prefix ignored
@item 2009: unknown register specified
@item 2010: using register %%%s instead of %%%s due to '%c' suffix
@item 2011: %%%s not allowed with '%c' suffix
@item 2012: illegal suffix '%c'
@item 2013: instruction has no suffix and no register operands - size is unknown
@item 2015: memory operand expected
@item 2016: you cannot pop %%%s
@item 2017: translating to %s %%%s,%%%s
@item 2018: translating to %s %%%s
@item 2019: absolute scale factor required
@item 2020: illegal scale factor (valid: 1,2,4,8)
@item 2021: data objects with %d bits size are not supported
@item 2022: need at least %d bits for a relocatable symbol
@item 2023: pc-relative jump destination out of range (%lld)
@item 2024: instruction doesn't support these operand sizes
@item 2025: cannot determine immediate operand size without a suffix
@item 2026: displacement doesn't fit into %d bits

@end itemize
