#!/usr/bin/env perl
# Ascetic x86_64 AT&T to MASM/NASM assembler translator by <appro>.
#
# Why AT&T to MASM and not vice versa? Several reasons. Because AT&T
# format is way easier to parse. Because it's simpler to "gear" from
# Unix ABI to Windows one [see cross-reference "card" at the end of
# file]. Because Linux targets were available first...
#
# In addition the script also "distills" code suitable for GNU
# assembler, so that it can be compiled with more rigid assemblers,
# such as Solaris /usr/ccs/bin/as.
#
# This translator is not designed to convert *arbitrary* assembler
# code from AT&T format to MASM one. It's designed to convert just
# enough to provide for dual-ABI OpenSSL modules development...
# There *are* limitations and you might have to modify your assembler
# code or this script to achieve the desired result...
#
# Currently recognized limitations:
#
# - can't use multiple ops per line;
#
# Dual-ABI styling rules.
#
# 1. Adhere to Unix register and stack layout [see cross-reference
# ABI "card" at the end for explanation].
# 2. Forget about "red zone," stick to more traditional blended
# stack frame allocation. If volatile storage is actually required
# that is. If not, just leave the stack as is.
# 3. Functions tagged with ".type name,@function" get crafted with
# unified Win64 prologue and epilogue automatically. If you want
# to take care of ABI differences yourself, tag functions as
# ".type name,@abi-omnipotent" instead.
# 4. To optimize the Win64 prologue you can specify number of input
# arguments as ".type name,@function,N." Keep in mind that if N is
# larger than 6, then you *have to* write "abi-omnipotent" code,
# because >6 cases can't be addressed with unified prologue.
# 5. Name local labels as .L*, do *not* use dynamic labels such as 1:
# (sorry about latter).
# 6. Don't use [or hand-code with .byte] "rep ret." "ret" mnemonic is
# required to identify the spots, where to inject Win64 epilogue!
# But on the pros, it's then prefixed with rep automatically:-)
# 7. Stick to explicit ip-relative addressing. If you have to use
# GOTPCREL addressing, stick to mov symbol@GOTPCREL(%rip),%r??.
# Both are recognized and translated to proper Win64 addressing
# modes. To support legacy code a synthetic directive, .picmeup,
# is implemented. It puts address of the *next* instruction into
# target register, e.g.:
#
# .picmeup %rax
# lea .Label-.(%rax),%rax
#
# 8. In order to provide for structured exception handling unified
# Win64 prologue copies %rsp value to %rax. For further details
# see SEH paragraph at the end.
# 9. .init segment is allowed to contain calls to functions only.
# a. If function accepts more than 4 arguments *and* >4th argument
# is declared as non 64-bit value, do clear its upper part.
my $flavour = shift;
my $output = shift;
if ($flavour =~ /\./) { $output = $flavour; undef $flavour; }
{ my ($stddev,$stdino,@junk)=stat(STDOUT);
my ($outdev,$outino,@junk)=stat($output);
open STDOUT,">$output" || die "can't open $output: $!"
if ($stddev!=$outdev || $stdino!=$outino);
}
my $gas=1; $gas=0 if ($output =~ /\.asm$/);
my $elf=1; $elf=0 if (!$gas);
my $win64=0;
my $prefix="";
my $decor=".L";
my $masmref=8 + 50727*2**-32; # 8.00.50727 shipped with VS2005
my $masm=0;
my $PTR=" PTR";
my $nasmref=2.03;
my $nasm=0;
if ($flavour eq "mingw64") { $gas=1; $elf=0; $win64=1;
$prefix=`echo __USER_LABEL_PREFIX__ | $ENV{CC} -E -P -`;
chomp($prefix);
}
elsif ($flavour eq "macosx") { $gas=1; $elf=0; $prefix="_"; $decor="L\$"; }
elsif ($flavour eq "masm") { $gas=0; $elf=0; $masm=$masmref; $win64=1; $decor="\$L\$"; }
elsif ($flavour eq "nasm") { $gas=0; $elf=0; $nasm=$nasmref; $win64=1; $decor="\$L\$"; $PTR=""; }
elsif (!$gas)
{ if ($ENV{ASM} =~ m/nasm/ && `nasm -v` =~ m/version ([0-9]+)\.([0-9]+)/i)
{ $nasm = $1 + $2*0.01; $PTR=""; }
elsif (`ml64 2>&1` =~ m/Version ([0-9]+)\.([0-9]+)(\.([0-9]+))?/)
{ $masm = $1 + $2*2**-16 + $4*2**-32; }
die "no assembler found on %PATH" if (!($nasm || $masm));
$win64=1;
$elf=0;
$decor="\$L\$";
}
my $current_segment;
my $current_function;
my %globals;
{ package opcode; # pick up opcodes
sub re {
my $self = shift; # single instance in enough...
local *line = shift;
undef $ret;
if ($line =~ /^([a-z][a-z0-9]*)/i) {
$self->{op} = $1;
$ret = $self;
$line = substr($line,@+[0]); $line =~ s/^\s+//;
undef $self->{sz};
if ($self->{op} =~ /^(movz)b.*/) { # movz is pain...
$self->{op} = $1;
$self->{sz} = "b";
} elsif ($self->{op} =~ /call|jmp/) {
$self->{sz} = "";
} elsif ($self->{op} =~ /^p/ && $' !~ /^(ush|op)/) { # SSEn
$self->{sz} = "";
} elsif ($self->{op} =~ /([a-z]{3,})([qlwb])$/) {
$self->{op} = $1;
$self->{sz} = $2;
}
}
$ret;
}
sub size {
my $self = shift;
my $sz = shift;
$self->{sz} = $sz if (defined($sz) && !defined($self->{sz}));
$self->{sz};
}
sub out {
my $self = shift;
if ($gas) {
if ($self->{op} eq "movz") { # movz is pain...
sprintf "%s%s%s",$self->{op},$self->{sz},shift;
} elsif ($self->{op} =~ /^set/) {
"$self->{op}";
} elsif ($self->{op} eq "ret") {
my $epilogue = "";
if ($win64 && $current_function->{abi} eq "svr4") {
$epilogue = "movq 8(%rsp),%rdi\n\t" .
"movq 16(%rsp),%rsi\n\t";
}
$epilogue . ".byte 0xf3,0xc3";
} elsif ($self->{op} eq "call" && !$elf && $current_segment eq ".init") {
".p2align\t3\n\t.quad";
} else {
"$self->{op}$self->{sz}";
}
} else {
$self->{op} =~ s/^movz/movzx/;
if ($self->{op} eq "ret") {
$self->{op} = "";
if ($win64 && $current_function->{abi} eq "svr4") {
$self->{op} = "mov rdi,QWORD${PTR}[8+rsp]\t;WIN64 epilogue\n\t".
"mov rsi,QWORD${PTR}[16+rsp]\n\t";
}
$self->{op} .= "DB\t0F3h,0C3h\t\t;repret";
} elsif ($self->{op} =~ /^(pop|push)f/) {
$self->{op} .= $self->{sz};
} elsif ($self->{op} eq "call" && $current_segment eq ".CRT\$XCU") {
$self->{op} = "\tDQ";
}
$self->{op};
}
}
sub mnemonic {
my $self=shift;
my $op=shift;
$self->{op}=$op if (defined($op));
$self->{op};
}
}
{ package const; # pick up constants, which start with $
sub re {
my $self = shift; # single instance in enough...
local *line = shift;
undef $ret;
if ($line =~ /^\$([^,]+)/) {
$self->{value} = $1;
$ret = $self;
$line = substr($line,@+[0]); $line =~ s/^\s+//;
}
$ret;
}
sub out {
my $self = shift;
if ($gas) {
# Solaris /usr/ccs/bin/as can't handle multiplications
# in $self->{value}
$self->{value} =~ s/(?<![\w\$\.])(0x?[0-9a-f]+)/oct($1)/egi;
$self->{value} =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg;
sprintf "\$%s",$self->{value};
} else {
$self->{value} =~ s/(0b[0-1]+)/oct($1)/eig;
$self->{value} =~ s/0x([0-9a-f]+)/0$1h/ig if ($masm);
sprintf "%s",$self->{value};
}
}
}
{ package ea; # pick up effective addresses: expr(%reg,%reg,scale)
sub re {
my $self = shift; # single instance in enough...
local *line = shift;
undef $ret;
# optional * ---vvv--- appears in indirect jmp/call
if ($line =~ /^(\*?)([^\(,]*)\(([%\w,]+)\)/) {
$self->{asterisk} = $1;
$self->{label} = $2;
($self->{base},$self->{index},$self->{scale})=split(/,/,$3);
$self->{scale} = 1 if (!defined($self->{scale}));
$ret = $self;
$line = substr($line,@+[0]); $line =~ s/^\s+//;
if ($win64 && $self->{label} =~ s/\@GOTPCREL//) {
die if (opcode->mnemonic() ne "mov");
opcode->mnemonic("lea");
}
$self->{base} =~ s/^%//;
$self->{index} =~ s/^%// if (defined($self->{index}));
}
$ret;
}
sub size {}
sub out {
my $self = shift;
my $sz = shift;
$self->{label} =~ s/([_a-z][_a-z0-9]*)/$globals{$1} or $1/gei;
$self->{label} =~ s/\.L/$decor/g;
# Silently convert all EAs to 64-bit. This is required for
# elder GNU assembler and results in more compact code,
# *but* most importantly AES module depends on this feature!
$self->{index} =~ s/^[er](.?[0-9xpi])[d]?$/r\1/;
$self->{base} =~ s/^[er](.?[0-9xpi])[d]?$/r\1/;
if ($gas) {
# Solaris /usr/ccs/bin/as can't handle multiplications
# in $self->{label}, new gas requires sign extension...
use integer;
$self->{label} =~ s/(?<![\w\$\.])(0x?[0-9a-f]+)/oct($1)/egi;
$self->{label} =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg;
$self->{label} =~ s/([0-9]+)/$1<<32>>32/eg;
$self->{label} =~ s/^___imp_/__imp__/ if ($flavour eq "mingw64");
if (defined($self->{index})) {
sprintf "%s%s(%%%s,%%%s,%d)",$self->{asterisk},
$self->{label},$self->{base},
$self->{index},$self->{scale};
} else {
sprintf "%s%s(%%%s)", $self->{asterisk},$self->{label},$self->{base};
}
} else {
%szmap = ( b=>"BYTE$PTR", w=>"WORD$PTR", l=>"DWORD$PTR", q=>"QWORD$PTR" );
$self->{label} =~ s/\./\$/g;
$self->{label} =~ s/(?<![\w\$\.])0x([0-9a-f]+)/0$1h/ig;
$self->{label} = "($self->{label})" if ($self->{label} =~ /[\*\+\-\/]/);
$sz="q" if ($self->{asterisk});
if (defined($self->{index})) {
sprintf "%s[%s%s*%d+%s]",$szmap{$sz},
$self->{label}?"$self->{label}+":"",
$self->{index},$self->{scale},
$self->{base};
} elsif ($self->{base} eq "rip") {
sprintf "%s[%s]",$szmap{$sz},$self->{label};
} else {
sprintf "%s[%s%s]",$szmap{$sz},
$self->{label}?"$self->{label}+":"",
$self->{base};
}
}
}
}
{ package register; # pick up registers, which start with %.
sub re {
my $class = shift; # muliple instances...
my $self = {};
local *line = shift;
undef $ret;
# optional * ---vvv--- appears in indirect jmp/call
if ($line =~ /^(\*?)%(\w+)/) {
bless $self,$class;
$self->{asterisk} = $1;
$self->{value} = $2;
$ret = $self;
$line = substr($line,@+[0]); $line =~ s/^\s+//;
}
$ret;
}
sub size {
my $self = shift;
undef $ret;
if ($self->{value} =~ /^r[\d]+b$/i) { $ret="b"; }
elsif ($self->{value} =~ /^r[\d]+w$/i) { $ret="w"; }
elsif ($self->{value} =~ /^r[\d]+d$/i) { $ret="l"; }
elsif ($self->{value} =~ /^r[\w]+$/i) { $ret="q"; }
elsif ($self->{value} =~ /^[a-d][hl]$/i){ $ret="b"; }
elsif ($self->{value} =~ /^[\w]{2}l$/i) { $ret="b"; }
elsif ($self->{value} =~ /^[\w]{2}$/i) { $ret="w"; }
elsif ($self->{value} =~ /^e[a-z]{2}$/i){ $ret="l"; }
$ret;
}
sub out {
my $self = shift;
if ($gas) { sprintf "%s%%%s",$self->{asterisk},$self->{value}; }
else { $self->{value}; }
}
}
{ package label; # pick up labels, which end with :
sub re {
my $self = shift; # single instance is enough...
local *line = shift;
undef $ret;
if ($line =~ /(^[\.\w]+)\:/) {
$self->{value} = $1;
$ret = $self;
$line = substr($line,@+[0]); $line =~ s/^\s+//;
$self->{value} =~ s/^\.L/$decor/;
}
$ret;
}
sub out {
my $self = shift;
if ($gas) {
my $func = ($globals{$self->{value}} or $self->{value}) . ":";
if ($win64 &&
$current_function->{name} eq $self->{value} &&
$current_function->{abi} eq "svr4") {
$func .= "\n";
$func .= " movq %rdi,8(%rsp)\n";
$func .= " movq %rsi,16(%rsp)\n";
$func .= " movq %rsp,%rax\n";
$func .= "${decor}SEH_begin_$current_function->{name}:\n";
my $narg = $current_function->{narg};
$narg=6 if (!defined($narg));
$func .= " movq %rcx,%rdi\n" if ($narg>0);
$func .= " movq %rdx,%rsi\n" if ($narg>1);
$func .= " movq %r8,%rdx\n" if ($narg>2);
$func .= " movq %r9,%rcx\n" if ($narg>3);
$func .= " movq 40(%rsp),%r8\n" if ($narg>4);
$func .= " movq 48(%rsp),%r9\n" if ($narg>5);
}
$func;
} elsif ($self->{value} ne "$current_function->{name}") {
$self->{value} .= ":" if ($masm && $ret!~m/^\$/);
$self->{value} . ":";
} elsif ($win64 && $current_function->{abi} eq "svr4") {
my $func = "$current_function->{name}" .
($nasm ? ":" : "\tPROC $current_function->{scope}") .
"\n";
$func .= " mov QWORD${PTR}[8+rsp],rdi\t;WIN64 prologue\n";
$func .= " mov QWORD${PTR}[16+rsp],rsi\n";
$func .= " mov rax,rsp\n";
$func .= "${decor}SEH_begin_$current_function->{name}:";
$func .= ":" if ($masm);
$func .= "\n";
my $narg = $current_function->{narg};
$narg=6 if (!defined($narg));
$func .= " mov rdi,rcx\n" if ($narg>0);
$func .= " mov rsi,rdx\n" if ($narg>1);
$func .= " mov rdx,r8\n" if ($narg>2);
$func .= " mov rcx,r9\n" if ($narg>3);
$func .= " mov r8,QWORD${PTR}[40+rsp]\n" if ($narg>4);
$func .= " mov r9,QWORD${PTR}[48+rsp]\n" if ($narg>5);
$func .= "\n";
} else {
"$current_function->{name}".
($nasm ? ":" : "\tPROC $current_function->{scope}");
}
}
}
{ package expr; # pick up expressioins
sub re {
my $self = shift; # single instance is enough...
local *line = shift;
undef $ret;
if ($line =~ /(^[^,]+)/) {
$self->{value} = $1;
$ret = $self;
$line = substr($line,@+[0]); $line =~ s/^\s+//;
$self->{value} =~ s/\@PLT// if (!$elf);
$self->{value} =~ s/([_a-z][_a-z0-9]*)/$globals{$1} or $1/gei;
$self->{value} =~ s/\.L/$decor/g;
}
$ret;
}
sub out {
my $self = shift;
if ($nasm && opcode->mnemonic()=~m/^j/) {
"NEAR ".$self->{value};
} else {
$self->{value};
}
}
}
{ package directive; # pick up directives, which start with .
sub re {
my $self = shift; # single instance is enough...
local *line = shift;
undef $ret;
my $dir;
my %opcode = # lea 2f-1f(%rip),%dst; 1: nop; 2:
( "%rax"=>0x01058d48, "%rcx"=>0x010d8d48,
"%rdx"=>0x01158d48, "%rbx"=>0x011d8d48,
"%rsp"=>0x01258d48, "%rbp"=>0x012d8d48,
"%rsi"=>0x01358d48, "%rdi"=>0x013d8d48,
"%r8" =>0x01058d4c, "%r9" =>0x010d8d4c,
"%r10"=>0x01158d4c, "%r11"=>0x011d8d4c,
"%r12"=>0x01258d4c, "%r13"=>0x012d8d4c,
"%r14"=>0x01358d4c, "%r15"=>0x013d8d4c );
if ($line =~ /^\s*(\.\w+)/) {
$dir = $1;
$ret = $self;
undef $self->{value};
$line = substr($line,@+[0]); $line =~ s/^\s+//;
SWITCH: for ($dir) {
/\.picmeup/ && do { if ($line =~ /(%r[\w]+)/i) {
$dir="\t.long";
$line=sprintf "0x%x,0x90000000",$opcode{$1};
}
last;
};
/\.global|\.globl|\.extern/
&& do { $globals{$line} = $prefix . $line;
$line = $globals{$line} if ($prefix);
last;
};
/\.type/ && do { ($sym,$type,$narg) = split(',',$line);
if ($type eq "\@function") {
undef $current_function;
$current_function->{name} = $sym;
$current_function->{abi} = "svr4";
$current_function->{narg} = $narg;
$current_function->{scope} = defined($globals{$sym})?"PUBLIC":"PRIVATE";
} elsif ($type eq "\@abi-omnipotent") {
undef $current_function;
$current_function->{name} = $sym;
$current_function->{scope} = defined($globals{$sym})?"PUBLIC":"PRIVATE";
}
$line =~ s/\@abi\-omnipotent/\@function/;
$line =~ s/\@function.*/\@function/;
last;
};
/\.asciz/ && do { if ($line =~ /^"(.*)"$/) {
$dir = ".byte";
$line = join(",",unpack("C*",$1),0);
}
last;
};
/\.rva|\.long|\.quad/
&& do { $line =~ s/([_a-z][_a-z0-9]*)/$globals{$1} or $1/gei;
$line =~ s/\.L/$decor/g;
last;
};
}
if ($gas) {
$self->{value} = $dir . "\t" . $line;
if ($dir =~ /\.extern/) {
$self->{value} = ""; # swallow extern
} elsif (!$elf && $dir =~ /\.type/) {
$self->{value} = "";
$self->{value} = ".def\t" . ($globals{$1} or $1) . ";\t" .
(defined($globals{$1})?".scl 2;":".scl 3;") .
"\t.type 32;\t.endef"
if ($win64 && $line =~ /([^,]+),\@function/);
} elsif (!$elf && $dir =~ /\.size/) {
$self->{value} = "";
if (defined($current_function)) {
$self->{value} .= "${decor}SEH_end_$current_function->{name}:"
if ($win64 && $current_function->{abi} eq "svr4");
undef $current_function;
}
} elsif (!$elf && $dir =~ /\.align/) {
$self->{value} = ".p2align\t" . (log($line)/log(2));
} elsif ($dir eq ".section") {
$current_segment=$line;
if (!$elf && $current_segment eq ".init") {
if ($flavour eq "macosx") { $self->{value} = ".mod_init_func"; }
elsif ($flavour eq "mingw64") { $self->{value} = ".section\t.ctors"; }
}
} elsif ($dir =~ /\.(text|data)/) {
$current_segment=".$1";
}
$line = "";
return $self;
}
# non-gas case or nasm/masm
SWITCH: for ($dir) {
/\.text/ && do { my $v=undef;
if ($nasm) {
$v="section .text code align=64\n";
} else {
$v="$current_segment\tENDS\n" if ($current_segment);
$current_segment = ".text\$";
$v.="$current_segment\tSEGMENT ";
$v.=$masm>=$masmref ? "ALIGN(64)" : "PAGE";
$v.=" 'CODE'";
}
$self->{value} = $v;
last;
};
/\.data/ && do { my $v=undef;
if ($nasm) {
$v="section .data data align=8\n";
} else {
$v="$current_segment\tENDS\n" if ($current_segment);
$current_segment = "_DATA";
$v.="$current_segment\tSEGMENT";
}
$self->{value} = $v;
last;
};
/\.section/ && do { my $v=undef;
$line =~ s/([^,]*).*/$1/;
$line = ".CRT\$XCU" if ($line eq ".init");
if ($nasm) {
$v="section $line";
if ($line=~/\.([px])data/) {
$v.=" rdata align=";
$v.=$1 eq "p"? 4 : 8;
} elsif ($line=~/\.CRT\$/i) {
$v.=" rdata align=8";
}
} else {
$v="$current_segment\tENDS\n" if ($current_segment);
$v.="$line\tSEGMENT";
if ($line=~/\.([px])data/) {
$v.=" READONLY";
$v.=" ALIGN(".($1 eq "p" ? 4 : 8).")" if ($masm>=$masmref);
} elsif ($line=~/\.CRT\$/i) {
$v.=" READONLY DWORD";
}
}
$current_segment = $line;
$self->{value} = $v;
last;
};
/\.extern/ && do { $self->{value} = "EXTERN\t".$line;
$self->{value} .= ":NEAR" if ($masm);
last;
};
/\.globl|.global/
&& do { $self->{value} = $masm?"PUBLIC":"global";
$self->{value} .= "\t".$line;
last;
};
/\.size/ && do { if (defined($current_function)) {
undef $self->{value};
if ($current_function->{abi} eq "svr4") {
$self->{value}="${decor}SEH_end_$current_function->{name}:";
$self->{value}.=":\n" if($masm);
}
$self->{value}.="$current_function->{name}\tENDP" if($masm);
undef $current_function;
}
last;
};
/\.align/ && do { $self->{value} = "ALIGN\t".$line; last; };
/\.(value|long|rva|quad)/
&& do { my $sz = substr($1,0,1);
my @arr = split(/,\s*/,$line);
my $last = pop(@arr);
my $conv = sub { my $var=shift;
$var=~s/^(0b[0-1]+)/oct($1)/eig;
$var=~s/^0x([0-9a-f]+)/0$1h/ig if ($masm);
if ($sz eq "D" && ($current_segment=~/.[px]data/ || $dir eq ".rva"))
{ $var=~s/([_a-z\$\@][_a-z0-9\$\@]*)/$nasm?"$1 wrt ..imagebase":"imagerel $1"/egi; }
$var;
};
$sz =~ tr/bvlrq/BWDDQ/;
$self->{value} = "\tD$sz\t";
for (@arr) { $self->{value} .= &$conv($_).","; }
$self->{value} .= &$conv($last);
last;
};
/\.byte/ && do { my @str=split(/,\s*/,$line);
map(s/(0b[0-1]+)/oct($1)/eig,@str);
map(s/0x([0-9a-f]+)/0$1h/ig,@str) if ($masm);
while ($#str>15) {
$self->{value}.="DB\t"
.join(",",@str[0..15])."\n";
foreach (0..15) { shift @str; }
}
$self->{value}.="DB\t"
.join(",",@str) if (@str);
last;
};
}
$line = "";
}
$ret;
}
sub out {
my $self = shift;
$self->{value};
}
}
if ($nasm) {
print <<___;
default rel
___
} elsif ($masm) {
print <<___;
OPTION DOTNAME
___
}
while($line=<>) {
chomp($line);
$line =~ s|[#!].*$||; # get rid of asm-style comments...
$line =~ s|/\*.*\*/||; # ... and C-style comments...
$line =~ s|^\s+||; # ... and skip white spaces in beginning
undef $label;
undef $opcode;
undef $sz;
undef @args;
if ($label=label->re(\$line)) { print $label->out(); }
if (directive->re(\$line)) {
printf "%s",directive->out();
} elsif ($opcode=opcode->re(\$line)) { ARGUMENT: while (1) {
my $arg;
if ($arg=register->re(\$line)) { opcode->size($arg->size()); }
elsif ($arg=const->re(\$line)) { }
elsif ($arg=ea->re(\$line)) { }
elsif ($arg=expr->re(\$line)) { }
else { last ARGUMENT; }
push @args,$arg;
last ARGUMENT if ($line !~ /^,/);
$line =~ s/^,\s*//;
} # ARGUMENT:
$sz=opcode->size();
if ($#args>=0) {
my $insn;
if ($gas) {
$insn = $opcode->out($#args>=1?$args[$#args]->size():$sz);
} else {
$insn = $opcode->out();
$insn .= $sz if (map($_->out() =~ /x?mm/,@args));
@args = reverse(@args);
undef $sz if ($nasm && $opcode->mnemonic() eq "lea");
}
printf "\t%s\t%s",$insn,join(",",map($_->out($sz),@args));
} else {
printf "\t%s",$opcode->out();
}
}
print $line,"\n";
}
print "\n$current_segment\tENDS\n" if ($current_segment && $masm);
print "END\n" if ($masm);
close STDOUT;
#################################################
# Cross-reference x86_64 ABI "card"
#
# Unix Win64
# %rax * *
# %rbx - -
# %rcx #4 #1
# %rdx #3 #2
# %rsi #2 -
# %rdi #1 -
# %rbp - -
# %rsp - -
# %r8 #5 #3
# %r9 #6 #4
# %r10 * *
# %r11 * *
# %r12 - -
# %r13 - -
# %r14 - -
# %r15 - -
#
# (*) volatile register
# (-) preserved by callee
# (#) Nth argument, volatile
#
# In Unix terms top of stack is argument transfer area for arguments
# which could not be accomodated in registers. Or in other words 7th
# [integer] argument resides at 8(%rsp) upon function entry point.
# 128 bytes above %rsp constitute a "red zone" which is not touched
# by signal handlers and can be used as temporal storage without
# allocating a frame.
#
# In Win64 terms N*8 bytes on top of stack is argument transfer area,
# which belongs to/can be overwritten by callee. N is the number of
# arguments passed to callee, *but* not less than 4! This means that
# upon function entry point 5th argument resides at 40(%rsp), as well
# as that 32 bytes from 8(%rsp) can always be used as temporal
# storage [without allocating a frame]. One can actually argue that
# one can assume a "red zone" above stack pointer under Win64 as well.
# Point is that at apparently no occasion Windows kernel would alter
# the area above user stack pointer in true asynchronous manner...
#
# All the above means that if assembler programmer adheres to Unix
# register and stack layout, but disregards the "red zone" existense,
# it's possible to use following prologue and epilogue to "gear" from
# Unix to Win64 ABI in leaf functions with not more than 6 arguments.
#
# omnipotent_function:
# ifdef WIN64
# movq %rdi,8(%rsp)
# movq %rsi,16(%rsp)
# movq %rcx,%rdi ; if 1st argument is actually present
# movq %rdx,%rsi ; if 2nd argument is actually ...
# movq %r8,%rdx ; if 3rd argument is ...
# movq %r9,%rcx ; if 4th argument ...
# movq 40(%rsp),%r8 ; if 5th ...
# movq 48(%rsp),%r9 ; if 6th ...
# endif
# ...
# ifdef WIN64
# movq 8(%rsp),%rdi
# movq 16(%rsp),%rsi
# endif
# ret
#
#################################################
# Win64 SEH, Structured Exception Handling.
#
# Unlike on Unix systems(*) lack of Win64 stack unwinding information
# has undesired side-effect at run-time: if an exception is raised in
# assembler subroutine such as those in question (basically we're
# referring to segmentation violations caused by malformed input
# parameters), the application is briskly terminated without invoking
# any exception handlers, most notably without generating memory dump
# or any user notification whatsoever. This poses a problem. It's
# possible to address it by registering custom language-specific
# handler that would restore processor context to the state at
# subroutine entry point and return "exception is not handled, keep
# unwinding" code. Writing such handler can be a challenge... But it's
# doable, though requires certain coding convention. Consider following
# snippet:
#
# .type function,@function
# function:
# movq %rsp,%rax # copy rsp to volatile register
# pushq %r15 # save non-volatile registers
# pushq %rbx
# pushq %rbp
# movq %rsp,%r11
# subq %rdi,%r11 # prepare [variable] stack frame
# andq $-64,%r11
# movq %rax,0(%r11) # check for exceptions
# movq %r11,%rsp # allocate [variable] stack frame
# movq %rax,0(%rsp) # save original rsp value
# magic_point:
# ...
# movq 0(%rsp),%rcx # pull original rsp value
# movq -24(%rcx),%rbp # restore non-volatile registers
# movq -16(%rcx),%rbx
# movq -8(%rcx),%r15
# movq %rcx,%rsp # restore original rsp
# ret
# .size function,.-function
#
# The key is that up to magic_point copy of original rsp value remains
# in chosen volatile register and no non-volatile register, except for
# rsp, is modified. While past magic_point rsp remains constant till
# the very end of the function. In this case custom language-specific
# exception handler would look like this:
#
# EXCEPTION_DISPOSITION handler (EXCEPTION_RECORD *rec,ULONG64 frame,
# CONTEXT *context,DISPATCHER_CONTEXT *disp)
# { ULONG64 *rsp = (ULONG64 *)context->Rax;
# if (context->Rip >= magic_point)
# { rsp = ((ULONG64 **)context->Rsp)[0];
# context->Rbp = rsp[-3];
# context->Rbx = rsp[-2];
# context->R15 = rsp[-1];
# }
# context->Rsp = (ULONG64)rsp;
# context->Rdi = rsp[1];
# context->Rsi = rsp[2];
#
# memcpy (disp->ContextRecord,context,sizeof(CONTEXT));
# RtlVirtualUnwind(UNW_FLAG_NHANDLER,disp->ImageBase,
# dips->ControlPc,disp->FunctionEntry,disp->ContextRecord,
# &disp->HandlerData,&disp->EstablisherFrame,NULL);
# return ExceptionContinueSearch;
# }
#
# It's appropriate to implement this handler in assembler, directly in
# function's module. In order to do that one has to know members'
# offsets in CONTEXT and DISPATCHER_CONTEXT structures and some constant
# values. Here they are:
#
# CONTEXT.Rax 120
# CONTEXT.Rcx 128
# CONTEXT.Rdx 136
# CONTEXT.Rbx 144
# CONTEXT.Rsp 152
# CONTEXT.Rbp 160
# CONTEXT.Rsi 168
# CONTEXT.Rdi 176
# CONTEXT.R8 184
# CONTEXT.R9 192
# CONTEXT.R10 200
# CONTEXT.R11 208
# CONTEXT.R12 216
# CONTEXT.R13 224
# CONTEXT.R14 232
# CONTEXT.R15 240
# CONTEXT.Rip 248
# CONTEXT.Xmm6 512
# sizeof(CONTEXT) 1232
# DISPATCHER_CONTEXT.ControlPc 0
# DISPATCHER_CONTEXT.ImageBase 8
# DISPATCHER_CONTEXT.FunctionEntry 16
# DISPATCHER_CONTEXT.EstablisherFrame 24
# DISPATCHER_CONTEXT.TargetIp 32
# DISPATCHER_CONTEXT.ContextRecord 40
# DISPATCHER_CONTEXT.LanguageHandler 48
# DISPATCHER_CONTEXT.HandlerData 56
# UNW_FLAG_NHANDLER 0
# ExceptionContinueSearch 1
#
# In order to tie the handler to the function one has to compose
# couple of structures: one for .xdata segment and one for .pdata.
#
# UNWIND_INFO structure for .xdata segment would be
#
# function_unwind_info:
# .byte 9,0,0,0
# .rva handler
#
# This structure designates exception handler for a function with
# zero-length prologue, no stack frame or frame register.
#
# To facilitate composing of .pdata structures, auto-generated "gear"
# prologue copies rsp value to rax and denotes next instruction with
# .LSEH_begin_{function_name} label. This essentially defines the SEH
# styling rule mentioned in the beginning. Position of this label is
# chosen in such manner that possible exceptions raised in the "gear"
# prologue would be accounted to caller and unwound from latter's frame.
# End of function is marked with respective .LSEH_end_{function_name}
# label. To summarize, .pdata segment would contain
#
# .rva .LSEH_begin_function
# .rva .LSEH_end_function
# .rva function_unwind_info
#
# Reference to functon_unwind_info from .xdata segment is the anchor.
# In case you wonder why references are 32-bit .rvas and not 64-bit
# .quads. References put into these two segments are required to be
# *relative* to the base address of the current binary module, a.k.a.
# image base. No Win64 module, be it .exe or .dll, can be larger than
# 2GB and thus such relative references can be and are accommodated in
# 32 bits.
#
# Having reviewed the example function code, one can argue that "movq
# %rsp,%rax" above is redundant. It is not! Keep in mind that on Unix
# rax would contain an undefined value. If this "offends" you, use
# another register and refrain from modifying rax till magic_point is
# reached, i.e. as if it was a non-volatile register. If more registers
# are required prior [variable] frame setup is completed, note that
# nobody says that you can have only one "magic point." You can
# "liberate" non-volatile registers by denoting last stack off-load
# instruction and reflecting it in finer grade unwind logic in handler.
# After all, isn't it why it's called *language-specific* handler...
#
# Attentive reader can notice that exceptions would be mishandled in
# auto-generated "gear" epilogue. Well, exception effectively can't
# occur there, because if memory area used by it was subject to
# segmentation violation, then it would be raised upon call to the
# function (and as already mentioned be accounted to caller, which is
# not a problem). If you're still not comfortable, then define tail
# "magic point" just prior ret instruction and have handler treat it...
#
# (*) Note that we're talking about run-time, not debug-time. Lack of
# unwind information makes debugging hard on both Windows and
# Unix. "Unlike" referes to the fact that on Unix signal handler
# will always be invoked, core dumped and appropriate exit code
# returned to parent (for user notification).