#!/usr/bin/env perl

# Ascetic x86_64 AT&T to MASM 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;
# - indirect calls and jumps are not supported;
#
# Dual-ABI styling rules.
#
# 1. Adhere to Unix register and stack layout [see 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:-)

my $output = shift;
open STDOUT,">$output" || die "can't open $output: $!";

my $masm=1 if ($output =~ /\.asm/);

my $current_segment;
my $current_function;

{ package opcode;	# pick up opcodes
    sub re {
	my	$self = shift;	# single instance in enough...
	local	*line = shift;
	undef	$ret;

	if ($line =~ /^([a-z]+)/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} =~ /([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 $self = shift;
	if (!$masm) {
	    if ($self->{op} eq "movz") {	# movz in pain...
		sprintf "%s%s%s",$self->{op},$self->{sz},shift;
	    } elsif ($self->{op} eq "ret") {
	    	".byte	0xf3,0xc3";
	    } else {
		"$self->{op}$self->{sz}";
	    }
	} else {
	    $self->{op} =~ s/movz/movzx/;
	    if ($self->{op} eq "ret") {
		$self->{op} = "";
		if ($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";
	    }
	    $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;
	sprintf $masm?"%s":"\$%s",$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;

	if ($line =~ /^([^\(,]*)\(([%\w,]+)\)/) {
	    $self->{label} = $1;
	    ($self->{base},$self->{index},$self->{scale})=split(/,/,$2);
	    $self->{scale} = 1 if (!defined($self->{scale}));
	    $ret = $self;
	    $line = substr($line,@+[0]); $line =~ s/^\s+//;

	    $self->{label} =~ s/\.L/\$L/g;
	    $self->{base}  =~ s/^%//;
	    $self->{index} =~ s/^%// if (defined($self->{index}));
	}
	$ret;
    }
    sub size {}
    sub out {
    	my $self = shift;
	my $sz = shift;

	if (!$masm) {
	    # elder GNU assembler insists on 64-bit EAs:-(
	    # on pros side, this results in more compact code:-)
	    $self->{index} =~ s/^[er](.?[0-9xp])[d]?$/r\1/;
	    $self->{base}  =~ s/^[er](.?[0-9xp])[d]?$/r\1/;

	    if (defined($self->{index})) {
		sprintf "%s(%%%s,%%%s,%d)",	$self->{label},$self->{base},
					$self->{index},$self->{scale};
	    }
	    else {
		sprintf "%s(%%%s)",	$self->{label},$self->{base};
	    }
	} else {
	    %szmap = ( b=>"BYTE", w=>"WORD", l=>"DWORD", q=>"QWORD" );

	    if (defined($self->{index})) {
		sprintf "%s PTR %s[%s*%d+%s]",$szmap{$sz},
					$self->{label},
					$self->{index},$self->{scale},
					$self->{base};
	    }
	    else {
		sprintf "%s PTR %s[%s]",$szmap{$sz},
					$self->{label},$self->{base};
	    }
	}
    }
}
{ package register;	# pick up registers, which start with %.
    sub re {
	my	$class = shift;	# muliple instances...
	my	$self = {};
	local	*line = shift;
	undef	$ret;

	if ($line =~ /^%(\w+)/) {
	    bless $self,$class;
	    $self->{value} = $1;
	    $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;
	sprintf $masm?"%s":"%%%s",$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+//;

	    $self->{value} =~ s/\.L/\$L/ if ($masm);
	}
	$ret;
    }
    sub out {
	my $self = shift;

	if (!$masm) {
	    $self->{value};
	} elsif ($self->{value} ne "$current_function->{name}:") {
	    $self->{value};
	} elsif ($current_function->{abi} eq "svr4") {
	    my $func =	"$current_function->{name}	PROC\n".
			"	mov	QWORD PTR 8[rsp],rdi\t;WIN64 prologue\n".
			"	mov	QWORD PTR 16[rsp],rsi\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}	PROC";
	}
    }
}
{ 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+//;

	    $self->{value} =~ s/\.L/\$L/g if ($masm);
	}
	$ret;
    }
    sub out {
	my $self = shift;
	$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;

	if ($line =~ /^\s*(\.\w+)/) {
	    if (!$masm) {
		$self->{value} = $1;
		$line =~ s/\@abi\-omnipotent/\@function/;
		$line =~ s/\@function.*/\@function/;
		$self->{value} = $line;
		$line = "";
		return $self;
	    }

	    $dir = $1;
	    $ret = $self;
	    undef $self->{value};
	    $line = substr($line,@+[0]); $line =~ s/^\s+//;
	    SWITCH: for ($dir) {
		/\.(text|data)/
			    && do { my $v=undef;
				    $v="$current_segment\tENDS\n" if ($current_segment);
				    $current_segment = "_$1";
				    $current_segment =~ tr/[a-z]/[A-Z]/;
				    $v.="$current_segment\tSEGMENT PARA";
				    $self->{value} = $v;
				    last;
				  };
		/\.globl/   && do { $self->{value} = "PUBLIC\t".$line; 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} = $narg;
				    }
				    elsif ($type eq "\@abi-omnipotent")
				    {	undef $current_function;
					$current_function->{name} = $sym;
				    }
				    last;
				  };
		/\.size/    && do { if (defined($current_function))
				    {	$self->{value}="$current_function->{name}\tENDP";
					undef $current_function;
				    }
				    last;
				  };
		/\.align/   && do { $self->{value} = "ALIGN\t".$line; last; };
		/\.(byte|value|long|quad)/
			    && do { my @arr = split(',',$line);
				    my $sz  = substr($1,0,1);
				    my $last = pop(@arr);

				    $sz =~ tr/bvlq/BWDQ/;
				    $self->{value} = "\tD$sz\t";
				    for (@arr) { $self->{value} .= sprintf"0%Xh,",oct; }
				    $self->{value} .= sprintf"0%Xh",oct($last);
				    last;
				  };
	    }
	    $line = "";
	}

	$ret;
    }
    sub out {
	my $self = shift;
	$self->{value};
    }
}

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 $dst;
    undef $src;
    undef $sz;

    if ($label=label->re(\$line))	{ print $label->out(); }

    if (directive->re(\$line)) {
	printf "%s",directive->out();
    } elsif ($opcode=opcode->re(\$line)) { ARGUMENT: {

	if ($src=register->re(\$line))	{ opcode->size($src->size()); }
	elsif ($src=const->re(\$line))	{ }
	elsif ($src=ea->re(\$line))	{ }
	elsif ($src=expr->re(\$line))	{ }

	last ARGUMENT if ($line !~ /^,/);

	$line = substr($line,1); $line =~ s/^\s+//;

	if ($dst=register->re(\$line))	{ opcode->size($dst->size()); }
	elsif ($dst=const->re(\$line))	{ }
	elsif ($dst=ea->re(\$line))	{ }

	} # ARGUMENT:

	$sz=opcode->size();

	if (defined($dst)) {
	    if (!$masm) {
		printf "\t%s\t%s,%s",	$opcode->out($dst->size()),
					$src->out($sz),$dst->out($sz);
	    }
	    else {
		printf "\t%s\t%s,%s",	$opcode->out(),
					$dst->out($sz),$src->out($sz);
	    }
	}
	elsif (defined($src)) {
	    printf "\t%s\t%s",$opcode->out(),$src->out($sz);
	} else {
	    printf "\t%s",$opcode->out();
	}
    }

    print $line,"\n";
}

print "\n$current_segment\tENDS\nEND\n" if ($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].
#
# 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
