753 lines
22 KiB
Perl
Executable File
753 lines
22 KiB
Perl
Executable File
#!/usr/bin/env perl
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# Ascetic x86_64 AT&T to MASM assembler translator by <appro>.
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#
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# Why AT&T to MASM and not vice versa? Several reasons. Because AT&T
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# format is way easier to parse. Because it's simpler to "gear" from
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# Unix ABI to Windows one [see cross-reference "card" at the end of
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# file]. Because Linux targets were available first...
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#
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# In addition the script also "distills" code suitable for GNU
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# assembler, so that it can be compiled with more rigid assemblers,
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# such as Solaris /usr/ccs/bin/as.
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#
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# This translator is not designed to convert *arbitrary* assembler
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# code from AT&T format to MASM one. It's designed to convert just
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# enough to provide for dual-ABI OpenSSL modules development...
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# There *are* limitations and you might have to modify your assembler
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# code or this script to achieve the desired result...
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#
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# Currently recognized limitations:
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#
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# - can't use multiple ops per line;
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#
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# Dual-ABI styling rules.
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#
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# 1. Adhere to Unix register and stack layout [see the end for
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# explanation].
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# 2. Forget about "red zone," stick to more traditional blended
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# stack frame allocation. If volatile storage is actually required
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# that is. If not, just leave the stack as is.
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# 3. Functions tagged with ".type name,@function" get crafted with
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# unified Win64 prologue and epilogue automatically. If you want
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# to take care of ABI differences yourself, tag functions as
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# ".type name,@abi-omnipotent" instead.
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# 4. To optimize the Win64 prologue you can specify number of input
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# arguments as ".type name,@function,N." Keep in mind that if N is
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# larger than 6, then you *have to* write "abi-omnipotent" code,
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# because >6 cases can't be addressed with unified prologue.
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# 5. Name local labels as .L*, do *not* use dynamic labels such as 1:
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# (sorry about latter).
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# 6. Don't use [or hand-code with .byte] "rep ret." "ret" mnemonic is
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# required to identify the spots, where to inject Win64 epilogue!
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# But on the pros, it's then prefixed with rep automatically:-)
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# 7. Due to MASM limitations [and certain general counter-intuitivity
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# of ip-relative addressing] generation of position-independent
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# code is assisted by synthetic directive, .picmeup, which puts
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# address of the *next* instruction into target register.
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#
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# Example 1:
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# .picmeup %rax
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# lea .Label-.(%rax),%rax
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# Example 2:
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# .picmeup %rcx
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# .Lpic_point:
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# ...
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# lea .Label-.Lpic_point(%rcx),%rbp
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my $output = shift;
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{ my ($stddev,$stdino,@junk)=stat(STDOUT);
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my ($outdev,$outino,@junk)=stat($output);
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open STDOUT,">$output" || die "can't open $output: $!"
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if ($stddev!=$outdev || $stdino!=$outino);
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}
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my $win64=1 if ($output =~ /\.asm/);
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my $masmref=8 + 50727*2**-32; # 8.00.50727 shipped with VS2005
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my $masm=0;
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my $PTR=" PTR";
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my $nasmref=2.03;
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my $nasm=0;
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if ($win64)
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{ if ($ENV{ASM} =~ m/nasm/ && `nasm -v` =~ m/version ([0-9]+)\.([0-9]+)/i)
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{ $nasm = $1 + $2*0.01; $PTR=""; }
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elsif (`ml64 2>&1` =~ m/Version ([0-9]+)\.([0-9]+)(\.([0-9]+))?/)
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{ $masm = $1 + $2*2**-16 + $4*2**-32; }
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die "no assembler found on %PATH" if (!($nasm || $masm));
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}
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my $current_segment;
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my $current_function;
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my %globals;
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{ package opcode; # pick up opcodes
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sub re {
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my $self = shift; # single instance in enough...
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local *line = shift;
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undef $ret;
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if ($line =~ /^([a-z][a-z0-9]*)/i) {
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$self->{op} = $1;
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$ret = $self;
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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undef $self->{sz};
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if ($self->{op} =~ /^(movz)b.*/) { # movz is pain...
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$self->{op} = $1;
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$self->{sz} = "b";
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} elsif ($self->{op} =~ /call|jmp/) {
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$self->{sz} = ""
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} elsif ($self->{op} =~ /([a-z]{3,})([qlwb])$/) {
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$self->{op} = $1;
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$self->{sz} = $2;
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}
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}
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$ret;
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}
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sub size {
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my $self = shift;
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my $sz = shift;
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$self->{sz} = $sz if (defined($sz) && !defined($self->{sz}));
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$self->{sz};
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}
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sub out {
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my $self = shift;
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if (!$win64) {
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if ($self->{op} eq "movz") { # movz is pain...
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sprintf "%s%s%s",$self->{op},$self->{sz},shift;
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} elsif ($self->{op} =~ /^set/) {
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"$self->{op}";
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} elsif ($self->{op} eq "ret") {
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".byte 0xf3,0xc3";
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} else {
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"$self->{op}$self->{sz}";
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}
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} else {
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$self->{op} =~ s/^movz/movzx/;
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if ($self->{op} eq "ret") {
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$self->{op} = "";
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if ($current_function->{abi} eq "svr4") {
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$self->{op} = "mov rdi,QWORD${PTR}[8+rsp]\t;WIN64 epilogue\n\t".
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"mov rsi,QWORD${PTR}[16+rsp]\n\t";
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}
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$self->{op} .= "DB\t0F3h,0C3h\t\t;repret";
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}
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$self->{op};
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}
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}
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sub mnemonic { shift->{op}; }
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}
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{ package const; # pick up constants, which start with $
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sub re {
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my $self = shift; # single instance in enough...
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local *line = shift;
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undef $ret;
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if ($line =~ /^\$([^,]+)/) {
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$self->{value} = $1;
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$ret = $self;
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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}
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$ret;
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}
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sub out {
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my $self = shift;
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if (!$win64) {
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# Solaris /usr/ccs/bin/as can't handle multiplications
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# in $self->{value}
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$self->{value} =~ s/(?<![0-9a-f])(0[x0-9a-f]+)/oct($1)/egi;
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$self->{value} =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg;
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sprintf "\$%s",$self->{value};
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} else {
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$self->{value} =~ s/0x([0-9a-f]+)/0$1h/ig;
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sprintf "%s",$self->{value};
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}
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}
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}
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{ package ea; # pick up effective addresses: expr(%reg,%reg,scale)
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sub re {
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my $self = shift; # single instance in enough...
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local *line = shift;
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undef $ret;
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# optional * ---vvv--- appears in indirect jmp/call
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if ($line =~ /^(\*?)([^\(,]*)\(([%\w,]+)\)/) {
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$self->{asterisk} = $1;
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$self->{label} = $2;
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($self->{base},$self->{index},$self->{scale})=split(/,/,$3);
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$self->{scale} = 1 if (!defined($self->{scale}));
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$ret = $self;
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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$self->{base} =~ s/^%//;
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$self->{index} =~ s/^%// if (defined($self->{index}));
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}
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$ret;
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}
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sub size {}
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sub out {
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my $self = shift;
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my $sz = shift;
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# Silently convert all EAs to 64-bit. This is required for
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# elder GNU assembler and results in more compact code,
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# *but* most importantly AES module depends on this feature!
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$self->{index} =~ s/^[er](.?[0-9xpi])[d]?$/r\1/;
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$self->{base} =~ s/^[er](.?[0-9xpi])[d]?$/r\1/;
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if (!$win64) {
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# Solaris /usr/ccs/bin/as can't handle multiplications
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# in $self->{label}
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$self->{label} =~ s/(?<![0-9a-f])(0[x0-9a-f]+)/oct($1)/egi;
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$self->{label} =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg;
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if (defined($self->{index})) {
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sprintf "%s%s(%%%s,%%%s,%d)",$self->{asterisk},
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$self->{label},$self->{base},
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$self->{index},$self->{scale};
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} else {
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sprintf "%s%s(%%%s)", $self->{asterisk},$self->{label},$self->{base};
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}
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} else {
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%szmap = ( b=>"BYTE$PTR", w=>"WORD$PTR", l=>"DWORD$PTR", q=>"QWORD$PTR" );
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$self->{label} =~ s/\./\$/g;
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$self->{label} =~ s/0x([0-9a-f]+)/0$1h/ig;
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$self->{label} = "($self->{label})" if ($self->{label} =~ /[\*\+\-\/]/);
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$sz="q" if ($self->{asterisk});
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if (defined($self->{index})) {
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sprintf "%s[%s%s*%d+%s]",$szmap{$sz},
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$self->{label}?"$self->{label}+":"",
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$self->{index},$self->{scale},
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$self->{base};
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} elsif ($self->{base} eq "rip") {
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sprintf "%s[%s]",$szmap{$sz},$self->{label};
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} else {
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sprintf "%s[%s%s]",$szmap{$sz},
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$self->{label}?"$self->{label}+":"",
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$self->{base};
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}
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}
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}
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}
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{ package register; # pick up registers, which start with %.
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sub re {
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my $class = shift; # muliple instances...
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my $self = {};
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local *line = shift;
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undef $ret;
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# optional * ---vvv--- appears in indirect jmp/call
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if ($line =~ /^(\*?)%(\w+)/) {
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bless $self,$class;
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$self->{asterisk} = $1;
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$self->{value} = $2;
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$ret = $self;
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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}
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$ret;
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}
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sub size {
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my $self = shift;
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undef $ret;
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if ($self->{value} =~ /^r[\d]+b$/i) { $ret="b"; }
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elsif ($self->{value} =~ /^r[\d]+w$/i) { $ret="w"; }
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elsif ($self->{value} =~ /^r[\d]+d$/i) { $ret="l"; }
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elsif ($self->{value} =~ /^r[\w]+$/i) { $ret="q"; }
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elsif ($self->{value} =~ /^[a-d][hl]$/i){ $ret="b"; }
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elsif ($self->{value} =~ /^[\w]{2}l$/i) { $ret="b"; }
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elsif ($self->{value} =~ /^[\w]{2}$/i) { $ret="w"; }
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elsif ($self->{value} =~ /^e[a-z]{2}$/i){ $ret="l"; }
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$ret;
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}
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sub out {
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my $self = shift;
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if (!$win64) { sprintf "%s%%%s",$self->{asterisk},$self->{value}; }
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else { $self->{value}; }
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}
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}
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{ package label; # pick up labels, which end with :
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sub re {
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my $self = shift; # single instance is enough...
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local *line = shift;
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undef $ret;
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if ($line =~ /(^[\.\w]+\:)/) {
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$self->{value} = $1;
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$ret = $self;
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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$self->{value} =~ s/\.L/\$L/ if ($win64);
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}
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$ret;
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}
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sub out {
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my $self = shift;
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if (!$win64) {
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$self->{value};
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} elsif ($self->{value} ne "$current_function->{name}:") {
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$self->{value} .= ":" if ($masm && $ret!~m/^\$/);
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$self->{value};
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} elsif ($current_function->{abi} eq "svr4") {
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my $func = "$current_function->{name}" .
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($nasm ? ":" : "\tPROC $current_function->{scope}") .
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"\n";
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$func .= " mov QWORD${PTR}[8+rsp],rdi\t;WIN64 prologue\n";
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$func .= " mov QWORD${PTR}[16+rsp],rsi\n";
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my $narg = $current_function->{narg};
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$narg=6 if (!defined($narg));
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$func .= " mov rdi,rcx\n" if ($narg>0);
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$func .= " mov rsi,rdx\n" if ($narg>1);
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$func .= " mov rdx,r8\n" if ($narg>2);
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$func .= " mov rcx,r9\n" if ($narg>3);
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$func .= " mov r8,QWORD${PTR}[40+rsp]\n" if ($narg>4);
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$func .= " mov r9,QWORD${PTR}[48+rsp]\n" if ($narg>5);
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$func .= "\n";
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} else {
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"$current_function->{name}".
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($nasm ? ":" : "\tPROC $current_function->{scope}");
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}
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}
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}
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{ package expr; # pick up expressioins
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sub re {
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my $self = shift; # single instance is enough...
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local *line = shift;
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undef $ret;
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if ($line =~ /(^[^,]+)/) {
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$self->{value} = $1;
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$ret = $self;
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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$self->{value} =~ s/\.L/\$L/g if ($win64);
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}
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$ret;
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}
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sub out {
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my $self = shift;
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if ($nasm && opcode->mnemonic()=~m/^j/) {
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"NEAR ".$self->{value};
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} else {
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$self->{value};
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}
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}
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}
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{ package directive; # pick up directives, which start with .
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sub re {
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my $self = shift; # single instance is enough...
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local *line = shift;
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undef $ret;
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my $dir;
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my %opcode = # lea 2f-1f(%rip),%dst; 1: nop; 2:
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( "%rax"=>0x01058d48, "%rcx"=>0x010d8d48,
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"%rdx"=>0x01158d48, "%rbx"=>0x011d8d48,
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"%rsp"=>0x01258d48, "%rbp"=>0x012d8d48,
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"%rsi"=>0x01358d48, "%rdi"=>0x013d8d48,
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"%r8" =>0x01058d4c, "%r9" =>0x010d8d4c,
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"%r10"=>0x01158d4c, "%r11"=>0x011d8d4c,
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"%r12"=>0x01258d4c, "%r13"=>0x012d8d4c,
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"%r14"=>0x01358d4c, "%r15"=>0x013d8d4c );
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if ($line =~ /^\s*(\.\w+)/) {
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if (!$win64) {
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$self->{value} = $1;
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$line =~ s/\@abi\-omnipotent/\@function/;
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$line =~ s/\@function.*/\@function/;
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if ($line =~ /\.picmeup\s+(%r[\w]+)/i) {
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$self->{value} = sprintf "\t.long\t0x%x,0x90000000",$opcode{$1};
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} elsif ($line =~ /\.asciz\s+"(.*)"$/) {
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$self->{value} = ".byte\t".join(",",unpack("C*",$1),0);
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} elsif ($line =~ /\.extern/) {
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$self->{value} = ""; # swallow extern
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} else {
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$self->{value} = $line;
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}
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$line = "";
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return $self;
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}
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$dir = $1;
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$ret = $self;
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undef $self->{value};
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$line = substr($line,@+[0]); $line =~ s/^\s+//;
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SWITCH: for ($dir) {
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/\.text/ && do { my $v=undef;
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if ($nasm) {
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$v="section .text code align=64\n";
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} else {
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$v="$current_segment\tENDS\n" if ($current_segment);
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$current_segment = ".text\$";
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$v.="$current_segment\tSEGMENT ";
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$v.=$masm>=$masmref ? "ALIGN(64)" : "PAGE";
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$v.=" 'CODE'";
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}
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$self->{value} = $v;
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last;
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};
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/\.data/ && do { my $v=undef;
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if ($nasm) {
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$v="section .data data align=8\n";
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} else {
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$v="$current_segment\tENDS\n" if ($current_segment);
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$current_segment = "_DATA";
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$v.="$current_segment\tSEGMENT";
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}
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$self->{value} = $v;
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last;
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};
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/\.section/ && do { my $v=undef;
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if ($nasm) {
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$v="section $line";
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if ($line=~/\.([px])data/) {
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$v.=" rdata align=";
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$v.=$1 eq "p"? 4 : 8;
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}
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} else {
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$v="$current_segment\tENDS\n" if ($current_segment);
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$v.="$line\tSEGMENT";
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if ($line=~/\.([px])data/) {
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$v.=" READONLY";
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$v.=" ALIGN(".($1 eq "p" ? 4 : 8).")" if ($masm>=$masmref);
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}
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}
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$current_segment = $line;
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$self->{value} = $v;
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last;
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};
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/\.extern/ && do { $self->{value} = "EXTERN\t".$line;
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$self->{value} .= ":NEAR" if ($masm);
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last;
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};
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/\.globl/ && do { $self->{value} = "PUBLIC\t".$line;
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$globals{$line} = $line;
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last;
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};
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/\.type/ && do { ($sym,$type,$narg) = split(',',$line);
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if ($type eq "\@function") {
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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{$sym})?"PUBLIC":"PRIVATE";
|
|
}
|
|
last;
|
|
};
|
|
/\.size/ && do { if (defined($current_function)) {
|
|
$self->{value}="$current_function->{name}\tENDP" if(!$nasm);
|
|
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);
|
|
my $conv = sub { my $var=shift;
|
|
$var=~s/0x([0-9a-f]+)/0$1h/ig;
|
|
if ($current_segment=~/.[px]data/)
|
|
{ $var=~s/\b([_a-z\$\@][_a-z0-9\$\@]*)/$nasm?"$1 wrt ..imagebase":"imagerel $1"/egi; }
|
|
$var;
|
|
};
|
|
|
|
$sz =~ tr/bvlq/BWDQ/;
|
|
$self->{value} = "\tD$sz\t";
|
|
for (@arr) { $self->{value} .= &$conv($_).","; }
|
|
$self->{value} .= &$conv($last);
|
|
last;
|
|
};
|
|
/\.picmeup/ && do { $self->{value} = sprintf"\tDD\t0%Xh,090000000h",$opcode{$line};
|
|
last;
|
|
};
|
|
/\.asciz/ && do { if ($line =~ /^"(.*)"$/) {
|
|
my @str=unpack("C*",$1);
|
|
push @str,0;
|
|
while ($#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
|
|
%define PUBLIC global
|
|
___
|
|
} 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 $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 (!$win64) {
|
|
printf "\t%s\t%s,%s", $opcode->out($dst->size()),
|
|
$src->out($sz),$dst->out($sz);
|
|
} else {
|
|
undef $sz if ($nasm && $opcode->mnemonic() eq "lea");
|
|
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 ($current_segment && $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
|
|
#
|
|
#################################################
|
|
# 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:
|
|
#
|
|
# 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
|
|
#
|
|
# 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;
|
|
# if (context->Rip<magic_point)
|
|
# rsp = (ULONG64 *)context->Rax;
|
|
# else
|
|
# { 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
|
|
# 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
|
|
#
|
|
# UNWIND_INFO structure for .xdata segment would be
|
|
# DB 9,0,0,0
|
|
# DD imagerel handler
|
|
# denoting exception handler for a function with zero-length prologue,
|
|
# no stack frame or frame register.
|
|
#
|
|
# P.S. Attentive reader can notice that effectively no exceptions are
|
|
# expected in "gear" prologue and epilogue [discussed in "ABI
|
|
# cross-reference" above]. No, there are not. This is because if
|
|
# memory area used by them was subject to segmentation violation,
|
|
# then exception would be raised upon call to our function and be
|
|
# accounted to caller and unwound from its frame, which is not a
|
|
# problem.
|
|
#
|
|
# (*) 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).
|