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boringssl/crypto/perlasm/x86_64-xlate.pl
David Benjamin 17d553d299 Add a CFI tester to CHECK_ABI. 
This uses the x86 trap flag and libunwind to test CFI works at each
instruction. For now, it just uses the system one out of pkg-config and
disables unwind tests if unavailable. We'll probably want to stick a
copy into //third_party and perhaps try the LLVM one later.

This tester caught two bugs in P-256 CFI annotations already:
I47b5f9798b3bcee1748e537b21c173d312a14b42 and
I9f576d868850312d6c14d1386f8fbfa85021b347

An earlier design used PTRACE_SINGLESTEP with libunwind's remote
unwinding features. ptrace is a mess around stop signals (see group-stop
discussion in ptrace(2)) and this is 10x faster, so I went with it. The
question of which is more future-proof is complex:

- There are two libunwinds with the same API,
  https://www.nongnu.org/libunwind/ and LLVM's. This currently uses the
  system nongnu.org for convenience. In future, LLVM's should be easier
  to bundle (less complex build) and appears to even support Windows,
  but I haven't tested this.  Moreover, setting the trap flag keeps the
  test single-process, which is less complex on Windows. That suggests
  the trap flag design and switching to LLVM later. However...

- Not all architectures have a trap flag settable by userspace. As far
  as I can tell, ARMv8's PSTATE.SS can only be set from the kernel. If
  we stick with nongnu.org libunwind, we can use PTRACE_SINGLESTEP and
  remote unwinding. Or we implement it for LLVM. Another thought is for
  the ptracer to bounce SIGTRAP back into the process, to share the
  local unwinding code.

- ARMv7 has no trap flag at all and PTRACE_SINGLESTEP fails. Debuggers
  single-step by injecting breakpoints instead. However, ARMv8's trap
  flag seems to work in both AArch32 and AArch64 modes, so we may be
  able to condition it on a 64-bit kernel.

Sadly, neither strategy works with Intel SDE. Adding flags to cpucap
vectors as we do with ARM would help, but it would not emulate CPUs
newer than the host CPU. For now, I've just had SDE tests disable these.

Annoyingly, CMake does not allow object libraries to have dependencies,
so make test_support a proper static library. Rename the target to
test_support_lib to avoid
https://gitlab.kitware.com/cmake/cmake/issues/17785

Update-Note: This adds a new optional test dependency, but it's disabled
by default (define BORINGSSL_HAVE_LIBUNWIND), so consumers do not need
to do anything. We'll probably want to adjust this in the future.

Bug: 181
Change-Id: I817263d7907aff0904a9cee83f8b26747262cc0c
Reviewed-on: https://boringssl-review.googlesource.com/c/33966
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
2019-01-03 22:01:55 +00:00

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#! /usr/bin/env perl
# Copyright 2005-2016 The OpenSSL Project Authors. All Rights Reserved.
#
# Licensed under the OpenSSL license (the "License"). You may not use
# this file except in compliance with the License. You can obtain a copy
# in the file LICENSE in the source distribution or at
# https://www.openssl.org/source/license.html
# 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.
#
# 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.
use strict;
my $flavour = shift;
my $output = shift;
if ($flavour =~ /\./) { $output = $flavour; undef $flavour; }
open STDOUT,">$output" || die "can't open $output: $!"
if (defined($output));
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;
# TODO(davidben): Before supporting the
# mingw64 perlasm flavour, do away with this
# environment variable check.
die "mingw64 not supported";
$prefix=`echo __USER_LABEL_PREFIX__ | $ENV{CC} -E -P -`;
$prefix =~ s|\R$||; # Better chomp
}
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) { die "unknown flavour $flavour"; }
my $current_segment;
my $current_function;
my %globals;
{ package opcode; # pick up opcodes
sub re {
my ($class, $line) = @_;
my $self = {};
my $ret;
if ($$line =~ /^([a-z][a-z0-9]*)/i) {
bless $self,$class;
$self->{op} = $1;
$ret = $self;
$$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
undef $self->{sz};
if ($self->{op} =~ /^(movz)x?([bw]).*/) { # movz is pain...
$self->{op} = $1;
$self->{sz} = $2;
} elsif ($self->{op} =~ /call|jmp/) {
$self->{sz} = "";
} elsif ($self->{op} =~ /^p/ && $' !~ /^(ush|op|insrw)/) { # SSEn
$self->{sz} = "";
} elsif ($self->{op} =~ /^[vk]/) { # VEX or k* such as kmov
$self->{sz} = "";
} elsif ($self->{op} =~ /mov[dq]/ && $$line =~ /%xmm/) {
$self->{sz} = "";
} elsif ($self->{op} =~ /^or([qlwb])$/) {
$self->{op} = "or";
$self->{sz} = $1;
} elsif ($self->{op} =~ /([a-z]{3,})([qlwb])$/) {
$self->{op} = $1;
$self->{sz} = $2;
}
}
$ret;
}
sub size {
my ($self, $sz) = @_;
$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, $op) = @_;
$self->{op}=$op if (defined($op));
$self->{op};
}
}
{ package const; # pick up constants, which start with $
sub re {
my ($class, $line) = @_;
my $self = {};
my $ret;
if ($$line =~ /^\$([^,]+)/) {
bless $self, $class;
$self->{value} = $1;
$ret = $self;
$$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
}
$ret;
}
sub out {
my $self = shift;
$self->{value} =~ s/\b(0b[0-1]+)/oct($1)/eig;
if ($gas) {
# Solaris /usr/ccs/bin/as can't handle multiplications
# in $self->{value}
my $value = $self->{value};
no warnings; # oct might complain about overflow, ignore here...
$value =~ s/(?<![\w\$\.])(0x?[0-9a-f]+)/oct($1)/egi;
if ($value =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg) {
$self->{value} = $value;
}
sprintf "\$%s",$self->{value};
} else {
my $value = $self->{value};
$value =~ s/0x([0-9a-f]+)/0$1h/ig if ($masm);
sprintf "%s",$value;
}
}
}
{ package ea; # pick up effective addresses: expr(%reg,%reg,scale)
my %szmap = ( b=>"BYTE$PTR", w=>"WORD$PTR",
l=>"DWORD$PTR", d=>"DWORD$PTR",
q=>"QWORD$PTR", o=>"OWORD$PTR",
x=>"XMMWORD$PTR", y=>"YMMWORD$PTR",
z=>"ZMMWORD$PTR" ) if (!$gas);
sub re {
my ($class, $line, $opcode) = @_;
my $self = {};
my $ret;
# optional * ----vvv--- appears in indirect jmp/call
if ($$line =~ /^(\*?)([^\(,]*)\(([%\w,]+)\)((?:{[^}]+})*)/) {
bless $self, $class;
$self->{asterisk} = $1;
$self->{label} = $2;
($self->{base},$self->{index},$self->{scale})=split(/,/,$3);
$self->{scale} = 1 if (!defined($self->{scale}));
$self->{opmask} = $4;
$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}));
$self->{opcode} = $opcode;
}
$ret;
}
sub size {}
sub out {
my ($self, $sz) = @_;
$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/;
# Solaris /usr/ccs/bin/as can't handle multiplications
# in $self->{label}...
use integer;
$self->{label} =~ s/(?<![\w\$\.])(0x?[0-9a-f]+)/oct($1)/egi;
$self->{label} =~ s/\b([0-9]+\s*[\*\/\%]\s*[0-9]+)\b/eval($1)/eg;
# Some assemblers insist on signed presentation of 32-bit
# offsets, but sign extension is a tricky business in perl...
if ((1<<31)<<1) {
$self->{label} =~ s/\b([0-9]+)\b/$1<<32>>32/eg;
} else {
$self->{label} =~ s/\b([0-9]+)\b/$1>>0/eg;
}
# if base register is %rbp or %r13, see if it's possible to
# flip base and index registers [for better performance]
if (!$self->{label} && $self->{index} && $self->{scale}==1 &&
$self->{base} =~ /(rbp|r13)/) {
$self->{base} = $self->{index}; $self->{index} = $1;
}
if ($gas) {
$self->{label} =~ s/^___imp_/__imp__/ if ($flavour eq "mingw64");
if (defined($self->{index})) {
sprintf "%s%s(%s,%%%s,%d)%s",
$self->{asterisk},$self->{label},
$self->{base}?"%$self->{base}":"",
$self->{index},$self->{scale},
$self->{opmask};
} else {
sprintf "%s%s(%%%s)%s", $self->{asterisk},$self->{label},
$self->{base},$self->{opmask};
}
} else {
$self->{label} =~ s/\./\$/g;
$self->{label} =~ s/(?<![\w\$\.])0x([0-9a-f]+)/0$1h/ig;
$self->{label} = "($self->{label})" if ($self->{label} =~ /[\*\+\-\/]/);
my $mnemonic = $self->{opcode}->mnemonic();
($self->{asterisk}) && ($sz="q") ||
($mnemonic =~ /^v?mov([qd])$/) && ($sz=$1) ||
($mnemonic =~ /^v?pinsr([qdwb])$/) && ($sz=$1) ||
($mnemonic =~ /^vpbroadcast([qdwb])$/) && ($sz=$1) ||
($mnemonic =~ /^v(?!perm)[a-z]+[fi]128$/) && ($sz="x");
$self->{opmask} =~ s/%(k[0-7])/$1/;
if (defined($self->{index})) {
sprintf "%s[%s%s*%d%s]%s",$szmap{$sz},
$self->{label}?"$self->{label}+":"",
$self->{index},$self->{scale},
$self->{base}?"+$self->{base}":"",
$self->{opmask};
} elsif ($self->{base} eq "rip") {
sprintf "%s[%s]",$szmap{$sz},$self->{label};
} else {
sprintf "%s[%s%s]%s", $szmap{$sz},
$self->{label}?"$self->{label}+":"",
$self->{base},$self->{opmask};
}
}
}
}
{ package register; # pick up registers, which start with %.
sub re {
my ($class, $line, $opcode) = @_;
my $self = {};
my $ret;
# optional * ----vvv--- appears in indirect jmp/call
if ($$line =~ /^(\*?)%(\w+)((?:{[^}]+})*)/) {
bless $self,$class;
$self->{asterisk} = $1;
$self->{value} = $2;
$self->{opmask} = $3;
$opcode->size($self->size());
$ret = $self;
$$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
}
$ret;
}
sub size {
my $self = shift;
my $ret;
if ($self->{value} =~ /^r[\d]+b$/i) { $ret="b"; }
elsif ($self->{value} =~ /^r[\d]+w$/i) { $ret="w"; }
elsif ($self->{value} =~ /^r[\d]+d$/i) { $ret="l"; }
elsif ($self->{value} =~ /^r[\w]+$/i) { $ret="q"; }
elsif ($self->{value} =~ /^[a-d][hl]$/i){ $ret="b"; }
elsif ($self->{value} =~ /^[\w]{2}l$/i) { $ret="b"; }
elsif ($self->{value} =~ /^[\w]{2}$/i) { $ret="w"; }
elsif ($self->{value} =~ /^e[a-z]{2}$/i){ $ret="l"; }
$ret;
}
sub out {
my $self = shift;
if ($gas) { sprintf "%s%%%s%s", $self->{asterisk},
$self->{value},
$self->{opmask}; }
else { $self->{opmask} =~ s/%(k[0-7])/$1/;
$self->{value}.$self->{opmask}; }
}
}
{ package label; # pick up labels, which end with :
sub re {
my ($class, $line) = @_;
my $self = {};
my $ret;
if ($$line =~ /(^[\.\w]+)\:/) {
bless $self,$class;
$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}") {
# Make all labels in masm global.
$self->{value} .= ":" if ($masm);
$self->{value} . ":";
} elsif ($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 $current_function->{scope}");
}
}
}
{ package expr; # pick up expressions
sub re {
my ($class, $line, $opcode) = @_;
my $self = {};
my $ret;
if ($$line =~ /(^[^,]+)/) {
bless $self,$class;
$self->{value} = $1;
$ret = $self;
$$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;
$self->{opcode} = $opcode;
}
$ret;
}
sub out {
my $self = shift;
if ($nasm && $self->{opcode}->mnemonic()=~m/^j(?![re]cxz)/) {
"NEAR ".$self->{value};
} else {
$self->{value};
}
}
}
{ package cfi_directive;
# CFI directives annotate instructions that are significant for
# stack unwinding procedure compliant with DWARF specification,
# see http://dwarfstd.org/. Besides naturally expected for this
# script platform-specific filtering function, this module adds
# three auxiliary synthetic directives not recognized by [GNU]
# assembler:
#
# - .cfi_push to annotate push instructions in prologue, which
# translates to .cfi_adjust_cfa_offset (if needed) and
# .cfi_offset;
# - .cfi_pop to annotate pop instructions in epilogue, which
# translates to .cfi_adjust_cfa_offset (if needed) and
# .cfi_restore;
# - [and most notably] .cfi_cfa_expression which encodes
# DW_CFA_def_cfa_expression and passes it to .cfi_escape as
# byte vector;
#
# CFA expressions were introduced in DWARF specification version
# 3 and describe how to deduce CFA, Canonical Frame Address. This
# becomes handy if your stack frame is variable and you can't
# spare register for [previous] frame pointer. Suggested directive
# syntax is made-up mix of DWARF operator suffixes [subset of]
# and references to registers with optional bias. Following example
# describes offloaded *original* stack pointer at specific offset
# from *current* stack pointer:
#
# .cfi_cfa_expression %rsp+40,deref,+8
#
# Final +8 has everything to do with the fact that CFA is defined
# as reference to top of caller's stack, and on x86_64 call to
# subroutine pushes 8-byte return address. In other words original
# stack pointer upon entry to a subroutine is 8 bytes off from CFA.
# Below constants are taken from "DWARF Expressions" section of the
# DWARF specification, section is numbered 7.7 in versions 3 and 4.
my %DW_OP_simple = ( # no-arg operators, mapped directly
deref => 0x06, dup => 0x12,
drop => 0x13, over => 0x14,
pick => 0x15, swap => 0x16,
rot => 0x17, xderef => 0x18,
abs => 0x19, and => 0x1a,
div => 0x1b, minus => 0x1c,
mod => 0x1d, mul => 0x1e,
neg => 0x1f, not => 0x20,
or => 0x21, plus => 0x22,
shl => 0x24, shr => 0x25,
shra => 0x26, xor => 0x27,
);
my %DW_OP_complex = ( # used in specific subroutines
constu => 0x10, # uleb128
consts => 0x11, # sleb128
plus_uconst => 0x23, # uleb128
lit0 => 0x30, # add 0-31 to opcode
reg0 => 0x50, # add 0-31 to opcode
breg0 => 0x70, # add 0-31 to opcole, sleb128
regx => 0x90, # uleb28
fbreg => 0x91, # sleb128
bregx => 0x92, # uleb128, sleb128
piece => 0x93, # uleb128
);
# Following constants are defined in x86_64 ABI supplement, for
# example available at https://www.uclibc.org/docs/psABI-x86_64.pdf,
# see section 3.7 "Stack Unwind Algorithm".
my %DW_reg_idx = (
"%rax"=>0, "%rdx"=>1, "%rcx"=>2, "%rbx"=>3,
"%rsi"=>4, "%rdi"=>5, "%rbp"=>6, "%rsp"=>7,
"%r8" =>8, "%r9" =>9, "%r10"=>10, "%r11"=>11,
"%r12"=>12, "%r13"=>13, "%r14"=>14, "%r15"=>15
);
my ($cfa_reg, $cfa_rsp);
# [us]leb128 format is variable-length integer representation base
# 2^128, with most significant bit of each byte being 0 denoting
# *last* most significant digit. See "Variable Length Data" in the
# DWARF specification, numbered 7.6 at least in versions 3 and 4.
sub sleb128 {
use integer; # get right shift extend sign
my $val = shift;
my $sign = ($val < 0) ? -1 : 0;
my @ret = ();
while(1) {
push @ret, $val&0x7f;
# see if remaining bits are same and equal to most
# significant bit of the current digit, if so, it's
# last digit...
last if (($val>>6) == $sign);
@ret[-1] |= 0x80;
$val >>= 7;
}
return @ret;
}
sub uleb128 {
my $val = shift;
my @ret = ();
while(1) {
push @ret, $val&0x7f;
# see if it's last significant digit...
last if (($val >>= 7) == 0);
@ret[-1] |= 0x80;
}
return @ret;
}
sub const {
my $val = shift;
if ($val >= 0 && $val < 32) {
return ($DW_OP_complex{lit0}+$val);
}
return ($DW_OP_complex{consts}, sleb128($val));
}
sub reg {
my $val = shift;
return if ($val !~ m/^(%r\w+)(?:([\+\-])((?:0x)?[0-9a-f]+))?/);
my $reg = $DW_reg_idx{$1};
my $off = eval ("0 $2 $3");
return (($DW_OP_complex{breg0} + $reg), sleb128($off));
# Yes, we use DW_OP_bregX+0 to push register value and not
# DW_OP_regX, because latter would require even DW_OP_piece,
# which would be a waste under the circumstances. If you have
# to use DWP_OP_reg, use "regx:N"...
}
sub cfa_expression {
my $line = shift;
my @ret;
foreach my $token (split(/,\s*/,$line)) {
if ($token =~ /^%r/) {
push @ret,reg($token);
} elsif ($token =~ /((?:0x)?[0-9a-f]+)\((%r\w+)\)/) {
push @ret,reg("$2+$1");
} elsif ($token =~ /(\w+):(\-?(?:0x)?[0-9a-f]+)(U?)/i) {
my $i = 1*eval($2);
push @ret,$DW_OP_complex{$1}, ($3 ? uleb128($i) : sleb128($i));
} elsif (my $i = 1*eval($token) or $token eq "0") {
if ($token =~ /^\+/) {
push @ret,$DW_OP_complex{plus_uconst},uleb128($i);
} else {
push @ret,const($i);
}
} else {
push @ret,$DW_OP_simple{$token};
}
}
# Finally we return DW_CFA_def_cfa_expression, 15, followed by
# length of the expression and of course the expression itself.
return (15,scalar(@ret),@ret);
}
sub re {
my ($class, $line) = @_;
my $self = {};
my $ret;
if ($$line =~ s/^\s*\.cfi_(\w+)\s*//) {
bless $self,$class;
$ret = $self;
undef $self->{value};
my $dir = $1;
SWITCH: for ($dir) {
# What is $cfa_rsp? Effectively it's difference between %rsp
# value and current CFA, Canonical Frame Address, which is
# why it starts with -8. Recall that CFA is top of caller's
# stack...
/startproc/ && do { ($cfa_reg, $cfa_rsp) = ("%rsp", -8); last; };
/endproc/ && do { ($cfa_reg, $cfa_rsp) = ("%rsp", 0); last; };
/def_cfa_register/
&& do { $cfa_reg = $$line; last; };
/def_cfa_offset/
&& do { $cfa_rsp = -1*eval($$line) if ($cfa_reg eq "%rsp");
last;
};
/adjust_cfa_offset/
&& do { $cfa_rsp -= 1*eval($$line) if ($cfa_reg eq "%rsp");
last;
};
/def_cfa/ && do { if ($$line =~ /(%r\w+)\s*,\s*(.+)/) {
$cfa_reg = $1;
$cfa_rsp = -1*eval($2) if ($cfa_reg eq "%rsp");
}
last;
};
/push/ && do { $dir = undef;
$cfa_rsp -= 8;
if ($cfa_reg eq "%rsp") {
$self->{value} = ".cfi_adjust_cfa_offset\t8\n";
}
$self->{value} .= ".cfi_offset\t$$line,$cfa_rsp";
last;
};
/pop/ && do { $dir = undef;
$cfa_rsp += 8;
if ($cfa_reg eq "%rsp") {
$self->{value} = ".cfi_adjust_cfa_offset\t-8\n";
}
$self->{value} .= ".cfi_restore\t$$line";
last;
};
/cfa_expression/
&& do { $dir = undef;
$self->{value} = ".cfi_escape\t" .
join(",", map(sprintf("0x%02x", $_),
cfa_expression($$line)));
last;
};
}
$self->{value} = ".cfi_$dir\t$$line" if ($dir);
$$line = "";
}
return $ret;
}
sub out {
my $self = shift;
return ($elf ? $self->{value} : undef);
}
}
{ package directive; # pick up directives, which start with .
sub re {
my ($class, $line) = @_;
my $self = {};
my $ret;
my $dir;
# chain-call to cfi_directive
$ret = cfi_directive->re($line) and return $ret;
if ($$line =~ /^\s*(\.\w+)/) {
bless $self,$class;
$dir = $1;
$ret = $self;
undef $self->{value};
$$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
SWITCH: for ($dir) {
/\.global|\.globl|\.extern/
&& do { $globals{$$line} = $prefix . $$line;
$$line = $globals{$$line} if ($prefix);
last;
};
/\.type/ && do { my ($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";
$$line = join(",",unpack("C*",$1),0);
}
last;
};
/\.rva|\.long|\.quad|\.byte/
&& do { $$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 ($dir =~ /\.extern/) {
if ($flavour eq "elf") {
$self->{value} .= "\n.hidden $$line";
} else {
$self->{value} = "";
}
} elsif (!$elf && $dir =~ /\.type/) {
$self->{value} = "";
$self->{value} = ".def\t" . ($globals{$1} or $1) . ";\t" .
(defined($globals{$1})?".scl 2;":".scl 3;") .
"\t.type 32;\t.endef"
if ($win64 && $$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=".$1";
} elsif ($dir =~ /\.global|\.globl|\.extern/) {
if ($flavour eq "macosx") {
$self->{value} .= "\n.private_extern $$line";
} else {
$self->{value} .= "\n.hidden $$line";
}
} elsif ($dir =~ /\.hidden/) {
if ($flavour eq "macosx") { $self->{value} = ".private_extern\t$prefix$$line"; }
elsif ($flavour eq "mingw64") { $self->{value} = ""; }
} elsif ($dir =~ /\.comm/) {
$self->{value} = "$dir\t$prefix$$line";
$self->{value} =~ s|,([0-9]+),([0-9]+)$|",$1,".log($2)/log(2)|e if ($flavour eq "macosx");
}
$$line = "";
return $self;
}
# non-gas case or nasm/masm
SWITCH: for ($dir) {
/\.text/ && do { my $v=undef;
if ($nasm) {
$v="section .text code align=64\n";
} else {
$v="$current_segment\tENDS\n" if ($current_segment);
$current_segment = ".text\$";
$v.="$current_segment\tSEGMENT ";
$v.=$masm>=$masmref ? "ALIGN(256)" : "PAGE";
$v.=" 'CODE'";
}
$self->{value} = $v;
last;
};
/\.data/ && do { my $v=undef;
if ($nasm) {
$v="section .data data align=8\n";
} else {
$v="$current_segment\tENDS\n" if ($current_segment);
$current_segment = "_DATA";
$v.="$current_segment\tSEGMENT";
}
$self->{value} = $v;
last;
};
/\.section/ && do { my $v=undef;
$$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 ";
$v.=$masm>=$masmref ? "ALIGN(8)" : "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".$$line;
last;
};
/\.size/ && do { if (defined($current_function)) {
undef $self->{value};
if ($current_function->{abi} eq "svr4") {
$self->{value}="${decor}SEH_end_$current_function->{name}:";
$self->{value}.=":\n" if($masm);
}
$self->{value}.="$current_function->{name}\tENDP" if($masm && $current_function->{name});
undef $current_function;
}
last;
};
/\.align/ && do { my $max = ($masm && $masm>=$masmref) ? 256 : 4096;
$self->{value} = "ALIGN\t".($$line>$max?$max:$$line);
last;
};
/\.(value|long|rva|quad)/
&& do { my $sz = substr($1,0,1);
my @arr = split(/,\s*/,$$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*/,$$line);
map(s/(0b[0-1]+)/oct($1)/eig,@str);
map(s/0x([0-9a-f]+)/0$1h/ig,@str) if ($masm);
while ($#str>15) {
$self->{value}.="DB\t"
.join(",",@str[0..15])."\n";
foreach (0..15) { shift @str; }
}
$self->{value}.="DB\t"
.join(",",@str) if (@str);
last;
};
/\.comm/ && do { my @str=split(/,\s*/,$$line);
my $v=undef;
if ($nasm) {
$v.="common $prefix@str[0] @str[1]";
} else {
$v="$current_segment\tENDS\n" if ($current_segment);
$current_segment = "_DATA";
$v.="$current_segment\tSEGMENT\n";
$v.="COMM @str[0]:DWORD:".@str[1]/4;
}
$self->{value} = $v;
last;
};
}
$$line = "";
}
$ret;
}
sub out {
my $self = shift;
$self->{value};
}
}
# Upon initial x86_64 introduction SSE>2 extensions were not introduced
# yet. In order not to be bothered by tracing exact assembler versions,
# but at the same time to provide a bare security minimum of AES-NI, we
# hard-code some instructions. Extensions past AES-NI on the other hand
# are traced by examining assembler version in individual perlasm
# modules...
my %regrm = ( "%eax"=>0, "%ecx"=>1, "%edx"=>2, "%ebx"=>3,
"%esp"=>4, "%ebp"=>5, "%esi"=>6, "%edi"=>7 );
sub rex {
my $opcode=shift;
my ($dst,$src,$rex)=@_;
$rex|=0x04 if($dst>=8);
$rex|=0x01 if($src>=8);
push @$opcode,($rex|0x40) if ($rex);
}
my $movq = sub { # elderly gas can't handle inter-register movq
my $arg = shift;
my @opcode=(0x66);
if ($arg =~ /%xmm([0-9]+),\s*%r(\w+)/) {
my ($src,$dst)=($1,$2);
if ($dst !~ /[0-9]+/) { $dst = $regrm{"%e$dst"}; }
rex(\@opcode,$src,$dst,0x8);
push @opcode,0x0f,0x7e;
push @opcode,0xc0|(($src&7)<<3)|($dst&7); # ModR/M
@opcode;
} elsif ($arg =~ /%r(\w+),\s*%xmm([0-9]+)/) {
my ($src,$dst)=($2,$1);
if ($dst !~ /[0-9]+/) { $dst = $regrm{"%e$dst"}; }
rex(\@opcode,$src,$dst,0x8);
push @opcode,0x0f,0x6e;
push @opcode,0xc0|(($src&7)<<3)|($dst&7); # ModR/M
@opcode;
} else {
();
}
};
my $pextrd = sub {
if (shift =~ /\$([0-9]+),\s*%xmm([0-9]+),\s*(%\w+)/) {
my @opcode=(0x66);
my $imm=$1;
my $src=$2;
my $dst=$3;
if ($dst =~ /%r([0-9]+)d/) { $dst = $1; }
elsif ($dst =~ /%e/) { $dst = $regrm{$dst}; }
rex(\@opcode,$src,$dst);
push @opcode,0x0f,0x3a,0x16;
push @opcode,0xc0|(($src&7)<<3)|($dst&7); # ModR/M
push @opcode,$imm;
@opcode;
} else {
();
}
};
my $pinsrd = sub {
if (shift =~ /\$([0-9]+),\s*(%\w+),\s*%xmm([0-9]+)/) {
my @opcode=(0x66);
my $imm=$1;
my $src=$2;
my $dst=$3;
if ($src =~ /%r([0-9]+)/) { $src = $1; }
elsif ($src =~ /%e/) { $src = $regrm{$src}; }
rex(\@opcode,$dst,$src);
push @opcode,0x0f,0x3a,0x22;
push @opcode,0xc0|(($dst&7)<<3)|($src&7); # ModR/M
push @opcode,$imm;
@opcode;
} else {
();
}
};
my $pshufb = sub {
if (shift =~ /%xmm([0-9]+),\s*%xmm([0-9]+)/) {
my @opcode=(0x66);
rex(\@opcode,$2,$1);
push @opcode,0x0f,0x38,0x00;
push @opcode,0xc0|($1&7)|(($2&7)<<3); # ModR/M
@opcode;
} else {
();
}
};
my $palignr = sub {
if (shift =~ /\$([0-9]+),\s*%xmm([0-9]+),\s*%xmm([0-9]+)/) {
my @opcode=(0x66);
rex(\@opcode,$3,$2);
push @opcode,0x0f,0x3a,0x0f;
push @opcode,0xc0|($2&7)|(($3&7)<<3); # ModR/M
push @opcode,$1;
@opcode;
} else {
();
}
};
my $pclmulqdq = sub {
if (shift =~ /\$([x0-9a-f]+),\s*%xmm([0-9]+),\s*%xmm([0-9]+)/) {
my @opcode=(0x66);
rex(\@opcode,$3,$2);
push @opcode,0x0f,0x3a,0x44;
push @opcode,0xc0|($2&7)|(($3&7)<<3); # ModR/M
my $c=$1;
push @opcode,$c=~/^0/?oct($c):$c;
@opcode;
} else {
();
}
};
my $rdrand = sub {
if (shift =~ /%[er](\w+)/) {
my @opcode=();
my $dst=$1;
if ($dst !~ /[0-9]+/) { $dst = $regrm{"%e$dst"}; }
rex(\@opcode,0,$dst,8);
push @opcode,0x0f,0xc7,0xf0|($dst&7);
@opcode;
} else {
();
}
};
my $rdseed = sub {
if (shift =~ /%[er](\w+)/) {
my @opcode=();
my $dst=$1;
if ($dst !~ /[0-9]+/) { $dst = $regrm{"%e$dst"}; }
rex(\@opcode,0,$dst,8);
push @opcode,0x0f,0xc7,0xf8|($dst&7);
@opcode;
} else {
();
}
};
# Not all AVX-capable assemblers recognize AMD XOP extension. Since we
# are using only two instructions hand-code them in order to be excused
# from chasing assembler versions...
sub rxb {
my $opcode=shift;
my ($dst,$src1,$src2,$rxb)=@_;
$rxb|=0x7<<5;
$rxb&=~(0x04<<5) if($dst>=8);
$rxb&=~(0x01<<5) if($src1>=8);
$rxb&=~(0x02<<5) if($src2>=8);
push @$opcode,$rxb;
}
my $vprotd = sub {
if (shift =~ /\$([x0-9a-f]+),\s*%xmm([0-9]+),\s*%xmm([0-9]+)/) {
my @opcode=(0x8f);
rxb(\@opcode,$3,$2,-1,0x08);
push @opcode,0x78,0xc2;
push @opcode,0xc0|($2&7)|(($3&7)<<3); # ModR/M
my $c=$1;
push @opcode,$c=~/^0/?oct($c):$c;
@opcode;
} else {
();
}
};
my $vprotq = sub {
if (shift =~ /\$([x0-9a-f]+),\s*%xmm([0-9]+),\s*%xmm([0-9]+)/) {
my @opcode=(0x8f);
rxb(\@opcode,$3,$2,-1,0x08);
push @opcode,0x78,0xc3;
push @opcode,0xc0|($2&7)|(($3&7)<<3); # ModR/M
my $c=$1;
push @opcode,$c=~/^0/?oct($c):$c;
@opcode;
} else {
();
}
};
# Intel Control-flow Enforcement Technology extension. All functions and
# indirect branch targets will have to start with this instruction...
my $endbranch = sub {
(0xf3,0x0f,0x1e,0xfa);
};
########################################################################
{
my $comment = "#";
$comment = ";" if ($masm || $nasm);
print <<___;
$comment This file is generated from a similarly-named Perl script in the BoringSSL
$comment source tree. Do not edit by hand.
___
}
if ($nasm) {
print <<___;
default rel
%define XMMWORD
%define YMMWORD
%define ZMMWORD
%ifdef BORINGSSL_PREFIX
%include "boringssl_prefix_symbols_nasm.inc"
%endif
___
} elsif ($masm) {
print <<___;
OPTION DOTNAME
___
}
if ($gas) {
print <<___;
#if defined(__has_feature)
#if __has_feature(memory_sanitizer) && !defined(OPENSSL_NO_ASM)
#define OPENSSL_NO_ASM
#endif
#endif
#if defined(__x86_64__) && !defined(OPENSSL_NO_ASM)
#if defined(BORINGSSL_PREFIX)
#include <boringssl_prefix_symbols_asm.h>
#endif
___
}
while(defined(my $line=<>)) {
$line =~ s|\R$||; # Better chomp
$line =~ s|[#!].*$||; # get rid of asm-style comments...
$line =~ s|/\*.*\*/||; # ... and C-style comments...
$line =~ s|^\s+||; # ... and skip white spaces in beginning
$line =~ s|\s+$||; # ... and at the end
if (my $label=label->re(\$line)) { print $label->out(); }
if (my $directive=directive->re(\$line)) {
printf "%s",$directive->out();
} elsif (my $opcode=opcode->re(\$line)) {
my $asm = eval("\$".$opcode->mnemonic());
if ((ref($asm) eq 'CODE') && scalar(my @bytes=&$asm($line))) {
print $gas?".byte\t":"DB\t",join(',',@bytes),"\n";
next;
}
my @args;
ARGUMENT: while (1) {
my $arg;
($arg=register->re(\$line, $opcode))||
($arg=const->re(\$line)) ||
($arg=ea->re(\$line, $opcode)) ||
($arg=expr->re(\$line, $opcode)) ||
last ARGUMENT;
push @args,$arg;
last ARGUMENT if ($line !~ /^,/);
$line =~ s/^,\s*//;
} # ARGUMENT:
if ($#args>=0) {
my $insn;
my $sz=$opcode->size();
if ($gas) {
$insn = $opcode->out($#args>=1?$args[$#args]->size():$sz);
@args = map($_->out($sz),@args);
printf "\t%s\t%s",$insn,join(",",@args);
} else {
$insn = $opcode->out();
foreach (@args) {
my $arg = $_->out();
# $insn.=$sz compensates for movq, pinsrw, ...
if ($arg =~ /^xmm[0-9]+$/) { $insn.=$sz; $sz="x" if(!$sz); last; }
if ($arg =~ /^ymm[0-9]+$/) { $insn.=$sz; $sz="y" if(!$sz); last; }
if ($arg =~ /^zmm[0-9]+$/) { $insn.=$sz; $sz="z" if(!$sz); last; }
if ($arg =~ /^mm[0-9]+$/) { $insn.=$sz; $sz="q" if(!$sz); last; }
}
@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);
print "#endif\n" if ($gas);
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 accommodated 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" existence,
# 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
# magic_epilogue:
# 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;
# ULONG64 rip = context->Rip;
#
# if (rip >= magic_point)
# { rsp = (ULONG64 *)context->Rsp;
# if (rip < magic_epilogue)
# { rsp = (ULONG64 *)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 function_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...
#
# SE handlers are also involved in unwinding stack when executable is
# profiled or debugged. Profiling implies additional limitations that
# are too subtle to discuss here. For now it's sufficient to say that
# in order to simplify handlers one should either a) offload original
# %rsp to stack (like discussed above); or b) if you have a register to
# spare for frame pointer, choose volatile one.
#
# (*) Note that we're talking about run-time, not debug-time. Lack of
# unwind information makes debugging hard on both Windows and
# Unix. "Unlike" refers to the fact that on Unix signal handler
# will always be invoked, core dumped and appropriate exit code
# returned to parent (for user notification).
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