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perlasm/x86_64-xlate.pl: recognize DWARF CFI directives.

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(Imports upstream's a3b5684fc1d4f3aabdf68dcf6c577f6dd24d2b2d.)

CFI directives annotate instructions that are significant for stack
unwinding procedure. In addition to directives recognized by GNU
assembler this module implements three synthetic ones:

- .cfi_push annotates push instructions in prologue and translates to
  .cfi_adjust_cfa_offset (if needed) and .cfi_offset;
- .cfi_pop annotates pop instructions in epilogue and translates to
  .cfi_adjust_cfs_offset (if needed) and .cfi_restore;
- .cfi_cfa_expression encodes DW_CFA_def_cfa_expression and passes it
  to .cfi_escape as byte vector;

CFA expression 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, Canonical Frame
Address, is reference to top of caller's stack, and on x86_64 call to
subroutine pushes 8-byte return address.

Change-Id: Ic675bf52b5405000be34e9da31c9cf1660f4b491
Reviewed-on: https://boringssl-review.googlesource.com/13765
Commit-Queue: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: David Benjamin <davidben@google.com>
This commit is contained in:
Adam Langley 2017-02-09 11:29:16 -08:00 committed by CQ bot account: commit-bot@chromium.org
parent 16b1b1d4d1
commit 9be3238e18
1 changed files with 237 additions and 0 deletions
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237
crypto/perlasm/x86_64-xlate.pl
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@ -460,6 +460,240 @@ my %globals;
}
}
}
{ 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 avaiable 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 significat 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 =~ /(\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) = @_;
@ -467,6 +701,9 @@ my %globals;
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;