您想要做的是转换表单的所有指令：
mov (%rcx,%rax,8),%rax
Into:
mov (%rcx,%rax,8),%r11
mov %r11,%rax
通过修改编译器生成的汇编程序源代码，可以更轻松地完成此操作。下面是一个perl脚本将通过读取和修改来完成所有必要的转换.s file.
只需更改构建即可生成.s文件而不是.o文件，应用脚本，然后生成.o与任一as or gcc
这是实际的脚本。我已经按照下面评论中的构建过程在我自己的一些来源上对其进行了测试。
该脚本具有以下特点：
- 扫描并定位所有函数定义
- 标识给定函数中使用的所有寄存器
- 找到函数的所有返回点
- 根据函数的寄存器使用情况选择要使用的临时寄存器（即它将使用一个临时寄存器not已被该函数使用）
- 用两个指令序列替换所有“麻烦”的指令
- 尝试使用未使用的临时寄存器（例如
%r11或未使用的参数寄存器）在尝试使用之前callee保存的寄存器
- 如果所选寄存器是callee已保存，将添加
push函数序言和pop发挥作用[多个]ret声明
- 维护所有分析和转换的日志，并将其作为注释附加到输出中
.s file
#!/usr/bin/perl
# pebsfix/pebsfixup -- fix assembler source for PEBS usage
#
# command line options:
# "-a" -- use only full 64 bit targets
# "-l" -- do _not_ use lea
# "-D[diff-file]" -- show differences (default output: "./DIFF")
# "-n10" -- do _not_ use register %r10 for temporary (default is use it)
# "-o" -- overwrite input files (can be multiple)
# "-O<outfile>" -- output file (only one .s input allowed)
# "-q" -- suppress warnings
# "-T[lvl]" -- debug trace
#
# "-o" and "-O" are mutually exclusive
#
# command line script test options:
# "-N[TPA]" -- disable temp register types [for testing]
# "-P" -- force push/pop on all functions
#
# command line arguments:
# 1-- list of .s files to process [or directory to search]
# for a given file "foo.s", output is to "foo.TMP"
# if (-o is given, "foo.TMP" is renamed to "foo.s")
#
# suggested usage:
# change build to produce .s files
# FROM:
# cc [options] -c foo.c
# TO:
# cc [options] -c -S foo.c
# pebsfixup -o foo.s
# cc -c foo.s
#
# suggested compiler options:
# [probably only really needed if push/pop required. use -NP to verify]
# (1) use either of
# -O2 -fno-optimize-sibling-calls
# -O1
# (2) use -mno-omit-leaf-frame-pointer
# (3) use -mno-red-zone [probably not required in any case]
#
# NOTES:
# (1) red zones are only really useful for leaf functions (i.e. if fncA calls
# fncB, fncA's red zone would be clobbered)
# (2) pushing onto the stack isn't a problem if there is a formal stack frame
# (3) the push is okay if the function has no more than six arguments (i.e.
# does _not_ use positive offsets from %rsp to access them)
#pragma pgmlns
use strict qw(vars subs);
our $pgmtail;
our $opt_a;
our $opt_T;
our $opt_D;
our $opt_l;
our $opt_n10;
our $opt_N;
our $opt_P;
our $opt_q;
our $opt_o;
our $opt_O;
our $opt_s;
our @reguse;
our %reguse_tobase;
our %reguse_isbase;
our $regusergx;
our @regtmplist;
our %regtmp_type;
our $diff;
our $sepflg;
our $fatal;
our @cmtprt;
master(@ARGV);
exit(0);
# master -- master control
sub master
{
my(@argv) = @_;
my($xfsrc);
my($file,@files);
my($bf);
$pgmtail = "pebsfixup";
optget(\@argv);
# define all known/usable registers
regusejoin();
# define all registers that we may use as a temporary
regtmpall();
if (defined($opt_D)) {
unlink($opt_D);
}
# show usage
if (@argv <= 0) {
$file = $0;
open($xfsrc,"<$file") ||
sysfault("$pgmtail: unable to open '%s' -- $!\n",$file);
while ($bf = <$xfsrc>) {
chomp($bf);
next if ($bf =~ /^#!/);
last unless ($bf =~ s/^#//);
$bf =~ s/^# ?//;
print($bf,"\n");
}
close($xfsrc);
exit(1);
}
foreach $file (@argv) {
if (-d $file) {
dodir(\@files,$file);
}
else {
push(@files,$file);
}
}
if (defined($opt_O)) {
sysfault("$pgmtail: -O may have only one input file\n")
if (@files != 1);
sysfault("$pgmtail: -O and -o are mutually exclusive\n")
if ($opt_o);
}
foreach $file (@files) {
dofile($file);
}
if (defined($opt_D)) {
exec("less",$opt_D);
}
}
# dodir -- process directory
sub dodir
{
my($files,$dir) = @_;
my($file,@files);
@files = (`find $dir -type f -name '*.s'`);
foreach $file (@files) {
chomp($file);
push(@$files,$file);
}
}
# dofile -- process file
sub dofile
{
my($file) = @_;
my($ofile);
my($xfsrc);
my($xfdst);
my($bf,$lno,$outoff);
my($fixoff);
my($lhs,$rhs);
my($xop,$arg);
my($ix);
my($sym,$val,$typ);
my(%sym_type);
my($fnc,$fnx,%fnx_lookup,@fnxlist);
my($retlist);
my($uselook,@uselist,%avail);
my($fixreg,$fixrtyp);
my($sixlist);
my($fix,$fixlist);
my($fixtot);
my(@fix);
my(@outlist);
my($relaxflg);
my($cmtchr);
undef($fatal);
undef(@cmtprt);
msgprt("\n")
if ($sepflg);
$sepflg = 1;
msgprt("$pgmtail: processing %s ...\n",$file);
$cmtchr = "#";
cmtprt("%s\n","-" x 78);
cmtprt("FILE: %s\n",$file);
# get the output file
$ofile = $file;
sysfault("$pgmtail: bad suffix -- file='%s'\n",$file)
unless ($ofile =~ s/[.]s$//);
$ofile .= ".TMP";
# use explicit output file
if (defined($opt_O)) {
$ofile = $opt_O;
sysfault("$pgmtail: output file may not be input file -- use -o instead\n")
if ($ofile eq $file);
}
open($xfsrc,"<$file") ||
sysfault("$pgmtail: unable to open '%s' -- $!\n",$file);
$lno = 0;
while ($bf = <$xfsrc>) {
chomp($bf);
$bf =~ s/\s+$//;
$outoff = $lno;
++$lno;
push(@outlist,$bf);
# clang adds comments
$ix = index($bf,"#");
if ($ix >= 0) {
$bf = substr($bf,0,$ix);
$bf =~ s/\s+$//;
}
# look for ".type blah, @function"
# NOTE: this always comes before the actual label line [we hope ;-)]
if ($bf =~ /^\s+[.]type\s+([^,]+),\s*(\S+)/) {
($sym,$val) = ($1,$2);
$val =~ s/^\@//;
$sym_type{$sym} = $val;
cmtprt("\n");
cmtprt("TYPE: %s --> %s\n",$sym,$val);
next;
}
# look for "label:"
if ($bf =~ /^([a-z_A-Z][a-z_A-Z0-9]*):$/) {
$sym = $1;
next if ($sym_type{$sym} ne "function");
$fnc = $sym;
cmtprt("FUNCTION: %s\n",$fnc);
$fnx = {};
$fnx_lookup{$sym} = $fnx;
push(@fnxlist,$fnx);
$fnx->{fnx_fnc} = $fnc;
$fnx->{fnx_outoff} = $outoff;
$uselook = {};
$fnx->{fnx_used} = $uselook;
$retlist = [];
$fnx->{fnx_retlist} = $retlist;
$fixlist = [];
$fnx->{fnx_fixlist} = $fixlist;
$sixlist = [];
$fnx->{fnx_sixlist} = $sixlist;
next;
}
# remember all registers used by function:
while ($bf =~ /($regusergx)/gpo) {
$sym = ${^MATCH};
$val = $reguse_tobase{$sym};
dbgprt(3,"dofile: REGUSE sym='%s' val='%s'\n",$sym,$val);
$uselook->{$sym} += 1;
$uselook->{$val} += 1
if ($val ne $sym);
}
# handle returns
if ($bf =~ /^\s+ret/) {
push(@$retlist,$outoff);
next;
}
if ($bf =~ /^\s+rep[a-z]*\s+ret/) {
push(@$retlist,$outoff);
next;
}
# split up "movq 16(%rax),%rax" ...
$ix = rindex($bf,",");
next if ($ix < 0);
# ... into "movq 16(%rax)"
$lhs = substr($bf,0,$ix);
$lhs =~ s/\s+$//;
# check for "movq 16(%rsp)" -- this means that the function has/uses
# more than six arguments (i.e. we may _not_ push/pop because it
# wreaks havoc with positive offsets)
# FIXME/CAE -- we'd have to adjust them by 8 which we don't do
(undef,$rhs) = split(" ",$lhs);
if ($rhs =~ /^(\d+)[(]%rsp[)]$/) {
push(@$sixlist,$outoff);
cmtprt("SIXARG: %s (line %d)\n",$rhs,$lno);
}
# ... and "%rax"
$rhs = substr($bf,$ix + 1);
$rhs =~ s/^\s+//;
# target must be a [simple] register [or source scan will blow up]
# (e.g. we actually had "cmp %ebp,(%rax,%r14)")
next if ($rhs =~ /[)]/);
# ensure we have the "%" prefix
next unless ($rhs =~ /^%/);
# we only want the full 64 bit reg as target
# (e.g. "mov (%rbx),%al" doesn't count)
$val = $reguse_tobase{$rhs};
if ($opt_a) {
next if ($val ne $rhs);
}
else {
next unless (defined($val));
}
# source operand must contain target [base] register
next unless ($lhs =~ /$val/);
###cmtprt("1: %s,%s\n",$lhs,$rhs);
# source operand must be of the "right" type
# FIXME/CAE -- we may need to revise this
next unless ($lhs =~ /[(]/);
cmtprt("NEEDFIX: %s,%s (line %d)\n",$lhs,$rhs,$lno);
# remember the place we need to fix for later
$fix = {};
push(@$fixlist,$fix);
$fix->{fix_outoff} = $outoff;
$fix->{fix_lhs} = $lhs;
$fix->{fix_rhs} = $rhs;
}
close($xfsrc);
# get total number of fixups
foreach $fnx (@fnxlist) {
$fixlist = $fnx->{fnx_fixlist};
$fixtot += @$fixlist;
}
msgprt("$pgmtail: needs %d fixups\n",$fixtot)
if ($fixtot > 0);
# fix each function
foreach $fnx (@fnxlist) {
cmtprt("\n");
cmtprt("FNC: %s\n",$fnx->{fnx_fnc});
$fixlist = $fnx->{fnx_fixlist};
# get the fixup register
($fixreg,$fixrtyp) = regtmploc($fnx,$fixlist);
# show number of return points
{
$retlist = $fnx->{fnx_retlist};
cmtprt(" RET: %d\n",scalar(@$retlist));
last if (@$retlist >= 1);
# NOTE: we display this warning because we may not be able to
# handle all situations
$relaxflg = (@$fixlist <= 0) || ($fixrtyp ne "P");
last if ($relaxflg && $opt_q);
errprt("$pgmtail: in file '%s'\n",$file);
errprt("$pgmtail: function '%s' has no return points\n",
$fnx->{fnx_fnc});
errprt("$pgmtail: suggest recompile with correct options\n");
if (@$fixlist <= 0) {
errprt("$pgmtail: working around because function needs no fixups\n");
last;
}
if ($fixrtyp ne "P") {
errprt("$pgmtail: working around because fixup reg does not need to be saved\n");
last;
}
}
# show stats on register usage in function
$uselook = $fnx->{fnx_used};
@uselist = sort(keys(%$uselook));
cmtprt(" USED:\n");
%avail = %reguse_isbase;
foreach $sym (@uselist) {
$val = $uselook->{$sym};
$typ = $regtmp_type{$sym};
$typ = sprintf(" (TYPE: %s)",$typ)
if (defined($typ));
cmtprt(" %s used %d%s\n",$sym,$val,$typ);
$val = $reguse_tobase{$sym};
delete($avail{$val});
}
# show function's available [unused] registers
@uselist = keys(%avail);
@uselist = sort(regusesort @uselist);
if (@uselist > 0) {
cmtprt(" AVAIL:\n");
foreach $sym (@uselist) {
$typ = $regtmp_type{$sym};
$typ = sprintf(" (TYPE: %s)",$typ)
if (defined($typ));
cmtprt(" %s%s\n",$sym,$typ);
}
}
# skip over any functions that don't need fixing _and_ have a temp
# register
if (@$fixlist <= 0 && (! $opt_P)) {
next if (defined($fixreg));
}
msgprt("$pgmtail: function %s\n",$fnx->{fnx_fnc});
# skip function because we don't have a fixup register but report it
# here
unless (defined($fixreg)) {
$bf = (@$fixlist > 0) ? "FATAL" : "can be ignored -- no fixups needed";
msgprt("$pgmtail: FIXNOREG (%s)\n",$bf);
cmtprt(" FIXNOREG (%s)\n",$bf);
next;
}
msgprt("$pgmtail: FIXREG --> %s (TYPE: %s)\n",$fixreg,$fixrtyp);
cmtprt(" FIXREG --> %s (TYPE: %s)\n",$fixreg,$fixrtyp);
foreach $fix (@$fixlist) {
$outoff = $fix->{fix_outoff};
undef(@fix);
cmtprt(" FIXOLD %s\n",$outlist[$outoff]);
# original
if ($opt_l) {
$bf = sprintf("%s,%s",$fix->{fix_lhs},$fixreg);
push(@fix,$bf);
$bf = sprintf("\tmov\t%s,%s",$fixreg,$fix->{fix_rhs});
push(@fix,$bf);
}
# use lea
else {
($xop,$arg) = split(" ",$fix->{fix_lhs});
$bf = sprintf("\tlea\t\t%s,%s",$arg,$fixreg);
push(@fix,$bf);
$bf = sprintf("\t%s\t(%s),%s",$xop,$fixreg,$fix->{fix_rhs});
push(@fix,$bf);
}
foreach $bf (@fix) {
cmtprt(" FIXNEW %s\n",$bf);
}
$outlist[$outoff] = [@fix];
}
unless ($opt_P) {
next if ($fixrtyp ne "P");
}
# fix the function prolog
$outoff = $fnx->{fnx_outoff};
$lhs = $outlist[$outoff];
$rhs = sprintf("\tpush\t%s",$fixreg);
$bf = [$lhs,$rhs,""];
$outlist[$outoff] = $bf;
# fix the function return points
$retlist = $fnx->{fnx_retlist};
foreach $outoff (@$retlist) {
$rhs = $outlist[$outoff];
$lhs = sprintf("\tpop\t%s",$fixreg);
$bf = ["",$lhs,$rhs];
$outlist[$outoff] = $bf;
}
}
open($xfdst,">$ofile") ||
sysfault("$pgmtail: unable to open '%s' -- $!\n",$ofile);
# output all the assembler text
foreach $bf (@outlist) {
# ordinary line
unless (ref($bf)) {
print($xfdst $bf,"\n");
next;
}
# apply a fixup
foreach $rhs (@$bf) {
print($xfdst $rhs,"\n");
}
}
# output all our reasoning as comments at the bottom
foreach $bf (@cmtprt) {
if ($bf eq "") {
print($xfdst $cmtchr,$bf,"\n");
}
else {
print($xfdst $cmtchr," ",$bf,"\n");
}
}
close($xfdst);
# get difference
if (defined($opt_D)) {
system("diff -u $file $ofile >> $opt_D");
}
# install fixed/modified file
{
last unless ($opt_o || defined($opt_O));
last if ($fatal);
msgprt("$pgmtail: installing ...\n");
rename($ofile,$file);
}
}
# regtmpall -- define all temporary register candidates
sub regtmpall
{
dbgprt(1,"regtmpall: ENTER\n");
regtmpdef("%r11","T");
# NOTES:
# (1) see notes on %r10 in ABI at bottom -- should we use it?
# (2) a web search on "shared chain" and "x86" only produces 28 results
# (3) some gcc code uses it as an ordinary register
# (4) so, use it unless told not to
regtmpdef("%r10","T")
unless ($opt_n10);
# argument registers (a6-a1)
regtmpdef("%r9","A6");
regtmpdef("%r8","A5");
regtmpdef("%rcx","A4");
regtmpdef("%rdx","A3");
regtmpdef("%rsi","A2");
regtmpdef("%rdi","A1");
# callee preserved registers
regtmpdef("%r15","P");
regtmpdef("%r14","P");
regtmpdef("%r13","P");
regtmpdef("%r12","P");
dbgprt(1,"regtmpall: EXIT\n");
}
# regtmpdef -- define usable temp registers
sub regtmpdef
{
my($sym,$typ) = @_;
dbgprt(1,"regtmpdef: SYM sym='%s' typ='%s'\n",$sym,$typ);
push(@regtmplist,$sym);
$regtmp_type{$sym} = $typ;
}
# regtmploc -- locate temp register to fix problem
sub regtmploc
{
my($fnx,$fixlist) = @_;
my($sixlist);
my($uselook);
my($regrhs);
my($fixcnt);
my($coretyp);
my($reglhs,$regtyp);
dbgprt(2,"regtmploc: ENTER fnx_fnc='%s'\n",$fnx->{fnx_fnc});
$sixlist = $fnx->{fnx_sixlist};
$fixcnt = @$fixlist;
$fixcnt = 1
if ($opt_P);
$uselook = $fnx->{fnx_used};
foreach $regrhs (@regtmplist) {
dbgprt(2,"regtmploc: TRYREG regrhs='%s' uselook=%d\n",
$regrhs,$uselook->{$regrhs});
unless ($uselook->{$regrhs}) {
$regtyp = $regtmp_type{$regrhs};
$coretyp = $regtyp;
$coretyp =~ s/\d+$//;
# function uses stack arguments -- we can't push/pop
if (($coretyp eq "P") && (@$sixlist > 0)) {
dbgprt(2,"regtmploc: SIXREJ\n");
next;
}
if (defined($opt_N)) {
dbgprt(2,"regtmploc: TRYREJ opt_N='%s' regtyp='%s'\n",
$opt_N,$regtyp);
next if ($opt_N =~ /$coretyp/);
}
$reglhs = $regrhs;
last;
}
}
{
last if (defined($reglhs));
errprt("regtmploc: unable to locate usable fixup register for function '%s'\n",
$fnx->{fnx_fnc});
last if ($fixcnt <= 0);
$fatal = 1;
}
dbgprt(2,"regtmploc: EXIT reglhs='%s' regtyp='%s'\n",$reglhs,$regtyp);
($reglhs,$regtyp);
}
# regusejoin -- get regex for all registers
sub regusejoin
{
my($reg);
dbgprt(1,"regusejoin: ENTER\n");
# rax
foreach $reg (qw(a b c d)) {
regusedef($reg,"r_x","e_x","_l","_h");
}
# rdi/rsi
foreach $reg (qw(d s)) {
regusedef($reg,"r_i","e_i","_i","_il");
}
# rsp/rbp
foreach $reg (qw(b s)) {
regusedef($reg,"r_p","e_p");
}
foreach $reg (8,9,10,11,12,13,14,15) {
regusedef($reg,"r_","r_d","r_w","r_b");
}
$regusergx = join("|",reverse(sort(@reguse)));
dbgprt(1,"regusejoin: EXIT regusergx='%s'\n",$regusergx);
}
# regusedef -- define all registers
sub regusedef
{
my(@argv) = @_;
my($mid);
my($pat);
my($base);
$mid = shift(@argv);
dbgprt(1,"regusedef: ENTER mid='%s'\n",$mid);
foreach $pat (@argv) {
$pat = "%" . $pat;
$pat =~ s/_/$mid/;
$base //= $pat;
dbgprt(1,"regusedef: PAT pat='%s' base='%s'\n",$pat,$base);
push(@reguse,$pat);
$reguse_tobase{$pat} = $base;
}
$reguse_isbase{$base} = 1;
dbgprt(1,"regusedef: EXIT\n");
}
# regusesort -- sort base register names
sub regusesort
{
my($symlhs,$numlhs);
my($symrhs,$numrhs);
my($cmpflg);
{
($symlhs,$numlhs) = _regusesort($a);
($symrhs,$numrhs) = _regusesort($b);
$cmpflg = $symlhs cmp $symrhs;
last if ($cmpflg);
$cmpflg = $numlhs <=> $numrhs;
}
$cmpflg;
}
# _regusesort -- split up base register name
sub _regusesort
{
my($sym) = @_;
my($num);
if ($sym =~ s/(\d+)$//) {
$num = $1;
$num += 0;
$sym =~ s/[^%]/z/g;
}
($sym,$num);
}
# optget -- get options
sub optget
{
my($argv) = @_;
my($bf);
my($sym,$val);
my($dft,%dft);
foreach $sym (qw(a l n10 P q o s T)) {
$dft{$sym} = 1;
}
$dft{"N"} = "T";
$dft{"D"} = "DIFF";
while (1) {
$bf = $argv->[0];
$sym = $bf;
last unless ($sym =~ s/^-//);
last if ($sym eq "-");
shift(@$argv);
{
if ($sym =~ /([^=]+)=(.+)$/) {
($sym,$val) = ($1,$2);
last;
}
if ($sym =~ /^(.)(.+)$/) {
($sym,$val) = ($1,$2);
last;
}
undef($val);
}
$dft = $dft{$sym};
sysfault("$pgmtail: unknown option -- '%s'\n",$bf)
unless (defined($dft));
$val //= $dft;
${"opt_" . $sym} = $val;
}
}
# cmtprt -- transformation comments
sub cmtprt
{
$_ = shift(@_);
$_ = sprintf($_,@_);
chomp($_);
push(@cmtprt,$_);
}
# msgprt -- progress output
sub msgprt
{
printf(STDERR @_);
}
# errprt -- show errors
sub errprt
{
cmtprt(@_);
printf(STDERR @_);
}
# sysfault -- abort on error
sub sysfault
{
printf(STDERR @_);
exit(1);
}
# dbgprt -- debug print
sub dbgprt
{
$_ = shift(@_);
goto &_dbgprt
if ($opt_T >= $_);
}
# _dbgprt -- debug print
sub _dbgprt
{
printf(STDERR @_);
}
UPDATE:
我更新了脚本以修复错误、添加更多检查和更多选项。Note:我必须删除底部的 ABI 以适应 30,000 的限制。
否则，奇怪的结果会出现在带括号的其他命令上cmpl %ebp, (%rax,%r14)分裂成lhs='cmpl %ebp, (%rax' and rhs='%r14)'这又导致/$rhs/失败。
是的，那是一个错误。固定的。
Your $rhs =~ /%[er](.x|\d+)/与字节或字加载不匹配di, or ax。但这不太可能。哦，我也觉得不匹配rdi / rsi。所以你不需要 r10d 中的尾随 d
固定的。查找所有变体。
哇，我认为这样的事情必须在编译时发生，而事后才这样做会太混乱。
无耻插件：谢谢你的“哇！”。perl非常适合像这样混乱的工作。我以前写过这样的汇编器“注入”脚本。 （例如）回到过去[在编译器支持之前]添加分析调用。
您可以将 %r10 标记为另一个调用保留寄存器。
经过几次网络搜索后，我只找到了大约 84 个匹配项"static chain" x86。唯一相关的是 x86 ABI。而且，除了作为脚注提及之外，它没有提供任何解释。另外，一些gcc代码使用r10 without任何另存为callee登记。所以，我现在默认使用该程序r10（如果需要，可以使用命令行选项禁用它）。
如果函数已经使用了所有寄存器会发生什么？
If it's truly全部，那么我们就不走运了。该脚本将检测并报告此情况，如果找不到备用寄存器，则会抑制修复。
And, it will通过注入使用“被调用者必须保留”寄存器push作为函数的第一个实例和相应的pop就在之前retinst [可以有多个]。可以通过一个选项禁用此功能。
你不能只是推/弹出，因为这会踩到红色区域
不，确实如此not。出于以下几个原因：
(1) 几乎作为旁注：红色区域仅在叶函数中有用。否则，如果fncA calls fncB，仅仅这样做的行为fncA会踩到自己的红色区域。请参阅脚本顶部注释块中的编译选项。
(2) 更重要的是，由于push/pop被注入。这push occurs before任何其他实例。这pop occurs after任何其他实例[就在ret].
红色区域仍然在那里——完好无损。它只是从原本的位置偏移了 -8。所有红色区域活动都被保留，因为这些insts使用negative偏移量%rsp
This is 不同的 than a push/pop在内联 asm 块内完成。通常的情况是红色区域代码正在执行（例如）mov $23,-4(%rsp)。随后出现一个内联汇编块，它执行以下操作push/pop would踩在那上面。
一些函数可以显示这一点：
# function_original -- original function before pebsfixup
# RETURNS: 23
function_original:
mov $23,-4(%rsp) # red zone code generated by compiler
...
mov -4(%rsp),%rax # will still have $23
ret
# function_pebsfixup -- pebsfixup modified
# RETURNS: 23
function_pebsfixup:
push %r12 # pebsfixup injected
mov $23,-4(%rsp) # red zone code generated by compiler
...
mov -4(%rsp),%rax # will still have $23
pop %r12 # pebsfixup injected
ret
# function_inline -- function with inline asm block and red zone
# RETURNS: unknown value
function_inline:
mov $23,-4(%rsp) # red zone code generated by compiler
# inline asm block -- steps on red zone
push %rdx
push %rcx
...
pop %rcx
pop %rdx
...
mov -4(%rsp),%rax # now -4(%rsp) no longer has $23
ret
哪里的push/pop does给我们带来麻烦的是如果该函数使用more超过 6 个参数（即 args 7+ 在堆栈上）。访问这些参数使用positive偏移量%rsp:
mov 32(%rsp),%rax
用我们的“绝招”push，偏移将不正确。正确的偏移量现在应该高 8：
mov 40(%rsp),%rax
该脚本将detect这并抱怨。但是，它[尚未]调整正偏移量，因为这种情况的概率很低。可能还需要大约五行代码才能解决这个问题。暂时踢球...
