将目标地址保持在寄存器中,直到指令退出

mov    0x18(%rdi),%rdi

mov    (%rcx,%rax,8),%rax

您想要做的是转换表单的所有说明：

mov    (%rcx,%rax

成：

mov    (%rcx,%r11
mov    %r11,%rax

这可以通过修改编译器生成的汇编器源来更容易地完成.下面是一个Perl脚本,它将通过读取和修改.s文件来完成所有必要的转换.

只需更改生成.s文件而不是.o文件,应用脚本,然后使用as或gcc生成.o

这是实际的脚本.我已经在几个我自己的来源测试了,按照下面的评论中的构建过程.

该脚本具有以下功能：

>扫描并定位所有函数定义
>标识给定功能中使用的所有寄存器
>定位函数的所有返回点
>根据功能的寄存器使用情况选择要使用的临时寄存器(即将使用尚未由功能使用的临时寄存器)
>用两个指令序列代替所有“麻烦”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),然后尝试使用被调用方保存的寄存器
>如果选择的注册表被保留,则会添加push到函数prolog并弹出功能[multiple] ret语句
>维护所有分析和转换的日志,并将其作为注释追加到输出.s文件

#!/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,$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",$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,$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 ($lhs =~ /[(]/);
        cmtprt("NEEDFIX: %s,%s (line %d)\n",$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",$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($typ));
                cmtprt("    %s%s\n",$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,$fixrtyp);
        cmtprt("  FIXREG --> %s (TYPE: %s)\n",$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);
                $bf = sprintf("\tmov\t%s,$fix->{fix_rhs});
                push(@fix,$bf);
            }

            # use lea
            else {
                ($xop,$arg) = split(" ",$fix->{fix_lhs});
                $bf = sprintf("\tlea\t\t%s,$arg,$bf);
                $bf = sprintf("\t%s\t(%s),$xop,$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,""];
        $outlist[$outoff] = $bf;

        # fix the function return points
        $retlist = $fnx->{fnx_retlist};
        foreach $outoff (@$retlist) {
            $rhs = $outlist[$outoff];
            $lhs = sprintf("\tpop\t%s",$fixreg);
            $bf = ["",$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," ","\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",$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,$2);
                last;
            }

            if ($sym =~ /^(.)(.+)$/) {
                ($sym,$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 @_);
}

更新：

我已经更新了脚本来修复错误,添加更多的检查和更多的选项.注意：我不得不删除ABI在底部以适应30,000限制.

Otherwise weird results appear on other commands with parentheses for example cmpl %ebp,%r14) splits into lhs='cmpl %ebp,(%rax' and rhs='%r14)' which in turn causes /$rhs/ to fail.

是的,那是一个bug.固定.

Your $rhs =~ /%[er](.x|\d+)/ doesn’t match byte or word loads to di,or ax. That’s unlikely,though. Oh,also,I think it fails to match rdi / rsi. so you don’t need the trailing d in r10d

固定.查找所有变体.

Wow,I assumed something like this would have to happen at compile time,and that doing it after the fact would be too messy.

无耻的插件：感谢“哇！”. perl对于像这样的凌乱的工作是非常好的.我以前写过这样的汇编器“注入”脚本. (例如)返回到[在编译器支持之前]添加分析调用的那一天.

You Could mark %r10 as another call-preserved register.

经过几次网页搜索,我只能在“静态链”x86上找到大约84场比赛.唯一的一个相关性是x86 ABI.而且,它不提供任何解释,除了提及它作为脚注.另外,一些gcc代码使用r10,没有任何保存作为被调用者注册.所以,我现在默认程序使用r10(如果需要,使用命令行选项来禁用它).

What happens if a function already uses all the registers?

如果真的是这样,那我们就不幸了.该脚本将检测并报告,并且如果找不到备用寄存器,则禁止fixup.

并且,它将使用“被调用者必须保留”注册,通过注入一个推送作为第一功能和相应的弹出就在ret inst [可以有多个]之前.这可以通过选项禁用.

You can’t just push/pop,because that steps on the red-zone

不,不是的.原因如下：

(1)几乎作为附注：红色区域仅在叶子功能中有用.否则,如果fncA调用fncB,则fncA执行此操作的唯一方法就是自己的红色区域.请参阅脚本的顶部注释块中的编译选项.

(2)更重要的是,由于push / pop的注入方式.推动发生在任何其他行为之前.流行音乐发生在任何其他动作之后[在ret之前].

红色区域仍然存在 – 完好无损.它只是偏离了-8,否则将被拒绝.所有红区活动都将被保留,因为这些insts使用来自％rsp的负偏移

这不同于内联asm块中的push / pop.通常的情况是红色区域代码(例如)mov $23,-4(％rsp).随后进行推送/弹出的内嵌asm块将会顺利进行.

一些功能显示：

# 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,%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

push / pop确实让我们陷入麻烦的是如果函数使用六个以上的参数(即args 7在堆栈上).访问这些参数使用％rsp的正偏移：

mov     32(%rsp),%rax

通过我们的“窍门”按钮,偏移量将不正确.现在正确的偏移量将高8：

mov     40(%rsp),%rax

脚本会检测到这个并抱怨.但是,由于这种情况是低概率,它还没有调整正偏移量.它可能需要大约五行代码来解决这个问题.现在打乒乓球