File Coverage

blib/lib/Games/Hack/Patch/i686.pm

Criterion	Covered	Total	%
statement	16	16	100.0
branch	12	12	100.0
condition			n/a
subroutine	1	1	100.0
pod	1	1	100.0
total	30	30	100.0

#!/usr/bin/perl
# vim: set sw=2 expandtab : #
# Master version is at https://developer.berlios.de/projects/games-hack/

package Games::Hack::Patch::i686;

$VERSION=0.52;

require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(GetNOP);




sub GetNOP
{
  my($adr_start, $adr_end, $disass)=@_;
  my($binary, $diff);

  $binary="";

### Floating point store? Stores always %ST(0).
  if ($disass =~ m#^f[bi]?st(p)?[sl]? #)
  {
    if ($1)
    {
# If the "Pop" flag is given in the "fst" ("floating point store")
# operation, we need to clean the floating point stack.
# We use the "ffreep st(0)" instruction, .
      $binary .= "\xdf\xc0";

      $adr_start += 2;
    }
# Rest gets done by jump.
  }
# Popping values from the stack
  elsif ($disass =~ m#^pop#)
  {
# increment esp; rest done by jump.
# is there a 64bit pop?
    $binary .= "\x83\xc4\x04";
    $adr_start += 3;
  }
### Integer move or direct modification
  elsif ($disass =~ m#^(mov|or|and)#)
  {
# done by jump.
  }
  else
  {
    warn "Unknown instruction '" . $disass . "', patching unsafe!";
    return undef;
  }


### short jump
  if (($diff=$adr_end-$adr_start) >= 2)
  {
# The opcode needs two bytes; these are already consumed, and so the jump
# distance has to be reduced.
    $binary .= "\xeb" . pack("C", $diff-2);
    $adr_end=$adr_start;
  }

### NOP.
# That should never be needed ... all instructions involving memory access
# (even via a register) have at least 2 bytes.
# (If some value would be persistently stored in a register, we wouldn't
# find it by looking at the memory contents.)
  $binary .= "\x90" x $diff
    if ($diff=$adr_end-$adr_start) >= 1;

  return $binary;
}

__END__