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#!/usr/bin/env python
# Work around x86emu bugs by replacing problematic instructions.
#
# Copyright (C) 2012 Kevin O'Connor <kevin@koconnor.net>
#
# This file may be distributed under the terms of the GNU GPLv3 license.
# The x86emu code widely used in Linux distributions when running Xorg
# in vesamode is known to have issues with "retl", "leavel", "entryl",
# "leal", and some variants of "calll". This code modifies those
# instructions that are known to be generated by gcc to avoid
# triggering the x86emu bugs.
# It is also known that the Windows vgabios emulator has issues with
# addressing negative offsets to the %esp register. That has been
# worked around by not using the gcc parameter "-fomit-frame-pointer"
# when compiling.
import sys, re
# leal parameter regex - example string: -3(%edx,%eax,8), %eax
re_leal = re.compile(
r'^\s*(?P<offset>[^(]*?)\s*'
r'\(\s*(?P<base>[^,)]*?)\s*(?:,\s*(?P<index>[^,)]*?)\s*)?'
r'(?:,\s*(?P<scale>[^,)]*?)\s*)?\)\s*'
r',\s*(?P<dest>.*?)\s*$')
# Find an alternate set of instructions for a given "leal" instruction
def handle_leal(sline):
m = re_leal.match(sline[5:])
if m is None or m.group('index') == '%esp':
print("Unable to fixup leal instruction: %s" % (sline,))
sys.exit(-1)
offset, base, index, scale, dest = m.group(
'offset', 'base', 'index', 'scale', 'dest')
if dest == '%esp':
# If destination is %esp then just use 16bit leaw instead
return 'leaw %s\n' % (sline[5:].replace('%e', '%'),)
if not scale:
scale = '1'
scale = {1: 0, 2: 1, 4: 2, 8: 3}[int(scale, 0)]
# Try to rearrange arguments to simplify 'base' (to improve code gen)
if not scale and base == index:
base, index, scale = '', index, 1
elif not index or (not scale and base in (dest, '%esp') and index != dest):
base, index, scale = index, base, 0
# Produce instructions to calculate "leal"
insns = ['pushfw']
if base != dest:
# Calculate "leal" directly in dest register
if index != dest:
insns.insert(0, 'movl %s, %s' % (index, dest))
if scale:
insns.append('shll $%d, %s' % (scale, dest))
if base:
if base == '%esp':
offset += '+2'
insns.append('addl %s, %s' % (base, dest))
elif base == index:
# Use "imull" method
insns.append('imull $%d, %s' % ((1<<scale)+1, dest))
else:
# Backup/restore index register and do scaling in index register
insns.append('pushl %s' % (index,))
insns.append('shll $%d, %s' % (scale, index))
insns.append('addl %s, %s' % (index, dest))
insns.append('popl %s' % (index,))
if offset and offset != '0':
insns.append('addl $%s, %s' % (offset, dest))
insns.append('popfw\n')
return ' ; '.join(insns)
def main():
infilename, outfilename = sys.argv[1:]
infile = open(infilename, 'r')
out = []
for line in infile:
sline = line.strip()
if sline == 'ret':
out.append('retw $2\n')
elif sline == 'leave':
out.append('movl %ebp, %esp ; popl %ebp\n')
elif sline.startswith('call'):
out.append('pushw %ax ; callw' + sline[4:] + '\n')
elif sline.startswith('leal'):
out.append(handle_leal(sline))
#print("-> %s\n %s" % (sline, out[-1].strip()))
else:
out.append(line)
infile.close()
outfile = open(outfilename, 'w')
outfile.write(''.join(out))
outfile.close()
if __name__ == '__main__':
main()
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