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