strip_asm.py

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#!/usr/bin/env python
 
"""
strip_asm.py - Cleanup ASM output for the specified file
"""
 
from argparse import ArgumentParser
import sys
import os
import re
 
def find_used_labels(asm):
    found = set()
    label_re = re.compile("\s*j[a-z]+\s+\.L([a-zA-Z0-9][a-zA-Z0-9_]*)")
    for l in asm.splitlines():
        m = label_re.match(l)
        if m:
            found.add('.L%s' % m.group(1))
    return found
 
 
def normalize_labels(asm):
    decls = set()
    label_decl = re.compile("^[.]{0,1}L([a-zA-Z0-9][a-zA-Z0-9_]*)(?=:)")
    for l in asm.splitlines():
        m = label_decl.match(l)
        if m:
            decls.add(m.group(0))
    if len(decls) == 0:
        return asm
    needs_dot = next(iter(decls))[0] != '.'
    if not needs_dot:
        return asm
    for ld in decls:
        asm = re.sub("(^|\s+)" + ld + "(?=:|\s)", '\\1.' + ld, asm)
    return asm
 
 
def transform_labels(asm):
    asm = normalize_labels(asm)
    used_decls = find_used_labels(asm)
    new_asm = ''
    label_decl = re.compile("^\.L([a-zA-Z0-9][a-zA-Z0-9_]*)(?=:)")
    for l in asm.splitlines():
        m = label_decl.match(l)
        if not m or m.group(0) in used_decls:
            new_asm += l
            new_asm += '\n'
    return new_asm
 
 
def is_identifier(tk):
    if len(tk) == 0:
        return False
    first = tk[0]
    if not first.isalpha() and first != '_':
        return False
    for i in range(1, len(tk)):
        c = tk[i]
        if not c.isalnum() and c != '_':
            return False
    return True
 
def process_identifiers(l):
    """
    process_identifiers - process all identifiers and modify them to have
    consistent names across all platforms; specifically across ELF and MachO.
    For example, MachO inserts an additional understore at the beginning of
    names. This function removes that.
    """
    parts = re.split(r'([a-zA-Z0-9_]+)', l)
    new_line = ''
    for tk in parts:
        if is_identifier(tk):
            if tk.startswith('__Z'):
                tk = tk[1:]
            elif tk.startswith('_') and len(tk) > 1 and \
                    tk[1].isalpha() and tk[1] != 'Z':
                tk = tk[1:]
        new_line += tk
    return new_line
 
 
def process_asm(asm):
    """
    Strip the ASM of unwanted directives and lines
    """
    new_contents = ''
    asm = transform_labels(asm)
 
    # TODO: Add more things we want to remove
    discard_regexes = [
        re.compile("\s+\..*$"), # directive
        re.compile("\s*#(NO_APP|APP)$"), #inline ASM
        re.compile("\s*#.*$"), # comment line
        re.compile("\s*\.globa?l\s*([.a-zA-Z_][a-zA-Z0-9$_.]*)"), #global directive
        re.compile("\s*\.(string|asciz|ascii|[1248]?byte|short|word|long|quad|value|zero)"),
    ]
    keep_regexes = [
 
    ]
    fn_label_def = re.compile("^[a-zA-Z_][a-zA-Z0-9_.]*:")
    for l in asm.splitlines():
        # Remove Mach-O attribute
        l = l.replace('@GOTPCREL', '')
        add_line = True
        for reg in discard_regexes:
            if reg.match(l) is not None:
                add_line = False
                break
        for reg in keep_regexes:
            if reg.match(l) is not None:
                add_line = True
                break
        if add_line:
            if fn_label_def.match(l) and len(new_contents) != 0:
                new_contents += '\n'
            l = process_identifiers(l)
            new_contents += l
            new_contents += '\n'
    return new_contents
 
def main():
    parser = ArgumentParser(
        description='generate a stripped assembly file')
    parser.add_argument(
        'input', metavar='input', type=str, nargs=1,
        help='An input assembly file')
    parser.add_argument(
        'out', metavar='output', type=str, nargs=1,
        help='The output file')
    args, unknown_args = parser.parse_known_args()
    input = args.input[0]
    output = args.out[0]
    if not os.path.isfile(input):
        print(("ERROR: input file '%s' does not exist") % input)
        sys.exit(1)
    contents = None
    with open(input, 'r') as f:
        contents = f.read()
    new_contents = process_asm(contents)
    with open(output, 'w') as f:
        f.write(new_contents)
 
 
if __name__ == '__main__':
    main()
 
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