trim.py

#!/usr/bin/env python

import sys
import mmap
import binascii

def main(args):
    if args is None or len(args) != 4:
        print("Usage: python trim.py [file.map] [file.bin] [base offset]")
        return

    class Triple(): pass
    initializer = Triple()
    initialized = Triple()
    zeroglobals = Triple()
    offset = int(args[3], 16)
    with open(args[1]) as mapfile:
        for line in mapfile:
            if line.startswith("_INITIALIZER"):
                parts = line.split()
                initializer.offset = int(parts[1], 16)-offset
                initializer.size = int(parts[2], 16)
                initializer.end = initializer.offset+initializer.size
            elif line.startswith("_INITIALIZED"):
                parts = line.split()
                initialized.offset = int(parts[1], 16)-offset
                initialized.size = int(parts[2], 16)
                initialized.end = initialized.offset+initialized.size
            elif line.startswith("_DATA"):
                parts = line.split()
                if len(parts) < 4: continue
                zeroglobals.offset = int(parts[1], 16)-offset
                zeroglobals.size = int(parts[2], 16)
                zeroglobals.end = zeroglobals.offset+zeroglobals.size

    if not hasattr(initialized, "offset") or \
       not hasattr(initializer, "offset") or \
       not hasattr(zeroglobals, "offset"):
           print("Map file has no globals, no relocations necessary.")
           sys.exit(0)

    print("Initialized: offset 0x{0:x}".format(initialized.offset),)
    print("size {0}".format(initialized.size))
    print("Initializer: offset 0x{0:x}".format(initializer.offset),)
    print("size {0}".format(initializer.size))
    print("Global variables: offset 0x{0:x}".format(zeroglobals.offset),)
    print("size {0}".format(zeroglobals.size))

    with open(args[2], "r+b") as binfile:
        mapped = mmap.mmap(binfile.fileno(), 0, access=mmap.ACCESS_WRITE)
        data = mapped[initializer.offset:initializer.end]
        print("Data to move: {0}".format(binascii.hexlify(data)))
        mapped.move(initialized.offset, initializer.offset, initializer.size)
        mapped.resize(mapped.size()-initialized.size)
        mapped.seek(zeroglobals.offset)
        mapped.write(b'\0'*zeroglobals.size)
        mapped.flush()
        mapped.close()

if __name__ == "__main__":
    main(sys.argv)