#!/usr/bin/env python3
"""Extract the first loadable section of a TI GSP COFF file as raw bytes.

GSPLNK writes a COFF whose section header carries the FULL 32-bit bit
address in `paddr`, so placement does not depend on gsprom's hex output
(whose addresses wrap at 64 KB -- documented in reference/tms34010-sdk.md).

Usage: cofextract.py hello.out payload.bin
Prints: origin=<bit address> size=<bytes> file_offset=<hex>
"""
import struct
import sys

# TI TMS34010 COFF: 20-byte file header, optional header size in the header.
# Section header: name[8] paddr(4) vaddr(4) size(4) scnptr(4) relptr(4)
#                 lnnoptr(4) nreloc(2) nlnno(2) flags(4)  = 40 bytes
def main(out_path, bin_path):
    d = open(out_path, "rb").read()
    if len(d) < 20:
        sys.exit("cofextract: file too short")
    magic, nscns, _timdat, _symptr, _nsyms, opthdr, _flags = struct.unpack_from(
        "<HHIIIHH", d, 0)
    if magic != 0x0090:
        sys.exit("cofextract: unexpected COFF magic %#06x" % magic)
    base = 20 + opthdr
    secs = []
    for i in range(nscns):
        off = base + i * 40
        name = d[off:off + 8].rstrip(b"\0").decode("latin1")
        paddr, vaddr, size, scnptr, _relptr, _lnnoptr, _nreloc, _nlnno, flags = \
            struct.unpack_from("<IIIIIIHHI", d, off + 8)
        secs.append((name, paddr, size, scnptr, flags))
    # .text is the only initialized section GSPLNK emits for our payload.
    text = [s for s in secs if s[0] == ".text"]
    if not text:
        sys.exit("cofextract: no .text section")
    name, paddr, size, scnptr, _flags = text[0]
    # size and paddr are bit units; bytes = size >> 3.
    nbytes = size >> 3
    payload = d[scnptr:scnptr + nbytes]
    if len(payload) != nbytes:
        sys.exit("cofextract: truncated section (%d of %d bytes)"
                 % (len(payload), nbytes))
    open(bin_path, "wb").write(payload)
    print("origin=%08X size=%d file_offset=%#x md5=%s" % (
        paddr, nbytes, scnptr,
        __import__("hashlib").md5(payload).hexdigest()))


if __name__ == "__main__":
    if len(sys.argv) != 3:
        sys.exit("usage: cofextract.py hello.out payload.bin")
    main(sys.argv[1], sys.argv[2])