#!/usr/bin/env python3
"""Position-independence lint for the pureboot image.

The self-staging design lets the identical binary run from any 512-byte
slot, which holds only if nothing in the image addresses itself absolutely.
Two link-time facts guarantee it, both asserted here from the built ELF:

  1. No absolute jmp/call opcodes — all control flow is PC-relative
     (rjmp/rcall/ijmp/icall). -mrelax normally guarantees this; a code
     change that grows a branch out of relaxation range would break it
     silently.
  2. The info block sits within the image's first 256 bytes: the 'b'
     command rebuilds its address as (running slot high byte : low byte of
     the link address), which needs the offset to fit that low byte.

Usage: check_pi.py <objdump> <nm> <elf> <text_start_hex>
"""

import re
import subprocess
import sys


def main():
    objdump, nm, elf, text_start = sys.argv[1:]
    text_start = int(text_start, 0)

    listing = subprocess.run([objdump, "-d", elf], capture_output=True, text=True, check=True).stdout
    absolute = [
        line
        for line in listing.splitlines()
        if re.search(r"\t(jmp|call)\t", line)
    ]
    if absolute:
        print("FAIL: absolute control flow in the image:")
        print("\n".join(absolute))
        sys.exit(1)

    symbols = subprocess.run([nm, "-C", elf], capture_output=True, text=True, check=True).stdout
    info = [line for line in symbols.splitlines() if "flash_table" in line and "::storage" in line]
    if len(info) != 1:
        print(f"FAIL: expected one info-block storage symbol, found {len(info)}")
        sys.exit(1)
    address = int(info[0].split()[0], 16)
    offset = address - text_start
    if not 0 <= offset < 256:
        print(f"FAIL: info block at image offset {offset:#x}, must sit in the first 256 bytes")
        sys.exit(1)

    print(f"PI lint: control flow PC-relative, info block at offset {offset:#x}")


if __name__ == "__main__":
    main()