#!/usr/bin/env python3
"""Position-independence lint: the two link-time facts that let the identical
image run from any slot, asserted from the built ELF.

  1. No absolute jmp/call — -mrelax normally guarantees it, but a branch that
     grows out of relaxation range would break it silently.
  2. The info block within the image's first 256 bytes: 'b' rebuilds its
     address as (running slot high byte : link address 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()