DuckDb native extensions require some footer-data. THis adds it to the the dynamic-lib.

add_duckdb_extension_footer.py

#!/usr/bin/env python3
"""
Append the DuckDB extension metadata footer to a compiled shared library.

DuckDB expects every extension file to end with a 512-byte footer:
  bytes [0..255]  : RSA signature (zeros = unsigned / community extension)
  bytes [256..511]: 8 x 32-byte metadata fields stored in *reverse* order:
    field[0] @ bytes [480..511]: magic value "4" (null-padded to 32 bytes)
    field[1] @ bytes [448..479]: platform  e.g. "linux_arm64"
    field[2] @ bytes [416..447]: duckdb_version e.g. "v1.5.0"
    field[3] @ bytes [384..415]: extension_version (may be empty)
    field[4] @ bytes [352..383]: abi_type "CPP"
    field[5..7]                : empty (zeros)

Usage:
    python3 add_extension_footer.py <extension_file> <duckdb_version> <platform>

Example:
    python3 add_extension_footer.py epf.duckdb_extension v1.5.0 linux_arm64
"""

import sys
import struct


def pad32(s: str) -> bytes:
    """Encode string and null-pad / truncate to exactly 32 bytes."""
    b = s.encode("utf-8")
    if len(b) > 32:
        raise ValueError(f"Field value too long (max 32 bytes): {s!r}")
    return b.ljust(32, b"\x00")


def build_footer(
    duckdb_version: str, platform: str, extension_version: str = ""
) -> bytes:
    SIGNATURE_SIZE = 256
    FIELD_SIZE = 32
    NUM_FIELDS = 8

    # The 8 fields in logical order (field[0] = magic, field[7] = empty)
    fields = [
        pad32("4"),  # field[0]: magic
        pad32(platform),  # field[1]: platform
        pad32(duckdb_version),  # field[2]: duckdb_version
        pad32(extension_version),  # field[3]: extension_version
        pad32("CPP"),  # field[4]: abi_type
        pad32(""),  # field[5]: unused
        pad32(""),  # field[6]: unused
        pad32(""),  # field[7]: unused
    ]

    # Stored in reverse order in the file
    fields_bytes = b"".join(reversed(fields))
    assert len(fields_bytes) == NUM_FIELDS * FIELD_SIZE == 256

    # Signature area is zeros (unsigned extension)
    signature = b"\x00" * SIGNATURE_SIZE

    # Footer layout: [metadata 256 bytes][signature 256 bytes]
    footer = fields_bytes + signature
    assert len(footer) == 512
    return footer


def main():
    if len(sys.argv) < 4:
        print(__doc__)
        sys.exit(1)

    ext_path, duckdb_version, platform = sys.argv[1], sys.argv[2], sys.argv[3]
    extension_version = sys.argv[4] if len(sys.argv) > 4 else ""

    footer = build_footer(duckdb_version, platform, extension_version)

    with open(ext_path, "ab") as f:
        f.write(footer)

    print(f"Appended DuckDB extension footer to {ext_path}")
    print(f"  platform:  {platform}")
    print(f"  duckdb:    {duckdb_version}")
    print(f"  abi_type:  CPP")


if __name__ == "__main__":
    main()