Re: [Intel-wired-lan] [PATCH bpf-next v3 4/5] selftests/bpf: Add selftest support for bpf_xdp_metadata_rx_checksum

bot+bpf-ci
2026-02-17T09:17:54Z

[-- Attachment #1: Type: text/plain, Size: 2116 bytes --]

> diff --git a/tools/testing/selftests/bpf/xdp_metadata.h b/tools/testing/selftests/bpf/xdp_metadata.h
> --- a/tools/testing/selftests/bpf/xdp_metadata.h
> +++ b/tools/testing/selftests/bpf/xdp_metadata.h

[ ... ]

> + struct {
> + __u8 ip_summed;
> + __u32 cksum_meta;
> + };

The ip_summed field is __u8 (1 byte), but bpf_xdp_metadata_rx_checksum()
takes an enum xdp_checksum * argument, which is 4 bytes.

In the BPF program:

> diff --git a/tools/testing/selftests/bpf/progs/xdp_metadata.c b/tools/testing/selftests/bpf/progs/xdp_metadata.c
> --- a/tools/testing/selftests/bpf/progs/xdp_metadata.c
> +++ b/tools/testing/selftests/bpf/progs/xdp_metadata.c

[ ... ]

> + bpf_xdp_metadata_rx_checksum(ctx,
> + (enum xdp_checksum *)&meta->ip_summed,
> + &meta->cksum_meta);

The cast here passes a pointer to a 1-byte field where the kfunc will
perform a 4-byte store. On little-endian this happens to work because
the value lands in the low byte and the remaining 3 bytes go into struct
padding.

On big-endian, the value would be stored in the high byte, so reading
back ip_summed as __u8 would yield 0 for any checksum result.

For comparison, the other metadata fields match their kfunc argument
sizes: rx_hash is __u32 matching u32 *, and rx_hash_type is __u32
matching enum xdp_rss_hash_type *.

Should ip_summed be __u32 (or enum xdp_checksum) to match the kfunc
signature and avoid the cast?

---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/22091902298

AI-authorship-score: low
AI-authorship-explanation: Code and commit message follow established kernel selftest patterns consistent with a known contributor, and the type choice reflects human engineering judgment.
issues-found: 1
issue-severity-score: low
issue-severity-explanation: Type size mismatch in selftest code where a __u8 field is cast to enum xdp_checksum * (4 bytes) for a kfunc call, causing incorrect behavior on big-endian architectures.