Re: [PATCH bpf-next v2 08/13] selftests/bpf: cover the low-32 link for sign-extending movs

[bot+bpf-ci]

> selftests/bpf: cover the low-32 link for sign-extending movs
>
> Five programs, mirroring the zero-extending set:
>
>  - sext_mov_wide_src: narrowing the source reaches the destination, and
>    the value that arrives is sign-extended rather than zero-extended
>  - sext_self_mov_keeps_link: r0 = (s32)r0 on an already-linked register
>    stays in its set, the shape a sign-extended int return takes
>  - sext_self_mov_no_link: the same mov on an unlinked register mints no id
>  - sext_no_sync_when_base_has_delta: a delta on the base stops propagation
>  - sext_no_sync_from_subreg_base: narrowing the link does not run
>    backwards into the rest of the set
>  - sext_kinds_reach_different_values: the same low half reaches -1 through
>    a sign extension and 0xffffffff through a zero extension
>
> Each guards a div by zero that is only unreachable if the propagation
> happened, so losing the link is a verification failure rather than a test
> that quietly stops checking anything.

This isn't a bug, but should the count read "six programs", and could the
closing sentence be scoped to the two __success programs, since
sext_self_mov_no_link has no div and the __failure ones expect it to be
reachable?

> diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
> index eb88d9ce6c34..45bfa02a5338 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_misc.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
> @@ -269,6 +269,14 @@
>  #define CAN_USE_BPF_ST
>  #endif
>
> +#if (defined(__TARGET_ARCH_arm64) || defined(__TARGET_ARCH_x86) ||	\
> +     (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64) ||		\
> +     defined(__TARGET_ARCH_arm) || defined(__TARGET_ARCH_s390) ||	\
> +     defined(__TARGET_ARCH_loongarch)) &&				\
> +	(__clang_major__ >= 18 || defined(__BPF_FEATURE_MOVSX))
> +#define CAN_USE_MOVSX
> +#endif
> +

This isn't a bug, but now that the gate lives in bpf_misc.h, would it be
worth switching verifier_movsx.c's inline #if over to #ifdef CAN_USE_MOVSX
so the arch/feature list exists in one place?

> diff --git a/tools/testing/selftests/bpf/progs/verifier_linked_scalars.c b/tools/testing/selftests/bpf/progs/verifier_linked_scalars.c
> index 65cb0efd268f..9d060d8b0c1f 100644

[ ... ]


---
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/34506184282