Re: [PATCH bpf-next v3 5/6] selftests/bpf: Verify decl tags emission in resolve_btfids test

> diff --git a/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c b/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
> index 8482f00046d4c..732cfed35e1c5 100644
> --- a/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
> +++ b/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c

[ ... ]

> @@ -260,6 +284,22 @@ void test_resolve_btfids(void)
>  	check_kfunc_set(&test_kfunc_set);
>  	check_kfunc_set(&test_kfunc_set_rev);
>
> +	/* Check resolve_btfids emitted a bpf_kfunc decl_tag for each kfunc */
> +	for (i = 0; i < ARRAY_SIZE(kfunc_symbols); i++) {
> +		ASSERT_TRUE(btf_has_decl_tag(btf, DECL_TAG_KFUNC,
> +					     kfunc_symbols[i].id),
> +			    kfunc_symbols[i].name);
> +	}
> +
> +	/* Check resolve_btfids emitted bpf_fastcall for KF_FASTCALL kfuncs */
> +	for (i = 0; i < ARRAY_SIZE(kfunc_symbols); i++) {
> +		if (kfunc_symbols[i].flags & KF_FASTCALL) {
> +			ASSERT_TRUE(btf_has_decl_tag(btf, DECL_TAG_FASTCALL,
> +						     kfunc_symbols[i].id),
> +				    kfunc_symbols[i].name);
> +		}
> +	}

This isn't a bug, but could the bpf_fastcall check use an ASSERT_EQ form
instead of the conditional ASSERT_TRUE?

The arena block below this code uses:

	ASSERT_EQ(is_arena_tagged_ptr(btf, proto->type),
		  !!(fl & KF_ARENA_RET), name);

which checks both directions: flagged functions have the tag, and unflagged
functions don't. As written here, the second loop only verifies that
flagged kfuncs get bpf_fastcall; it doesn't check that kfunc_a, kfunc_c,
and kfunc_d (which lack KF_FASTCALL) are correctly left untagged.

Using the same form as the arena check would fold the two loops into one
and cover the negative case as well.


---
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/31144437704