Re: [PATCH bpf-next v1 04/14] selftests/bpf: Add kfunc set test to resolve_btfids

On Mon Jun 1, 2026 at 6:17 PM EDT, Ihor Solodrai wrote:
> Extend the resolve_btfids selftest to cover kfunc sets defined with
> BTF_KFUNCS_START/BTF_KFUNCS_END.
>
> The test verifies that resolve_btfids correctly processes BTF_ID_FLAGS,
> resolves function IDs, and checks the kfunc set is sorted.
>
> Signed-off-by: Ihor Solodrai <[email protected]>

Reviewed-by: Emil Tsalapatis <[email protected]>

One nit below.

> ---
>  .../selftests/bpf/prog_tests/resolve_btfids.c | 56 +++++++++++++++++++
>  tools/testing/selftests/bpf/progs/btf_data.c  | 10 ++++
>  2 files changed, 66 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c b/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
> index d0e51979d455..f6fd79b9dd23 100644
> --- a/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
> +++ b/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
> @@ -10,6 +10,10 @@
>  #include <linux/btf_ids.h>
>  #include "test_progs.h"
>  
> +#ifndef KF_FASTCALL
> +#define KF_FASTCALL (1 << 12)
> +#endif
> +
>  struct symbol {
>  	const char	*name;
>  	int		 type;
> @@ -26,6 +30,17 @@ struct symbol test_symbols[] = {
>  	{ "func",    BTF_KIND_FUNC,    -1 },
>  };
>  
> +struct kfunc_symbol {
> +	const char	*name;
> +	s32		 id;
> +	u32		 flags;
> +};
> +
> +static struct kfunc_symbol kfunc_symbols[] = {
> +	{ "kfunc_a", -1, 0 },
> +	{ "kfunc_b", -1, KF_FASTCALL },
> +};
> +
>  /* Align the .BTF_ids section to 4 bytes */
>  asm (
>  ".pushsection " BTF_IDS_SECTION " ,\"a\"; \n"
> @@ -77,7 +92,13 @@ BTF_ID(union,   U)
>  BTF_ID(func,    func)
>  BTF_SET_END(test_set)
>  
> +BTF_KFUNCS_START(test_kfunc_set)
> +BTF_ID_FLAGS(func, kfunc_a)
> +BTF_ID_FLAGS(func, kfunc_b, KF_FASTCALL)
> +BTF_KFUNCS_END(test_kfunc_set)
> +
>  #pragma GCC visibility pop
> +
>  static int
>  __resolve_symbol(struct btf *btf, int type_id)
>  {
> @@ -108,6 +129,18 @@ __resolve_symbol(struct btf *btf, int type_id)
>  			test_symbols[i].id = type_id;
>  	}
>  
> +	if (BTF_INFO_KIND(type->info) == BTF_KIND_FUNC) {
> +		str = btf__name_by_offset(btf, type->name_off);
> +		if (str) {

This can be rewritten to collapse the nesting:
if (BTF_INFO_KIND(type->info) != BTF_KIND_FUNC) 
	return 0;

str = btf__name_by_offset(btf, type->name_off);
if (!str)
	return 0;

<the rest>

> +			for (i = 0; i < ARRAY_SIZE(kfunc_symbols); i++) {
> +				if (kfunc_symbols[i].id >= 0)
> +					continue;
> +				if (!strcmp(str, kfunc_symbols[i].name))
> +					kfunc_symbols[i].id = type_id;
> +			}
> +		}
> +	}
> +
>  	return 0;
>  }
>  
> @@ -162,6 +195,29 @@ void test_resolve_btfids(void)
>  			ASSERT_LE(test_set.ids[i - 1], test_set.ids[i], "sort_check");
>  	}
>  
> +	/* Check BTF_KFUNCS_START(test_kfunc_set) */
> +	ASSERT_EQ(test_kfunc_set.flags, BTF_SET8_KFUNCS, "kfunc_set_flags");
> +	ASSERT_EQ(test_kfunc_set.cnt, ARRAY_SIZE(kfunc_symbols), "kfunc_set_cnt");
> +
> +	for (i = 0; i < test_kfunc_set.cnt; i++) {
> +		bool found = false;
> +
> +		for (j = 0; j < ARRAY_SIZE(kfunc_symbols); j++) {
> +			if (kfunc_symbols[j].id != (s32)test_kfunc_set.pairs[i].id)
> +				continue;
> +			found = true;
> +			ASSERT_EQ(test_kfunc_set.pairs[i].flags,
> +				  kfunc_symbols[j].flags, "kfunc_flags_check");
> +			break;
> +		}
> +
> +		ASSERT_TRUE(found, "kfunc_id_found");
> +
> +		if (i > 0)
> +			ASSERT_LE(test_kfunc_set.pairs[i - 1].id,
> +				  test_kfunc_set.pairs[i].id, "kfunc_sort_check");
> +	}
> +
>  out:
>  	btf__free(btf);
>  }
> diff --git a/tools/testing/selftests/bpf/progs/btf_data.c b/tools/testing/selftests/bpf/progs/btf_data.c
> index baa525275bde..8587658012c3 100644
> --- a/tools/testing/selftests/bpf/progs/btf_data.c
> +++ b/tools/testing/selftests/bpf/progs/btf_data.c
> @@ -48,3 +48,13 @@ int func(struct root_struct *root)
>  {
>  	return 0;
>  }
> +
> +int kfunc_a(struct root_struct *root)
> +{
> +	return 0;
> +}
> +
> +int kfunc_b(struct root_struct *root)
> +{
> +	return 0;
> +}