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

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 6/16/26 12:07 AM, Emil Tsalapatis wrote:
> 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 <ihor.solodrai@linux.dev>
> 
> Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
> 
> 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>
> 

Hi Emil, thank you for the reviews.

I'm going to drop this string check following Andrii's suggestion, so
this condition will be removed.

Good nit though.

>> +			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;
>> +}
>