Re: [PATCH v3 bpf-next 06/11] selftests/bpf: BTF distill tests to ensure LOC[_PARAM|_PROTO] add to split BTF

[Alan Maguire <alan.maguire@oracle.com>]

On 18/09/2026 20:59, Eduard Zingerman wrote:
> On Wed, 2026-09-16 at 08:41 +0100, Alan Maguire wrote:
>> When creating distilled BTF, BTF_KIND_FUNC, _LOC_PARAM and _LOC_PROTO
>> should be added to split BTF.  This means potentially some duplication
>> of location information, but only for out-of-tree modules that use
>> distilled base/split BTF.
>> 
>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>> ---
>>  .../selftests/bpf/prog_tests/btf_distill.c    | 101 ++++++++++++++++++
>>  1 file changed, 101 insertions(+)
>> 
>> diff --git a/tools/testing/selftests/bpf/prog_tests/btf_distill.c b/tools/testing/selftests/bpf/prog_tests/btf_distill.c
>> index fb67ae195a73..141a4cb1f405 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/btf_distill.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/btf_distill.c
>> @@ -671,6 +671,105 @@ static void test_distilled_base_embedded_err(void)
>>  	btf__free(btf1);
>>  }
>>  
>> +/* LOC_PARAM, LOC_PROTO should be added to split BTF. */
>> +static void test_distilled_loc(void)
>> +{
>> +	struct btf *btf1 = NULL, *btf2 = NULL, *btf3 = NULL;
>> +	struct btf *btf4 = NULL, *btf5 = NULL;
>> +
>> +	btf1 = btf__new_empty();
>> +	if (!ASSERT_OK_PTR(btf1, "empty_main_btf"))
>> +		return;
>> +
>> +	btf__add_int(btf1, "int", 4, BTF_INT_SIGNED);	/* [1] int */
>> +	btf__add_func_proto(btf1, 1);                   /* [2] int (*)(int); */
>> +	btf__add_func_param(btf1, "p1", 1);
>> +	btf__add_func(btf1, "foo", BTF_FUNC_STATIC, 2);	/* [3] int foo(int); */
>> +	btf__add_loc_param(btf1, 4, BTF_LOC_PARAM_SIGNED | BTF_LOC_PARAM_CONST);
>> +	btf__add_loc_param_value(btf1, -1);		/* [4] loc value */
>> +	btf__add_loc_proto(btf1);			/* [5] loc proto */
>> +	btf__add_loc_proto_param(btf1, 4);		/*  param value */
>> +
>> +	VALIDATE_RAW_BTF(
>> +		btf1,
>> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
>> +		"[2] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1\n"
>> +		"\t'p1' type_id=1",
>> +		"[3] FUNC 'foo' type_id=2 linkage=static",
>> +		"[4] LOC_PARAM '(anon)' size=4 flags=0x3 vlen=1\n"
>> +		"\tvalue=-1",
>> +		"[5] LOC_PROTO '(anon)' vlen=1\n"
>> +		"\ttype_id=4");
> 
> Maybe also add an unrelated type to the base, such that effects of the
> distill are visible?
>

yep, good idea, will do.

 
>> +	btf2 = btf__new_empty_split(btf1);
>> +	if (!ASSERT_OK_PTR(btf2, "empty_split_btf"))
>> +		goto cleanup;
>> +
>> +	btf__add_locsec(btf2, "inline.text");		/* [6] locsec */
>> +	btf__add_locsec_loc(btf2, 3, 5, 256);		/* "foo" offset 256 */
>> +	VALIDATE_RAW_BTF(
>> +		btf2,
>> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
>> +		"[2] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1\n"
>> +		"\t'p1' type_id=1",
>> +		"[3] FUNC 'foo' type_id=2 linkage=static",
>> +		"[4] LOC_PARAM '(anon)' size=4 flags=0x3 vlen=1\n"
>> +		"\tvalue=-1",
>> +		"[5] LOC_PROTO '(anon)' vlen=1\n"
>> +		"\ttype_id=4",
>> +		"[6] LOCSEC 'inline.text' vlen=1\n"
>> +		"\tfunc_type_id=3 loc_proto_type_id=5 offset=256");
>> +
>> +	if (!ASSERT_EQ(0, btf__distill_base(btf2, &btf3, &btf4),
>> +		       "distilled_base") ||
>> +	    !ASSERT_OK_PTR(btf3, "distilled_base") ||
>> +	    !ASSERT_OK_PTR(btf4, "distilled_split") ||
>> +	    !ASSERT_EQ(2, btf__type_cnt(btf3), "distilled_base_type_cnt"))
>> +		goto cleanup;
>> +
>> +	VALIDATE_RAW_BTF(
>> +		btf4,
>> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
>> +		/* remainder is split BTF */
>> +		"[2] LOCSEC 'inline.text' vlen=1\n"
>> +		"\tfunc_type_id=4 loc_proto_type_id=6 offset=256",
>> +		"[3] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1\n"
>> +		"\t'p1' type_id=1",
>> +		"[4] FUNC 'foo' type_id=3 linkage=static",
>> +		"[5] LOC_PARAM '(anon)' size=4 flags=0x3 vlen=1\n"
>> +		"\tvalue=-1",
>> +		"[6] LOC_PROTO '(anon)' vlen=1\n"
>> +		"\ttype_id=5");
>> +
>> +	btf5 = btf__new_empty();
>> +	if (!ASSERT_OK_PTR(btf5, "empty_reloc_btf"))
>> +		goto cleanup;
> 
> I'd add another btf__add_<something> here to shift the ides and make
> sure that relocate actually did something.
> 

makes sense. Will add for v4. Thanks!