Re: [PATCH RESEND bpf-next v7 0/4] Add prog_kfunc feature probe

[Tao Chen <chen.dylane@gmail.com>]

在 2025/2/19 06:51, Eduard Zingerman 写道:
> On Mon, 2025-02-17 at 13:21 +0800, Tao Chen wrote:
>> 在 2025/2/12 23:39, Tao Chen 写道:
>>> More and more kfunc functions are being added to the kernel.
>>> Different prog types have different restrictions when using kfunc.
>>> Therefore, prog_kfunc probe is added to check whether it is supported,
>>> and the use of this api will be added to bpftool later.
>>>
>>> Change list:
>>> - v6 -> v7:
>>>     - wrap err with libbpf_err
>>>     - comments fix
>>>     - handle btf_fd < 0 as vmlinux
>>>     - patchset Reviewed-by: Jiri Olsa <jolsa@kernel.org>
>>> - v6
>>>     https://lore.kernel.org/bpf/20250211111859.6029-1-chen.dylane@gmail.com
>>>
>>> - v5 -> v6:
>>>     - remove fd_array_cnt
>>>     - test case clean code
>>> - v5
>>>     https://lore.kernel.org/bpf/20250210055945.27192-1-chen.dylane@gmail.com
>>>
>>> - v4 -> v5:
>>>     - use fd_array on stack
>>>     - declare the scope of use of btf_fd
>>> - v4
>>>     https://lore.kernel.org/bpf/20250206051557.27913-1-chen.dylane@gmail.com/
>>>
>>> - v3 -> v4:
>>>     - add fd_array init for kfunc in mod btf
>>>     - add test case for kfunc in mod btf
>>>     - refactor common part as prog load type check for
>>>       libbpf_probe_bpf_{helper,kfunc}
>>> - v3
>>>     https://lore.kernel.org/bpf/20250124144411.13468-1-chen.dylane@gmail.com
>>>
>>> - v2 -> v3:
>>>     - rename parameter off with btf_fd
>>>     - extract the common part for libbpf_probe_bpf_{helper,kfunc}
>>> - v2
>>>     https://lore.kernel.org/bpf/20250123170555.291896-1-chen.dylane@gmail.com
>>>
>>> - v1 -> v2:
>>>     - check unsupported prog type like probe_bpf_helper
>>>     - add off parameter for module btf
>>>     - check verifier info when kfunc id invalid
>>> - v1
>>>     https://lore.kernel.org/bpf/20250122171359.232791-1-chen.dylane@gmail.com
>>>
>>> Tao Chen (4):
>>>     libbpf: Extract prog load type check from libbpf_probe_bpf_helper
>>>     libbpf: Init fd_array when prog probe load
>>>     libbpf: Add libbpf_probe_bpf_kfunc API
>>>     selftests/bpf: Add libbpf_probe_bpf_kfunc API selftests
>>>
>>>    tools/lib/bpf/libbpf.h                        |  19 ++-
>>>    tools/lib/bpf/libbpf.map                      |   1 +
>>>    tools/lib/bpf/libbpf_probes.c                 |  86 +++++++++++---
>>>    .../selftests/bpf/prog_tests/libbpf_probes.c  | 111 ++++++++++++++++++
>>>    4 files changed, 201 insertions(+), 16 deletions(-)
>>>
>>
>> Ping...
>>
>> Hi Andrii, Eduard,
>>
>> I've revised the previous suggestions. Please review it again. Thanks.
>>
> 
> I tried the test enumerating all kfuncs in BTF and doing
> libbpf_probe_bpf_kfunc for BPF_PROG_TYPE_{KPROBE,XDP}.
> (Source code at the end of the email).
> 
> The set of kfuncs returned for XDP looks correct.
> The set of kfuncs returned for KPROBE contains a few incorrect entries:
> - bpf_xdp_metadata_rx_hash
> - bpf_xdp_metadata_rx_timestamp
> - bpf_xdp_metadata_rx_vlan_tag
> 
> This is because of a different string reported by verifier for these
> three functions.
> 
> Ideally, I'd write some script looking for
> register_btf_kfunc_id_set(BPF_PROG_TYPE_***, kfunc_set)
> calls in the kernel source code and extracting the prog type /
> functions in the set, and comparing results of this script with
> output of the test below for all program types.
> But up to you if you'd like to do such rigorous verification or not.
> 
> Otherwise patch-set looks good to me, for all patch-set:
> 
> Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
> 

Hi Eduard,

I try to run your test case, but it seems btf_is_decl_tag always return 
false, Are there any special restrictions for the tag feature of btf？

My compilation environment：

pahole --version
v1.29
clang --version
Ubuntu clang version 18.1.3 (1ubuntu1)

> --- 8< -----------------------------------------------------
> 
> static const struct {
> 	const char *name;
> 	int code;
> } program_types[] = {
> #define _T(n) { #n, BPF_PROG_TYPE_ ## n }
> 	_T(KPROBE),
> 	_T(XDP),
> #undef _T
> };
> 
> void test_libbpf_probe_kfuncs_many(void)
> {
> 	int i, kfunc_id, ret, id;
> 	const struct btf_type *t;
> 	struct btf *btf = NULL;
> 	const char *kfunc;
> 	const char *tag;
> 
> 	btf = btf__parse("/sys/kernel/btf/vmlinux", NULL);
> 	if (!ASSERT_OK_PTR(btf, "btf_parse"))
> 		return;
> 
> 	for (id = 0; id < btf__type_cnt(btf); ++id) {
> 		t = btf__type_by_id(btf, id);
> 		if (!btf_is_decl_tag(t))
> 			continue;
> 		tag = btf__name_by_offset(btf, t->name_off);
> 		if (strcmp(tag, "bpf_kfunc") != 0)
> 			continue;
> 		kfunc_id = t->type;
> 		t = btf__type_by_id(btf, kfunc_id);
> 		if (!btf_is_func(t))
> 			continue;
> 		kfunc = btf__name_by_offset(btf, t->name_off);
> 		printf("[%-6d] %-42s ", kfunc_id, kfunc);
> 		for (i = 0; i < ARRAY_SIZE(program_types); ++i) {
> 			ret = libbpf_probe_bpf_kfunc(program_types[i].code, kfunc_id, -1, NULL);
> 			if (ret < 0)
> 				printf("%-8d  ", ret);
> 			else if (ret == 0)
> 				printf("%8s  ", "");
> 			else
> 				printf("%8s  ", program_types[i].name);
> 		}
> 		printf("\n");
> 	}
> 	btf__free(btf);
> }
> 
> ----------------------------------------------------- >8 ---
> 


-- 
Best Regards
Tao Chen