Re: [PATCH bpf-next RESEND v2] libbpf: Fix expected_attach_type set when kernel not support

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

在 2024/9/14 04:46, Andrii Nakryiko 写道:
> On Fri, Sep 13, 2024 at 9:44 AM Tao Chen <chen.dylane@gmail.com> wrote:
>>
>> The commit "5902da6d8a52" set expected_attach_type again with
>> filed of bpf_program after libpf_prepare_prog_load, which makes
>> expected_attach_type = 0 no sense when kenrel not support the
>> attach_type feature, so fix it.
>>
>> Fixes: 5902da6d8a52 ("libbpf: Add uprobe multi link support to bpf_program__attach_usdt")
>> Suggested-by: Jiri Olsa <jolsa@kernel.org>
>> Signed-off-by: Tao Chen <chen.dylane@gmail.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> Change list:
>> - v1 -> v2:
>>      - restore the original initialization way suggested by Jiri
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 219facd0e66e..df2244397ba1 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7353,7 +7353,7 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
>>
>>          /* special check for usdt to use uprobe_multi link */
>>          if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK))
>> -               prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
>> +               opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
>>
> 
> Ok, took me a bit to understand what the issue is. But the above is
> not quite correct, for the above case of setting
> BPF_TRACE_UPROBE_MULTI we do want to record BPF_TRACE_UPROBE_MULTI in
> prog->expected_attach_type, because user might want to query that
> later.
> 
> So I agree with the part of the fix below, but here I think we need
> *both* update opts' and prog's expected_attach_type, so we will have:
> 
>         prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
>         opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> 
> pw-bot: cr
> 
>>          if ((def & SEC_ATTACH_BTF) && !prog->attach_btf_id) {
>>                  int btf_obj_fd = 0, btf_type_id = 0, err;
>> @@ -7443,6 +7443,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
>>          load_attr.attach_btf_id = prog->attach_btf_id;
>>          load_attr.kern_version = kern_version;
>>          load_attr.prog_ifindex = prog->prog_ifindex;
>> +       load_attr.expected_attach_type = prog->expected_attach_type;
>>
>>          /* specify func_info/line_info only if kernel supports them */
>>          if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
>> @@ -7474,9 +7475,6 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
>>                  insns_cnt = prog->insns_cnt;
>>          }
>>
>> -       /* allow prog_prepare_load_fn to change expected_attach_type */
>> -       load_attr.expected_attach_type = prog->expected_attach_type;
>> -
>>          if (obj->gen_loader) {
>>                  bpf_gen__prog_load(obj->gen_loader, prog->type, prog->name,
>>                                     license, insns, insns_cnt, &load_attr,
>> --
>> 2.25.1
>>

Hi, Andrii, thank you for your reply. I will send v3 as you suggested.

-- 
Best Regards
Dylane Chen