linux-kernel - Re: [PATCH bpf-next] libbpf: Fix expected_attach

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Message-ID: <0e26d4c9-3e14-4bf9-85d3-86131e6a07f8@gmail.com>
Date: Fri, 13 Sep 2024 23:14:17 +0800
From: Tao Chen <chen.dylane@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman
 <eddyz87@...il.com>, Daniel Borkmann <daniel@...earbox.net>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] libbpf: Fix expected_attach_type set when kernel
 not support

在 2024/9/13 21:48, Jiri Olsa 写道:
> On Fri, Sep 13, 2024 at 08:16:27PM +0800, Tao Chen 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")
>> Signed-off-by: Tao Chen <chen.dylane@...il.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 219facd0e66e..9035edf763a3 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7343,7 +7343,7 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
>>   
>>   	/* old kernels might not support specifying expected_attach_type */
>>   	if ((def & SEC_EXP_ATTACH_OPT) && !kernel_supports(prog->obj, FEAT_EXP_ATTACH_TYPE))
>> -		opts->expected_attach_type = 0;
>> +		prog->expected_attach_type = 0;
>>   
>>   	if (def & SEC_SLEEPABLE)
>>   		opts->prog_flags |= BPF_F_SLEEPABLE;
>> -- 
>> 2.25.1
>>
> 
> good catch! thanks
> 
> I can't remember why it was needed, perhaps we should go back to where it
> was before?
> 
> I'm guessing prog->expected_attach_type might not get updated properly and
> that might cause issues, not sure
> 
> thanks,
> jirka
> 
> 
> ---
> 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;
>   
>   	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,


Hi, Jiri, thank you for your reply.
It looks better your way, i will send it in v2.

-- 
Best Regards
Dylane Chen