From: Song Liu <songliubraving@fb.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
Martin Lau <kafai@fb.com>, Yonghong Song <yhs@fb.com>,
Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>
Subject: Re: [RFC PATCH bpf-next] bpf: Iterate through all PT_NOTE sections when looking for build id
Date: Wed, 12 Aug 2020 15:26:43 +0000 [thread overview]
Message-ID: <5238E896-6A88-4857-B8D4-3C2E8C4E9F2C@fb.com> (raw)
In-Reply-To: <20200812123102.20032-1-jolsa@kernel.org>
> On Aug 12, 2020, at 5:31 AM, Jiri Olsa <jolsa@kernel.org> wrote:
>
> Currently when we look for build id within bpf_get_stackid helper
> call, we check the first NOTE section and we fail if build id is
> not there.
>
> However on some system (Fedora) there can be multiple NOTE sections
> in binaries and build id data is not always the first one, like:
>
> $ readelf -a /usr/bin/ls
> ...
> [ 2] .note.gnu.propert NOTE 0000000000000338 00000338
> 0000000000000020 0000000000000000 A 0 0 8358
> [ 3] .note.gnu.build-i NOTE 0000000000000358 00000358
> 0000000000000024 0000000000000000 A 0 0 437c
> [ 4] .note.ABI-tag NOTE 000000000000037c 0000037c
> ...
>
> So the stack_map_get_build_id function will fail on build id retrieval
> and fallback to BPF_STACK_BUILD_ID_IP.
>
> This patch is changing the stack_map_get_build_id code to iterate
> through all the NOTE sections and try to get build id data from
> each of them.
>
> When tracing on sched_switch tracepoint that does bpf_get_stackid
> helper call kernel build, I can see about 60% increase of successful
> build id retrieval. The rest seems fails on -EFAULT.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
LGTM. Thanks for the fix!
Acked-by: Song Liu <songliubraving@fb.com>
next prev parent reply other threads:[~2020-08-12 15:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 12:31 [RFC PATCH bpf-next] bpf: Iterate through all PT_NOTE sections when looking for build id Jiri Olsa
2020-08-12 15:26 ` Song Liu [this message]
2020-08-13 1:20 ` Alexei Starovoitov
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