From: "Daniel Xu" <dxu@dxuuu.xyz>
To: "Daniel Borkmann" <daniel@iogearbox.net>,
"John Fastabend" <john.fastabend@gmail.com>,
<bpf@vger.kernel.org>, <ast@kernel.org>, <songliubraving@fb.com>,
<yhs@fb.com>, <andriin@fb.com>
Cc: <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
<peterz@infradead.org>, <mingo@redhat.com>, <acme@kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: Add bpf_perf_prog_read_branches() helper
Date: Thu, 23 Jan 2020 15:27:07 -0800 [thread overview]
Message-ID: <C03K644SLHQ9.1FOCEKF12GEJE@dlxu-fedora-R90QNFJV> (raw)
In-Reply-To: <9341443f-b29a-e92e-0e12-7990927b4e33@iogearbox.net>
On Thu Jan 23, 2020 at 11:44 PM, Daniel Borkmann wrote:
[...]
> >> Different question related to your set. It looks like br_stack is only
> >> available
> >> on x86, is that correct? For other archs this will always bail out on
> >> !br_stack
> >> test. Perhaps we should document this fact so users are not surprised
> >> why their
> >> prog using this helper is not working on !x86. Wdyt?
> >
> > I think perf_event_open() should fail on !x86 if a user tries to configure
> > it with branch stack collection. So there would not be the opportunity for
> > the bpf prog to be attached and run. I haven't tested this, though. I'll
> > look through the code / install a VM and test it.
>
>
> As far as I can see the prog would still be attachable and runnable,
> just that
> the helper always will return -EINVAL on these archs. Maybe error code
> should be
> changed into -ENOENT to avoid confusion wrt whether user provided some
> invalid
> input args.
Ok, will add.
> Should this actually bail out with -EINVAL if size is not a
> multiple
> of sizeof(struct perf_branch_entry) as otherwise we'd end up copying
> half broken
> branch entry information?
Sure, makes sense.
>
>
> Thanks,
> Daniel
>
>
>
>
next prev parent reply other threads:[~2020-01-23 23:27 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 20:22 [PATCH v2 bpf-next 0/3] " Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 1/3] bpf: " Daniel Xu
2020-01-23 5:39 ` John Fastabend
2020-01-23 20:09 ` Daniel Xu
2020-01-23 22:23 ` Daniel Borkmann
2020-01-23 22:30 ` Daniel Xu
2020-01-23 22:41 ` Andrii Nakryiko
2020-01-23 23:09 ` Daniel Borkmann
2020-01-23 22:44 ` Daniel Borkmann
2020-01-23 23:07 ` Martin Lau
2020-01-23 23:27 ` Daniel Xu [this message]
2020-01-22 20:22 ` [PATCH v2 bpf-next 2/3] tools/bpf: Sync uapi header bpf.h Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 3/3] selftests/bpf: add bpf_perf_prog_read_branches() selftest Daniel Xu
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