linux-kernel - Re: [PATCH v7 2/2] selftests/bpf: Force -O2 for USDT selftests to cover SIB handling logic

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Message-ID: <CAEf4Bzbpu9PM6GHV6ewE_hJJ7=94Rn1ZYq5QWVnpoH6_LRQDCw@mail.gmail.com>
Date: Wed, 20 Aug 2025 16:00:35 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Yonghong Song <yonghong.song@...ux.dev>
Cc: 赵佳炜 <phoenix500526@....com>, ast@...nel.org, 
	daniel@...earbox.net, andrii@...nel.org, bpf@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/2] selftests/bpf: Force -O2 for USDT selftests to
 cover SIB handling logic

On Mon, Aug 18, 2025 at 10:35 AM Yonghong Song <yonghong.song@...ux.dev> wrote:
>
>
>
> On 8/17/25 6:43 AM, 赵佳炜 wrote:
> >
> >
> >
> >
> >
> >
> > Hi, Yonghong. I've already filed an issue[1] in GCC  community.
> >
> >
> > Accroding to the discussion, it's not a gcc bug but may be a systemtap bug.
> > I don't know how to report this bug to systemtap, but I found that the
> > libbpf/usdt have the same problem. I've filed an issue in libbpf/usdt repo[2].
> >
> > I also have some ideas about it. I wrote it down in the issue[2] comment.
> > May be we can discuss there.
> >
> > [1]. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121569
> > [2]. https://github.com/libbpf/usdt/issues/13
>
> Thanks for filing an issue on gcc and getting some feedback/suggestions
> from gcc community.
>
> Currently, libbpf/usdt does not suport format like '-1@ti(%rip)'. If we do

Exactly, it doesn't. I haven't yet ran into a case where real-world
applications would use such an argument format, so there was no
incentive in trying to support it.

Was this issue discovered as part of testing on some real world
application, or it's mostly through testing on synthetic cases?

> intend to implement this. libbpf/usdt can reject that if 'ti' is a
> static variable. libbpf can provide some hints about how to make it
> work (see above [1] and [2]). Then, it would be user's reponsibility to
> change code so libbpf can support it.
>
> >
> >
> >

[...]