From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Jiri Olsa <olsajiri@gmail.com>
Cc: Feng Yang <yangfeng59949@163.com>,
mhiramat@kernel.org, alexei.starovoitov@gmail.com,
andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
daniel@iogearbox.net, eddyz87@gmail.com, haoluo@google.com,
john.fastabend@gmail.com, kpsingh@kernel.org,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
martin.lau@linux.dev, sdf@fomichev.me, song@kernel.org,
yonghong.song@linux.dev
Subject: Re: [BUG] Failed to obtain stack trace via bpf_get_stackid on ARM64 architecture
Date: Thu, 25 Sep 2025 06:56:41 +0900 [thread overview]
Message-ID: <20250925065641.5e066b03db123e96791d5671@kernel.org> (raw)
In-Reply-To: <aNQRWlNIno3ThMkv@krava>
On Wed, 24 Sep 2025 17:42:18 +0200
Jiri Olsa <olsajiri@gmail.com> wrote:
> On Wed, Sep 24, 2025 at 02:25:36PM +0800, Feng Yang wrote:
>
> SNIP
>
> > > Hmm, can you also dump the regs and insert pr_info() to find
> > > which function fails?
> > >
> > > Thanks,
> > >
> >
> > After testing, it was found that the stack could not be obtained because user_mode(regs) returned 1.
> > Referring to the arch_ftrace_fill_perf_regs function in your email
> > (https://lore.kernel.org/all/173518997908.391279.15910334347345106424.stgit@devnote2/),
> > I made the following modification: by setting the value of pstate, the stack can now be obtained successfully.
> >
> > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> > index 058a99aa44bd..f2814175e958 100644
> > --- a/arch/arm64/include/asm/ftrace.h
> > +++ b/arch/arm64/include/asm/ftrace.h
> > @@ -159,11 +159,13 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
> > {
> > struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs);
> >
> > memcpy(regs->regs, afregs->regs, sizeof(afregs->regs));
> > regs->sp = afregs->sp;
> > regs->pc = afregs->pc;
> > regs->regs[29] = afregs->fp;
> > regs->regs[30] = afregs->lr;
> > + regs->pstate = PSR_MODE_EL1h;
> > return regs;
> > }
> > However, I'm not sure if there will be any other impacts...
>
> nice, the test works for me with this change.. could you please send
> formal patch? I can polish and send out the test [1]
Yeah, and Cc to arm64 maintainers, also Closes: to this thread.
Thanks,
>
> thanks,
> jirka
>
>
> [1] https://github.com/kernel-patches/bpf/pull/9845/commits/11b31cd465a83b8719cb06331c8e81794cca40fa
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
prev parent reply other threads:[~2025-09-24 21:56 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-19 7:19 [BUG] Failed to obtain stack trace via bpf_get_stackid on ARM64 architecture Feng Yang
2025-09-20 2:56 ` Alexei Starovoitov
2025-09-20 22:17 ` Jiri Olsa
2025-09-21 13:30 ` Masami Hiramatsu
2025-09-22 2:15 ` Feng Yang
2025-09-23 15:32 ` Masami Hiramatsu
2025-09-24 6:25 ` Feng Yang
2025-09-24 7:31 ` Masami Hiramatsu
2025-09-24 8:04 ` Masami Hiramatsu
2025-09-24 10:53 ` Feng Yang
2025-09-24 22:00 ` Masami Hiramatsu
2025-09-24 15:42 ` Jiri Olsa
2025-09-24 21:56 ` Masami Hiramatsu [this message]
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