Re: [BUG] Failed to obtain stack trace via bpf_get_stackid on ARM64 architecture

Masami Hiramatsu
2025-09-24T21:56:47Z

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>