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

Jiri Olsa
2025-09-24T15:42:22Z

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]

thanks,
jirka

[1] https://github.com/kernel-patches/bpf/pull/9845/commits/11b31cd465a83b8719cb06331c8e81794cca40fa