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

On Wed, 24 Sep 2025 17:42:18 +0200
Jiri Olsa [off-list ref] wrote:

On Wed, Sep 24, 2025 at 02:25:36PM +0800, Feng Yang wrote:

SNIP

quoted

quoted

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/ (local)), 
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) [off-list ref]