Re: [PATCH bpf-next 1/3] arm64: perf: Don't report the caller twice in caller-regs callchains

[sashiko-bot@kernel.org]

> perf_arch_fetch_caller_regs() sets regs->pc to the return address of
> the function it is used in (CALLER_ADDR0), but points regs->regs[29]
> at that function's own frame record, whose saved LR is that same
> return address. perf_callchain_kernel() reports regs->pc and then
> unwinds from the frame record at x29, so the caller shows up twice at
> the top of every kernel callchain built from perf_fetch_caller_regs():
> tracepoint events, software events emitted by __perf_sw_event_sched()
> (context-switches, cgroup-switches, cpu-migrations), and
> bpf_get_stack() and bpf_get_stackid() in tracepoint, raw tracepoint,
> tp_btf and fentry/fexit programs. E.g., for a tracepoint program
> attached to sched_process_fork:
> 
>   __traceiter_sched_process_fork+0x44
>   __traceiter_sched_process_fork+0x44
>   kernel_clone+0x250
>   ...
> 
> Use __builtin_frame_address(1), the caller's frame record, the same
> way kunwind_init_from_caller() does, so that pc and x29 describe the
> same frame.
> 
> x86 had the same duplicate entry, fixed by commit 6d08340d1e35
> ("Revert "perf/x86: Always store regs->ip in perf_callchain_kernel()"").
> 
> Fixes: 5b09a094f2fb ("arm64: perf: Fix callchain parse error with kernel tracepoint events")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261114001846.873499-1-andrii@kernel.org?part=1