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

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Fri, Nov 13, 2026 at 04:18 PM Andrii Nakryiko <andrii@kernel.org> wrote:
> 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()"").

riscv has the same duplicate it seems.
Its perf_arch_fetch_caller_regs() stores __builtin_frame_address(0)
in s0. walk_stackframe() reports epc, then frame->ra of that frame.
Can be a follow up by riscv folks.

> @@ -15,7 +15,7 @@
>
>  #define perf_arch_fetch_caller_regs(regs, __ip) { \
>  	(regs)->pc = (__ip);    \
> -	(regs)->regs[29] = (unsigned long) __builtin_frame_address(0); \
> +	(regs)->regs[29] = (unsigned long) __builtin_frame_address(1); \
>  	(regs)->sp = current_stack_pointer; \
>  	(regs)->pstate = PSR_MODE_EL1h;	\
>  }

Will, Mark,
this looks correct to me.
Mind if I take it via bpf-next together with the selftests?