Commit 6d08340d authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

Revert "perf/x86: Always store regs->ip in perf_callchain_kernel()" 



This reverts commit 83f44ae0.

Currently we store initial stacktrace entry twice for non-HW ot_regs, which
means callers that fail perf_hw_regs(regs) condition in perf_callchain_kernel.

It's easy to reproduce this bpftrace:

  # bpftrace -e 'tracepoint:sched:sched_process_exec { print(kstack()); }'
  Attaching 1 probe...

        bprm_execve+1767
        bprm_execve+1767
        do_execveat_common.isra.0+425
        __x64_sys_execve+56
        do_syscall_64+133
        entry_SYSCALL_64_after_hwframe+118

When perf_callchain_kernel calls unwind_start with first_frame, AFAICS
we do not skip regs->ip, but it's added as part of the unwind process.
Hence reverting the extra perf_callchain_store for non-hw regs leg.

I was not able to bisect this, so I'm not really sure why this was needed
in v5.2 and why it's not working anymore, but I could see double entries
as far as v5.10.

I did the test for both ORC and framepointer unwind with and without the
this fix and except for the initial entry the stacktraces are the same.

Acked-by: default avatarSong Liu <song@kernel.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251104215405.168643-2-jolsa@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 44e8f13f

arch/x86/events/core.c

+5 −5
Original line number Diff line number Diff line
@@ -2789,13 +2789,13 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re 
		return;

	}



	if (perf_hw_regs(regs)) {

		if (perf_callchain_store(entry, regs->ip))

			return;



	if (perf_hw_regs(regs))

		unwind_start(&state, current, regs, NULL);

	else

	} else {

		unwind_start(&state, current, NULL, (void *)regs->sp);

	}



	for (; !unwind_done(&state); unwind_next_frame(&state)) {

		addr = unwind_get_return_address(&state);