On Mon, Nov 03, 2025 at 11:09:21PM +0100, Jiri Olsa wrote:
> This reverts commit 83f44ae0f8afcc9da659799db8693f74847e66b3.
>
> 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.
Probably some ftrace/bpf glue code that doesn't adhere to the contract
set by perf_hw_regs(); as you find in the next patch.
