On Thu, Jul 17, 2025 at 10:19:54PM -0700, Josh Poimboeuf wrote: > On Thu, Jul 17, 2025 at 02:20:12PM +0200, Jens Remus wrote: > > > Also, if distros aren't even compiling with -mbackchain, I wonder if we > > > can just not do this altogether :-) > > > > My original intent was to use unwind user's for_each_user_frame() to > > replace the exiting stack tracing logic in arch_stack_walk_user_common() > > in arch/s390/kernel/stacktrace.c, which currently supports backchain. > > Given that for_each_user_frame() was made private in the latest unwind > > user series version hinders me. The use was also low, because the > > currentl arch_stack_walk_user_common() implementation does not support > > page faults, so that the attempt to use unwind user sframe would always > > fail and fallback to unwind user backchain. My hope was that somebody > > with more Kernel skills could give me a few hints at how it could be > > made to support deferred unwind. :-) > > I believe stack_trace_save_user() is only used by ftrace, and that will > no longer be needed once ftrace starts using unwind_user. > > Maybe Heiko knows if that backchain user stacktrace code has any users? > > If distros aren't building with -mbackchain, maybe backchain support can > be considered obsoleted by sframe, and we can get away with not > implementing it.
I guess that's a valid option. I know only of some special cases where users compile everything on their own with -mbackchain to make this work on a per-case basis. It shouldn't cause to much pain for them to switch to sframe, as soon as that is available.
