ARM: 9251/1: perf: Fix stacktraces for tracepoint events in THUMB2 kernels
authorTomislav Novak <tnovak@fb.com>
Mon, 26 Sep 2022 15:09:12 +0000 (16:09 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 14 Dec 2022 10:37:15 +0000 (11:37 +0100)
commitd81c62e3121f365bfcc170d6208dc3fc597af20e
treedd697c2e2147f0e18ad5d54dd0c11d2e281caaf8
parent66717ad03b80802752c9931afeedfcbd6806a8c2
ARM: 9251/1: perf: Fix stacktraces for tracepoint events in THUMB2 kernels

[ Upstream commit 612695bccfdbd52004551308a55bae410e7cd22f ]

Store the frame address where arm_get_current_stackframe() looks for it
(ARM_r7 instead of ARM_fp if CONFIG_THUMB2_KERNEL=y). Otherwise frame->fp
gets set to 0, causing unwind_frame() to fail.

  # bpftrace -e 't:sched:sched_switch { @[kstack] = count(); exit(); }'
  Attaching 1 probe...
  @[
      __schedule+1059
  ]: 1

A typical first unwind instruction is 0x97 (SP = R7), so after executing
it SP ends up being 0 and -URC_FAILURE is returned.

  unwind_frame(pc = ac9da7d7 lr = 00000000 sp = c69bdda0 fp = 00000000)
  unwind_find_idx(ac9da7d7)
  unwind_exec_insn: insn = 00000097
  unwind_exec_insn: fp = 00000000 sp = 00000000 lr = 00000000 pc = 00000000

With this patch:

  # bpftrace -e 't:sched:sched_switch { @[kstack] = count(); exit(); }'
  Attaching 1 probe...
  @[
      __schedule+1059
      __schedule+1059
      schedule+79
      schedule_hrtimeout_range_clock+163
      schedule_hrtimeout_range+17
      ep_poll+471
      SyS_epoll_wait+111
      sys_epoll_pwait+231
      __ret_fast_syscall+1
  ]: 1

Link: https://lore.kernel.org/r/20220920230728.2617421-1-tnovak@fb.com/
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tomislav Novak <tnovak@fb.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
arch/arm/include/asm/perf_event.h