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ARM: 9251/1: perf: Fix stacktraces for tracepoint events in THUMB2 kernels

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[ 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>
This commit is contained in:
Tomislav Novak 2022-09-26 16:09:12 +01:00 committed by Greg Kroah-Hartman
parent 3f39d53bc7
commit 29917e381e
1 changed files with 1 additions and 1 deletions
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2
arch/arm/include/asm/perf_event.h
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@ -17,7 +17,7 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
#define perf_arch_fetch_caller_regs(regs, __ip) { \
(regs)->ARM_pc = (__ip); \
(regs)->ARM_fp = (unsigned long) __builtin_frame_address(0); \
frame_pointer((regs)) = (unsigned long) __builtin_frame_address(0); \
(regs)->ARM_sp = current_stack_pointer; \
(regs)->ARM_cpsr = SVC_MODE; \
}