linux-kernel - [PATCH AUTOSEL 5.15 08/24] ARM: 9251/1: perf: Fix stacktraces for tracepoint events in THUMB2 kernels

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Message-Id: <20221128174027.1441921-8-sashal@kernel.org>
Date:   Mon, 28 Nov 2022 12:40:08 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Tomislav Novak <tnovak@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Sasha Levin <sashal@...nel.org>, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, will@...nel.org,
        mark.rutland@....com, linux@...linux.org.uk,
        linux-perf-users@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH AUTOSEL 5.15 08/24] ARM: 9251/1: perf: Fix stacktraces for tracepoint events in THUMB2 kernels

From: Tomislav Novak <tnovak@...com>

[ 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@...aro.org>
Signed-off-by: Tomislav Novak <tnovak@...com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm/include/asm/perf_event.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/perf_event.h b/arch/arm/include/asm/perf_event.h
index fe87397c3d8c..bdbc1e590891 100644
--- a/arch/arm/include/asm/perf_event.h
+++ b/arch/arm/include/asm/perf_event.h
@@ -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; \
 }
-- 
2.35.1