Patch "ARM: 9251/1: perf: Fix stacktraces for tracepoint events in THUMB2 kernels" has been added to the 4.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm-9251-1-perf-fix-stacktraces-for-tracepoint-event.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c7e26b1ff5d5120b09d5ce95acb6d00edc056e50
Author: Tomislav Novak <tnovak@xxxxxx>
Date:   Mon Sep 26 16:09:12 2022 +0100

    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@xxxxxx/
    
    Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
    Signed-off-by: Tomislav Novak <tnovak@xxxxxx>
    Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/arm/include/asm/perf_event.h b/arch/arm/include/asm/perf_event.h
index 4f9dec489931..c5d27140834e 100644
--- a/arch/arm/include/asm/perf_event.h
+++ b/arch/arm/include/asm/perf_event.h
@@ -21,7 +21,7 @@ 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; \
 }