From: Tomislav Novak tnovak@fb.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@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 | 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; \ }