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Date: Wed, 15 Jul 2015 09:22:34 +0900 From: AKASHI Takahiro <takahiro.akashi@...aro.org> To: Steven Rostedt <rostedt@...dmis.org> CC: catalin.marinas@....com, will.deacon@....com, jungseoklee85@...il.com, olof@...om.net, broonie@...nel.org, david.griego@...aro.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [RFC 1/3] ftrace: adjust a function's pc to search for in check_stack() for arm64 On 07/14/2015 12:24 AM, Steven Rostedt wrote: > On Mon, 13 Jul 2015 14:29:33 +0900 > AKASHI Takahiro <takahiro.akashi@...aro.org> wrote: > >> Ftace's stack tracer on arm64 returns wrong information about call stacks: >> >> Depth Size Location (50 entries) >> ----- ---- -------- >> 0) 5256 0 notifier_call_chain+0x30/0x94 >> 1) 5256 0 ftrace_call+0x0/0x4 >> 2) 5256 0 notifier_call_chain+0x2c/0x94 >> 3) 5256 0 raw_notifier_call_chain+0x34/0x44 >> 4) 5256 0 timekeeping_update.constprop.9+0xb8/0x114 >> 5) 5256 0 update_wall_time+0x408/0x6dc >> >> Most of 'Size' fields are unexpectedly zero. >> >> This is because stack tracer fails to recognize each function's stack frame >> in check_stack(). Stack tracer searches for a function's pc in the stack >> based on the list returned by save_stack_trace(), but save_stack_trace() on >> arm64 does not return the exact return address saved in a stack frame, but >> a value decrmented by 4 (which means a branch instruction's address). >> This behavior was introduced by >> commit e306dfd06fcb ("ARM64: unwind: Fix PC calculation") >> >> So the matching doesn't succeed in most cases. >> >> This problem can be fixed either by >> a) reverting the commit above >> b) adding an arm64-specific hack to check_patch() >> >> This patch does b). >> >> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org> >> --- >> kernel/trace/trace_stack.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c >> index 3f34496..7086fc3 100644 >> --- a/kernel/trace/trace_stack.c >> +++ b/kernel/trace/trace_stack.c >> @@ -143,7 +143,11 @@ check_stack(unsigned long ip, unsigned long *stack) >> p = start; >> >> for (; p < top && i < max_stack_trace.nr_entries; p++) { >> +#ifdef CONFIG_ARM64 >> + if (*p == (stack_dump_trace[i] + 4)) { >> +#else >> if (*p == stack_dump_trace[i]) { >> +#endif > > Instead of the ugly #ifdef in this code, please add a macro > FTRACE_STACK_FRAME_OFFSET > > Then in include/linux/ftrace.h have: > > #ifndef FTRACE_STACK_FRAME_OFFSET > # define FTRACE_STACK_FRAME_OFFSET 0 > #endif > > And in arch/arm64/include/asm/ftrace.h > > #define FTRACE_STACK_FRAME_OFFSET 4 > > And then just do: > > if (*p == (stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET)) { Yes. Thanks, -Takahiro AKASHI > -- Steve > >> this_size = stack_dump_index[i++] = >> (top - p) * sizeof(unsigned long); >> found = 1; > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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