Messages in this thread | | | Date | Mon, 13 Jul 2015 11:24:39 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC 1/3] ftrace: adjust a function's pc to search for in check_stack() for arm64 |
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On Mon, 13 Jul 2015 14:29:33 +0900 AKASHI Takahiro <takahiro.akashi@linaro.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@linaro.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)) {
-- Steve
> this_size = stack_dump_index[i++] = > (top - p) * sizeof(unsigned long); > found = 1;
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