Messages in this thread Patch in this message | | | From | AKASHI Takahiro <> | Subject | [RFC 1/3] ftrace: adjust a function's pc to search for in check_stack() for arm64 | Date | Mon, 13 Jul 2015 14:29:33 +0900 |
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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 this_size = stack_dump_index[i++] = (top - p) * sizeof(unsigned long); found = 1; -- 1.7.9.5
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