From: Chenggang Qin <chenggang....@taobao.com>
For x86_64, the exact value of user stack's esp should be got by
KSTK_ESP(current).
current->thread.usersp is copied from PDA while enter ring0.
Now, we output the value of sp from pt_regs. But pt_regs->sp has changed before
it was pushed into kernel stack.
So, we cannot get the correct callchain while unwind some user stacks.
For example, if the stack contains __lll_unlock_wake()/__lll_lock_wait(), the
callchain will break some times with the latest version of libunwind.
The root cause is the sp that is used by libunwind may be wrong.
If we use KSTK_ESP(current), the correct callchain can be got everytime.
Other architectures also have KSTK_ESP() macro.
Signed-off-by: Chenggang Qin <chenggang....@taobao.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Arjan van de Ven <ar...@linux.intel.com>
Cc: David Ahern <dsah...@gmail.com>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Mike Galbraith <efa...@gmx.de>
Cc: Namhyung Kim <namhy...@gmail.com>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Wu Fengguang <fengguang...@intel.com>
Cc: Yanmin Zhang <yanmin.zh...@intel.com>
---
arch/x86/kernel/perf_regs.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index e309cc5..5da8df8 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -60,6 +60,9 @@ u64 perf_reg_value(struct pt_regs *regs, int idx)
if (WARN_ON_ONCE(idx >= ARRAY_SIZE(pt_regs_offset)))
return 0;
+ if (idx == PERF_REG_X86_SP)
+ return KSTK_ESP(current);
+
return regs_get_register(regs, pt_regs_offset[idx]);
}
--
1.9.1
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