Messages in this thread Patch in this message | | | From | root <> | Subject | [PATCH] perf core: Use KSTK_ESP() instead of pt_regs->sp while output user regs | Date | Tue, 23 Dec 2014 14:22:25 +0800 |
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From: Chenggang Qin <chenggang.qcg@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.qcg@taobao.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: David Ahern <dsahern@gmail.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Namhyung Kim <namhyung@gmail.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Yanmin Zhang <yanmin.zhang@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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