Messages in this thread | | | Date | Tue, 23 Dec 2014 00:30:51 -0800 | From | Andy Lutomirski <> | Subject | Re: [PATCH] perf core: Use KSTK_ESP() instead of pt_regs->sp while output user regs |
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On 12/22/2014 10:22 PM, root wrote: > 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); > +
This patch is probably fine, but KSTK_ESP seems to be bogus:
unsigned long KSTK_ESP(struct task_struct *task) { return (test_tsk_thread_flag(task, TIF_IA32)) ? (task_pt_regs(task)->sp) : ((task)->thread.usersp); }
I swear that every time I've looked at anything that references TIF_IA32 in the last two weeks, it's been wrong. This should be something like:
if (task_thread_info(task)->status & TS_COMPAT) return task_pt_regs(task)->sp; else if (task == current && task is in a syscall) return current_user_stack_pointer(); else if (task is not running && task is in a syscall) return task->thread.usersp; else if (task is not in a syscall) return task_pt_regs(task)->sp; else we're confused; give up.
What context are you using KSTK_ESP in?
--Andy
> return regs_get_register(regs, pt_regs_offset[idx]); > } > >
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