On 12/22/2014 10:22 PM, root wrote:
> 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);
> +
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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