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From: Andy Lutomirski <luto@amacapital.net>
To: root <chenggang.qin@gmail.com>, linux-kernel@vger.kernel.org
Cc: Chenggang Qin <chenggang.qcg@taobao.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Arjan van de Ven <arjan@linux.intel.com>,
	David Ahern <dsahern@gmail.com>, Ingo Molnar <mingo@redhat.com>,
	Mike Galbraith <efault@gmx.de>, Namhyung Kim <namhyung@gmail.com>,
	Paul Mackerras <paulus@samba.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Wu Fengguang <fengguang.wu@intel.com>,
	Yanmin Zhang <yanmin.zhang@intel.com>
Subject: Re: [PATCH] perf core: Use KSTK_ESP() instead of pt_regs->sp while output user regs
Date: Tue, 23 Dec 2014 00:30:51 -0800	[thread overview]
Message-ID: <5499283B.7020002@amacapital.net> (raw)
In-Reply-To: <1419315745-20767-1-git-send-email-user@chenggang-laptop>

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]);
>  }
>  
> 


  reply	other threads:[~2014-12-23  8:30 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-23  6:22 root
2014-12-23  8:30 ` Andy Lutomirski [this message]
     [not found] ` <c027bde0-5f4f-441f-8d45-3e7f6f702231@alibaba-inc.com>
2014-12-25 15:48   ` 答复:[PATCH] " Andy Lutomirski
2014-12-25 16:21     ` Andy Lutomirski
2014-12-30 19:03     ` Peter Zijlstra
2014-12-30 23:29       ` Andy Lutomirski
2014-12-31  2:00         ` Andy Lutomirski
2015-01-02 16:11           ` Jan Beulich
2015-01-02 18:03             ` Andy Lutomirski
2015-01-05  8:47               ` Jan Beulich
2015-01-04 16:10       ` Jiri Olsa
2015-01-04 17:18         ` Andy Lutomirski
2015-01-04 17:41           ` Jiri Olsa
2015-01-04 18:36             ` [PATCH 0/2] perf: Improve user regs sampling Andy Lutomirski
2015-01-04 18:36               ` [PATCH 1/2] perf: Move task_pt_regs sampling into arch code Andy Lutomirski
2015-01-05 14:07                 ` Peter Zijlstra
2015-01-05 16:13                   ` Andy Lutomirski
2015-01-05 16:44                     ` Peter Zijlstra
2015-01-05 18:28                       ` Andy Lutomirski
2015-01-09 12:32                 ` [tip:perf/urgent] " tip-bot for Andy Lutomirski
2015-01-04 18:36               ` [PATCH 2/2] x86_64, perf: Improve user regs sampling Andy Lutomirski
2015-01-09 12:32                 ` [tip:perf/urgent] perf/x86_64: " tip-bot for Andy Lutomirski
2015-01-05 10:46               ` [PATCH 0/2] perf: " Jiri Olsa

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