linux-kernel - Re: [PATCH RESEND 1/2] vsprintf: introduce %pT format specifier

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Date:	Wed, 23 Mar 2011 14:49:01 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Namhyung Kim <namhyung@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RESEND 1/2] vsprintf: introduce %pT format specifier

2011/3/23 Steven Rostedt <rostedt@...dmis.org>:
> On Wed, 2011-03-23 at 22:29 +0900, Namhyung Kim wrote:
>> The %pT format specifier is for stack backtrace. Its handler
>> sprint_trace() does symbol lookup using (address-1) to ensure
>> the address will not point outside of the function.
>>
>> If there is a tail-call to the function marked "noreturn",
>> gcc optimized out the code after the call then causes saved
>> return address points outside of the function (i.e. the start
>> of the next function), so pollutes call trace somewhat.
>> This patch will fix it.
>>
>> before:
>> [   18.345923] Call Trace:
>> [   18.346001]  [<ffffffff812a8502>] panic+0x8c/0x18d
>> [   18.346257]  [<ffffffffa000012a>] deep01+0x0/0x38 [test_panic]  <--- bad
>> [   18.346347]  [<ffffffff81104666>] proc_file_write+0x73/0x8d
>> [   18.346432]  [<ffffffff811000b3>] proc_reg_write+0x8d/0xac
>> [   18.346516]  [<ffffffff810c7d32>] vfs_write+0xa1/0xc5
>> [   18.346603]  [<ffffffff810c7e0f>] sys_write+0x45/0x6c
>> [   18.346801]  [<ffffffff8f02943b>] system_call_fastpath+0x16/0x1b
>>
>> after:
>> [   22.224483] Call Trace:
>> [   22.224569]  [<ffffffff812bce69>] panic+0x8c/0x18d
>> [   22.224848]  [<ffffffffa000012a>] panic_write+0x20/0x20 [test_panic]  <--- ok
>> [   22.224979]  [<ffffffff81115fab>] proc_file_write+0x73/0x8d
>> [   22.225089]  [<ffffffff81111a5f>] proc_reg_write+0x8d/0xac
>> [   22.225199]  [<ffffffff810d90ee>] vfs_write+0xa1/0xc5
>> [   22.225304]  [<ffffffff810d91cb>] sys_write+0x45/0x6c
>> [   22.225408]  [<ffffffff812c07fb>] system_call_fastpath+0x16/0x1b
>
> Nice
>
> Acked-by: Steven Rostedt <rostedt@...dmis.org>

Same for me:

Acked-by: Frederic Weisbecker <fweisbec@...il.com>
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