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

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Date:	Wed, 23 Mar 2011 09:43:44 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RESEND 1/2] vsprintf: introduce %pT format specifier

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>

-- Steve


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