linux-kernel - Re: [ANNOUNCE][RFC][PATCH] Crash-utility, tracing: enable crash to analyze tracing from core-file (make tracing can act as a flight recorder)

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Date:	Tue, 04 Aug 2009 12:36:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Dave Anderson <anderson@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <clark.williams@...il.com>,
	Jon Masters <jonathan@...masters.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Zhaolei <zhaolei@...fujitsu.com>, kosaki.motohiro@...fujitsu.com,
	Li Zefan <lizf@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Jason Baron <jbaron@...hat.com>, srostedt@...hat.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [ANNOUNCE][RFC][PATCH] Crash-utility, tracing: enable crash to
 analyze tracing from core-file (make tracing can act as a flight recorder)

On Tue, 2009-08-04 at 14:52 +0800, Lai Jiangshan wrote:
> Peter Zijlstra wrote:
> > On Mon, 2009-08-03 at 22:48 +0800, Lai Jiangshan wrote:
> >> + /* SIGH, we cann't get "print fmt" from core-file */
> > 
> > doesn't crash have a vmlinux around to look at?
> 
> 
> I don't known how to look at it:
> 
> static int								\
> ftrace_format_##call(struct trace_seq *s)				\
> {									\
> 	struct ftrace_raw_##call field __attribute__((unused));		\
> 	int ret = 0;							\
> 									\
> 	tstruct;							\
> 									\
> 	trace_seq_printf(s, "\nprint fmt: " print);			\
> 									\
> 	return ret;							\
> }
> 
> We need the address of the const string <"\nprint fmt: " print>,
> I don't know how to get it current from vmlinux.
> 
> I have sent a patch which try to reduce the size of .txt in kernel
> and reduce coupling. This patch has a little side-effect:
> the "print fmt"'s address is saved in struct ftrace_event_call.

Aah, right, I thought the fmt string was easily obtainable from the
_ftrace_events section, but now I see it is not, the patch you mention
below does indeed make it so.

> [
> http://lkml.org/lkml/2009/7/30/30
> 
> This patch is really useful for kernel. We don't change the kernel
> even a single line for the purpose of we can read the core-file easier.

Well, I see no harm in changing the kernel a little when it makes no
difference to the kernel but makes post-mortem analysis a little bit
easier.

> This patch is also helpful for crash more or less. So I mention it.
> ]

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