linux-kernel - Re: [PATCH] ftrace: use kretprobe trampoline name to test in output

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Date:	Mon, 3 Nov 2008 10:41:59 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Abhishek Sagar <sagar.abhishek@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>, ananth@...ibm.com,
	jkenisto@...ibm.com, mhiramat@...hat.com
Subject: Re: [PATCH] ftrace: use kretprobe trampoline name to test in output


* Steven Rostedt <rostedt@...dmis.org> wrote:

> [
>   Ingo,
> 
>   Can you get this ready for 2.6.28. Without this fix, tracing
>   breaks the ia64 build.
> ]
> 
> When a function is kprobed, the return address is set to the
> kprobe_trampoline, or something similar. This caused the output
> of the trace to look confusing when the parent seemed to be this
> "kprobe_trampoline" function.
> 
> To fix this, Abhishek Sagar added a test of the instruction pointer
> of the parent to see if it matched the kprobe_trampoline. If it
> did, the output would print a "[unknown/kretprobe'd]" instead.
> 
> Unfortunately, not all archs do this the same way, and the trampoline
> function may not be exported, which causes failures in builds.
> 
> This patch will compare the name instead of the pointer to see
> if it matches. This prevents us from depending on a function from
> being exported, and should work on all archs. The worst that can
> happen is that an arch might use a different name and then we
> go back to the confusing output. At least the arch will still build.
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> Tested-by: Abhishek Sagar <sagar.abhishek@...il.com>
> Acked-by: Abhishek Sagar <sagar.abhishek@...il.com>
> ---
>  kernel/trace/trace.c |   39 +++++++++++++++++++++------------------
>  1 file changed, 21 insertions(+), 18 deletions(-)

applied to tip/tracing/urgent, thanks!

	Ingo
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