linux-kernel - Re: [PATCH] ftrace: distinguish kretprobe'd functions in trace logs

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Date:	Thu, 30 Oct 2008 22:30:18 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Abhishek Sagar <sagar.abhishek@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] ftrace: distinguish kretprobe'd functions in trace
 logs


On Wed, 28 May 2008, Abhishek Sagar wrote:
> Hi Steven,
> 
> Tracing functions via ftrace which have a kretprobe installed on them, can produce misleading output in their trace logs. E.g, consider the correct trace of the following sequence:
> 
> do_IRQ()
> {
> ~
>   irq_enter();
> ~
> }
> 
> 
> Trace log (sample):
> <idle>-0     [00] 4154504455.781616: irq_enter <- do_IRQ
> 
> 
> But if irq_enter() has a kretprobe installed on it, the return value stored on the stack at each invocation is modified to divert the return to a kprobe trampoline function called kretprobe_trampoline(). So with this the trace would (currently) look like:
> 
> <idle>-0     [00] 4154504455.781616: irq_enter <- kretprobe_trampoline
> 
> Now this is quite misleading to the end user, as it suggests something that didn't actually happen. So just to avoid such misinterpretations, the inlined patch aims to output such a log as:
> 
> <idle>-0     [00] 4154504455.781616: irq_enter <- [unknown/kretprobe'd]
> 
> 

[...]

> +
> +#ifdef CONFIG_KRETPROBES
> +static inline int kretprobed(unsigned long addr)
> +{
> +	return addr == (unsigned long)kretprobe_trampoline;

Hi Abhishek,

Now that this code is in mainline, it has become apparent that 
kretprobe_trampoline is not defined on all archs as a global like it is in 
x86. This needs to be fixed (it breaks ia64 build).

Thanks,

-- Steve


> +}
> +#else
> +static inline int kretprobed(unsigned long addr)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_KRETPROBES */
--
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