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SubjectRe: [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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