linux-kernel - Re: [PATCH] Kprobes: Add kprobes smoke tests that run on boot

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Date:	Tue, 08 Jan 2008 15:10:41 -0800
From:	Jim Keniston <jkenisto@...ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	ananth@...ibm.com, akpm@...ux-foundation.org,
	lkml <linux-kernel@...r.kernel.org>, mingo@...e.hu,
	mhiramat@...hat.com, davem@...emloft.net, hskinnemoen@...el.com
Subject: Re: [PATCH] Kprobes: Add kprobes smoke tests that run on boot

On Tue, 2008-01-08 at 22:00 +0100, Andi Kleen wrote:
> Ananth N Mavinakayanahalli <ananth@...ibm.com> writes:
> >  kernel/kprobes.c        |    2 
> >  kernel/test_kprobes.c   |  216 ++++++++++++++++++++++++++++++++++++++++++++++++
> 
> Can you put this somewhere else please? I know there are already some
> test files in kernel/* but imho they all belong into some other directory.
> 
> +	if (!err)
> +		init_test_probes();
>  	return err;
> 
> Couldn't this be just a normal initcall? Perhaps even a module_init(),
> then it would be possible to use as a module too.
> 
> -Andi

I have no problem with that, but if we want to make it buildable as a
module, the call to get_kprobe() needs to be replaced with some other
gcc-inline-defeating mechanism, or we need to export get_probe().  I
much prefer the former, since get_kprobe() is a kprobes-internal
function.

Anybody know an architecture-independent way (other than noinline, which
doesn't always work) of making gcc decide not to inline a function?
E.g., does taking (and using) the function's address do it?

Jim Keniston

>>From Ananth's patch:
+static noinline u32 kprobe_target(u32 value)
+{
+       /*
+        * gcc ignores noinline on some architectures unless we stuff
+        * sufficient lard into the function. The get_kprobe() here is
+        * just for that.
+        *
+        * NOTE: We aren't concerned about the correctness of
get_kprobe()
+        * here; hence, this call is neither under !preempt nor with the
+        * kprobe_mutex held. This is fine(tm)
+        */
+       if (get_kprobe((void *)0xdeadbeef))
+               printk(KERN_INFO "Kprobe smoke test: probe on
0xdeadbeef!\n");
+
+       return (value / div_factor);
+}

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