linux-kernel - Re: [PATCH RT] Don't call mcount from vsyscall

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Date:	Tue, 19 Jun 2007 10:41:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH RT] Don't call mcount from vsyscall_fn's


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

> This bit me in the butt.
> 
> I couldn't understand why my init app was segfaulting, with a kernel 
> address, but a user RIP and RSP.  Well, the RIP I think was bogus, but 
> the kernel address was always the start of "mcount".  Looking deeper, 
> I printed out what was in the RSP (even though it was a user stack).  
> It ended up showing me that the calling address was from the VDSO 
> area. Looking even further, I found the offending culprit, which was 
> vread_hpet.
> 
> Looking at the assembly dump, I saw the vread_hpet was calling mcount, 
> but I could not see it in the code. Nor could I see it in hpet.i (-E 
> option of compiling).
> 
> Well, I guess Ingo is a magician when it comes to compiler tricks, and 
> has the mcount being called by "every!!" function, unless you add the 
> "notrace" option.
> 
> This patch adds the notrace to vsyscall_fn, so that we don't have user 
> land apps calling mcount and crashing!

doh - applied. Thanks!

	Ingo
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