linux-kernel - Re: [tip:perf/uprobes] uprobes/core: Clean up, refactor and improve the code

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Message-ID: <20120220105129.GB24200@elte.hu>
Date:	Mon, 20 Feb 2012 11:51:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	jkenisto@...ibm.com, a.p.zijlstra@...llo.nl, ananth@...ibm.com,
	anton@...hat.com, masami.hiramatsu.pt@...achi.com,
	acme@...radead.org, oleg@...hat.com, tglx@...utronix.de,
	Benjamin Herrenschmidt <benh@....ibm.com>,
	Josh Stone <jistone@...hat.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/uprobes] uprobes/core: Clean up,  refactor and improve
 the code


* Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:

> * Ingo Molnar <mingo@...e.hu> [2012-02-20 08:38:23]:
> 
> > 
> > * Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:
> > 
> > > The volatiles were added to arch/x86/kernel/kprobes.c because 
> > > of commit 7115e3fcf45 and 315eb8a2a1b. The volatiles are 
> > > required because gcc 4.6 gave a warning about the asm operand 
> > > for test_bit.  So the same were added to 
> > > arch/x86/kernel/uprobes.c.
> > 
> > Seems like a GCC bug - a bogus warning - or does it generate bad 
> > code as well?
> 
> Yes it is a gcc bug and was fixed by Jakub.
> As per Josh, only the first long is output if compiled on the buggy gcc.

That's an important piece of information - the more reason to 
document the quirk.

> > In any case, kprobes.c did it correctly, it added the volatile 
> > *and a comment*, pointing out that it's a GCC bug. No such 
> > warning was added to uprobes.c, making the volatile look 
> > entirely spurious.
> 
> okay. 

Thanks,

	Ingo
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