linux-kernel - Re: Is gcc thread-unsafe?

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Message-ID: <alpine.LFD.0.999.0710251628440.30120@woody.linux-foundation.org>
Date:	Thu, 25 Oct 2007 16:32:53 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <ak@...e.de>
cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Is gcc thread-unsafe?

On Fri, 26 Oct 2007, Andi Kleen wrote:
> 
> No it can't (at least not on x86) as I have explained in the rest of the mail 
> you conveniently snipped.

I "conveniently snipped it" because it was pointless.

"adc" or "cmov" has nothing what-so-ever to do with it. If some routine 
returns 0-vs-1 and gcc then turns "if (routine()) x++" into 
"x+=routine()", what does that have to do with adc or cmov?

The fact is, these kinds of optimizations are *bogus* and they are 
dangerous.

Now, it's equally true that we probably don't have those kinds of patterns 
in the kernel, and we'll probabaly not hit it, but wouldn't it be much 
better to make sure that compilers shouldn't do that?

			Linus
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