linux-kernel - Re: Linux 2.6.27.27

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Message-ID: <alpine.LFD.2.01.0907211759180.19335@localhost.localdomain>
Date:	Tue, 21 Jul 2009 18:07:50 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Troy Moure <twmoure@...pr.net>
cc:	Krzysztof Oledzki <olel@....pl>, Greg KH <gregkh@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, stable@...nel.org,
	lwn@....net, Ian Lance Taylor <iant@...gle.com>
Subject: Re: Linux 2.6.27.27

On Tue, 21 Jul 2009, Linus Torvalds wrote:
> 
> Just out of curiosity, how did you find it? Now that I know where to look, 
> it's very obvious in the assembler diffs, but I didn't notice it until you 
> pointed it out just because there is so _much_ of the diffs...

Ahh. I think I see how you found it. Looking at the diffs, there's only a 
few places where the number of instructions changed by a big fraction. And 
there's only _one_ place that has a factor-of-three difference (26 lines 
in the correct cases, and 7 lines in the wrong one). Clever.

There's also a case in do_page_fault() where -fno-strict-overflow 
generates a _lot_ more instructions than the other cases (but not by a 
factor of three - but it expands 63 instructions to 100). I'm not seeing 
quite _why_ it does that, but it does various stupid things like multiply 
by 0x38 etc. But it doesn't look buggy, it just looks stupid.

Or did you just brute-force it and spend a lot of time eyeballing things?

			Linus
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