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Date: Tue, 2 Jan 2007 14:01:06 -0800 (PST) From: Linus Torvalds <torvalds@...l.org> To: Adrian Bunk <bunk@...sta.de> cc: Alistair John Strachan <s0348365@....ed.ac.uk>, "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>, LKML <linux-kernel@...r.kernel.org>, Greg KH <greg@...ah.com>, Chuck Ebbert <76306.1226@...puserve.com>, Andrew Morton <akpm@...l.org> Subject: Re: kernel + gcc 4.1 = several problems On Tue, 2 Jan 2007, Adrian Bunk wrote: > > My point is that we have several reported problems only visible > with gcc 4.1. > > Other bug reports are e.g. [2] and [3], but they are only present with > using gcc 4.1 _and_ using -Os. Traditionally, afaik, -Os has tended to show compiler problems that _could_ happen with -O2 too, but never do in practice. It may be that gcc-4.1 without -Os miscompiles some very unusual code, and then with -Os we just hit more cases of that. That said, I th ink gcc-4.1.1 is very common - I know it's the Fedora compiler. Also, CC_OPTIMIZE_FOR_SIZE defaults to 'y' if you have EXPERIMENTAL on, and from all the bug-reports about other features that are marked EXPERIMENTAL, I know that a lot of people do seem to select for it. So I would expect that gcc-4.1.1 and -Os is actually a fairly common combination. I just checked, and it's what I use personally, for example. Of course, my main machine is an x86-64, and it has more registers. At least some historical -Os bug was about bad things happening under register pressure, iirc, and so x86-64 would show fewer problems than regular 32-bit x86 (which has far fewer registers for the compiler to use). It is a bit worrisome. These things seem to be about 50:50 real kernel bugs (just hidden by some common code generation sequence) and real honest-to-goodness compiler bugs. But they are hard as hell to find. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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