linux-kernel - Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load

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Message-ID: <CA+55aFz_wx5BVir=WviqwE_ysKMXb1Ka8T7L+Gq2NT9S=yo2_w@mail.gmail.com>
Date:	Tue, 5 Aug 2014 16:59:28 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	Jakub Jelinek <jakub@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	Michel Dänzer <michel@...nzer.net>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Josh Stone <jistone@...hat.com>
Subject: Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance()
 in scheduler

On Tue, Aug 5, 2014 at 4:30 PM, Frank Ch. Eigler <fche@...hat.com> wrote:
>
> Would you consider a patch that does a gcc COMPARE_DEBUG-based test?

Yes. But as mentioned, we don't have a really good way to do that. I
guess we can do something similar to what "cc-option" does, but that
will end up doing it for every single kernel build. I'd love to have
something like this be done at kconfig time (along with all the
*other* crazy conditional compiler options we do), but I guess that's
a largely independent issue.

And afaik, it will basically disallow every gcc version since 4.5 up
until 4.9.2 gets released. And afaik, even current gcc actually fails
the compare-debug test for at least some inputs, so ...

                 Linus
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