Date: Wed, 30 Jul 2014 09:27:47 +0200
From: Markus Trippelsdorf <markus@trippelsdorf.de>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Michel =?iso-8859-1?Q?D=E4nzer?= <michel@daenzer.net>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of
 load_balance()  in scheduler
Message-ID: <20140730072747.GG22904@x4>
References: <20140730014827.565626091@linuxfoundation.org>
 <20140730014829.344302554@linuxfoundation.org>
 <20140730065312.GA1652@laptop.redhat.com>
 <20140730071308.GF22904@x4>
 <20140730072120.GB1652@laptop.redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org

On 2014.07.30 at 09:21 +0200, Jakub Jelinek wrote:
> On Wed, Jul 30, 2014 at 09:13:08AM +0200, Markus Trippelsdorf wrote:
> > On 2014.07.30 at 08:53 +0200, Jakub Jelinek wrote:
> > > On Tue, Jul 29, 2014 at 06:49:09PM -0700, Greg Kroah-Hartman wrote:
> > > > 3.15-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > IMNSHO this is a too big hammer approach.  The bug happened on a single
> > > file only (right?), so if anything, IMHO it could be disabled for that
> > > single file only, and better do it only for compilers with the bug.
> > 
> > No. There are many more files affected. It just happens that Linus
> > analyzed the assembly of this single file (fair.c) and found a bug. 
> > Just build your redhat distro kernel with GCC_COMPARE_DEBUG=1 and you'll
> > see. So unless someone analyzes the assembly output of all other
> > affected files by hand and finds no issues, one has to assume the worst.
> 
> I'm talking about wrong-code issues.  For -fcompare-debug, we indeed check
> it primarily during gcc bootstrap (through bootstrap-debug) and some
> testcases, and we'll certainly try to build some more code with
> -fcompare-debug and fix the issues.

Yes, I'm talking about wrong-code issues, too. For example the pr61801.c
testcase was reduced from kernel/exit.c.

-- 
Markus
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