linux-kernel - Re: kernel + gcc 4.1 = several problems

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Message-ID: <20070102232429.GE20714@stusta.de>
Date:	Wed, 3 Jan 2007 00:24:29 +0100
From:	Adrian Bunk <bunk@...sta.de>
To:	"D. Hazelton" <dhazelton@...er.net>
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>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: kernel + gcc 4.1 = several problems

On Tue, Jan 02, 2007 at 05:06:14PM -0500, D. Hazelton wrote:
> On Tuesday 02 January 2007 16:56, Alistair John Strachan wrote:
> > On Tuesday 02 January 2007 21:10, Adrian Bunk wrote:
> > [snip]
> >
> > > > > Comparing your report and [1], it seems that if these are the same
> > > > > problem, it's not a hardware bug but a gcc or kernel bug.
> > > >
> > > > This bug specifically indicates some kind of miscompilation in a
> > > > driver, causing boot time hangs. My problem is quite different, and
> > > > more subtle. The crash happens in the same place every time, which does
> > > > suggest determinism (even with various options toggled on and off, and
> > > > a 300K smaller kernel image), but it takes 8-12 hours to manifest and
> > > > only happens with GCC 4.1.1. ...
> > >
> > > Sorry if my point goes a bit away from your problem:
> > >
> > > 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.
> >
> > I find [2] most compelling, and I can confirm that I do have the same
> > problem with or without optimisation for size. I don't use selinux nor has
> > it ever been enabled.
> >
> > At any rate, I have absolute confirmation that it is GCC 4.1.1, because
> > with GCC 3.4.6 the same kernel I reported booting three days ago is still
> > cheerfully working. I regularly get uptimes of 60+ days on that machine,
> > rebooting only for kernel upgrades. 2.6.19 seems to be no worse in this
> > regard.
> >
> > Perhaps fortunately, the configs I've tried have consistently failed to
> > shake the crash, so I have a semi-reproducible test case here on C3-2
> > hardware if somebody wants to investigate the problem (though it still
> > takes 6-12 hours).
> 
> The GCC code generator appears to have been rewritten between 3.4.6 and 
> 4.1.1....
> 
> I took a look at the dump he posted and there are some minor and some massive 
> differences between the code. In one case some of the code is swapped, in 
> another there is code in the 3.4.6 version that isn't in the 4.1.1... Finally 
> the 4.1.1 version of the function has what appears to be function calls and 
> these don't appear in the code generated by 3.4.6

Differences are expected since we disable unit-at-a-time for gcc < 4 
and gcc development didn't stall between 3.4 and 4.1.

> In other words - the code generation for 4.1.1 appears to be broken when it 
> comes to generating system code.

Bug number for an either already open or created by you bug in the gcc 
Bugzilla for what you claim to be a bug in gcc?

> DRH

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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