linux-kernel - Re: Fedora's latest gcc produces unbootable kernels

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Date:	Mon, 3 Dec 2007 12:34:17 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jakub Jelinek <jakub@...hat.com>
cc:	Thomas Gleixner <tglx@....tglx.de>,
	Pierre Ossman <drzeus-list@...eus.cx>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Fedora's latest gcc produces unbootable kernels

On Mon, 3 Dec 2007, Jakub Jelinek wrote:

> On Mon, Dec 03, 2007 at 09:17:22AM +0100, Thomas Gleixner wrote:
> > I looked at the disassembly but I can not spot the problem.
> > 
> > I think the real problem is somewhere else. Likely candidates are
> > hrtimer_forward() or hrtimer_start() - in that order.
> 
> Should be hopefully fixed in latest Fedora gcc.  The problem was in code like
> typedef union { long long int s; } U;
> typedef struct { U u; } S;
> 
> void foo (S *s, long long int x, unsigned long int y)
> {
>   s->u = ({ (U) { .s = s->u.s + x * y }; });
> }
> 
> where a backport of a recent optimization of mine, without which gcc handles
> terribly initializers from compound literals (which is something hrtimer
> uses just everywhere - why can't ktime.h for #if BITS_PER_LONG == 64 || defined(CONFIG_KTIME_SCALAR)
> just use a scalar rather than union with a scalar in it??),

Of course just to annoy you :)

Seriously, we want the same code/initializers for both the scalar and the
sec/nsec case. That's where the union comes from.

Thanks,

	tglx
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