linux-kernel - Re: [PATCH] x86: unify x86 Makefile(s)

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Date:	Sat, 29 Dec 2007 03:14:23 +0100
From:	Andi Kleen <ak@...e.de>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: unify x86 Makefile(s)

On Friday 28 December 2007 23:13:24 Adrian Bunk wrote:
> On Fri, Dec 28, 2007 at 10:23:41PM +0100, Sam Ravnborg wrote:
> >...
> > Noteworthy remarks on the unification:
> >...
> > - -funit-at-a-time should be easy to unify but it looks like we have a bug
> >   in 32 bit. We only enable -funit-at-a-time for gcc less than 0400 if they
> >   support it
> 
> No, we _dis_able it on 32bit if a gcc < 4.0 supports it.
> 
> > (and I recall it is a gcc 4.00 feature). [-lt -> -gt]
> >...
> 
> unit-at-a-time was introduced in upstream gcc 3.4 and backported to some 
> popular 3.3 x86_64 branch.
> 
> i386 and x86_64 go in exactly opposite directions regarding when to use 
> unit-at-a-time, but that was intentional and we should keep it that way.

i386 disabled it because there were claims that it increased stack size
too much, but I haven't seen any real evidence for that. That is why I never
added it to x86-64. On the other hand it tends to shrink text size considerably.

I think it should be reevaluated and enabled by default on i386 again.

BTW there is a patch pending for gcc 4.3+ that prevents optimizations
that increase stack size unduly. Not sure it has been added there yet,
but that was the right fix for these problems anyways.

-Andi


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