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

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Message-ID: <20071229095253.GC27360@does.not.exist>
Date:	Sat, 29 Dec 2007 11:52:53 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: unify x86 Makefile(s)

On Sat, Dec 29, 2007 at 10:39:04AM +0100, Sam Ravnborg wrote:
> On Sat, Dec 29, 2007 at 12:13:24AM +0200, 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.
> I have:
> $ gcc --version
> gcc (GCC) 4.1.2 20070925 (Red Hat 4.1.2-33)
> 
> And with the current code in arch/x86/Makefile_32 I do not
> have -funit-at-a-time.
>...

You do not have this option, but you do not need it since it's enabled 
with -O in all gcc versions that support it except for some vendor 
backports to gcc 3.3.

>...
> This is the relevant snippet from the Makefile:
> KBUILD_CFLAGS += $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)
> 
> It reads:
> If gcc version is less than 4.00 then enable -funit-at-a-time only for gcc that supports it.
> -funit-at-a-time is NOT enabled for gcc >= 4.00

It is not _explicitely_ enabled for gcc >= 4.0 since it's anyway enabled.

> So it will enable -funit-at-a-time for gcc 3.4 as it is now.
> Which was what we wanted to avoid..
> So I see no reason not to enable it uncondintionally (if gcc supports it) as we have
> used it for 3.4 for as long as we have introduced -funit-at-a-time.

We have never used it with gcc 3.4 on i386.

> 	Sam

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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