linux-kernel - Re: [PATCH,v2] Only add '-fwrapv' to gcc CFLAGS for gcc 4.2 and later

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Message-Id: <200907180043.53257.elendil@planet.nl>
Date:	Sat, 18 Jul 2009 00:43:51 +0200
From:	Frans Pop <elendil@...net.nl>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-kbuild@...r.kernel.org, barryn@...ox.com
Subject: Re: [PATCH,v2] Only add '-fwrapv' to gcc CFLAGS for gcc 4.2 and later

On Saturday 18 July 2009, Sam Ravnborg wrote:
> >  # disable invalid "can't wrap" optimizations for signed / pointers
> > -KBUILD_CFLAGS	+= $(call cc-option,-fwrapv)
> > +KBUILD_CFLAGS  += $(shell if [ $(call cc-version) -ge 0402 ]; then \
> > +		    echo $(call cc-option,-fwrapv); fi ;)
>
> This would be simpler if you use:

That's now academic as Linus decided on a different fix.

> # cc-ifversion
> # Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
> cc-ifversion = $(shell [ $(call cc-version, $(CC)) $(1) $(2) ] && echo $(3))
>
> We have only one user at the moment so I understand why you missed it.

:-)

I based my patch on arch/x86/Makefile:
35:        KBUILD_CFLAGS += $(shell if [ $(call cc-version) -lt 0400 ] ; then \
36:                echo $(call cc-option,-fno-unit-at-a-time); fi ;)

Guess that could be improved to use cc-ifversion then.

And a quick git grep gives a few other potential candidates:
arch/ia64/Makefile:44:ifeq ($(call cc-version),0304)
arch/parisc/Makefile:129:       @if test "$(call cc-version)" -lt "0303"; then \
arch/powerpc/Makefile:80:GCC_BROKEN_VEC := $(shell if [ $(call cc-version) -lt 0400 ] ; then echo "y"; fi)
arch/powerpc/Makefile:219:      @if test "$(call cc-version)" = "0304" ; then \
arch/um/Makefile-i386:38:KBUILD_CFLAGS += $(shell if [ $(call cc-version) -lt 0400 ] ; then \

Cheers,
FJP
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