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SubjectRe: [PATCH,v2] Only add '-fwrapv' to gcc CFLAGS for gcc 4.2 and later
On Fri, Jul 10, 2009 at 10:05:47PM +0200, Frans Pop wrote:
> On Friday 10 July 2009, Frans Pop wrote:
> > The discussion on issue looks to have died, but it has bitten Debian
> > stable ("Lenny") [1] as it causes init to die on s390 after a kernel
> > update.
> >
> > Here's a possible patch. The exact gcc version to check for is still a
> > bit open I guess. For the s390 issue I've confirmed that 4.2.4 is OK,
> > but for safety and because of Andrew's comment above I've set the test
> > for 4.3 in the patch.
>
> Here's an updated patch as I found the gcc version check was incorrect
> (0430 should have been 0403; sorry).
>
> I've now changed the check to allow -fwrapv for gcc 4.2 as that has been
> shown to work and because of the consideration mentioned in my previous
> mail.
>
> ---
> From: Frans Pop <elendil@planet.nl>
> Subject: Only add '-fwrapv' to gcc CFLAGS for gcc 4.2 and later
>
> This flag has been shown to cause init to segfault for kernels
> compiled with gcc-4.1. gcc version 4.2.4 has been shown to be OK.
>
> This fixes http://bugzilla.kernel.org/show_bug.cgi?id=13012.
>
> Reported-by: Barry K. Nathan <barryn@pobox.com>
> Signed-off-by: Frans Pop <elendil@planet.nl>
>
> diff --git a/Makefile b/Makefile
> index 0aeec59..2519fde 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -565,7 +565,8 @@ KBUILD_CFLAGS += $(call
> cc-option,-Wdeclaration-after-statement,)
> KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
>
> # 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:
# 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.

Sam


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