From: Don Zickus <dzickus@redhat.com>
Date: Mon, 18 May 2009 14:07:43 -0400
Subject: [misc] compile: add -fwrapv to gcc CFLAGS
Message-id: 20090518180743.GA16867@redhat.com
O-Subject: [PATCH RHEL-5.4] compile: Add -fwrapv to gcc CFLAGS
Bugzilla: 491266
RH-Acked-by: Pete Zaitcev <zaitcev@redhat.com>
RH-Acked-by: Amerigo Wang <amwang@redhat.com>
RH-Acked-by: Eugene Teo <eugene@redhat.com>

https://bugzilla.redhat.com/show_bug.cgi?id=491266

Turn wrapping garbage into something predicatable.
Sounds like a good thing to do ..

commit 68df3755e383e6fecf2354a67b08f92f18536594
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu Mar 19 11:10:17 2009 -0700

    Add '-fwrapv' to gcc CFLAGS

    This makes sure that gcc doesn't try to optimize away wrapping
    arithmetic, which the kernel occasionally uses for overflow testing, ie
    things like

    	if (ptr + offset < ptr)

    which technically is undefined for non-unsigned types. See

    	http://bugzilla.kernel.org/show_bug.cgi?id=12597

    for details.

    Not all versions of gcc support it, so we need to make it conditional
    (it looks like it was introduced in gcc-3.4).

    Reminded-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Compiled and booted on an x86_64.  rpm built a kernel just to stress test
it a little.  I know this is a little late to be throwing into a beta
kernel, but it is marked urgent by the security team and the risk seems
low.

Please ACK

Cheers,
Don

diff --git a/Makefile b/Makefile
index e6956da..8411cbe 100644
--- a/Makefile
+++ b/Makefile
@@ -307,6 +307,7 @@ CPPFLAGS        := -D__KERNEL__ $(LINUXINCLUDE)
 
 CFLAGS          := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
                    -fno-strict-aliasing -fno-common -Wstrict-prototypes -Wundef -Werror-implicit-function-declaration
+CFLAGS		+= $(call cc-option,-fwrapv)
 AFLAGS          := -D__ASSEMBLY__
 
 # Read KERNELRELEASE from include/config/kernel.release (if it exists)