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dann frazier 03-20-2009 06:29 PM

Bug#520548: Add -fwrapv to CFLAGS
Package: linux-2.6
Version: 2.6.26-13lenny2
Severity: important
Tags: patch

We should include this in stable updates. No ABI changes were detected
in a test build of the 686 flavor.

commit 68df3755e383e6fecf2354a67b08f92f18536594
Author: Linus Torvalds <>
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

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 <>
Signed-off-by: Linus Torvalds <>

Adjusted to apply to Debian's 2.6.26 by dann frazier <>

diff -urpN linux-source-2.6.26.orig/Makefile linux-source-2.6.26/Makefile
--- linux-source-2.6.26.orig/Makefile 2009-03-09 16:22:35.000000000 -0600
+++ linux-source-2.6.26/Makefile 2009-03-20 11:14:43.000000000 -0600
@@ -321,6 +321,7 @@ KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXI
KBUILD_CFLAGS := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs
-fno-strict-aliasing -fno-common
+KBUILD_CFLAGS += $(call cc-option,-fwrapv)

# Read KERNELRELEASE from include/config/kernel.release (if it exists)

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