From: Linus Torvalds Date: Thu, 19 Mar 2009 18:10:17 +0000 (-0700) Subject: Add '-fwrapv' to gcc CFLAGS Patch-mainline: 2.6.29 Git-commit: 68df3755e383e6fecf2354a67b08f92f18536594 References: bko#12597 bnc#487106 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 Signed-off-by: Linus Torvalds Acked-by: Jeff Mahoney --- Makefile | 1 + 1 file changed, 1 insertion(+) --- a/Makefile +++ b/Makefile @@ -341,6 +341,7 @@ KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXI KBUILD_CFLAGS := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \ -fno-strict-aliasing -fno-common \ -Werror-implicit-function-declaration +KBUILD_CFLAGS += $(call cc-option,-fwrapv) KBUILD_AFLAGS := -D__ASSEMBLY__ # Warn about unsupported modules in kernels built inside Autobuild