Add '-fwrapv' to gcc CFLAGS

commit 68df3755e383e6fecf2354a67b08f92f18536594 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/Makefile b/Makefile
index 9f4860d0d7dfdabb7a45f0508a25a1b16c2503f7..95fe83e85328c87ae51d943a27d7b16d94c236fa 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -341,6 +341,7 @@ KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXINCLUDE)
 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__
 
 # Read KERNELRELEASE from include/config/kernel.release (if it exists)