Don't use '-fwrapv' compiler option: it's buggy in gcc-4.1.x
Linus Torvalds [Sun, 12 Jul 2009 18:25:04 +0000 (11:25 -0700)]
This causes kernel images that don't run init to completion with certain
broken gcc versions.

This fixes kernel bugzilla entry:
http://bugzilla.kernel.org/show_bug.cgi?id=13012

I suspect the gcc problem is this:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28230

Fix the problem by using the -fno-strict-overflow flag instead, which
not only does not exist in the known-to-be-broken versions of gcc (it
was introduced later than fwrapv), but seems to be much less disturbing
to gcc too: the difference in the generated code by -fno-strict-overflow
are smaller (compared to using neither flag) than when using -fwrapv.

Reported-by: Barry K. Nathan <barryn@pobox.com>
Pushed-by: Frans Pop <elendil@planet.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Makefile

index 0aeec59..bbe8453 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -565,7 +565,7 @@ 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  += $(call cc-option,-fno-strict-overflow)
 
 # revert to pre-gcc-4.4 behaviour of .eh_frame
 KBUILD_CFLAGS  += $(call cc-option,-fno-dwarf2-cfi-asm)