[patch 24/24] Dont use -fwrapv compiler option: its buggy in gcc-4.1.x

Greg KH
2009-07-17T20:20:48Z

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2.6.30-stable review patch. If anyone has any objections, please let us know.

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From: Linus Torvalds <torvalds@linux-foundation.org>

commit a137802ee839ace40079bebde24cfb416f73208a upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/Makefile
+++ b/Makefile
@@ -574,7 +574,7 @@ KBUILD_CFLAGS += $(call cc-option,-Wdecl
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)