* On Mon, Jul 04, 2011 at 11:38:30PM +0100, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote:
On 4 July 2011 23:00, Raghavendra D Prabhu <raghu.prabhu13@xxxxxxxxx> wrote:
This is to avoid gcc optimizating out the comparison in assert,
due to assumption of signed overflow being undefined by default (-Werror=strict-overflow).
--- a/Makefile.hw
+++ b/Makefile.hw
@@ -9,7 +9,7 @@ include $(SRC_PATH)/rules.mak
$(call set-vpath, $(SRC_PATH):$(SRC_PATH)/hw)
-QEMU_CFLAGS+=-I.. -I$(SRC_PATH)/fpu
+QEMU_CFLAGS+=-I.. -I$(SRC_PATH)/fpu -fno-strict-overflow
Can you give a more detailed description of the problem this is trying
to solve? I think it would be nicer if we could remove the assumptions
about signed overflows instead, if that's practical.
Following line in pcie.c:pcie_add_capability:505
assert(offset < offset + size);
is what the compiler was warning about. The compiler optimizes out that
comparison without fno-strict-overflow flag. More information about it
is here - http://www.airs.com/blog/archives/120 -- as already mentioned by Stefan.
(Also, if we do want to add this compiler flag then it ought to be
done in configure I think, as we do for -fno-strict-aliasing.)
Globally adding that flag can limits the optimizations of gcc since in
other places (loops) the undefined behavior can be advantageous, hence
added only to Makefile.hw.
-- PMM
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Raghavendra Prabhu
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