On Friday 01 March 2013, Sedat Dilek wrote: > I have seen a lot of such failures when using the Freetz (a small > router project) build-system with gcc-4.7-x where "-Os" is default > optimization-level. > > Last, when I tried to integrate ltrace GIT snapshots into Freetz. > All these "build-errors" could be solved in changing ltrace code. > So, I would not talk about "false positives". But the point is that we should not be changing the source code to unnecessary initializations, because that may hide real bugs if the code is modified in a way that relies on a sane value of some variable. They are false positives if the code is actually correct and does not need to be changed. I actually have a newer version of my patch (see below) that uses the cc-disable-warning macro in order to avoid some of the side-effects of setting an unknown option on older gcc versions. > Furthermore, "-Wno-maybe-uninitialized" gcc-option is available > gcc-4-7+, so your patch is incomplete. O don't understand. The patch avoids the warnings when building with gcc-4.7 or higher with -Os. Arnd >From d313219a2f2e0753b8e96105b7a944e1c22566ae Mon Sep 17 00:00:00 2001 From: Arnd Bergmann <arnd@xxxxxxxx> Date: Fri, 15 Feb 2013 21:23:58 +0100 Subject: [PATCH] Turn off -Wmaybe-uninitialized when building with -Os gcc-4.7 and higher add a lot of false positive warnings about potential uses of uninitialized warnings, but only when optimizing for size (-Os). This is the default when building allyesconfig, which turns on CONFIG_CC_OPTIMIZE_FOR_SIZE. In order to avoid getting a lot of patches that initialize such variables and accidentally hide real errors along the way, let's just turn off this warning on the respective gcc versions when building with size optimizations. The -Wmaybe-uninitialized option was introduced in the same gcc version (4.7) that is now causing the false positives, so there is no effect on older compilers. A side effect is that when building with CONFIG_CC_OPTIMIZE_FOR_SIZE, we might now see /fewer/ warnings about possibly uninitialized warnings than with -O2, but that is still much better than seeing warnings known to be bogus. Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> diff --git a/Makefile b/Makefile index 473beb1..f0ec9bc 100644 --- a/Makefile +++ b/Makefile @@ -570,7 +570,7 @@ endif # $(dot-config) all: vmlinux ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE -KBUILD_CFLAGS += -Os +KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,) else KBUILD_CFLAGS += -O2 endif -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
