On Fri, Mar 1, 2013 at 6:16 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > 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. > If the ...$(call cc-disable-warning...) line is checking $compiler for $feature_is-available than I have misunderstood it. Looks good, thanks. - Sedat - > 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
