* Uros Bizjak <ubizjak@xxxxxxxxx> wrote: > On Fri, Oct 13, 2023 at 11:06 AM Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > > > > > * Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > > > > > On Fri, Oct 13, 2023 at 09:30:46AM +0200, Ingo Molnar wrote: > > > > > > > Ugh, why on Earth didn't GCC warn about this? The bad pattern is pretty > > > > simple & obvious once pointed out ... compilers should have no trouble > > > > realizing that 'ret' is returned uninitialized in some of these control > > > > paths. Yet not a peep from the compiler ... > > > > > > We disabled that warning years ago (5?) because GCC had too many false > > > positives. > > > > GCC had some pretty bogus notions about 'possible' uninitialized use that > > encouraged some bad code patterns, but in this case there's readily > > provable uninitialized use, that a compiler should warn about. > > > > Is it possible to disable just the unreliable, probabilistic part of GCC's > > uninitialized variables warnings? > > -Wno-maybe-uninitialized? No combination of the relevant compiler options appears to be able to get GCC to notice this bug. On top of tip:master, the patch below produces no compiler warnings with GCC 12.3.0: $ git revert 7543365739a4 $ rm -f arch/x86/events/amd/uncore.o $ make V=1 W=1e arch/x86/events/amd/uncore.o The "W=1e" incantation activates, with the patch below applied, among many other GCC options, the following options: -Wall -Wuninitialized -Wmaybe-uninitialized -Werror Which should have found this bug, right? [ The V=1 helps double checking the compiler options. ] Thanks, Ingo scripts/Makefile.extrawarn | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 2fe6f2828d37..9d245fcff419 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -108,6 +108,8 @@ KBUILD_CFLAGS += $(call cc-option, -Wformat-overflow) KBUILD_CFLAGS += $(call cc-option, -Wformat-truncation) KBUILD_CFLAGS += $(call cc-option, -Wstringop-overflow) KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation) +KBUILD_CFLAGS += $(call cc-option, -Wuninitialized) +KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized) KBUILD_CPPFLAGS += -Wundef KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 @@ -176,7 +178,7 @@ KBUILD_CFLAGS += -Wno-shift-negative-value ifdef CONFIG_CC_IS_CLANG KBUILD_CFLAGS += -Wno-initializer-overrides else -KBUILD_CFLAGS += -Wno-maybe-uninitialized +#KBUILD_CFLAGS += -Wno-maybe-uninitialized endif endif
