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From:   Sedat Dilek <sedat.dilek@gmail.com>
Date:   Wed, 28 Aug 2019 16:18:51 +0200
Message-ID: <CA+icZUUhhOLfOgwoKP4nKOdPakNJF7XafJ09ERP6r7dOUduMsg@mail.gmail.com>
Subject: Re: [PATCH 1/2] kbuild: refactor scripts/Makefile.extrawarn
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     linux-kbuild@vger.kernel.org,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Michal Marek <michal.lkml@markovi.net>,
        Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
        linux-kernel@vger.kernel.org
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On Wed, Aug 28, 2019 at 9:20 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Wed, Aug 28, 2019 at 7:55 AM Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
> >
> > Instead of the warning-[123] magic, let's accumulate compiler options
> > to KBUILD_CFLAGS directly as the top Makefile does. I think this makes
> > easier to understand what is going on in this file.
> >
> > This commit slightly changes the behavior, I think all of which are OK.
> >
> > [1] Currently, cc-option calls are needlessly evaluated. For example,
> >       warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
> >     needs evaluating only when W=3, but it is actually evaluated for
> >     W=1, W=2 as well. With this commit, only relevant cc-option calls
> >     will be evaluated. This is a slight optimization.
> >
> > [2] Currently, unsupported level like W=4 is checked by:
> >       $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
> >     This will no longer be checked, but I do not think it is a big
> >     deal.
> >
>
> Hi Masahiro Yamada,
>
> thanks for your patch series.
>
> If KBUILD_ENABLE_EXTRA_GCC_CHECKS does extra(-warning)-checks for GCC and Clang,
> please rename the Kconfig into...
>
> KBUILD_ENABLE_EXTRA_CC_CHECKS
>
> ...or something similiar (and maybe with some notes in its Kconfig help-text?).
>

I have tested both patches against recent kbuild-next and can boot on
bare metal with clang.

I have *not* passed any W= to my make, but I see that clang's W=1
kbuild-cflags are active.

[ scripts/Makefile.extrawarn ]

ifeq ("$(origin W)", "command line")
  export KBUILD_ENABLE_EXTRA_GCC_CHECKS := $(W)
endif

#
# W=1 - warnings that may be relevant and does not occur too often
#
ifneq ($(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
[ ... ]
KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1

else

# W=1 also stops suppressing some warnings

ifdef CONFIG_CC_IS_CLANG
KBUILD_CFLAGS += -Wno-initializer-overrides
KBUILD_CFLAGS += -Wno-format
KBUILD_CFLAGS += -Wno-sign-compare
KBUILD_CFLAGS += -Wno-format-zero-length
endif # CONFIG_CC_IS_CLANG

endif # KBUILD_ENABLE_EXTRA_GCC_CHECKS

These clang KBUILD_CFLAGS are active independently of passing W=1.

$ grep '\-Wno-initializer-overrides'
build-log_5.3.0-rc6-2-amd64-cbl-asmgoto.txt | wc -l
27195

So the above comment is misleading?

Is W=1 activated by default?

Or do I miss something?

[ Documentation/kbuild/kbuild.rst ]

KBUILD_ENABLE_EXTRA_GCC_CHECKS
------------------------------
If enabled over the make command line with "W=1", it turns on additional
gcc -W... options for more extensive build-time checking.

What about?

KBUILD_CC_EXTRA_CHECKS (or KBUILD_EXTRA_CC_CHECKS)
------------------------------
If enabled over the make command line with "W=...", it turns on additional
compiler warning options like -Wmissing-declarations for more extensive
build-time checking. For more details see <Documentation/kbuild/kbuild.rst>.

W=1 - warnings that may be relevant and does not occur too often
W=1 - also stops suppressing some warnings
W=2 - warnings that occur quite often but may still be relevant
W=3 - the more obscure warnings, can most likely be ignored

- Sedat -