Re: [PATCH net-next v2 1/2] Makefile.extrawarn: Add symbol for W=1 warnings for today

From: Nick Desaulniers <ndesaulniers@google.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: netdev <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Rohit Maheshwari <rohitm@chelsio.com>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH net-next v2 1/2] Makefile.extrawarn: Add symbol for W=1 warnings for today
Date: Thu, 1 Oct 2020 16:09:43 -0700	[thread overview]
Message-ID: <CAKwvOdnVC8F1=QT03W5Zh9pJdTxxNfRcqXeob5_b4CXycvG1+g@mail.gmail.com> (raw)
In-Reply-To: <20201001011232.4050282-2-andrew@lunn.ch>

On Wed, Sep 30, 2020 at 6:12 PM Andrew Lunn <andrew@lunn.ch> wrote:
>
> There is a movement to try to make more and more of /drivers W=1
> clean. But it will only stay clean if new warnings are quickly
> detected and fixed, ideally by the developer adding the new code.
>
> To allow subdirectories to sign up to being W=1 clean for a given
> definition of W=1, export the current set of additional compile flags
> using the symbol KBUILD_CFLAGS_W1_20200930. Subdirectory Makefiles can
> then use:
>
> subdir-ccflags-y := $(KBUILD_CFLAGS_W1_20200930)
>
> To indicate they want to W=1 warnings as defined on 20200930.
>
> Additional warnings can be added to the W=1 definition. This will not
> affect KBUILD_CFLAGS_W1_20200930 and hence no additional warnings will
> start appearing unless W=1 is actually added to the command
> line. Developers can then take their time to fix any new W=1 warnings,
> and then update to the latest KBUILD_CFLAGS_W1_<DATESTAMP> symbol.

I'm not a fan of this approach.  Are DATESTAMP configs just going to
keep being added? Is it going to complicate isolating the issue from a
randconfig build?  If we want more things to build warning-free at
W=1, then why don't we start moving warnings from W=1 into the
default, until this is no W=1 left?  That way we're cutting down on
the kernel's configuration combinatorial explosion, rather than adding
to it?

>
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> ---
>  scripts/Makefile.extrawarn | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 95e4cdb94fe9..957dca35ae3e 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -20,24 +20,26 @@ export KBUILD_EXTRA_WARN
>  #
>  # W=1 - warnings which may be relevant and do not occur too often
>  #
> -ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
> -
> -KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
> -KBUILD_CFLAGS += -Wmissing-declarations
> -KBUILD_CFLAGS += -Wmissing-format-attribute
> -KBUILD_CFLAGS += -Wmissing-prototypes
> -KBUILD_CFLAGS += -Wold-style-definition
> -KBUILD_CFLAGS += -Wmissing-include-dirs
> -KBUILD_CFLAGS += $(call cc-option, -Wunused-but-set-variable)
> -KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
> -KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned)
> -KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation)
> +KBUILD_CFLAGS_W1_20200930 += -Wextra -Wunused -Wno-unused-parameter
> +KBUILD_CFLAGS_W1_20200930 += -Wmissing-declarations
> +KBUILD_CFLAGS_W1_20200930 += -Wmissing-format-attribute
> +KBUILD_CFLAGS_W1_20200930 += -Wmissing-prototypes
> +KBUILD_CFLAGS_W1_20200930 += -Wold-style-definition
> +KBUILD_CFLAGS_W1_20200930 += -Wmissing-include-dirs
> +KBUILD_CFLAGS_W1_20200930 += $(call cc-option, -Wunused-but-set-variable)
> +KBUILD_CFLAGS_W1_20200930 += $(call cc-option, -Wunused-const-variable)
> +KBUILD_CFLAGS_W1_20200930 += $(call cc-option, -Wpacked-not-aligned)
> +KBUILD_CFLAGS_W1_20200930 += $(call cc-option, -Wstringop-truncation)
>  # The following turn off the warnings enabled by -Wextra
> -KBUILD_CFLAGS += -Wno-missing-field-initializers
> -KBUILD_CFLAGS += -Wno-sign-compare
> -KBUILD_CFLAGS += -Wno-type-limits
> +KBUILD_CFLAGS_W1_20200930 += -Wno-missing-field-initializers
> +KBUILD_CFLAGS_W1_20200930 += -Wno-sign-compare
> +KBUILD_CFLAGS_W1_20200930 += -Wno-type-limits
> +
> +export KBUILD_CFLAGS_W1_20200930
> +
> +ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
>
> -KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
> +KBUILD_CPPFLAGS += $(KBUILD_CFLAGS_W1_20200930) -DKBUILD_EXTRA_WARN1
>
>  else
>
> --
> 2.28.0
>
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-- 
Thanks,
~Nick Desaulniers