linux-kernel - Re: [PATCH -v4] kbuild: Add extra gcc checks

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Message-Id: <201102282207.33489.arnd@arndb.de>
Date:	Mon, 28 Feb 2011 22:07:33 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Sam Ravnborg <sam@...nborg.org>, Michal Marek <mmarek@...e.cz>,
	torvalds@...ux-foundation.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	linux-kbuild@...r.kernel.org, bp@...64.org
Subject: Re: [PATCH -v4] kbuild: Add extra gcc checks

On Monday 21 February 2011 12:03:22 Borislav Petkov wrote:
> Add a 'W=1' Makefile switch which adds additional checking per build
> object.
>
> The idea behind this option is targeted at developers who, in the
> process of writing their code, want to do the occasional
>
> make W=1 [target.o]

Great stuff, I really like the idea!

> +# $(call cc-option... ) handles gcc -W.. options which
> +# are not supported by all versions of the compiler
> +ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
> +ifneq ($(call cc-version),)
> +KBUILD_EXTRA_WARNINGS := -Wextra
> +KBUILD_EXTRA_WARNINGS += -Wunused -Wno-unused-parameter
> +KBUILD_EXTRA_WARNINGS += -Waggregate-return
> +KBUILD_EXTRA_WARNINGS += -Wbad-function-cast
> +KBUILD_EXTRA_WARNINGS += -Wcast-qual
> +KBUILD_EXTRA_WARNINGS += -Wcast-align
> +KBUILD_EXTRA_WARNINGS += -Wconversion
> +KBUILD_EXTRA_WARNINGS += -Wdisabled-optimization
> +KBUILD_EXTRA_WARNINGS += -Wlogical-op
> +KBUILD_EXTRA_WARNINGS += -Wmissing-declarations
> +KBUILD_EXTRA_WARNINGS += -Wmissing-format-attribute
> +KBUILD_EXTRA_WARNINGS += $(call cc-option, -Wmissing-include-dirs,)
> +KBUILD_EXTRA_WARNINGS += -Wmissing-prototypes
> +KBUILD_EXTRA_WARNINGS += -Wnested-externs
> +KBUILD_EXTRA_WARNINGS += -Wold-style-definition
> +KBUILD_EXTRA_WARNINGS += $(call cc-option, -Woverlength-strings,)
> +KBUILD_EXTRA_WARNINGS += -Wpacked
> +KBUILD_EXTRA_WARNINGS += -Wpacked-bitfield-compat
> +KBUILD_EXTRA_WARNINGS += -Wpadded
> +KBUILD_EXTRA_WARNINGS += -Wpointer-arith
> +KBUILD_EXTRA_WARNINGS += -Wredundant-decls
> +KBUILD_EXTRA_WARNINGS += -Wshadow
> +KBUILD_EXTRA_WARNINGS += -Wswitch-default
> +KBUILD_EXTRA_WARNINGS += $(call cc-option, -Wvla,)
> +KBUILD_CFLAGS += $(KBUILD_EXTRA_WARNINGS)
> +endif
> +endif

I would be a little more selective here. Maybe we can have two levels
W=1 and W=2, with the full set getting enabled by W=2, and the smaller
set getting enabled in W=1. The reason is that many of the warnings
are pointless or even hurting code quality, while others (e.g.
-Wmissing-declarations) are generally useful and the only reason for
not enabling them is that they cause too many warnings with existing
code.

	Arnd
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