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

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Date:	Sun, 20 Feb 2011 20:52:22 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Borislav Petkov <bp@...en8.de>, 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
Subject: Re: [PATCH] kbuild: Add extra gcc checks

> 
> diff --git a/Makefile b/Makefile
> index c9c8c8f..03989a1 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -102,6 +102,15 @@ ifeq ("$(origin O)", "command line")
>    KBUILD_OUTPUT := $(O)
>  endif
>  
> +ifeq ("$(origin W)", "command line")
> +  KBUILD_ENABLE_EXTRA_GCC_CHECKS = 1
> +endif
> +ifndef KBUILD_ENABLE_EXTRA_GCC_CHECKS
> +  KBUILD_ENABLE_EXTRA_GCC_CHECKS = 0
> +endif

I do not see the purpose of setting KBUILD_ENABLE_EXTRA_GCC_CHECKS
equal to 0.

> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 4eb99ab..5bf9f40 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -30,6 +30,33 @@ ldflags-y  :=
>  subdir-asflags-y :=
>  subdir-ccflags-y :=
>  
> +# make W=1 settings
> +ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS

The symbol KBUILD_ENABLE_EXTRA_GCC_CHECKS is always defined,
as you set it to "0" in the top-level Makefile.
So you will always have the extra checks enabled.

You also need to move the assignments down.
As it is now any kbuild file that assign
EXTRA_CFLAGS with

    EXTRA_CFLAGS := -D DEBUG

Will drop all the extra warnings.

>From Makefile.build:
# If the save-* variables changed error out
ifeq ($(KBUILD_NOPEDANTIC),)
        ifneq ("$(save-cflags)","$(CFLAGS)")
                $(error CFLAGS was changed in "$(kbuild-file)". Fix it to use EXTRA_CFLAGS)
        endif
endif

<<<<< Here would be the better place to add this.

include scripts/Makefile.lib

> +EXTRA_CFLAGS += -Wextra -Wno-unused

Use of EXTRA_CFLAGS is deprecated - so that is not the right choice.
I suggest to use KBUILD_CFLAGS that is an KBUILD internal variable.

	Sam
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