linux-kernel - Re: [PATCH -v3] kbuild: Add extra gcc checks

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Message-ID: <AANLkTimZhB8Ong=nJ_mjit+VRtb7g+TQhT9_wvojQ0-e@mail.gmail.com>
Date:	Sun, 20 Feb 2011 22:26:13 -0500
From:	Arnaud Lacombe <lacombar@...il.com>
To:	Borislav Petkov <bp@...en8.de>, 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
Subject: Re: [PATCH -v3] kbuild: Add extra gcc checks

Hi,

On Sun, Feb 20, 2011 at 9:23 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Sun, Feb 20, 2011 at 08:52:22PM +0100, Sam Ravnborg wrote:
>
> ..
>
>> 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.
>
> Hey Sam,
>
> thanks for the suggestions/review, here's hopefully a better version:
>
> --
> From: Borislav Petkov <bp@...en8.de>
> Date: Sun, 20 Feb 2011 17:18:40 +0100
> Subject: [PATCH -v3] kbuild: Add extra gcc checks
>
> 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]
>
> and let gcc do more extensive code checking for them. Then, they
> could eyeball the output for valid gcc warnings about various
> bugs/discrepancies which are not reported during the normal build
> process.
>
> For more background information and a use case, read through this
> thread: http://marc.info/?l=kernel-janitors&m=129802065918147&w=2
>
> Cc: Michal Marek <mmarek@...e.cz>
> Cc: Sam Ravnborg <sam@...nborg.org>
> Cc: linux-kbuild@...r.kernel.org
> Acked-by: Ingo Molnar <mingo@...e.hu>
> Signed-off-by: Borislav Petkov <bp@...en8.de>
> ---
>  Makefile               |    6 ++++++
>  scripts/Makefile.build |   29 ++++++++++++++++++++++++++++-
>  2 files changed, 34 insertions(+), 1 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index c9c8c8f..c3bca9c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -102,6 +102,11 @@ ifeq ("$(origin O)", "command line")
>   KBUILD_OUTPUT := $(O)
>  endif
>
> +ifeq ("$(origin W)", "command line")
> +  KBUILD_ENABLE_EXTRA_GCC_CHECKS = 1
> +  export KBUILD_ENABLE_EXTRA_GCC_CHECKS
> +endif
> +
You never check CC is gcc. How can you assert this ? Moreover, can you
certify that all the compiler supported to build Linux do support the
set of new warnings ? What about icc ? old gcc ? LLVM/clang ?

>  # That's our default target when none is given on the command line
>  PHONY := _all
>  _all:
> @@ -1262,6 +1267,7 @@ help:
>        @echo  '  make O=dir [targets] Locate all output files in "dir", including .config'
>        @echo  '  make C=1   [targets] Check all c source with $$CHECK (sparse by default)'
>        @echo  '  make C=2   [targets] Force check of all c source with $$CHECK'
> +       @echo  '  make W=1   [targets] Enable extra gcc checks'
same as above.

>        @echo  ''
>        @echo  'Execute "make" or "make all" to build all targets marked with [*] '
>        @echo  'For further info see the ./README file'
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 4eb99ab..b4d7661 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -49,6 +49,34 @@ ifeq ($(KBUILD_NOPEDANTIC),)
>                 $(error CFLAGS was changed in "$(kbuild-file)". Fix it to use EXTRA_CFLAGS)
>         endif
>  endif
> +
> +# make W=1 settings
> +ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
> +KBUILD_CFLAGS += -Wextra -Wno-unused
> +KBUILD_CFLAGS += -Waggregate-return
> +KBUILD_CFLAGS += -Wbad-function-cast
> +KBUILD_CFLAGS += -Wcast-qual
> +KBUILD_CFLAGS += -Wcast-align
> +KBUILD_CFLAGS += -Wconversion
> +KBUILD_CFLAGS += -Wdisabled-optimization
> +KBUILD_CFLAGS += -Wlogical-op
> +KBUILD_CFLAGS += -Wmissing-declarations
> +KBUILD_CFLAGS += -Wmissing-format-attribute
> +KBUILD_CFLAGS += -Wmissing-include-dirs
> +KBUILD_CFLAGS += -Wmissing-prototypes
> +KBUILD_CFLAGS += -Wnested-externs
> +KBUILD_CFLAGS += -Wold-style-definition
> +KBUILD_CFLAGS += -Woverlength-strings
> +KBUILD_CFLAGS += -Wpacked
> +KBUILD_CFLAGS += -Wpacked-bitfield-compat
> +KBUILD_CFLAGS += -Wpadded
> +KBUILD_CFLAGS += -Wpointer-arith
> +KBUILD_CFLAGS += -Wredundant-decls
> +KBUILD_CFLAGS += -Wshadow
> +KBUILD_CFLAGS += -Wswitch-default
> +KBUILD_CFLAGS += -Wvla
> +endif
> +
Why not making it simple at the beginning by:
 1) s/GCC/CC/
 2) using `cc-option' provided by Kbuild for each new option. As an
example, for `-Wvla':

KBUILD_CFLAGS += $(call cc-option, -Wvla)

so so on.

 - Arnaud

>  include scripts/Makefile.lib
>
>  ifdef host-progs
> @@ -403,7 +431,6 @@ ifneq ($(cmd_files),)
>   include $(cmd_files)
>  endif
>
> -
>  # Declare the contents of the .PHONY variable as phony.  We keep that
>  # information in a variable se we can use it in if_changed and friends.
>
> --
> 1.7.4.1.48.g5673d
>
>
>
> --
> Regards/Gruss,
>    Boris.
> --
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