linux-kernel - Re: [PATCH v3] x86, kconfig: Default to ARCH=x86 to avoid overriding CONFIG

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Message-ID: <CACqU3MUMj4PzOzyHUXwQKu5LqNZzY+W9amPPiw555Ae9QKqpng@mail.gmail.com>
Date:	Sun, 31 Jul 2011 01:18:59 -0400
From:	Arnaud Lacombe <lacombar@...il.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Michal Marek <mmarek@...e.cz>, "Ted Ts'o" <tytso@....edu>,
	Ingo Molnar <mingo@...e.hu>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	hpa@...or.com
Subject: Re: [PATCH v3] x86, kconfig: Default to ARCH=x86 to avoid overriding CONFIG_64BIT

Hi,

On Fri, Jul 29, 2011 at 8:49 PM, David Woodhouse <dwmw2@...radead.org> wrote:
> I *frequently* waste a bunch of time when I take a 32-bit .config from a
> test machine and try to build it on a faster 64-bit system, and its
> existing setting of CONFIG_64BIT=n gets *changed* to match the build host.
>
> This is because the default setting for $ARCH when discovered from
> 'uname' is one of the legacy pre-x86-merge values (i386 or x86_64),
> which effectively force the setting of CONFIG_64BIT to match. We should
> default to ARCH=x86 instead, finally completing the merge that we
> started so long ago.
>
> This patch preserves the behaviour of the legacy ARCH settings for commands
> such as:
>
>   make ARCH=x86_64 randconfig
>   make ARCH=i386 randconfig
>
> ... although since my commit "Enable 'make CONFIG_FOO=y oldconfig'" those
> would be better expressed as:
>
>   make CONFIG_64BIT=y randconfig
>   make CONFIG_64BIT=n randconfig
>
> ... since that is a more generic way to set *any* config option, and
> there's no other technical reason to keep the legacy ARCH values around
> any more just to achieve that purpose; they could be removed at any
> time.
>
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
> Link: http://lkml.kernel.org/r/1306707270.2029.377.camel@i7.infradead.org
> ---
> v2: Explicitly turn off CONFIG_64BIT in i386_defconfig. The default for
>    CONFIG_64BIT has *changed* (from n to y) for ARCH=x86, so it needs to
>    be explicitly turned off or 'make i386_defconfig' will give you 64-bit.
> v3: Same patch as before; just updated changelog.
>
>  Makefile                        |    3 ++-
>  arch/x86/Kconfig                |    2 +-
>  arch/x86/Makefile               |    4 ++++
>  arch/x86/configs/i386_defconfig |    1 +
>  4 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index d018956..303df9b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -165,7 +165,8 @@ export srctree objtree VPATH
>  # then ARCH is assigned, getting whatever value it gets normally, and
>  # SUBARCH is subsequently ignored.
>
> -SUBARCH := $(shell uname -m | sed -e s/i.86/i386/ -e s/sun4u/sparc64/ \
> +SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
> +                                 -e s/sun4u/sparc64/ \
>                                  -e s/arm.*/arm/ -e s/sa110/arm/ \
>                                  -e s/s390x/s390/ -e s/parisc64/parisc/ \
>                                  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 153aa6f..9467fdd 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1,7 +1,7 @@
>  # Select 32 or 64 bit
>  config 64BIT
>        bool "64-bit kernel" if ARCH = "x86"
> -       default ARCH = "x86_64"
> +       default ARCH != "i386"
If I'm reading this correctly, does this mean that someone doing an
'allyesconfig' on an i386 machine will get a configuration for a
64bits kernel[0] ? With your logic, you would require the user to
manually specify CONFIG_64BIT=n, which should be automatic on such a
system...

This logic seems broken to me.

 - Arnaud

[0]: both ARCH and SUBARCH will be x86, so the conditional will translate to 'y'

>        ---help---
>          Say yes to build a 64-bit kernel - formerly known as x86_64
>          Say no to build a 32-bit kernel - formerly known as i386
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index b02e509..94c2d8c 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -2,7 +2,11 @@
>
>  # select defconfig based on actual architecture
>  ifeq ($(ARCH),x86)
> +  ifeq ($(shell uname -m),x86_64)
> +        KBUILD_DEFCONFIG := x86_64_defconfig
> +  else
>         KBUILD_DEFCONFIG := i386_defconfig
> +  endif
>  else
>         KBUILD_DEFCONFIG := $(ARCH)_defconfig
>  endif
> diff --git a/arch/x86/configs/i386_defconfig b/arch/x86/configs/i386_defconfig
> index 2bf18059f..5f96c1c 100644
> --- a/arch/x86/configs/i386_defconfig
> +++ b/arch/x86/configs/i386_defconfig
> @@ -1,3 +1,4 @@
> +# CONFIG_64BIT is not set
>  CONFIG_EXPERIMENTAL=y
>  # CONFIG_LOCALVERSION_AUTO is not set
>  CONFIG_SYSVIPC=y
> --
> 1.7.6
>
>
>
> --
> dwmw2
>
>
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