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

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Message-ID: <CACqU3MXQLcFVA6fHEYe17x4hMPs4fDpxqBhV84KFeG1XBdc7gQ@mail.gmail.com>
Date:	Sun, 31 Jul 2011 17:51:49 -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

On Sun, Jul 31, 2011 at 5:47 PM, Arnaud Lacombe <lacombar@...il.com> wrote:
> 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.
>>
> AFAICS, `scripts/mkcompile_h' ends up using ${ARCH} to build
> UTS_MACHINE, so it ends up being directly visible to userland. I would
> wonder which userland application (both script and binaries), relying
> on this interface, you are breaking...
>
my bad, mkcompile_h uses an UTS_MACHINE variable defined by the
arch/x86/Makefile.

 - Arnaud

>  - Arnaud
>
>> 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 := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
>> +                                 -e s/sun4u/sparc64/ \
>>                                  -e s/arm.*/arm/ -e s/sa110/arm/ \
>>                                  -e s/s390x/s390/ -e s/parisc64/parisc/ \
>>                                  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 153aa6f..9467fdd 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1,7 +1,7 @@
>>  # Select 32 or 64 bit
>>  config 64BIT
>>        bool "64-bit kernel" if ARCH = "x86"
>> -       default ARCH = "x86_64"
>> +       default ARCH != "i386"
>>        ---help---
>>          Say yes to build a 64-bit kernel - formerly known as x86_64
>>          Say no to build a 32-bit kernel - formerly known as i386
>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>> index b02e509..94c2d8c 100644
>> --- a/arch/x86/Makefile
>> +++ b/arch/x86/Makefile
>> @@ -2,7 +2,11 @@
>>
>>  # select defconfig based on actual architecture
>>  ifeq ($(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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