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Message-ID: <20071119221554.GB15377@uranus.ravnborg.org>
Date: Mon, 19 Nov 2007 23:15:54 +0100
From: Sam Ravnborg <sam@...nborg.org>
To: Andreas Herrmann <andreas.herrmann3@....com>
Cc: "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] x86: document kernel config and build
On Mon, Nov 19, 2007 at 06:33:20PM +0100, Andreas Herrmann wrote:
> Hi,
>
> I suggest to add some documentation snippet to
>
> Documentation/x86/{kbuild,kconfig,README}
>
> or whatsoever to primarily describe the new ARCH=x86 build.
> As a starter I named it Documentation/x86/kbuild.
I would prefer a general document that has a target specific
section.
Something like Documentation/make/headers_install and your text merged.
And the resuting file could be named kernel-build-howto.txt (or similar)
and located in Documentation/kbuild/
On top of this we should enhance the arch specific help for x86
to tell how to select bit-size. But I have left that until we unify
the 32 and 64 bit Makefiles.
I have yet to read your document - too late for that now..
Sam
>
> The following text is based on my observations with
> Linus' git (v2.6.24-rc3-19-g2ffbb83).
> Some text was shamelessly stolen from one of Sam's patch
> descriptions.
>
> Comments are welcome.
>
>
> Regards,
>
> Andreas
>
> --
> Added documentation about kernel configuration and build for ARCH=x86.
>
> Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
> ---
> arch/x86/kbuild | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 71 insertions(+), 0 deletions(-)
> create mode 100644 arch/x86/kbuild
>
> diff --git a/arch/x86/kbuild b/arch/x86/kbuild
> new file mode 100644
> index 0000000..7a918a9
> --- /dev/null
> +++ b/arch/x86/kbuild
> @@ -0,0 +1,71 @@
> +Kernel configuration
> +
> + The general rule is that ARCH={i386,x86_64} and native
> + architecture take precedence over the configuration.
> + So make ARCH=i386 [whatever] will always build a 32-bit
> + kernel no matter what the configuration says.
> + The configuration will be updated to 32-bit if it was
> + configured to 64-bit and the other way around:
> +
> + /=================================================\
> + | Target kernel architecture for |
> + | $ make [ARCH=...] <config-target> |
> + |-------------------------------------------------|
> + | option \ host arch | i386 | x86_64 |
> + |=================================================|
> + | ./. | i386 | x86_64 |
> + | ARCH=i386 | i386 | i386 |
> + | ARCH=x86_64 | x86_64 | x86_64 |
> + \=================================================/
> +
> + This behaviour is consistent with previous behaviour so
> + no surprises here.
> +
> + "make ARCH=x86" is special. It is the only ARCH= value that
> + allows the user to select between 32-bit and 64-bit using
> + menuconfig. This has impact on most config targets. Following
> + table shows what kernel will be configured depending on host
> + architecture and config-target.
> +
> + /=========================================================\
> + | Target kernel architecture for |
> + | $ make ARCH=x86 <config-target> |
> + |---------------------------------------------------------|
> + | config-target \ host arch | i386 | x86_64 |
> + |=========================================================|
> + | [menu]config (*1) | i386/x86_64 | i386/x86_64 |
> + | {old,silentold}config (*2) | i386/x86_64 | i386/x86_64 |
> + | defconfig | i386 | i386 |
> + | randconfig (*3) | i386/x86_64 | i386/x86_64 |
> + | allnoconfig | i386 | i386 |
> + | allyesconfig | x86_64 | x86_64 |
> + | allmodconfig | x86_64 | x86_64 |
> + |---------------------------------------------------------|
> + | (*1) The default selection equals the host architecture |
> + | for new configurations. Otherwise it depends on the |
> + | setting of CONFIG_64BIT in the old configuration. |
> + |---------------------------------------------------------|
> + | (*2) The default selection depends on the setting of |
> + | CONFIG_64BIT in the old configuration. |
> + |---------------------------------------------------------|
> + | (*3) Both configurations are possible. |
> + \=========================================================/
> +
> +
> +Cross compilation
> +
> + (1) To compile a 32-bit kernel on a x86_64 system you have to
> + disable 64-bit support in the kernel configuration
> + (CONFIG_64BIT=n).
> +
> + A subsequent kernel compile will build a 32-bit kernel. No
> + cross compiler is needed.
> +
> + (2) To compile a 64-bit kernel on a i386 system you have to switch
> + on 64-bit support in the kernel configuration (CONFIG_64BIT=y).
> + In the subsequent kernel compile a cross compiler (supporting
> + x86_64) is needed. You have to use a command line like
> +
> + $ make CROSS_COMPILE=x86_64-pc-linux-gnu-
> +
> + to cross compile your kernel.
> --
> 1.5.3.4
>
>
>
>
-
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