Patchworkβ [11/18] kconfig CROSS_COMPILE option

On Fri, Sep 18, 2009 at 12:49:30PM -0700, akpm@linux-foundation.org wrote:
> From: Roland McGrath <roland@redhat.com>
> 
> This adds CROSS_COMPILE as a kconfig string so you can store it in
> .config.  Then you can use plain "make" in the configured kernel build
> directory to do the right cross compilation without setting the
> command-line or environment variable every time.
> 
> With this, you can set up different build directories for different kernel
> configurations, whether native or cross-builds, and then use the simple:
> 
> 	make -C /build/dir M=module-source-dir
> 
> idiom to build modules for any given target kernel, indicating which one
> by nothing but the build directory chosen.
> 
> I tried a version that defaults the string with env="CROSS_COMPILE" so
> that in a "make oldconfig" with CROSS_COMPILE in the environment you can
> just hit return to store the way you're building it.  But the kconfig
> prompt for strings doesn't give you any way to say you want an empty
> string instead of the default, so I punted that.
> 
> Signed-off-by: Roland McGrath <roland@redhat.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>


I had queued this patch (but for various reasons it had
not hit -next - sigh).
It does not save/restore SUBARCH - but that should
be doable too.

For my testing it works and we save both ARCH and CROSS_COMPILE.

	Sam

commit 07d291e7ad3bff028e7a452e5c2ad66dfdeef146
Author: Sam Ravnborg <sam@ravnborg.org>
Date:   Mon Jul 20 11:49:54 2009 +0200

    kbuild: save ARCH & CROSS_COMPILE when building a kernel
    
    When building a kernel for a different architecture
    kbuild requires the user always to specify ARCH and
    CROSS_COMPILE on the command-line.
    
    We use the asm symlink to detect if user forgets to
    specify the correct ARCH value - but that symlink
    is about to die. And we do now want to loose this check.
    
    This patch save the settings of ARCH and CROSS_COMPILE
    in a file named ".kbuild".
    The settings are saved during "make *config" time
    and always read.
    
    If user try to change the settings we error out.
    
    This works both for plain builds and for O=...
    builds.
    So now you can do:
    $ mkdir sparc64
    $ make O=sparc64 ARCH=sparc64 CROSS_COMPILE=sparc64-linux- defconfig
    $ cd sparc64
    $ make
    
    Notice that you no longer need to tell kbuild
    the settings of ARCH and CROSS_COMPILE when you type make
    in the output directory.
    Likewise for plain builds where you do not use O=...
    
    Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

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Cool.  I had done a hack locally to save ARCH in a different way, but
had not gotten around to finishing it up to submit.  My tack was to
write an include/config/kernel.arch file analogous to kernel.release,
and then use that.  It was about the same as yours I guess, but without
all the fancy sanity checks.  

One thing I'd thought to do in "finishing it up" was to write just the
$ARCH string alone to kernel.arch (then needing a kernel.subarch too)
rather than a makefile fragment.  My thinking is that any scripty things
that would like to look at a given build dir (as in the installed
/lib/modules/foo/build in kernel-devel packages) would like to extract
the arch name as well as the kernel release string, and not necessarily
do it by running make or parsing makeish assignment lines.


Thanks,
Roland
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