[Buildroot] Question about kernel defconfig

Sam Ravnborg sam at ravnborg.org
Mon Nov 22 21:33:18 UTC 2010

On Mon, Nov 22, 2010 at 06:33:27PM +0100, Thomas Petazzoni wrote:
> Hello Sam,
> I am currently working on cleaning up how Buildroot handles board
> configuration [1]. As part of this clean up, I'd like to move away from
> full kernel .config files and instead use minimal kernel configs (only
> non-default options are stored, the kernel configuration files are
> produced with savedefconfig).
> So, for example for the Qemu Versatile platform, I have the kernel
> configuration file visible at
> http://git.buildroot.net/~tpetazzoni/git/buildroot/tree/board/qemu/arm-versatile/linux-2.6.36.config?h=for-2010.11/boards-cleanup&id=8033fd6cbacfa96a3bcfce74caad8c423bf60cd1.
> When Buildroot configures the kernel, it simply copies the given kernel
> configuration file to .config into the kernel source tree. See
> http://git.buildroot.net/buildroot/tree/linux/linux.mk#n89.
> Unfortunately, with those minimal configuration files, the kernel
> "Restart config" and then asks interactively for the value of all
> options not specificied in the minimal configuration file.
> I'd like to have the same behaviour the kernel has when using its own
> internal defconfigs files from arch/$(ARCH)/configs. Is this possible ?

kconfig behaves in different ways depending on what type of input it receives.
To use the minimal configs generated by "savedefconfig" you need to read
them using "--defconfig".
And there is today no way to specify your own defconfig file.

One workaround could be to copy the file to:


And then use:

    make buildroot_defconfig

This will read the minimal config in the same way the kernel usually does it.

You can also experiment with calling scripts/kconfig/conf --defconfig foobar arch/$ARCH/Kconfig
But I think the solution where you use buildroot_defconfig is the easiest
to maintain.


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