[Buildroot] [PATCH] linux: Fix User-Mode Linux build failures

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear Worth, Kevin,

On Thu, 2 May 2013 21:14:45 +0000, Worth, Kevin wrote:
> Pass KERNEL_SUBARCH environment variable needed for User Mode Linux builds
>  e.g. build with 'make KERNEL_ARCH=um KERNEL_SUBARCH=i386'
> Create $(KERNEL_ARCH_PATH)/configs/ if it doesn't exist (for arches like uml)
>  Otherwise build fails trying to cp to non-existent directory
> 
> Signed-off-by: Kevin Worth <kevin.worth@hp.com>
> ---
>  linux/linux.mk | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/linux/linux.mk b/linux/linux.mk
> index 0352acd..db26fc6 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -44,6 +44,7 @@ LINUX_MAKE_FLAGS = \
>  	HOSTCC="$(HOSTCC)" \
>  	HOSTCFLAGS="$(HOSTCFLAGS)" \
>  	ARCH=$(KERNEL_ARCH) \
> +	SUBARCH=$(KERNEL_SUBARCH) \
>  	INSTALL_MOD_PATH=$(TARGET_DIR) \
>  	CROSS_COMPILE="$(CCACHE) $(TARGET_CROSS)" \
>  	DEPMOD=$(HOST_DIR)/usr/sbin/depmod
> @@ -156,6 +157,7 @@ KERNEL_SOURCE_CONFIG = $(BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE)
>  endif
>  
>  define LINUX_CONFIGURE_CMDS
> +	mkdir -p $(KERNEL_ARCH_PATH)/configs/
>  	cp $(KERNEL_SOURCE_CONFIG) $(KERNEL_ARCH_PATH)/configs/buildroot_defconfig
>  	$(TARGET_MAKE_ENV) $(MAKE1) $(LINUX_MAKE_FLAGS) -C $(@D) buildroot_defconfig
>  	rm $(KERNEL_ARCH_PATH)/configs/buildroot_defconfig

Are you still interested in User Mode Linux support in Buildroot?

If so, I am not sure this is the right patch. You're manually passing
KERNEL_ARCH and KERNEL_SUBARCH from the Buildroot make command-line,
but they should be passed automatically by Buildroot.

So if we want to support User Mode Linux, maybe when the selected
architecture is x86 or x86-64, there should be a sub-option in the
Kernel menu to say that you want a UML kernel. In this case, linux.mk
should pass ARCH=um and SUBARCH=$(KERNEL_ARCH) I believe.

Also, I don't understand why you need the mkdir for the configs
directory. In my kernel tree, arch/um/configs/ does exist.

Please let us know if you're interested in pursuing this, so we can
update the status of the patch accordingly.

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com