arch/um: make it work with defconfig and x86_64

arch/um/defconfig only lists one default configuration, and that applies
only to the i386 architecture.  Replace it with two minimal
configuration files generated using `make savedefconfig`:

  i386_defconfig and x86_64_defconfig

The build scripts now require two updates:

1. um's Kconfig (arch/x86/um/Kconfig) should specify an ARCH_DEFCONFIG
   section explicitly pointing to these scripts if the required
   variables are set.  Take care to remove the DEFCONFIG_LIST section
   defined in the included file arch/um/Kconfig.common.

2. um's Makefile (arch/um/Makefile) should set KBUILD_DEFCONFIG properly
   for the top-level Makefile to pick up.  Copy the logic in
   arch/x86/Makefile to properly pick the defconfig file depending on
   the actual architecture; except we're working with $SUBARCH here,
   instead of $ARCH.

Now, you can do:

  $ ARCH=um make defconfig
  $ ARCH=um make

and successfully build User-Mode Linux on an x86_64 box in default
configuration.

Cc: Richard Weinberger <richard@nod.at>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index 14ef8d1dbc33..ed56a1c4ae73 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -31,6 +31,11 @@ config X86_64
 	def_bool 64BIT
 	select MODULES_USE_ELF_RELA
 
+config ARCH_DEFCONFIG
+	string
+	default "arch/um/configs/i386_defconfig" if X86_32
+	default "arch/um/configs/x86_64_defconfig" if X86_64
+
 config RWSEM_XCHGADD_ALGORITHM
 	def_bool 64BIT