kconfig: add savedefconfig

savedefconfig will save a minimal config to a file
named "defconfig".

The config symbols are saved in the same order as
they appear in the menu structure so it should
be possible to map them to the relevant menus
if desired.

The implementation was tested against several minimal
configs for arm which was created using brute-force.

There was one regression related to default numbers
which had their valid range further limited by another symbol.

Sample:

config FOO
	int "foo"
	default 4

config BAR
	int "bar"
	range 0 FOO

If FOO is set to 3 then BAR cannot take a value higher than 3.
But the current implementation will set BAR equal to 4.

This is seldomly used and the final configuration is OK,
and the fix was non-trivial.
So it was documented in the code and left as is.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Michal Marek <mmarek@suse.cz>

1 files changed, 5 insertions, 1 deletions

diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
index 72973591c0f1..c0e459e2b014 100644
--- a/scripts/kconfig/Makefile
+++ b/scripts/kconfig/Makefile
@@ -90,11 +90,14 @@ PHONY += allnoconfig allyesconfig allmodconfig alldefconfig randconfig
 allnoconfig allyesconfig allmodconfig alldefconfig randconfig: $(obj)/conf
         $< --$@ $(Kconfig)
 
-PHONY += listnewconfig oldnoconfig defconfig
+PHONY += listnewconfig oldnoconfig savedefconfig defconfig
 
 listnewconfig oldnoconfig: $(obj)/conf
         $< --$@ $(Kconfig)
 
+savedefconfig: $(obj)/conf
+        $< --$@=defconfig $(Kconfig)
+
 defconfig: $(obj)/conf
 ifeq ($(KBUILD_DEFCONFIG),)
         $< --defconfig $(Kconfig)
@@ -118,6 +121,7 @@ help:
         @echo  '  localyesconfig  - Update current config converting local mods to core'
         @echo  '  silentoldconfig - Same as oldconfig, but quietly, additionally update deps'
         @echo  '  defconfig       - New config with default from ARCH supplied defconfig'
+        @echo  '  savedefconfig   - Save current config as ./defconfig (minimal config)'
         @echo  '  allnoconfig     - New config where all options are answered with no'
         @echo  '  allyesconfig    - New config where all options are accepted with yes'
         @echo  '  allmodconfig    - New config selecting modules when possible'