KBuild: Allow scripts/* to be cross compiled

BugLink: http://bugs.launchpad.net/bugs/963823

Cross compiling the binaries in scripts/* is not possible
because various makefiles assume that $(obj)/whatever is
executable on the build host.

This patch introduces a new variable called KBUILD_SCRIPTROOT
that points to script/binaries to use while cross compiling.

Usage:

Build scripts for the build host:
	make O=path/to/buildhost/buildscripts \
		silentoldconfig prepare scripts
Then cross build script for target:
	make O=path/to/target/buildscripts \
		HOSTCC=$CROSS_COMPILE \
		KBUILD_SCRIPTROOT=path/to/buildhost/buildscripts
		silentoldconfig prepare scripts

This patch does not use KBUILD_SCRIPTROOT for all script invocations
it only redefines the following if KBUILD_SCRIPTROOT is defined.

scripts/Makefile.build
	scripts/basic/fixdep --> $(KBUILD_SCRIPTROOT)/scripts/basic/fixdep

scripts/kconfig/Makefile
	$(obj)/conf --> $(KBUILD_SCRIPTROOT)/scripts/kconfig/conf

scripts/mod/Makefile
	$(obj)mk_elfconfig --> $(KBUILD_SCRIPTROOT)/scripts/mod/mk_elfconfig

Signed-off-by: John Rigby <john.rigby@linaro.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index be39cd1c74c..30103da6e38 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -218,11 +218,15 @@ if_changed = $(if $(strip $(any-prereq) $(arg-check)),                       \
         $(echo-cmd) $(cmd_$(1));                                             \
         echo 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd)
 
+ifeq ($(KBUILD_SCRIPTROOT),)
+KBUILD_SCRIPTROOT=.
+endif
+
 # Execute the command and also postprocess generated .d dependencies file.
 if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ),                  \
         @set -e;                                                             \
         $(echo-cmd) $(cmd_$(1));                                             \
-        scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
+        $(KBUILD_SCRIPTROOT)/scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
         rm -f $(depfile);                                                    \
         mv -f $(dot-target).tmp $(dot-target).cmd)