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, 8 insertions, 2 deletions

diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
index ff954f8168c..258d4ba32d5 100644
--- a/scripts/mod/Makefile
+++ b/scripts/mod/Makefile
@@ -1,6 +1,12 @@
 hostprogs-y     := modpost mk_elfconfig
 always          := $(hostprogs-y) empty.o
 
+ifdef KBUILD_SCRIPTROOT
+MKELFCONFIG = $(KBUILD_SCRIPTROOT)/scripts/mod/mk_elfconfig
+else
+MKELFCONFIG = $(obj)/mk_elfconfig
+endif
+
 modpost-objs    := modpost.o file2alias.o sumversion.o
 
 # dependencies on generated files need to be listed explicitly
@@ -8,9 +14,9 @@ modpost-objs	:= modpost.o file2alias.o sumversion.o
 $(obj)/modpost.o $(obj)/file2alias.o $(obj)/sumversion.o: $(obj)/elfconfig.h
 
 quiet_cmd_elfconfig = MKELF   $@
-      cmd_elfconfig = $(obj)/mk_elfconfig < $< > $@
+      cmd_elfconfig = $(MKELFCONFIG) < $< > $@
 
-$(obj)/elfconfig.h: $(obj)/empty.o $(obj)/mk_elfconfig FORCE
+$(obj)/elfconfig.h: $(obj)/empty.o $(MKELFCONFIG) FORCE
         $(call if_changed,elfconfig)
 
 targets += elfconfig.h