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>

4 files changed, 38 insertions, 18 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)
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a0fd5029cfe..40c3e3de323 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -288,13 +288,17 @@ cmd_record_mcount = 						\
         fi;
 endif
 
+ifeq ($(KBUILD_SCRIPTROOT),)
+KBUILD_SCRIPTROOT=.
+endif
+
 define rule_cc_o_c
         $(call echo-cmd,checksrc) $(cmd_checksrc)                         \
         $(call echo-cmd,cc_o_c) $(cmd_cc_o_c);                            \
         $(cmd_modversions)                                                \
         $(call echo-cmd,record_mcount)                                    \
         $(cmd_record_mcount)                                              \
-        scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
+        $(KBUILD_SCRIPTROOT)/scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
                                                       $(dot-target).tmp;  \
         rm -f $(depfile);                                                 \
         mv -f $(dot-target).tmp $(dot-target).cmd
diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
index faa9a4701b6..ada56df8714 100644
--- a/scripts/kconfig/Makefile
+++ b/scripts/kconfig/Makefile
@@ -11,6 +11,12 @@ else
 Kconfig := Kconfig
 endif
 
+ifdef KBUILD_SCRIPTROOT
+CONF = $(KBUILD_SCRIPTROOT)/scripts/kconfig/conf
+else
+CONF = $(obj)/conf
+endif
+
 xconfig: $(obj)/qconf
         $< $(Kconfig)
 
@@ -20,16 +26,16 @@ gconfig: $(obj)/gconf
 menuconfig: $(obj)/mconf
         $< $(Kconfig)
 
-config: $(obj)/conf
+config: $(CONF)
         $< --oldaskconfig $(Kconfig)
 
 nconfig: $(obj)/nconf
         $< $(Kconfig)
 
-oldconfig: $(obj)/conf
+oldconfig: $(CONF)
         $< --$@ $(Kconfig)
 
-silentoldconfig: $(obj)/conf
+silentoldconfig: $(CONF)
         $(Q)mkdir -p include/generated
         $< --$@ $(Kconfig)
 
@@ -41,22 +47,22 @@ ifeq ($(findstring /,$(LSMOD)),)
 endif
 endif
 
-localmodconfig: $(obj)/streamline_config.pl $(obj)/conf
+localmodconfig: $(obj)/streamline_config.pl $(CONF)
         $(Q)mkdir -p include/generated
         $(Q)perl $< $(srctree) $(Kconfig) $(LSMOD_F) > .tmp.config
         $(Q)if [ -f .config ]; then                                     \
                         cmp -s .tmp.config .config ||                   \
                         (mv -f .config .config.old.1;                   \
                          mv -f .tmp.config .config;                     \
-                         $(obj)/conf --silentoldconfig $(Kconfig);      \
+                         $(CONF) --silentoldconfig $(Kconfig);  \
                          mv -f .config.old.1 .config.old)               \
         else                                                            \
                         mv -f .tmp.config .config;                      \
-                        $(obj)/conf --silentoldconfig $(Kconfig);       \
+                        $(CONF) --silentoldconfig $(Kconfig);   \
         fi
         $(Q)rm -f .tmp.config
 
-localyesconfig: $(obj)/streamline_config.pl $(obj)/conf
+localyesconfig: $(obj)/streamline_config.pl $(CONF)
         $(Q)mkdir -p include/generated
         $(Q)perl $< $(srctree) $(Kconfig) $(LSMOD_F) > .tmp.config
         $(Q)sed -i s/=m/=y/ .tmp.config
@@ -64,11 +70,11 @@ localyesconfig: $(obj)/streamline_config.pl $(obj)/conf
                         cmp -s .tmp.config .config ||                   \
                         (mv -f .config .config.old.1;                   \
                          mv -f .tmp.config .config;                     \
-                         $(obj)/conf --silentoldconfig $(Kconfig);      \
+                         $(CONF) --silentoldconfig $(Kconfig);  \
                          mv -f .config.old.1 .config.old)               \
         else                                                            \
                         mv -f .tmp.config .config;                      \
-                        $(obj)/conf --silentoldconfig $(Kconfig);       \
+                        $(CONF) --silentoldconfig $(Kconfig);   \
         fi
         $(Q)rm -f .tmp.config
 
@@ -98,18 +104,18 @@ update-po-config: $(obj)/kxgettext $(obj)/gconf.glade.h
 
 PHONY += allnoconfig allyesconfig allmodconfig alldefconfig randconfig
 
-allnoconfig allyesconfig allmodconfig alldefconfig randconfig: $(obj)/conf
+allnoconfig allyesconfig allmodconfig alldefconfig randconfig: $(CONF)
         $< --$@ $(Kconfig)
 
 PHONY += listnewconfig oldnoconfig savedefconfig defconfig
 
-listnewconfig oldnoconfig: $(obj)/conf
+listnewconfig oldnoconfig: $(CONF)
         $< --$@ $(Kconfig)
 
-savedefconfig: $(obj)/conf
+savedefconfig: $(CONF)
         $< --$@=defconfig $(Kconfig)
 
-defconfig: $(obj)/conf
+defconfig: $(CONF)
 ifeq ($(KBUILD_DEFCONFIG),)
         $< --defconfig $(Kconfig)
 else
@@ -117,7 +123,7 @@ else
         $(Q)$< --defconfig=arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG) $(Kconfig)
 endif
 
-%_defconfig: $(obj)/conf
+%_defconfig: $(CONF)
         $(Q)$< --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig)
 
 # Help text used by make help
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