kbuild: Don't build final .ko yet when descending with CONFIG_MODVERSIONING

With CONFIG_MODVERSIONING, we need to record the versions of the unresolved
symbols in the final <module>.ko, which we only know after we finished
the descending build. So we only build <module>.o in that case.
  
Also, keep track of the modules we built, the post-processing step needs
a list of all modules. Keeping track is done by touching
.tmp_versions/path/to/module.ko

Makefile

@@ -260,6 +260,20 @@ ifndef CONFIG_FRAME_POINTER
 CFLAGS		+= -fomit-frame-pointer
 endif
 
+#	When we're building modules with modversions, we need to consider
+#	the built-in objects during the descend as well, in order to
+#	make sure the checksums are uptodate before we use them.
+
+ifdef CONFIG_MODVERSIONING
+ifeq ($(KBUILD_MODULES),1)
+ifneq ($(KBUILD_BUILTIN),1)
+  KBUILD_BUILTIN := 1
+endif
+endif
+endif
+
+export MODVERDIR := .tmp_versions
+
 #
 # INSTALL_PATH specifies where to place the updated kernel and system map
 # images.  Uncomment if you want to place them anywhere other than root.
@@ -388,6 +402,16 @@ $(SUBDIRS): prepare
 
 .PHONY: prepare
 prepare: include/linux/version.h include/asm include/config/MARKER
+ifdef CONFIG_MODVERSIONING
+ifdef KBUILD_MODULES
+ifeq ($(origin SUBDIRS),file)
+	$(Q)rm -rf $(MODVERDIR)
+else
+	@echo '*** Warning: Overriding SUBDIRS on the command line can cause'
+	@echo '***          inconsistencies with module symbol versions'
+endif
+endif
+endif
 	@echo '  Starting the build. KBUILD_BUILTIN=$(KBUILD_BUILTIN) KBUILD_MODULES=$(KBUILD_MODULES)'
 
 #	We need to build init/vermagic.o before descending since all modules

scripts/Makefile.build

@@ -45,8 +45,15 @@ O_TARGET := $(obj)/built-in.o
 endif
 endif
 
+ifdef CONFIG_MODVERSIONING
+modules := $(obj-m)
+touch-module = @mkdir -p $(MODVERDIR)/$(@D); touch $(MODVERDIR)/$(@:.o=.ko)
+else
+modules := $(obj-m:.o=.ko)
+endif
+
 __build: $(if $(KBUILD_BUILTIN),$(O_TARGET) $(L_TARGET) $(EXTRA_TARGETS)) \
-	 $(if $(KBUILD_MODULES),$(obj-m:.o=.ko)) \
+	 $(if $(KBUILD_MODULES),$(modules)) \
 	 $(subdir-ym) $(build-targets)
 	@:
 
@@ -152,6 +159,15 @@ else
 	$(call if_changed_dep,cc_o_c)
 endif
 
+# For modversioning, we need to special case single-part modules
+# to mark them in $(MODVERDIR)
+
+ifdef CONFIG_MODVERSIONING
+$(single-used-m): %.o: %.c FORCE
+	$(touch-module)
+	$(call if_changed_rule,vcc_o_c)
+endif
+
 quiet_cmd_cc_lst_c = MKLST   $@
       cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
 		     $(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
@@ -242,6 +258,11 @@ targets += $(multi-used-y) $(multi-used-m)
 #
 # Rule to link modules ( .o -> .ko )
 #
+
+# With CONFIG_MODVERSIONING, generation of the final .ko is handled
+# by scripts/Makefile.modver
+ifndef CONFIG_MODVERSIONING
+
 quiet_cmd_link_module = LD [M]  $@
 cmd_link_module = $(LD) $(LDFLAGS) $(EXTRA_LDFLAGS) $(LDFLAGS_MODULE) -o $@ $< init/vermagic.o
 
@@ -255,6 +276,8 @@ $(single-used-m:.o=.ko) $(multi-used-m:.o=.ko): %.ko: %.o init/vermagic.o FORCE
 
 targets += $(single-used-m:.o=.ko) $(multi-used-m:.o=.ko)
 
+endif
+
 # Compile programs on the host
 # ===========================================================================
 # host-progs := bin2hex