kbuild: Move the version magic generation into module postprocessing

Since we'll have to always do module postprocessing shortly, we can as well
get rid of the special cased init/vermagic.o which needed to be compiled
before descending, and instead include the current version magic string
during post processing. For that purpose, the generation of the string is
moved from init/vermagic.c to include/linux/vermagic.h.

People who externally maintain modules will also be happy about that.

Makefile

@@ -416,17 +416,6 @@ 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
-#	(*.ko) need it already
-
-ifdef CONFIG_MODULES
-
-prepare: init/vermagic.o
-
-init/vermagic.o: include/linux/version.h
-
-endif
-
 #	This can be used by arch/$ARCH/Makefile to preprocess
 #	their vmlinux.lds.S file
 

init/vermagic.c → include/linux/vermagic.h

@@ -16,7 +16,8 @@
 #define MODULE_ARCH_VERMAGIC ""
 #endif
 
-const char vermagic[] __attribute__((section("__vermagic"))) =
-       UTS_RELEASE " "
-       MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT MODULE_ARCH_VERMAGIC
-       "gcc-" __stringify(__GNUC__) "." __stringify(__GNUC_MINOR__);
+#define VERMAGIC_STRING 						\
+	UTS_RELEASE " "							\
+	MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT 			\
+	MODULE_ARCH_VERMAGIC 						\
+	"gcc-" __stringify(__GNUC__) "." __stringify(__GNUC_MINOR__)

init/Makefile

@@ -3,7 +3,6 @@
 #
 
 obj-y			:= main.o version.o do_mounts.o initramfs.o
-obj-$(CONFIG_MODULES)	+= vermagic.o
 
 # files to be removed upon make clean
 clean-files := ../include/linux/compile.h

kernel/module.c

@@ -30,6 +30,7 @@
 #include <linux/moduleparam.h>
 #include <linux/errno.h>
 #include <linux/err.h>
+#include <linux/vermagic.h>
 #include <asm/uaccess.h>
 #include <asm/semaphore.h>
 #include <asm/pgalloc.h>
@@ -725,6 +726,8 @@ static int obsolete_params(const char *name,
 }
 #endif /* CONFIG_OBSOLETE_MODPARM */
 
+static const char vermagic[] = VERMAGIC_STRING;
+
 #ifdef CONFIG_MODVERSIONS
 static int check_version(Elf_Shdr *sechdrs,
 			 unsigned int versindex,
@@ -1036,9 +1039,6 @@ static void set_license(struct module *mod, Elf_Shdr *sechdrs, int licenseidx)
 	}
 }
 
-/* From init/vermagic.o */
-extern char vermagic[];
-
 /* Allocate and load the module: note that size of section 0 is always
    zero, and we rely on this for optional sections. */
 static struct module *load_module(void *umod,

scripts/Makefile.modver

@@ -5,6 +5,7 @@
 .PHONY: __modversions
 __modversions:
 
+include .config
 include scripts/Makefile.lib
 
 #
@@ -28,7 +29,7 @@ quiet_cmd_ld_ko_o = LD [M]  $@
 
 init/vermagic.o: ;
 
-$(modules): %.ko :%.o $(if $(CONFIG_MODVERSIONS),%.ver.o) init/vermagic.o FORCE
+$(modules): %.ko :%.o %.ver.o FORCE
 	$(call if_changed,ld_ko_o)
 
 targets += $(modules)
@@ -45,9 +46,16 @@ targets += $(modules:.ko=.ver.o)
 
 # Generate C source with version info for unresolved symbols
 
+ifdef CONFIG_MODVERSIONS
+
 define rule_mkver_o_c
 	echo '  MKVER   $@';						\
 	( echo "#include <linux/module.h>";				\
+	  echo "#include <linux/vermagic.h>";				\
+	  echo "";							\
+	  echo "const char vermagic[]";					\
+	  echo "__attribute__((section(\"__vermagic\"))) =";		\
+	  echo "VERMAGIC_STRING;";					\
 	  echo "";							\
 	  echo "static const struct modversion_info ____versions[]";	\
 	  echo "__attribute__((section(\"__versions\"))) = {"; 		\
@@ -59,9 +67,35 @@ define rule_mkver_o_c
 	) > $@
 endef
 
-$(modules:.ko=.ver.c): %.ver.c: %.o .tmp_all-versions FORCE
+# We have a fake dependency on compile.h to make sure that we notice
+# if the compiler version changes under us.
+
+$(modules:.ko=.ver.c):							\
+%.ver.c: %.o .tmp_all-versions include/linux/compile.h FORCE
+	$(call if_changed_rule,mkver_o_c)
+
+else
+
+define rule_mkver_o_c
+	echo '  MKVER   $@';						\
+	( echo "#include <linux/module.h>";				\
+	  echo "#include <linux/vermagic.h>";				\
+	  echo "";							\
+	  echo "const char vermagic[]";					\
+	  echo "__attribute__((section(\"__vermagic\"))) =";		\
+	  echo "VERMAGIC_STRING;";					\
+	) > $@
+endef
+
+# We have a fake dependency on compile.h to make sure that we notice
+# if the compiler version changes under us.
+
+$(modules:.ko=.ver.c):							\
+%.ver.c: %.o include/linux/compile.h FORCE
 	$(call if_changed_rule,mkver_o_c)
 
+endif
+
 targets += $(modules:.ko=.ver.c))
 
 # Extract all checksums for all exported symbols