kbuild: create modules.builtin without Makefile.modbuiltin or tristate.conf

Commit bc081dd6e9f6 ("kbuild: generate modules.builtin") added
infrastructure to generate modules.builtin, the list of all
builtin modules.

Basically, it works like this:

  - Kconfig generates include/config/tristate.conf, the list of
    tristate CONFIG options with a value in a capital letter.

  - scripts/Makefile.modbuiltin makes Kbuild descend into
    directories to collect the information of builtin modules.

I am not a big fan of it because Kbuild ends up with traversing
the source tree twice.

I am not sure how perfectly it should work, but this approach cannot
avoid false positives; even if the relevant CONFIG option is tristate,
some Makefiles forces obj-m to obj-y.

Some examples are:

  arch/powerpc/platforms/powermac/Makefile:
    obj-$(CONFIG_NVRAM:m=y)         += nvram.o

  net/ipv6/Makefile:
    obj-$(subst m,y,$(CONFIG_IPV6)) += inet6_hashtables.o

  net/netlabel/Makefile:
    obj-$(subst m,y,$(CONFIG_IPV6)) += netlabel_calipso.o

Nobody has complained about (or noticed) it, so it is probably fine to
have false positives in modules.builtin.

This commit simplifies the implementation. Let's exploit the fact
that every module has MODULE_LICENSE(). (modpost shows a warning if
MODULE_LICENSE is missing. If so, 0-day bot would already have blocked
such a module.)

I added MODULE_FILE to <linux/module.h>. When the code is being compiled
as builtin, it will be filled with the file path of the module, and
collected into modules.builtin.info. Then, scripts/link-vmlinux.sh
extracts the list of builtin modules out of it.

This new approach fixes the false-positives above, but adds another
type of false-positives; non-modular code may have MODULE_LICENSE()
by mistake. This is not a big deal, it is just the code is always
orphan. We can clean it up if we like. You can see cleanup examples by:

  $ git log --grep='make.* explicitly non-modular'

To sum up, this commits deletes lots of code, but still produces almost
equivalent results. Please note it does not increase the vmlinux size at
all. As you can see in include/asm-generic/vmlinux.lds.h, the .modinfo
section is discarded in the link stage.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

1 files changed, 5 insertions, 16 deletions

diff --git a/Makefile b/Makefile
index e4c2d0327d8c..4f01de6cd43c 100644
--- a/Makefile
+++ b/Makefile
@@ -674,7 +674,7 @@ $(KCONFIG_CONFIG):
 #
 # This exploits the 'multi-target pattern rule' trick.
 # The syncconfig should be executed only once to make all the targets.
-%/auto.conf %/auto.conf.cmd %/tristate.conf: $(KCONFIG_CONFIG)
+%/auto.conf %/auto.conf.cmd: $(KCONFIG_CONFIG)
 	$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
 else # !may-sync-config
 # External modules and some install targets need include/generated/autoconf.h
@@ -1278,24 +1278,13 @@ all: modules
 # using awk while concatenating to the final file.
 
 PHONY += modules
-modules: $(if $(KBUILD_BUILTIN),vmlinux) modules.order modules.builtin
+modules: $(if $(KBUILD_BUILTIN),vmlinux) modules.order
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/modules-check.sh
 
 modules.order: descend
 	$(Q)$(AWK) '!x[$$0]++' $(addsuffix /$@, $(build-dirs)) > $@
 
-modbuiltin-dirs := $(addprefix _modbuiltin_, $(build-dirs))
-
-modules.builtin: $(modbuiltin-dirs)
-	$(Q)$(AWK) '!x[$$0]++' $(addsuffix /$@, $(build-dirs)) > $@
-
-PHONY += $(modbuiltin-dirs)
-# tristate.conf is not included from this Makefile. Add it as a prerequisite
-# here to make it self-healing in case somebody accidentally removes it.
-$(modbuiltin-dirs): include/config/tristate.conf
-	$(Q)$(MAKE) $(modbuiltin)=$(patsubst _modbuiltin_%,%,$@)
-
 # Target to prepare building external modules
 PHONY += modules_prepare
 modules_prepare: prepare
@@ -1315,7 +1304,7 @@ _modinst_:
 		ln -s $(CURDIR) $(MODLIB)/build ; \
 	fi
 	@sed 's:^:kernel/:' modules.order > $(MODLIB)/modules.order
-	@sed 's:^:kernel/:' modules.builtin > $(MODLIB)/modules.builtin
+	@cp -f modules.builtin $(MODLIB)/
 	@cp -f $(objtree)/modules.builtin.modinfo $(MODLIB)/
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modinst
 
@@ -1357,7 +1346,7 @@ endif # CONFIG_MODULES
 
 # Directories & files removed with 'make clean'
 CLEAN_DIRS  += include/ksym
-CLEAN_FILES += modules.builtin.modinfo modules.nsdeps
+CLEAN_FILES += modules.builtin modules.builtin.modinfo modules.nsdeps
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_DIRS  += include/config include/generated          \
@@ -1712,7 +1701,7 @@ clean: $(clean-dirs)
 		-o -name '*.lex.c' -o -name '*.tab.[ch]' \
 		-o -name '*.asn1.[ch]' \
 		-o -name '*.symtypes' -o -name 'modules.order' \
-		-o -name modules.builtin -o -name '.tmp_*.o.*' \
+		-o -name '.tmp_*.o.*' \
 		-o -name '*.c.[012]*.*' \
 		-o -name '*.ll' \
 		-o -name '*.gcno' \) -type f -print | xargs rm -f