kbuild: modpost: do not parse unnecessary rules for vmlinux modpost

Since commit ff9b45c55b ("kbuild: modpost: read modules.order instead
of $(MODVERDIR)/*.mod"), 'make vmlinux' emits a warning, like this:

$ make defconfig vmlinux
  [ snip ]
  LD      vmlinux.o
cat: modules.order: No such file or directory
  MODPOST vmlinux.o
  MODINFO modules.builtin.modinfo
  KSYM    .tmp_kallsyms1.o
  KSYM    .tmp_kallsyms2.o
  LD      vmlinux
  SORTEX  vmlinux
  SYSMAP  System.map

When building only vmlinux, KBUILD_MODULES is not set. Hence, the
modules.order is not generated. For the vmlinux modpost, it is not
necessary at all.

Separate scripts/Makefile.modpost for the vmlinux/modules stages.
This works more efficiently because the vmlinux modpost does not
need to include .*.cmd files.

Fixes: ff9b45c55b ("kbuild: modpost: read modules.order instead of $(MODVERDIR)/*.mod")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.modpost

@@ -38,12 +38,39 @@
 # symbols in the final module linking stage
 # KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
 # This is solely useful to speed up test compiles
-PHONY := _modpost
-_modpost: __modpost
+
+PHONY := __modpost
+__modpost:
 
 include include/config/auto.conf
 include scripts/Kbuild.include
 
+kernelsymfile := $(objtree)/Module.symvers
+modulesymfile := $(firstword $(KBUILD_EXTMOD))/Module.symvers
+
+MODPOST = scripts/mod/modpost						\
+	$(if $(CONFIG_MODVERSIONS),-m)					\
+	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)			\
+	$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile)			\
+	$(if $(KBUILD_EXTMOD),-I $(modulesymfile))			\
+	$(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS)))	\
+	$(if $(KBUILD_EXTMOD),-o $(modulesymfile))			\
+	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)			\
+	$(if $(KBUILD_MODPOST_WARN),-w)
+
+ifdef MODPOST_VMLINUX
+
+__modpost: vmlinux.o
+
+quiet_cmd_modpost = MODPOST $@
+      cmd_modpost = $(MODPOST) $@
+
+PHONY += vmlinux.o
+vmlinux.o:
+	$(call cmd,modpost)
+
+else
+
 # When building external modules load the Kbuild file to retrieve EXTRA_SYMBOLS info
 ifneq ($(KBUILD_EXTMOD),)
 
@@ -58,50 +85,27 @@ endif
 
 include scripts/Makefile.lib
 
-kernelsymfile := $(objtree)/Module.symvers
-modulesymfile := $(firstword $(KBUILD_EXTMOD))/Module.symvers
-
 modorder := $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)modules.order
 
-# Step 1), find all modules listed in modules.order
-ifdef CONFIG_MODULES
+# find all modules listed in modules.order
 modules := $(sort $(shell cat $(modorder)))
-endif
 
 # Stop after building .o files if NOFINAL is set. Makes compile tests quicker
-_modpost: $(if $(KBUILD_MODPOST_NOFINAL), $(modules:.ko:.o),$(modules))
+__modpost: $(if $(KBUILD_MODPOST_NOFINAL), $(modules:.ko:.o),$(modules))
+	@:
 
-# Step 2), invoke modpost
-#  Includes step 3,4
-modpost = scripts/mod/modpost                    \
- $(if $(CONFIG_MODVERSIONS),-m)                  \
- $(if $(CONFIG_MODULE_SRCVERSION_ALL),-a,)       \
- $(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile)   \
- $(if $(KBUILD_EXTMOD),-I $(modulesymfile))      \
- $(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
- $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
- $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)  \
- $(if $(KBUILD_MODPOST_WARN),-w)
-
-MODPOST_OPT=$(subst -i,-n,$(filter -i,$(MAKEFLAGS)))
+MODPOST += $(subst -i,-n,$(filter -i,$(MAKEFLAGS))) -s -T - $(wildcard vmlinux)
 
 # We can go over command line length here, so be careful.
 quiet_cmd_modpost = MODPOST $(words $(modules)) modules
-      cmd_modpost = sed 's/ko$$/o/' $(modorder) | $(modpost) $(MODPOST_OPT) -s -T -
+      cmd_modpost = sed 's/ko$$/o/' $(modorder) | $(MODPOST)
 
-PHONY += __modpost
-__modpost:
-	$(call cmd,modpost) $(wildcard vmlinux)
-
-quiet_cmd_kernel-mod = MODPOST $@
-      cmd_kernel-mod = $(modpost) $@
-
-vmlinux.o: FORCE
-	$(call cmd,kernel-mod)
+PHONY += modules-modpost
+modules-modpost:
+	$(call cmd,modpost)
 
 # Declare generated files as targets for modpost
-$(modules:.ko=.mod.c): __modpost ;
-
+$(modules:.ko=.mod.c): modules-modpost
 
 # Step 5), compile all *.mod.c files
 
@@ -149,4 +153,6 @@ existing-targets := $(wildcard $(sort $(targets)))
 
 -include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
 
+endif
+
 .PHONY: $(PHONY)

scripts/link-vmlinux.sh

@@ -210,7 +210,7 @@ info LD vmlinux.o
 modpost_link vmlinux.o
 
 # modpost vmlinux.o to check for section mismatches
-${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o
+${MAKE} -f "${srctree}/scripts/Makefile.modpost" MODPOST_VMLINUX=1
 
 info MODINFO modules.builtin.modinfo
 ${OBJCOPY} -j .modinfo -O binary vmlinux.o modules.builtin.modinfo