kbuild: reuse $(cmd_objtool) for cmd_cc_lto_link_modules

For CONFIG_LTO_CLANG=y, the objtool processing is not possible at the
compilation, hence postponed by the link time.

Reuse $(cmd_objtool) for CONFIG_LTO_CLANG=y by defining objtool-enabled
properly.

For CONFIG_LTO_CLANG=y:

  objtool-enabled is off for %.o compilation
  objtool-enabled is on  for %.lto link

For CONFIG_LTO_CLANG=n:

  objtool-enabled is on for %.o compilation
      (but, it depends on OBJECT_FILE_NON_STANDARD)

Set part-of-module := y for %.lto.o to avoid repeating --module.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

scripts/Makefile.build

@@ -236,20 +236,26 @@ objtool_args =								\
 	$(if $(CONFIG_X86_SMAP), --uaccess)				\
 	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)
 
-ifndef CONFIG_LTO_CLANG
+cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
+cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
+
+endif # CONFIG_STACK_VALIDATION
+
+ifdef CONFIG_LTO_CLANG
+
+# Skip objtool for LLVM bitcode
+$(obj)/%.o: objtool-enabled :=
+
+else
 
 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
 
-objtool-enabled = $(if $(filter-out y%, \
+$(obj)/%.o: objtool-enabled = $(if $(filter-out y%, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n),y)
 
-cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
-cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
-
-endif # CONFIG_LTO_CLANG
-endif # CONFIG_STACK_VALIDATION
+endif
 
 ifdef CONFIG_TRIM_UNUSED_KSYMS
 cmd_gen_ksymdeps = \
@@ -289,13 +295,13 @@ cmd_cc_lto_link_modules =						\
 	$(LD) $(ld_flags) -r -o $@					\
 		$(shell [ -s $(@:.lto.o=.o.symversions) ] &&		\
 			echo -T $(@:.lto.o=.o.symversions))		\
-		--whole-archive $(filter-out FORCE,$^)
+		--whole-archive $(filter-out FORCE,$^)			\
+		$(cmd_objtool)
 
-ifdef CONFIG_STACK_VALIDATION
 # objtool was skipped for LLVM bitcode, run it now that we have compiled
 # modules into native code
-cmd_cc_lto_link_modules += ; $(objtool) $(objtool_args) --module $@
-endif
+$(obj)/%.lto.o: objtool-enabled = y
+$(obj)/%.lto.o: part-of-module := y
 
 $(obj)/%.lto.o: $(obj)/%.o FORCE
 	$(call if_changed,cc_lto_link_modules)