kbuild: pass KBUILD_MODFILE when compiling builtin objects

When compiling, Kbuild passes KBUILD_BASENAME (basename of the object)
and KBUILD_MODNAME (basename of the module).

This commit adds another one, KBUILD_MODFILE, which is the path of
the module. (or, the path of the module it would end up in if it were
compiled as a module.)

The next commit will use this to generate modules.builtin without
tristate.conf.

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

scripts/Makefile.lib

@@ -84,12 +84,14 @@ multi-used-m	:= $(addprefix $(obj)/,$(multi-used-m))
 subdir-ym	:= $(addprefix $(obj)/,$(subdir-ym))
 
 # Finds the multi-part object the current object will be linked into.
-# If the object belongs to two or more multi-part objects, all of them are
-# concatenated with a colon separator.
-modname-multi = $(subst $(space),:,$(sort $(foreach m,$(multi-used),\
-		$(if $(filter $*.o, $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m))),$(m:.o=)))))
+# If the object belongs to two or more multi-part objects, list them all.
+modname-multi = $(sort $(foreach m,$(multi-used),\
+		$(if $(filter $*.o, $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m))),$(m:.o=))))
 
-modname = $(if $(modname-multi),$(modname-multi),$(basetarget))
+__modname = $(if $(modname-multi),$(modname-multi),$(basetarget))
+
+modname = $(subst $(space),:,$(__modname))
+modfile = $(addprefix $(obj)/,$(__modname))
 
 # target with $(obj)/ and its suffix stripped
 target-stem = $(basename $(patsubst $(obj)/%,%,$@))
@@ -100,6 +102,7 @@ target-stem = $(basename $(patsubst $(obj)/%,%,$@))
 name-fix = $(call stringify,$(subst $(comma),_,$(subst -,_,$1)))
 basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget))
 modname_flags  = -DKBUILD_MODNAME=$(call name-fix,$(modname))
+modfile_flags  = -DKBUILD_MODFILE=$(call stringify,$(modfile))
 
 orig_c_flags   = $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) \
                  $(ccflags-y) $(CFLAGS_$(target-stem).o)
@@ -158,7 +161,7 @@ quiet_modtag = $(if $(part-of-module),[M],   )
 modkern_cflags =                                          \
 	$(if $(part-of-module),                           \
 		$(KBUILD_CFLAGS_MODULE) $(CFLAGS_MODULE), \
-		$(KBUILD_CFLAGS_KERNEL) $(CFLAGS_KERNEL))
+		$(KBUILD_CFLAGS_KERNEL) $(CFLAGS_KERNEL) $(modfile_flags))
 
 modkern_aflags = $(if $(part-of-module),				\
 			$(KBUILD_AFLAGS_MODULE) $(AFLAGS_MODULE),	\