kbuild: set y instead of 1 to KBUILD_{BUILTIN,MODULES}

KBUILD_BUILTIN is set to 1 unless you are building only modules.

KBUILD_MODULES is set to 1 when you are building only modules
(a typical use case is "make modules").

It is more useful to set them to 'y' instead, so we can do
something like:

always-$(KBUILD_BUILTIN) += vmlinux.lds

This works equivalently to:

extra-y += vmlinux.lds

This allows us to deprecate extra-y. extra-y and always-y are quite
similar, and we do not need both.

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Reviewed-by: Nicolas Schier <[e-mail]>

Documentation/kbuild/makefiles.rst

···
   # arch/x86/kernel/Makefile
   extra-y	+= vmlinux.lds
 
+extra-y is now deprecated because this is equivalent to:
+
+  always-$(KBUILD_BUILTIN) += vmlinux.lds
+
 $(extra-y) should only contain targets needed for vmlinux.
 
 Kbuild skips extra-y when vmlinux is apparently not a final goal.

Makefile

···
 # Normally, just do built-in.
 
 KBUILD_MODULES :=
-KBUILD_BUILTIN := 1
+KBUILD_BUILTIN := y
 
 # If we have only "make modules", don't compile built-in objects.
 ifeq ($(MAKECMDGOALS),modules)
···
 # Just "make" or "make all" shall build modules as well
 
 ifneq ($(filter all modules nsdeps compile_commands.json clang-%,$(MAKECMDGOALS)),)
-  KBUILD_MODULES := 1
+  KBUILD_MODULES := y
 endif
 
 ifeq ($(MAKECMDGOALS),)
-  KBUILD_MODULES := 1
+  KBUILD_MODULES := y
 endif
 
 export KBUILD_MODULES KBUILD_BUILTIN
···
 ifdef CONFIG_TRIM_UNUSED_KSYMS
 # For the kernel to actually contain only the needed exported symbols,
 # we have to build modules as well to determine what those symbols are.
-KBUILD_MODULES := 1
+KBUILD_MODULES := y
 endif
 
 # '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
···
 # the built-in objects during the descend as well, in order to
 # make sure the checksums are up to date before we record them.
 ifdef CONFIG_MODVERSIONS
-  KBUILD_BUILTIN := 1
+  KBUILD_BUILTIN := y
 endif
 
 # Build modules
···
 # *.ko are usually independent of vmlinux, but CONFIG_DEBUG_INFO_BTF_MODULES
 # is an exception.
 ifdef CONFIG_DEBUG_INFO_BTF_MODULES
-KBUILD_BUILTIN := 1
+KBUILD_BUILTIN := y
 modules: vmlinux
 endif
 
···
 
 # We are always building only modules.
 KBUILD_BUILTIN :=
-KBUILD_MODULES := 1
+KBUILD_MODULES := y
 
 build-dir := .
 
···
 
 single-goals := $(addprefix $(build-dir)/, $(single-no-ko))
 
-KBUILD_MODULES := 1
+KBUILD_MODULES := y
 
 endif