kbuild: move core-y and drivers-y to ./Kbuild

Use the ordinary obj-y to list subdirectories.

Note1:
GNU Make seems to transform './.modules.order' to '.modules.order'
before matching it against the target pattern. Split ./.modules.order
to a dedicated rule to avoid "doesn't match the target pattern"
warning. [1]

Note2:
Previously, the link order of lib-y depended on CONFIG_MODULES; lib-y
was linked before drivers-y when CONFIG_MODULES=y, otherwise after
drivers-y. This was a bug of commit 7273ad2 ("kbuild: link lib-y
objects to vmlinux forcibly when CONFIG_MODULES=y"), but it was not a
big deal after all. Now, libs-y (all objects that come from lib/ and
arch/*/lib/) is linked last, irrespective of CONFIG_MODULES.

Note3:
Now, the single target build in arch/*/lib/ works correctly. There was
a bug report about this. [2]

  $ make ARCH=arm arch/arm/lib/findbit.o
    CALL    scripts/checksyscalls.sh
    AS      arch/arm/lib/findbit.o

[1]: https://lists.gnu.org/archive/html/bug-make/2022-08/msg00059.html
[2]: https://lore.kernel.org/linux-kbuild/YvUQOwL6lD4%2F5%2FU6@shell.armlinux.org.uk/

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

Kbuild

@@ -72,3 +72,26 @@ $(atomic-checks): $(obj)/.checked-%: include/linux/atomic/%  FORCE
 PHONY += prepare
 prepare: $(offsets-file) missing-syscalls $(atomic-checks)
 	@:
+
+# Ordinary directory descending
+# ---------------------------------------------------------------------------
+
+obj-y			+= init/
+obj-y			+= usr/
+obj-y			+= arch/$(SRCARCH)/
+obj-y			+= $(ARCH_CORE)
+obj-y			+= kernel/
+obj-y			+= certs/
+obj-y			+= mm/
+obj-y			+= fs/
+obj-y			+= ipc/
+obj-y			+= security/
+obj-y			+= crypto/
+obj-$(CONFIG_BLOCK)	+= block/
+obj-$(CONFIG_IO_URING)	+= io_uring/
+obj-y			+= drivers/
+obj-y			+= sound/
+obj-$(CONFIG_SAMPLES)	+= samples/
+obj-$(CONFIG_NET)	+= net/
+obj-y			+= virt/
+obj-y			+= $(ARCH_DRIVERS)

Makefile

@@ -676,11 +676,8 @@ endif
 
 ifeq ($(KBUILD_EXTMOD),)
 # Objects we will link into vmlinux / subdirs we need to visit
-core-y		:= init/ usr/ arch/$(SRCARCH)/
-drivers-y	:= drivers/ sound/
-drivers-$(CONFIG_SAMPLES) += samples/
-drivers-$(CONFIG_NET) += net/
-drivers-y	+= virt/
+core-y		:=
+drivers-y	:=
 libs-y		:= lib/
 endif # KBUILD_EXTMOD
 
@@ -1101,31 +1098,27 @@ export MODORDER := $(extmod_prefix)modules.order
 export MODULES_NSDEPS := $(extmod_prefix)modules.nsdeps
 
 ifeq ($(KBUILD_EXTMOD),)
-core-y			+= kernel/ certs/ mm/ fs/ ipc/ security/ crypto/
-core-$(CONFIG_BLOCK)	+= block/
-core-$(CONFIG_IO_URING)	+= io_uring/
 
-vmlinux-dirs	:= $(patsubst %/,%,$(filter %/, \
-		     $(core-y) $(core-m) $(drivers-y) $(drivers-m) \
-		     $(libs-y) $(libs-m)))
+vmlinux-dirs	:= . $(patsubst %/,%,$(filter %/, $(libs-y) $(libs-m)))
 
-vmlinux-alldirs	:= $(sort $(vmlinux-dirs) Documentation . \
+vmlinux-alldirs	:= $(sort $(vmlinux-dirs) Documentation \
 		     $(patsubst %/,%,$(filter %/, $(core-) \
 			$(drivers-) $(libs-))))
 
 build-dirs	:= $(vmlinux-dirs)
 clean-dirs	:= $(vmlinux-alldirs)
 
+export ARCH_CORE	:= $(core-y)
+export ARCH_DRIVERS	:= $(drivers-y)
 # Externally visible symbols (used by link-vmlinux.sh)
-KBUILD_VMLINUX_OBJS := $(head-y) $(patsubst %/,%/built-in.a, $(core-y))
+KBUILD_VMLINUX_OBJS := $(head-y) ./built-in.a
 KBUILD_VMLINUX_OBJS += $(addsuffix built-in.a, $(filter %/, $(libs-y)))
 ifdef CONFIG_MODULES
 KBUILD_VMLINUX_OBJS += $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)))
 KBUILD_VMLINUX_LIBS := $(filter-out %/, $(libs-y))
 else
 KBUILD_VMLINUX_LIBS := $(patsubst %/,%/lib.a, $(libs-y))
 endif
-KBUILD_VMLINUX_OBJS += $(patsubst %/,%/built-in.a, $(drivers-y))
 
 export KBUILD_VMLINUX_OBJS KBUILD_VMLINUX_LIBS
 export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
@@ -1752,7 +1745,10 @@ ifdef CONFIG_MODULES
 
 subdir-modorder := $(addsuffix /.modules.order, $(build-dirs))
 
-$(sort $(subdir-modorder)): %/.modules.order: % ;
+# Split ./.modules.order into a dedicate target to avoid
+# "doesn't match the target pattern" warning
+./.modules.order: . ;
+$(sort $(filter-out ./.modules.order, $(subdir-modorder))): %/.modules.order: % ;
 
 cmd_modules_order = cat $(real-prereqs) > $@
 
@@ -1823,7 +1819,8 @@ single_modpost: $(single-no-ko) modules_prepare
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
 	$(Q)rm -f $(MODORDER)
 
-single-goals := $(addprefix $(extmod_prefix), $(single-no-ko))
+single-goals := $(foreach x, $(addprefix $(extmod_prefix), $(single-no-ko)), \
+		$(if $(filter $(addsuffix /%, $(build-dirs)), $x),,./)$x)
 
 # trim unrelated directories
 build-dirs := $(foreach d, $(build-dirs), \

scripts/Makefile.lib

@@ -89,6 +89,7 @@ always-y			+= $(dtb-y)
 
 # Add subdir path
 
+ifneq ($(obj),.)
 extra-y		:= $(addprefix $(obj)/,$(extra-y))
 always-y	:= $(addprefix $(obj)/,$(always-y))
 targets		:= $(addprefix $(obj)/,$(targets))
@@ -100,6 +101,7 @@ multi-obj-m	:= $(addprefix $(obj)/, $(multi-obj-m))
 multi-dtb-y	:= $(addprefix $(obj)/, $(multi-dtb-y))
 real-dtb-y	:= $(addprefix $(obj)/, $(real-dtb-y))
 subdir-ym	:= $(addprefix $(obj)/,$(subdir-ym))
+endif
 
 # Finds the multi-part object the current object will be linked into.
 # If the object belongs to two or more multi-part objects, list them all.