kbuild: use KBUILD_DEFCONFIG as the fallback for DEFCONFIG_LIST

Most of the Kconfig commands (except defconfig and all*config) read
the .config file as a base set of CONFIG options.

When it does not exist, the files in DEFCONFIG_LIST are searched in
this order and loaded if found.

I do not see much sense in the last two lines in DEFCONFIG_LIST.

[1] ARCH_DEFCONFIG

The entry for DEFCONFIG_LIST is guarded by 'depends on !UML'. So, the
ARCH_DEFCONFIG definition in arch/x86/um/Kconfig is meaningless.

arch/{sh,sparc,x86}/Kconfig define ARCH_DEFCONFIG depending on 32 or
64 bit variant symbols. This is a little bit strange; ARCH_DEFCONFIG
should be a fixed string because the base config file is loaded before
the symbol evaluation stage.

Using KBUILD_DEFCONFIG makes more sense because it is fixed before
Kconfig is invoked. Fortunately, arch/{sh,sparc,x86}/Makefile define it
in the same way, and it works as expected. Hence, replace ARCH_DEFCONFIG
with "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)".

[2] arch/$(ARCH)/defconfig

This file path is no longer valid. The defconfig files are always located
in the arch configs/ directories.

  $ find arch -name defconfig | sort
  arch/alpha/configs/defconfig
  arch/arm64/configs/defconfig
  arch/csky/configs/defconfig
  arch/nds32/configs/defconfig
  arch/riscv/configs/defconfig
  arch/s390/configs/defconfig
  arch/unicore32/configs/defconfig

The path arch/*/configs/defconfig is already covered by
"arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)". So, this file path is
not necessary.

I moved the default KBUILD_DEFCONFIG to the top Makefile. Otherwise,
the 7 architectures listed above would end up with endless loop of
syncconfig.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -388,6 +388,9 @@ endif
 KCONFIG_CONFIG	?= .config
 export KCONFIG_CONFIG
 
+# Default file for 'make defconfig'. This may be overridden by arch-Makefile.
+export KBUILD_DEFCONFIG := defconfig
+
 # SHELL used by kbuild
 CONFIG_SHELL := sh
 

arch/sh/Kconfig

@@ -87,11 +87,6 @@ config SUPERH64
 	select HAVE_EXIT_THREAD
 	select KALLSYMS
 
-config ARCH_DEFCONFIG
-	string
-	default "arch/sh/configs/shx3_defconfig" if SUPERH32
-	default "arch/sh/configs/cayman_defconfig" if SUPERH64
-
 config GENERIC_BUG
 	def_bool y
 	depends on BUG && SUPERH32

arch/sparc/Kconfig

@@ -95,11 +95,6 @@ config SPARC64
 	select PCI_DOMAINS if PCI
 	select ARCH_HAS_GIGANTIC_PAGE
 
-config ARCH_DEFCONFIG
-	string
-	default "arch/sparc/configs/sparc32_defconfig" if SPARC32
-	default "arch/sparc/configs/sparc64_defconfig" if SPARC64
-
 config ARCH_PROC_KCORE_TEXT
 	def_bool y
 

arch/x86/Kconfig

@@ -240,11 +240,6 @@ config OUTPUT_FORMAT
 	default "elf32-i386" if X86_32
 	default "elf64-x86-64" if X86_64
 
-config ARCH_DEFCONFIG
-	string
-	default "arch/x86/configs/i386_defconfig" if X86_32
-	default "arch/x86/configs/x86_64_defconfig" if X86_64
-
 config LOCKDEP_SUPPORT
 	def_bool y
 

arch/x86/um/Kconfig

@@ -27,11 +27,6 @@ config X86_64
 	def_bool 64BIT
 	select MODULES_USE_ELF_RELA
 
-config ARCH_DEFCONFIG
-	string
-	default "arch/um/configs/i386_defconfig" if X86_32
-	default "arch/um/configs/x86_64_defconfig" if X86_64
-
 config 3_LEVEL_PGTABLES
 	bool "Three-level pagetables" if !64BIT
 	default 64BIT

init/Kconfig

@@ -6,8 +6,7 @@ config DEFCONFIG_LIST
 	default "/lib/modules/$(shell,uname -r)/.config"
 	default "/etc/kernel-config"
 	default "/boot/config-$(shell,uname -r)"
-	default ARCH_DEFCONFIG
-	default "arch/$(ARCH)/defconfig"
+	default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)"
 
 config CC_IS_GCC
 	def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc)

scripts/kconfig/Makefile

@@ -12,10 +12,6 @@ else
 Kconfig := Kconfig
 endif
 
-ifndef KBUILD_DEFCONFIG
-KBUILD_DEFCONFIG := defconfig
-endif
-
 ifeq ($(quiet),silent_)
 silent := -s
 endif