kconfig: change defconfig_list option to environment variable

"defconfig_list" is a weird option that defines a static symbol that
declares the list of base config files in case the .config does not
exist yet.

This is quite different from other normal symbols; we just abused the
"string" type and the "default" properties to list out the input files.
They must be fixed values since these are searched for and loaded in
the parse stage.

It is an ugly hack, and should not exist in the first place. Providing
this feature as an environment variable is a saner approach.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index 226ae07..3cbccfc 100644
--- a/Documentation/kbuild/kconfig-language.rst
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -229,11 +229,6 @@
   which can modify the behaviour of the menu entry and its config
   symbol. These options are currently possible:
 
-  - "defconfig_list"
-    This declares a list of default entries which can be used when
-    looking for the default configuration (which is used when the main
-    .config doesn't exists yet.)
-
   - "modules"
     This declares the symbol to be used as the MODULES symbol, which
     enables the third modular state for all config symbols.
diff --git a/Documentation/kbuild/kconfig.rst b/Documentation/kbuild/kconfig.rst
index dce6801..5967c79 100644
--- a/Documentation/kbuild/kconfig.rst
+++ b/Documentation/kbuild/kconfig.rst
@@ -41,6 +41,14 @@
 This environment variable can be used to specify a default kernel config
 file name to override the default name of ".config".
 
+KCONFIG_DEFCONFIG_LIST
+----------------------
+
+This environment variable specifies a list of config files which can be used
+as a base configuration in case the .config does not exist yet. Entries in
+the list are separated with whitespaces to each other, and the first one
+that exists is used.
+
 KCONFIG_OVERWRITECONFIG
 -----------------------
 If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
diff --git a/init/Kconfig b/init/Kconfig
index 5f5c776..8578c60 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1,13 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
-config DEFCONFIG_LIST
-	string
-	depends on !UML
-	option defconfig_list
-	default "/lib/modules/$(shell,uname -r)/.config"
-	default "/etc/kernel-config"
-	default "/boot/config-$(shell,uname -r)"
-	default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)"
-
 config CC_VERSION_TEXT
 	string
 	default "$(CC_VERSION_TEXT)"
diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
index 8c19b82..31c5735 100644
--- a/scripts/kconfig/Makefile
+++ b/scripts/kconfig/Makefile
@@ -13,6 +13,16 @@
 silent := -s
 endif
 
+export KCONFIG_DEFCONFIG_LIST :=
+ifneq ($(SRCARCH),um)
+kernel-release := $(shell uname -r)
+KCONFIG_DEFCONFIG_LIST := \
+	/lib/modules/$(kernel-release)/.config \
+	/etc/kernel-config \
+	/boot/config-$(kernel-release) \
+	arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)
+endif
+
 # We need this, in case the user has it in its environment
 unexport CONFIG_
 
diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index 198f709..f3998d5 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -360,28 +360,46 @@ int conf_read_simple(const char *name, int def)
 	if (name) {
 		in = zconf_fopen(name);
 	} else {
-		struct property *prop;
+		char *env;
 
 		name = conf_get_configname();
 		in = zconf_fopen(name);
 		if (in)
 			goto load;
 		sym_add_change_count(1);
-		if (!sym_defconfig_list)
+
+		env = getenv("KCONFIG_DEFCONFIG_LIST");
+		if (!env)
 			return 1;
 
-		for_all_defaults(sym_defconfig_list, prop) {
-			if (expr_calc_value(prop->visible.expr) == no ||
-			    prop->expr->type != E_SYMBOL)
-				continue;
-			sym_calc_value(prop->expr->left.sym);
-			name = sym_get_string_value(prop->expr->left.sym);
-			in = zconf_fopen(name);
+		while (1) {
+			bool is_last;
+
+			while (isspace(*env))
+				env++;
+
+			if (!*env)
+				break;
+
+			p = env;
+			while (*p && !isspace(*p))
+				p++;
+
+			is_last = (*p == '\0');
+
+			*p = '\0';
+
+			in = zconf_fopen(env);
 			if (in) {
 				conf_message("using defaults found in %s",
-					 name);
+					     env);
 				goto load;
 			}
+
+			if (is_last)
+				break;
+
+			env = p + 1;
 		}
 	}
 	if (!in)
diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index bbca80a0..dc17152 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -287,7 +287,6 @@ struct file *lookup_file(const char *name);
 
 extern struct symbol symbol_yes, symbol_no, symbol_mod;
 extern struct symbol *modules_sym;
-extern struct symbol *sym_defconfig_list;
 extern int cdebug;
 struct expr *expr_alloc_symbol(struct symbol *sym);
 struct expr *expr_alloc_one(enum expr_type type, struct expr *ce);
diff --git a/scripts/kconfig/lexer.l b/scripts/kconfig/lexer.l
index 9c22cb5..e918950 100644
--- a/scripts/kconfig/lexer.l
+++ b/scripts/kconfig/lexer.l
@@ -99,7 +99,6 @@
 "def_bool"		return T_DEF_BOOL;
 "def_tristate"		return T_DEF_TRISTATE;
 "default"		return T_DEFAULT;
-"defconfig_list"	return T_DEFCONFIG_LIST;
 "depends"		return T_DEPENDS;
 "endchoice"		return T_ENDCHOICE;
 "endif"			return T_ENDIF;
diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
index 1c15e3c..7378e96 100644
--- a/scripts/kconfig/lkc.h
+++ b/scripts/kconfig/lkc.h
@@ -96,7 +96,6 @@ struct property *menu_add_prompt(enum prop_type type, char *prompt, struct expr
 void menu_add_expr(enum prop_type type, struct expr *expr, struct expr *dep);
 void menu_add_symbol(enum prop_type type, struct symbol *sym, struct expr *dep);
 void menu_add_option_modules(void);
-void menu_add_option_defconfig_list(void);
 void menu_add_option_allnoconfig_y(void);
 void menu_finalize(struct menu *parent);
 void menu_set_type(int type);
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index a5fbd6c..5dcfc17 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -219,15 +219,6 @@ void menu_add_option_modules(void)
 	modules_sym = current_entry->sym;
 }
 
-void menu_add_option_defconfig_list(void)
-{
-	if (!sym_defconfig_list)
-		sym_defconfig_list = current_entry->sym;
-	else if (sym_defconfig_list != current_entry->sym)
-		zconf_error("trying to redefine defconfig symbol");
-	sym_defconfig_list->flags |= SYMBOL_NO_WRITE;
-}
-
 void menu_add_option_allnoconfig_y(void)
 {
 	current_entry->sym->flags |= SYMBOL_ALLNOCONFIG_Y;
diff --git a/scripts/kconfig/parser.y b/scripts/kconfig/parser.y
index 190f111..f11d838 100644
--- a/scripts/kconfig/parser.y
+++ b/scripts/kconfig/parser.y
@@ -53,7 +53,6 @@
 %token T_COMMENT
 %token T_CONFIG
 %token T_DEFAULT
-%token T_DEFCONFIG_LIST
 %token T_DEF_BOOL
 %token T_DEF_TRISTATE
 %token T_DEPENDS
@@ -223,11 +222,6 @@
 	menu_add_option_modules();
 };
 
-config_option: T_OPTION T_DEFCONFIG_LIST T_EOL
-{
-	menu_add_option_defconfig_list();
-};
-
 config_option: T_OPTION T_ALLNOCONFIG_Y T_EOL
 {
 	menu_add_option_allnoconfig_y();
diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
index fe38e6f..36b0fcb 100644
--- a/scripts/kconfig/symbol.c
+++ b/scripts/kconfig/symbol.c
@@ -35,7 +35,6 @@ static struct symbol symbol_empty = {
 	.flags = SYMBOL_VALID,
 };
 
-struct symbol *sym_defconfig_list;
 struct symbol *modules_sym;
 static tristate modules_val;
 
diff --git a/scripts/kconfig/tests/conftest.py b/scripts/kconfig/tests/conftest.py
index 0345ef6..af8774a 100644
--- a/scripts/kconfig/tests/conftest.py
+++ b/scripts/kconfig/tests/conftest.py
@@ -53,6 +53,10 @@
         # Override 'srctree' environment to make the test as the top directory
         extra_env['srctree'] = self._test_dir
 
+        # Clear KCONFIG_DEFCONFIG_LIST to keep unit tests from being affected
+        # by the user's environment.
+        extra_env['KCONFIG_DEFCONFIG_LIST'] = ''
+
         # Run Kconfig in a temporary directory.
         # This directory is automatically removed when done.
         with tempfile.TemporaryDirectory() as temp_dir: