kbuild: generate modules.builtin

To make it easier for module-init-tools and scripts like mkinitrd to
distinguish builtin and missing modules, install a modules.builtin file
listing all builtin modules. This is done by generating an additional
config file (tristate.conf) with tristate options set to uppercase 'Y'
or 'M'. If we source that config file, the builtin modules appear in
obj-Y.

Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/confdata.c

@@ -677,7 +677,7 @@ int conf_write_autoconf(void)
 	struct symbol *sym;
 	const char *str;
 	const char *name;
-	FILE *out, *out_h;
+	FILE *out, *tristate, *out_h;
 	time_t now;
 	int i, l;
 
@@ -692,9 +692,16 @@ int conf_write_autoconf(void)
 	if (!out)
 		return 1;
 
+	tristate = fopen(".tmpconfig_tristate", "w");
+	if (!tristate) {
+		fclose(out);
+		return 1;
+	}
+
 	out_h = fopen(".tmpconfig.h", "w");
 	if (!out_h) {
 		fclose(out);
+		fclose(tristate);
 		return 1;
 	}
 
@@ -707,6 +714,9 @@ int conf_write_autoconf(void)
 		     "# %s"
 		     "#\n",
 		     sym_get_string_value(sym), ctime(&now));
+	fprintf(tristate, "#\n"
+			  "# Automatically generated - do not edit\n"
+			  "\n");
 	fprintf(out_h, "/*\n"
 		       " * Automatically generated C config: don't edit\n"
 		       " * Linux kernel version: %s\n"
@@ -727,10 +737,14 @@ int conf_write_autoconf(void)
 				break;
 			case mod:
 				fprintf(out, "CONFIG_%s=m\n", sym->name);
+				fprintf(tristate, "CONFIG_%s=M\n", sym->name);
 				fprintf(out_h, "#define CONFIG_%s_MODULE 1\n", sym->name);
 				break;
 			case yes:
 				fprintf(out, "CONFIG_%s=y\n", sym->name);
+				if (sym->type == S_TRISTATE)
+					fprintf(tristate, "CONFIG_%s=Y\n",
+							sym->name);
 				fprintf(out_h, "#define CONFIG_%s 1\n", sym->name);
 				break;
 			}
@@ -772,6 +786,7 @@ int conf_write_autoconf(void)
 		}
 	}
 	fclose(out);
+	fclose(tristate);
 	fclose(out_h);
 
 	name = getenv("KCONFIG_AUTOHEADER");
@@ -779,6 +794,11 @@ int conf_write_autoconf(void)
 		name = "include/generated/autoconf.h";
 	if (rename(".tmpconfig.h", name))
 		return 1;
+	name = getenv("KCONFIG_TRISTATE");
+	if (!name)
+		name = "include/config/tristate.conf";
+	if (rename(".tmpconfig_tristate", name))
+		return 1;
 	name = conf_get_autoconfig_name();
 	/*
 	 * This must be the last step, kbuild has a dependency on auto.conf