[PATCHv2] kconfig: add warn-unknown-symbols sanity check

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Introduce KCONFIG_WARN_UNKNOWN_SYMBOLS environment variable,
which makes Kconfig warn about unknown config symbols.

This is especially useful for continuous kernel uprevs when
some symbols can be either removed or renamed between kernel
releases (which can go unnoticed otherwise).

By default KCONFIG_WARN_UNKNOWN_SYMBOLS generates warnings,
which are non-terminal. There is an additional environment
variable KCONFIG_WERROR that overrides this behaviour and
turns warnings into errors.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/kbuild/kconfig.rst |  9 +++++++++
 scripts/kconfig/confdata.c       | 21 +++++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/kconfig.rst b/Documentation/kbuild/kconfig.rst
index 6530ecd99da3..c946eb44bd13 100644
--- a/Documentation/kbuild/kconfig.rst
+++ b/Documentation/kbuild/kconfig.rst
@@ -56,6 +56,15 @@ KCONFIG_OVERWRITECONFIG
 If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
 break symlinks when .config is a symlink to somewhere else.
 
+KCONFIG_WARN_UNKNOWN_SYMBOLS
+----------------------------
+This environment variable makes Kconfig warn about all unrecognized
+symbols in the config input.
+
+KCONFIG_WERROR
+--------------
+If set, Kconfig treats warnings as errors.
+
 `CONFIG_`
 ---------
 If you set `CONFIG_` in the environment, Kconfig will prefix all symbols
diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index 992575f1e976..4a6811d77d18 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -349,7 +349,11 @@ int conf_read_simple(const char *name, int def)
 	char *p, *p2;
 	struct symbol *sym;
 	int i, def_flags;
+	const char *warn_unknown;
+	const char *werror;
 
+	warn_unknown = getenv("KCONFIG_WARN_UNKNOWN_SYMBOLS");
+	werror = getenv("KCONFIG_WERROR");
 	if (name) {
 		in = zconf_fopen(name);
 	} else {
@@ -437,6 +441,10 @@ int conf_read_simple(const char *name, int def)
 			if (def == S_DEF_USER) {
 				sym = sym_find(line + 2 + strlen(CONFIG_));
 				if (!sym) {
+					if (warn_unknown)
+						conf_warning("unknown symbol: %s",
+							     line + 2 + strlen(CONFIG_));
+
 					conf_set_changed(true);
 					continue;
 				}
@@ -471,7 +479,7 @@ int conf_read_simple(const char *name, int def)
 
 			sym = sym_find(line + strlen(CONFIG_));
 			if (!sym) {
-				if (def == S_DEF_AUTO)
+				if (def == S_DEF_AUTO) {
 					/*
 					 * Reading from include/config/auto.conf
 					 * If CONFIG_FOO previously existed in
@@ -479,8 +487,13 @@ int conf_read_simple(const char *name, int def)
 					 * include/config/FOO must be touched.
 					 */
 					conf_touch_dep(line + strlen(CONFIG_));
-				else
+				} else {
+					if (warn_unknown)
+						conf_warning("unknown symbol: %s",
+							     line + strlen(CONFIG_));
+
 					conf_set_changed(true);
+				}
 				continue;
 			}
 
@@ -519,6 +532,10 @@ int conf_read_simple(const char *name, int def)
 	}
 	free(line);
 	fclose(in);
+
+	if (conf_warnings && werror)
+		exit(1);
+
 	return 0;
 }
 
-- 
2.42.0.rc2.253.gd59a3bf2b4-goog