[RFC PATCH 1/2] gcc-plugins: add cleanup_plugin for uninitialized cleanup detection

[Li Chen <me@linux.beauty>]

From: Li Chen <chenl311@chinatelecom.cn>

Add a GCC plugin to warn about uninitialized automatic variables with
cleanup attributes. This helps catch this potential interdependency problem
as documented in include/linux/cleanup.h.

The plugin detects uninitialized cleanup variables and warns developers
without blocking builds (warnings are not converted to errors by -Werror).

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 scripts/Makefile.gcc-plugins         |   1 +
 scripts/gcc-plugins/Kconfig          |   6 ++
 scripts/gcc-plugins/cleanup_plugin.c | 106 +++++++++++++++++++++++++++
 3 files changed, 113 insertions(+)
 create mode 100644 scripts/gcc-plugins/cleanup_plugin.c

diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index b0e1423b09c21..b948261c142e6 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
+gcc-plugin-$(CONFIG_GCC_PLUGIN_CLEANUP_ATTRIBUTE_WARN) += cleanup_plugin.so
 gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= latent_entropy_plugin.so
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)		\
 		+= -DLATENT_ENTROPY_PLUGIN
diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
index 6b34ba19358d8..906d50eb5efa6 100644
--- a/scripts/gcc-plugins/Kconfig
+++ b/scripts/gcc-plugins/Kconfig
@@ -36,4 +36,10 @@ config GCC_PLUGIN_LATENT_ENTROPY
 	   * https://grsecurity.net/
 	   * https://pax.grsecurity.net/
 
+config GCC_PLUGIN_CLEANUP_ATTRIBUTE_WARN
+	def_bool y
+	help
+	  Warn when local automatic variables annotated with
+	  __attribute__((cleanup(...))) are declared without an initializer.
+
 endif
diff --git a/scripts/gcc-plugins/cleanup_plugin.c b/scripts/gcc-plugins/cleanup_plugin.c
new file mode 100644
index 0000000000000..d28f8969186de
--- /dev/null
+++ b/scripts/gcc-plugins/cleanup_plugin.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Warn about uninitialized automatic variables that use the
+ * __attribute__((cleanup(...))) attribute.
+ */
+
+#include "gcc-common.h"
+
+__visible int plugin_is_GPL_compatible;
+
+static struct plugin_info cleanup_plugin_info = {
+	.version = PLUGIN_VERSION,
+	.help = "Warn when cleanup attribute variables lack initializers\n",
+};
+
+static bool has_cleanup_attribute(tree var)
+{
+	tree attrs;
+
+	attrs = DECL_ATTRIBUTES(var);
+	if (!attrs)
+		return false;
+
+	return lookup_attribute("cleanup", attrs) != NULL_TREE;
+}
+
+static bool is_candidate_decl(tree var)
+{
+	if (TREE_CODE(var) != VAR_DECL)
+		return false;
+
+	if (DECL_ARTIFICIAL(var))
+		return false;
+
+	if (TREE_STATIC(var) || DECL_EXTERNAL(var))
+		return false;
+
+	if (!has_cleanup_attribute(var))
+		return false;
+
+	return true;
+}
+
+static bool has_declaration_initializer(tree var)
+{
+	if (DECL_INITIAL(var))
+		return true;
+
+#ifdef DECL_INITIALIZED_P
+	if (DECL_INITIALIZED_P(var))
+		return true;
+#endif
+
+	return false;
+}
+
+static void warn_if_uninitialized(tree var)
+{
+	location_t loc;
+	bool saved_warning_as_error;
+
+	if (has_declaration_initializer(var))
+		return;
+
+	loc = DECL_SOURCE_LOCATION(var);
+	if (loc == UNKNOWN_LOCATION)
+		return;
+
+	/* Temporarily disable treating warnings as errors for this specific warning */
+	saved_warning_as_error = global_dc->warning_as_error_requested_p();
+	global_dc->set_warning_as_error_requested(false);
+	warning_at(
+		loc, 0,
+		"%qD declared with cleanup attribute is not initialized at declaration",
+		var);
+	/* Restore the original setting */
+	global_dc->set_warning_as_error_requested(saved_warning_as_error);
+}
+
+static void cleanup_finish_decl(void *gcc_data, void *user_data)
+{
+	tree var = (tree)gcc_data;
+
+	(void)user_data;
+
+	if (!is_candidate_decl(var))
+		return;
+
+	warn_if_uninitialized(var);
+}
+
+__visible int plugin_init(struct plugin_name_args *plugin_info,
+			  struct plugin_gcc_version *version)
+{
+	if (!plugin_default_version_check(version, &gcc_version)) {
+		error(G_("incompatible gcc/plugin versions"));
+		return 1;
+	}
+
+	register_callback(plugin_info->base_name, PLUGIN_INFO, NULL,
+			  &cleanup_plugin_info);
+	register_callback(plugin_info->base_name, PLUGIN_FINISH_DECL,
+			  cleanup_finish_decl, NULL);
+
+	return 0;
+}
-- 
2.51.0