[PATCH v5 03/36] compiler-context-analysis: Add test stub

[Marco Elver <elver@google.com>]

Add a simple test stub where we will add common supported patterns that
should not generate false positives for each new supported context lock.

Signed-off-by: Marco Elver <elver@google.com>
---
v5:
* Rename "context guard" -> "context lock".

v4:
* Rename capability -> context analysis.
---
 lib/Kconfig.debug           | 14 ++++++++++++++
 lib/Makefile                |  3 +++
 lib/test_context-analysis.c | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 lib/test_context-analysis.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cd557e7653a4..8ca42526ee43 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2835,6 +2835,20 @@ config LINEAR_RANGES_TEST
 
 	  If unsure, say N.
 
+config CONTEXT_ANALYSIS_TEST
+	bool "Compiler context-analysis warnings test"
+	depends on EXPERT
+	help
+	  This builds the test for compiler-based context analysis. The test
+	  does not add executable code to the kernel, but is meant to test that
+	  common patterns supported by the analysis do not result in false
+	  positive warnings.
+
+	  When adding support for new context locks, it is strongly recommended
+	  to add supported patterns to this test.
+
+	  If unsure, say N.
+
 config CMDLINE_KUNIT_TEST
 	tristate "KUnit test for cmdline API" if !KUNIT_ALL_TESTS
 	depends on KUNIT
diff --git a/lib/Makefile b/lib/Makefile
index aaf677cf4527..89defefbf6c0 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -331,4 +331,7 @@ obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 
 obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o
 
+CONTEXT_ANALYSIS_test_context-analysis.o := y
+obj-$(CONFIG_CONTEXT_ANALYSIS_TEST) += test_context-analysis.o
+
 subdir-$(CONFIG_FORTIFY_SOURCE) += test_fortify
diff --git a/lib/test_context-analysis.c b/lib/test_context-analysis.c
new file mode 100644
index 000000000000..68f075dec0e0
--- /dev/null
+++ b/lib/test_context-analysis.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Compile-only tests for common patterns that should not generate false
+ * positive errors when compiled with Clang's context analysis.
+ */
+
+#include <linux/build_bug.h>
+
+/*
+ * Test that helper macros work as expected.
+ */
+static void __used test_common_helpers(void)
+{
+	BUILD_BUG_ON(context_unsafe(3) != 3); /* plain expression */
+	BUILD_BUG_ON(context_unsafe((void)2; 3) != 3); /* does not swallow semi-colon */
+	BUILD_BUG_ON(context_unsafe((void)2, 3) != 3); /* does not swallow commas */
+	context_unsafe(do { } while (0)); /* works with void statements */
+}
-- 
2.52.0.322.g1dd061c0dc-goog