[PATCH RFC 04/24] compiler-capability-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 positive of each new supported capability.

Signed-off-by: Marco Elver <elver@google.com>
---
 lib/Kconfig.debug              | 14 ++++++++++++++
 lib/Makefile                   |  3 +++
 lib/test_capability-analysis.c | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 lib/test_capability-analysis.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 801ad28fe6d7..b76fa3dc59ec 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2764,6 +2764,20 @@ config LINEAR_RANGES_TEST
 
 	  If unsure, say N.
 
+config CAPABILITY_ANALYSIS_TEST
+	bool "Compiler capability-analysis warnings test"
+	depends on EXPERT
+	help
+	  This builds the test for compiler-based capability 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 capabilities, 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 d5cfc7afbbb8..1dbb59175eb0 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -394,6 +394,9 @@ obj-$(CONFIG_CRC_KUNIT_TEST) += crc_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o
 obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o
 
+CAPABILITY_ANALYSIS_test_capability-analysis.o := y
+obj-$(CONFIG_CAPABILITY_ANALYSIS_TEST) += test_capability-analysis.o
+
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 
 obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
new file mode 100644
index 000000000000..a0adacce30ff
--- /dev/null
+++ b/lib/test_capability-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 capability analysis.
+ */
+
+#include <linux/build_bug.h>
+
+/*
+ * Test that helper macros work as expected.
+ */
+static void __used test_common_helpers(void)
+{
+	BUILD_BUG_ON(capability_unsafe(3) != 3); /* plain expression */
+	BUILD_BUG_ON(capability_unsafe((void)2; 3;) != 3); /* does not swallow semi-colon */
+	BUILD_BUG_ON(capability_unsafe((void)2, 3) != 3); /* does not swallow commas */
+	capability_unsafe(do { } while (0)); /* works with void statements */
+}
-- 
2.48.1.502.g6dc24dfdaf-goog