testing/selftests: Add tests for the is_signed_type() macro

Although not documented, is_signed_type() must support the 'bool' and
pointer types next to scalar and enumeration types. Add a selftest that
verifies that this macro handles all supported types correctly.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Isabella Basso <isabbasso@riseup.net>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sander Vanheule <sander@svanheule.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Isabella Basso <isabbasso@riseup.net>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220826162116.1050972-2-bvanassche@acm.org

lib/Kconfig.debug

@@ -2506,6 +2506,18 @@ config MEMCPY_KUNIT_TEST
 
 	  If unsure, say N.
 
+config IS_SIGNED_TYPE_KUNIT_TEST
+	tristate "Test is_signed_type() macro" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  Builds unit tests for the is_signed_type() macro.
+
+	  For more information on KUnit and unit tests in general please refer
+	  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.
+
 config OVERFLOW_KUNIT_TEST
 	tristate "Test check_*_overflow() functions at runtime" if !KUNIT_ALL_TESTS
 	depends on KUNIT

lib/Makefile

@@ -377,6 +377,7 @@ obj-$(CONFIG_BITS_TEST) += test_bits.o
 obj-$(CONFIG_CMDLINE_KUNIT_TEST) += cmdline_kunit.o
 obj-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o
 obj-$(CONFIG_MEMCPY_KUNIT_TEST) += memcpy_kunit.o
+obj-$(CONFIG_IS_SIGNED_TYPE_KUNIT_TEST) += is_signed_type_kunit.o
 obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
 CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
 obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o

lib/is_signed_type_kunit.c

+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ *	./tools/testing/kunit/kunit.py run is_signed_type [--raw_output]
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/overflow.h>
+
+enum unsigned_enum {
+	constant_a = 3,
+};
+
+enum signed_enum {
+	constant_b = -1,
+	constant_c = 2,
+};
+
+static void is_signed_type_test(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, is_signed_type(bool), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(signed char), true);
+	KUNIT_EXPECT_EQ(test, is_signed_type(unsigned char), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(int), true);
+	KUNIT_EXPECT_EQ(test, is_signed_type(unsigned int), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(long), true);
+	KUNIT_EXPECT_EQ(test, is_signed_type(unsigned long), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(long long), true);
+	KUNIT_EXPECT_EQ(test, is_signed_type(unsigned long long), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(enum unsigned_enum), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(enum signed_enum), true);
+	KUNIT_EXPECT_EQ(test, is_signed_type(void *), false);
+	KUNIT_EXPECT_EQ(test, is_signed_type(const char *), false);
+}
+
+static struct kunit_case is_signed_type_test_cases[] = {
+	KUNIT_CASE(is_signed_type_test),
+	{}
+};
+
+static struct kunit_suite is_signed_type_test_suite = {
+	.name = "is_signed_type",
+	.test_cases = is_signed_type_test_cases,
+};
+
+kunit_test_suite(is_signed_type_test_suite);
+
+MODULE_LICENSE("Dual MIT/GPL");