[v2] Kunit to check the longest symbol length

diff --git a/arch/x86/tools/insn_decoder_test.c b/arch/x86/tools/insn_decoder_test.c
index 472540aeabc2..6c2986d2ad11 100644
--- a/arch/x86/tools/insn_decoder_test.c
+++ b/arch/x86/tools/insn_decoder_test.c
@@ -10,6 +10,7 @@ 
 #include <assert.h>
 #include <unistd.h>
 #include <stdarg.h>
+#include <linux/kallsyms.h>
 
 #define unlikely(cond) (cond)
 
@@ -106,7 +107,7 @@  static void parse_args(int argc, char **argv)
 	}
 }
 
-#define BUFSIZE 256
+#define BUFSIZE (256 + KSYM_NAME_LEN)
 
 int main(int argc, char **argv)
 {
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cc7d53d9dc01..a531abece0a7 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2769,6 +2769,15 @@  config FORTIFY_KUNIT_TEST
 	  by the str*() and mem*() family of functions. For testing runtime
 	  traps of FORTIFY_SOURCE, see LKDTM's "FORTIFY_*" tests.
 
+config LONGEST_SYM_KUNIT_TEST
+	tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS
+	depends on KUNIT && KPROBES
+	default KUNIT_ALL_TESTS
+	help
+	  Tests the longest symbol possible
+
+	  If unsure, say N.
+
 config HW_BREAKPOINT_KUNIT_TEST
 	bool "Test hw_breakpoint constraints accounting" if !KUNIT_ALL_TESTS
 	depends on HAVE_HW_BREAKPOINT
diff --git a/lib/Makefile b/lib/Makefile
index 6b09731d8e61..f72003d5869b 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -406,6 +406,8 @@  obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
 obj-$(CONFIG_STRCAT_KUNIT_TEST) += strcat_kunit.o
 obj-$(CONFIG_STRSCPY_KUNIT_TEST) += strscpy_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o
+obj-$(CONFIG_LONGEST_SYM_KUNIT_TEST) += longest_symbol_kunit.o
+CFLAGS_longest_symbol_kunit.o += $(call cc-disable-warning, missing-prototypes)
 
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 
diff --git a/lib/longest_symbol_kunit.c b/lib/longest_symbol_kunit.c
new file mode 100644
index 000000000000..998563018f7a
--- /dev/null
+++ b/lib/longest_symbol_kunit.c
@@ -0,0 +1,122 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test the longest symbol length. Execute with:
+ *  ./tools/testing/kunit/kunit.py run longest-symbol
+ *  --arch=x86_64 --kconfig_add CONFIG_KPROBES=y --kconfig_add CONFIG_MODULES=y
+ *  --kconfig_add CONFIG_RETPOLINE=n
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/stringify.h>
+#include <linux/kprobes.h>
+#include <linux/kallsyms.h>
+
+#define DI(name) s##name##name
+#define DDI(name) DI(n##name##name)
+#define DDDI(name) DDI(n##name##name)
+#define DDDDI(name) DDDI(n##name##name)
+#define DDDDDI(name) DDDDI(n##name##name)
+
+#define PLUS1(name) __PASTE(name, e)
+
+/*Generate a symbol whose name length is 511 */
+#define LONGEST_SYM_NAME  DDDDDI(g1h2i3j4k5l6m7n)
+
+/*Generate a symbol whose name length is 512 */
+#define LONGEST_SYM_NAME_PLUS1 PLUS1(LONGEST_SYM_NAME)
+
+#define RETURN_LONGEST_SYM 0xAAAAA
+#define RETURN_LONGEST_SYM_PLUS1 0x55555
+
+noinline int LONGEST_SYM_NAME(void);
+noinline int LONGEST_SYM_NAME(void)
+{
+	return RETURN_LONGEST_SYM;
+}
+
+noinline int LONGEST_SYM_NAME_PLUS1(void);
+noinline int LONGEST_SYM_NAME_PLUS1(void)
+{
+	return RETURN_LONGEST_SYM_PLUS1;
+}
+
+_Static_assert(sizeof(__stringify(LONGEST_SYM_NAME)) == KSYM_NAME_LEN,
+"Incorrect symbol length found. Expected KSYM_NAME_LEN: "
+__stringify(KSYM_NAME) ", but found: "
+__stringify(sizeof(LONGEST_SYM_NAME)));
+
+static void test_longest_symbol(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM, LONGEST_SYM_NAME());
+};
+
+static void test_longest_symbol_kallsyms(struct kunit *test)
+{
+	unsigned long (*kallsyms_lookup_name)(const char *name);
+	static int (*longest_sym)(void);
+
+	struct kprobe kp = {
+		.symbol_name = "kallsyms_lookup_name",
+	};
+
+	if (register_kprobe(&kp) < 0) {
+		pr_info("%s: kprobe not registered\n", __func__);
+		KUNIT_FAIL(test, "test_longest_symbol kallsysms: kprobe not registered\n");
+		return;
+	}
+
+	kunit_warn(test, "test_longest_symbol kallsyms: kprobe registered\n");
+	kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
+	unregister_kprobe(&kp);
+
+	longest_sym =
+	    (void *) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME));
+	KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM, longest_sym());
+};
+
+static void test_longest_symbol_plus1(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM_PLUS1, LONGEST_SYM_NAME_PLUS1());
+};
+
+static void test_longest_symbol_plus1_kallsyms(struct kunit *test)
+{
+	unsigned long (*kallsyms_lookup_name)(const char *name);
+	static int (*longest_sym_plus1)(void);
+
+	struct kprobe kp = {
+		.symbol_name = "kallsyms_lookup_name",
+	};
+
+	if (register_kprobe(&kp) < 0) {
+		pr_info("%s: kprobe not registered\n", __func__);
+		KUNIT_FAIL(test, "test_longest_symbol kallsysms: kprobe not registered\n");
+		return;
+	}
+
+	kunit_warn(test, "test_longest_symbol_plus1 kallsyms: kprobe registered\n");
+	kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
+	unregister_kprobe(&kp);
+
+	longest_sym_plus1 =
+	    (void *) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME_PLUS1));
+	KUNIT_EXPECT_NULL(test, longest_sym_plus1);
+};
+
+static struct kunit_case longest_symbol_test_cases[] = {
+	KUNIT_CASE(test_longest_symbol),
+	KUNIT_CASE(test_longest_symbol_kallsyms),
+	KUNIT_CASE(test_longest_symbol_plus1),
+	KUNIT_CASE(test_longest_symbol_plus1_kallsyms),
+	{}
+};
+
+static struct kunit_suite longest_symbol_test_suite = {
+	.name = "longest-symbol",
+	.test_cases = longest_symbol_test_cases,
+};
+kunit_test_suite(longest_symbol_test_suite);
+
+MODULE_LICENSE("GPL");