diff --git a/lib/test_stackinit.c b/lib/test_stackinit.c
new file mode 100644
index 0000000..2d7d257
--- /dev/null
+++ b/lib/test_stackinit.c
@@ -0,0 +1,387 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for compiler-based stack variable zeroing via future
+ * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+/* Exfiltration buffer. */
+#define MAX_VAR_SIZE	128
+static u8 check_buf[MAX_VAR_SIZE];
+
+/* Character array to trigger stack protector in all functions. */
+#define VAR_BUFFER	 32
+
+/* Volatile mask to convince compiler to copy memory with 0xff. */
+static volatile u8 forced_mask = 0xff;
+
+/* Location and size tracking to validate fill and test are colocated. */
+static void *fill_start, *target_start;
+static size_t fill_size, target_size;
+
+static bool range_contains(char *haystack_start, size_t haystack_size,
+			   char *needle_start, size_t needle_size)
+{
+	if (needle_start >= haystack_start &&
+	    needle_start + needle_size <= haystack_start + haystack_size)
+		return true;
+	return false;
+}
+
+#define DO_NOTHING_TYPE_SCALAR(var_type)	var_type
+#define DO_NOTHING_TYPE_STRING(var_type)	void
+#define DO_NOTHING_TYPE_STRUCT(var_type)	void
+
+#define DO_NOTHING_RETURN_SCALAR(ptr)		*(ptr)
+#define DO_NOTHING_RETURN_STRING(ptr)		/**/
+#define DO_NOTHING_RETURN_STRUCT(ptr)		/**/
+
+#define DO_NOTHING_CALL_SCALAR(var, name)			\
+		(var) = do_nothing_ ## name(&(var))
+#define DO_NOTHING_CALL_STRING(var, name)			\
+		do_nothing_ ## name(var)
+#define DO_NOTHING_CALL_STRUCT(var, name)			\
+		do_nothing_ ## name(&(var))
+
+#define FETCH_ARG_SCALAR(var)		&var
+#define FETCH_ARG_STRING(var)		var
+#define FETCH_ARG_STRUCT(var)		&var
+
+#define FILL_SIZE_STRING		16
+
+#define INIT_CLONE_SCALAR		/**/
+#define INIT_CLONE_STRING		[FILL_SIZE_STRING]
+#define INIT_CLONE_STRUCT		/**/
+
+#define INIT_SCALAR_none		/**/
+#define INIT_SCALAR_zero		= 0
+
+#define INIT_STRING_none		[FILL_SIZE_STRING] /**/
+#define INIT_STRING_zero		[FILL_SIZE_STRING] = { }
+
+#define INIT_STRUCT_none		/**/
+#define INIT_STRUCT_zero		= { }
+#define INIT_STRUCT_static_partial	= { .two = 0, }
+#define INIT_STRUCT_static_all		= { .one = arg->one,		\
+					    .two = arg->two,		\
+					    .three = arg->three,	\
+					    .four = arg->four,		\
+					}
+#define INIT_STRUCT_dynamic_partial	= { .two = arg->two, }
+#define INIT_STRUCT_dynamic_all		= { .one = arg->one,		\
+					    .two = arg->two,		\
+					    .three = arg->three,	\
+					    .four = arg->four,		\
+					}
+#define INIT_STRUCT_runtime_partial	;				\
+					var.two = 0
+#define INIT_STRUCT_runtime_all		;				\
+					var.one = 0;			\
+					var.two = 0;			\
+					var.three = 0;			\
+					memset(&var.four, 0,		\
+					       sizeof(var.four))
+
+/*
+ * @name: unique string name for the test
+ * @var_type: type to be tested for zeroing initialization
+ * @which: is this a SCALAR, STRING, or STRUCT type?
+ * @init_level: what kind of initialization is performed
+ */
+#define DEFINE_TEST_DRIVER(name, var_type, which)		\
+/* Returns 0 on success, 1 on failure. */			\
+static noinline __init int test_ ## name (void)			\
+{								\
+	var_type zero INIT_CLONE_ ## which;			\
+	int ignored;						\
+	u8 sum = 0, i;						\
+								\
+	/* Notice when a new test is larger than expected. */	\
+	BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE);		\
+								\
+	/* Fill clone type with zero for per-field init. */	\
+	memset(&zero, 0x00, sizeof(zero));			\
+	/* Clear entire check buffer for 0xFF overlap test. */	\
+	memset(check_buf, 0x00, sizeof(check_buf));		\
+	/* Fill stack with 0xFF. */				\
+	ignored = leaf_ ##name((unsigned long)&ignored, 1,	\
+				FETCH_ARG_ ## which(zero));	\
+	/* Verify all bytes overwritten with 0xFF. */		\
+	for (sum = 0, i = 0; i < target_size; i++)		\
+		sum += (check_buf[i] != 0xFF);			\
+	if (sum) {						\
+		pr_err(#name ": leaf fill was not 0xFF!?\n");	\
+		return 1;					\
+	}							\
+	/* Clear entire check buffer for later bit tests. */	\
+	memset(check_buf, 0x00, sizeof(check_buf));		\
+	/* Extract stack-defined variable contents. */		\
+	ignored = leaf_ ##name((unsigned long)&ignored, 0,	\
+				FETCH_ARG_ ## which(zero));	\
+								\
+	/* Validate that compiler lined up fill and target. */	\
+	if (!range_contains(fill_start, fill_size,		\
+			    target_start, target_size)) {	\
+		pr_err(#name ": stack fill missed target!?\n");	\
+		pr_err(#name ": fill %zu wide\n", fill_size);	\
+		pr_err(#name ": target offset by %d\n",	\
+			(int)((ssize_t)(uintptr_t)fill_start -	\
+			(ssize_t)(uintptr_t)target_start));	\
+		return 1;					\
+	}							\
+								\
+	/* Look for any bytes still 0xFF in check region. */	\
+	for (sum = 0, i = 0; i < target_size; i++)		\
+		sum += (check_buf[i] == 0xFF);			\
+								\
+	if (sum == 0)						\
+		pr_info(#name " ok\n");				\
+	else							\
+		pr_warn(#name " FAIL (uninit bytes: %d)\n",	\
+			sum);					\
+								\
+	return (sum != 0);					\
+}
+#define DEFINE_TEST(name, var_type, which, init_level)		\
+/* no-op to force compiler into ignoring "uninitialized" vars */\
+static noinline __init DO_NOTHING_TYPE_ ## which(var_type)	\
+do_nothing_ ## name(var_type *ptr)				\
+{								\
+	/* Will always be true, but compiler doesn't know. */	\
+	if ((unsigned long)ptr > 0x2)				\
+		return DO_NOTHING_RETURN_ ## which(ptr);	\
+	else							\
+		return DO_NOTHING_RETURN_ ## which(ptr + 1);	\
+}								\
+static noinline __init int leaf_ ## name(unsigned long sp,	\
+					 bool fill,		\
+					 var_type *arg)		\
+{								\
+	char buf[VAR_BUFFER];					\
+	var_type var INIT_ ## which ## _ ## init_level;		\
+								\
+	target_start = &var;					\
+	target_size = sizeof(var);				\
+	/*							\
+	 * Keep this buffer around to make sure we've got a	\
+	 * stack frame of SOME kind...				\
+	 */							\
+	memset(buf, (char)(sp & 0xff), sizeof(buf));		\
+	/* Fill variable with 0xFF. */				\
+	if (fill) {						\
+		fill_start = &var;				\
+		fill_size = sizeof(var);			\
+		memset(fill_start,				\
+		       (char)((sp & 0xff) | forced_mask),	\
+		       fill_size);				\
+	}							\
+								\
+	/* Silence "never initialized" warnings. */		\
+	DO_NOTHING_CALL_ ## which(var, name);			\
+								\
+	/* Exfiltrate "var". */					\
+	memcpy(check_buf, target_start, target_size);		\
+								\
+	return (int)buf[0] | (int)buf[sizeof(buf) - 1];		\
+}								\
+DEFINE_TEST_DRIVER(name, var_type, which)
+
+/* Structure with no padding. */
+struct test_packed {
+	unsigned long one;
+	unsigned long two;
+	unsigned long three;
+	unsigned long four;
+};
+
+/* Simple structure with padding likely to be covered by compiler. */
+struct test_small_hole {
+	size_t one;
+	char two;
+	/* 3 byte padding hole here. */
+	int three;
+	unsigned long four;
+};
+
+/* Try to trigger unhandled padding in a structure. */
+struct test_aligned {
+	u32 internal1;
+	u64 internal2;
+} __aligned(64);
+
+struct test_big_hole {
+	u8 one;
+	u8 two;
+	u8 three;
+	/* 61 byte padding hole here. */
+	struct test_aligned four;
+} __aligned(64);
+
+struct test_trailing_hole {
+	char *one;
+	char *two;
+	char *three;
+	char four;
+	/* "sizeof(unsigned long) - 1" byte padding hole here. */
+};
+
+/* Test if STRUCTLEAK is clearing structs with __user fields. */
+struct test_user {
+	u8 one;
+	unsigned long two;
+	char __user *three;
+	unsigned long four;
+};
+
+#define DEFINE_SCALAR_TEST(name, init)				\
+		DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
+
+#define DEFINE_SCALAR_TESTS(init)				\
+		DEFINE_SCALAR_TEST(u8, init);			\
+		DEFINE_SCALAR_TEST(u16, init);			\
+		DEFINE_SCALAR_TEST(u32, init);			\
+		DEFINE_SCALAR_TEST(u64, init);			\
+		DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
+
+#define DEFINE_STRUCT_TEST(name, init)				\
+		DEFINE_TEST(name ## _ ## init,			\
+			    struct test_ ## name, STRUCT, init)
+
+#define DEFINE_STRUCT_TESTS(init)				\
+		DEFINE_STRUCT_TEST(small_hole, init);		\
+		DEFINE_STRUCT_TEST(big_hole, init);		\
+		DEFINE_STRUCT_TEST(trailing_hole, init);	\
+		DEFINE_STRUCT_TEST(packed, init)
+
+/* These should be fully initialized all the time! */
+DEFINE_SCALAR_TESTS(zero);
+DEFINE_STRUCT_TESTS(zero);
+/* Static initialization: padding may be left uninitialized. */
+DEFINE_STRUCT_TESTS(static_partial);
+DEFINE_STRUCT_TESTS(static_all);
+/* Dynamic initialization: padding may be left uninitialized. */
+DEFINE_STRUCT_TESTS(dynamic_partial);
+DEFINE_STRUCT_TESTS(dynamic_all);
+/* Runtime initialization: padding may be left uninitialized. */
+DEFINE_STRUCT_TESTS(runtime_partial);
+DEFINE_STRUCT_TESTS(runtime_all);
+/* No initialization without compiler instrumentation. */
+DEFINE_SCALAR_TESTS(none);
+DEFINE_STRUCT_TESTS(none);
+DEFINE_TEST(user, struct test_user, STRUCT, none);
+
+/*
+ * Check two uses through a variable declaration outside either path,
+ * which was noticed as a special case in porting earlier stack init
+ * compiler logic.
+ */
+static int noinline __leaf_switch_none(int path, bool fill)
+{
+	switch (path) {
+		uint64_t var;
+
+	case 1:
+		target_start = &var;
+		target_size = sizeof(var);
+		if (fill) {
+			fill_start = &var;
+			fill_size = sizeof(var);
+
+			memset(fill_start, forced_mask | 0x55, fill_size);
+		}
+		memcpy(check_buf, target_start, target_size);
+		break;
+	case 2:
+		target_start = &var;
+		target_size = sizeof(var);
+		if (fill) {
+			fill_start = &var;
+			fill_size = sizeof(var);
+
+			memset(fill_start, forced_mask | 0xaa, fill_size);
+		}
+		memcpy(check_buf, target_start, target_size);
+		break;
+	default:
+		var = 5;
+		return var & forced_mask;
+	}
+	return 0;
+}
+
+static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
+					      uint64_t *arg)
+{
+	return __leaf_switch_none(1, fill);
+}
+
+static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
+					      uint64_t *arg)
+{
+	return __leaf_switch_none(2, fill);
+}
+
+DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR);
+DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR);
+
+static int __init test_stackinit_init(void)
+{
+	unsigned int failures = 0;
+
+#define test_scalars(init)	do {				\
+		failures += test_u8_ ## init ();		\
+		failures += test_u16_ ## init ();		\
+		failures += test_u32_ ## init ();		\
+		failures += test_u64_ ## init ();		\
+		failures += test_char_array_ ## init ();	\
+	} while (0)
+
+#define test_structs(init)	do {				\
+		failures += test_small_hole_ ## init ();	\
+		failures += test_big_hole_ ## init ();		\
+		failures += test_trailing_hole_ ## init ();	\
+		failures += test_packed_ ## init ();		\
+	} while (0)
+
+	/* These are explicitly initialized and should always pass. */
+	test_scalars(zero);
+	test_structs(zero);
+	/* Padding here appears to be accidentally always initialized? */
+	test_structs(dynamic_partial);
+	/* Padding initialization depends on compiler behaviors. */
+	test_structs(static_partial);
+	test_structs(static_all);
+	test_structs(dynamic_all);
+	test_structs(runtime_partial);
+	test_structs(runtime_all);
+
+	/* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
+	test_scalars(none);
+	failures += test_switch_1_none();
+	failures += test_switch_2_none();
+
+	/* STRUCTLEAK_BYREF should cover from here down. */
+	test_structs(none);
+
+	/* STRUCTLEAK will only cover this. */
+	failures += test_user();
+
+	if (failures == 0)
+		pr_info("all tests passed!\n");
+	else
+		pr_err("failures: %u\n", failures);
+
+	return failures ? -EINVAL : 0;
+}
+module_init(test_stackinit_init);
+
+static void __exit test_stackinit_exit(void)
+{ }
+module_exit(test_stackinit_exit);
+
+MODULE_LICENSE("GPL");