diff --git a/lib/test_printf.c b/lib/test_printf.c
new file mode 100644
index 0000000..c5a666a
--- /dev/null
+++ b/lib/test_printf.c
@@ -0,0 +1,362 @@
+/*
+ * Test cases for printf facility.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include <linux/socket.h>
+#include <linux/in.h>
+
+#define BUF_SIZE 256
+#define FILL_CHAR '$'
+
+#define PTR1 ((void*)0x01234567)
+#define PTR2 ((void*)(long)(int)0xfedcba98)
+
+#if BITS_PER_LONG == 64
+#define PTR1_ZEROES "000000000"
+#define PTR1_SPACES "         "
+#define PTR1_STR "1234567"
+#define PTR2_STR "fffffffffedcba98"
+#define PTR_WIDTH 16
+#else
+#define PTR1_ZEROES "0"
+#define PTR1_SPACES " "
+#define PTR1_STR "1234567"
+#define PTR2_STR "fedcba98"
+#define PTR_WIDTH 8
+#endif
+#define PTR_WIDTH_STR stringify(PTR_WIDTH)
+
+static unsigned total_tests __initdata;
+static unsigned failed_tests __initdata;
+static char *test_buffer __initdata;
+
+static int __printf(4, 0) __init
+do_test(int bufsize, const char *expect, int elen,
+	const char *fmt, va_list ap)
+{
+	va_list aq;
+	int ret, written;
+
+	total_tests++;
+
+	memset(test_buffer, FILL_CHAR, BUF_SIZE);
+	va_copy(aq, ap);
+	ret = vsnprintf(test_buffer, bufsize, fmt, aq);
+	va_end(aq);
+
+	if (ret != elen) {
+		pr_warn("vsnprintf(buf, %d, \"%s\", ...) returned %d, expected %d\n",
+			bufsize, fmt, ret, elen);
+		return 1;
+	}
+
+	if (!bufsize) {
+		if (memchr_inv(test_buffer, FILL_CHAR, BUF_SIZE)) {
+			pr_warn("vsnprintf(buf, 0, \"%s\", ...) wrote to buffer\n",
+				fmt);
+			return 1;
+		}
+		return 0;
+	}
+
+	written = min(bufsize-1, elen);
+	if (test_buffer[written]) {
+		pr_warn("vsnprintf(buf, %d, \"%s\", ...) did not nul-terminate buffer\n",
+			bufsize, fmt);
+		return 1;
+	}
+
+	if (memcmp(test_buffer, expect, written)) {
+		pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote '%s', expected '%.*s'\n",
+			bufsize, fmt, test_buffer, written, expect);
+		return 1;
+	}
+	return 0;
+}
+
+static void __printf(3, 4) __init
+__test(const char *expect, int elen, const char *fmt, ...)
+{
+	va_list ap;
+	int rand;
+	char *p;
+
+	BUG_ON(elen >= BUF_SIZE);
+
+	va_start(ap, fmt);
+
+	/*
+	 * Every fmt+args is subjected to four tests: Three where we
+	 * tell vsnprintf varying buffer sizes (plenty, not quite
+	 * enough and 0), and then we also test that kvasprintf would
+	 * be able to print it as expected.
+	 */
+	failed_tests += do_test(BUF_SIZE, expect, elen, fmt, ap);
+	rand = 1 + prandom_u32_max(elen+1);
+	/* Since elen < BUF_SIZE, we have 1 <= rand <= BUF_SIZE. */
+	failed_tests += do_test(rand, expect, elen, fmt, ap);
+	failed_tests += do_test(0, expect, elen, fmt, ap);
+
+	p = kvasprintf(GFP_KERNEL, fmt, ap);
+	if (p) {
+		if (memcmp(p, expect, elen+1)) {
+			pr_warn("kvasprintf(..., \"%s\", ...) returned '%s', expected '%s'\n",
+				fmt, p, expect);
+			failed_tests++;
+		}
+		kfree(p);
+	}
+	va_end(ap);
+}
+
+#define test(expect, fmt, ...)					\
+	__test(expect, strlen(expect), fmt, ##__VA_ARGS__)
+
+static void __init
+test_basic(void)
+{
+	/* Work around annoying "warning: zero-length gnu_printf format string". */
+	char nul = '\0';
+
+	test("", &nul);
+	test("100%", "100%%");
+	test("xxx%yyy", "xxx%cyyy", '%');
+	__test("xxx\0yyy", 7, "xxx%cyyy", '\0');
+}
+
+static void __init
+test_number(void)
+{
+	test("0x1234abcd  ", "%#-12x", 0x1234abcd);
+	test("  0x1234abcd", "%#12x", 0x1234abcd);
+	test("0|001| 12|+123| 1234|-123|-1234", "%d|%03d|%3d|%+d|% d|%+d|% d", 0, 1, 12, 123, 1234, -123, -1234);
+}
+
+static void __init
+test_string(void)
+{
+	test("", "%s%.0s", "", "123");
+	test("ABCD|abc|123", "%s|%.3s|%.*s", "ABCD", "abcdef", 3, "123456");
+	test("1  |  2|3  |  4|5  ", "%-3s|%3s|%-*s|%*s|%*s", "1", "2", 3, "3", 3, "4", -3, "5");
+	/*
+	 * POSIX and C99 say that a missing precision should be
+	 * treated as a precision of 0. However, the kernel's printf
+	 * implementation treats this case as if the . wasn't
+	 * present. Let's add a test case documenting the current
+	 * behaviour; should anyone ever feel the need to follow the
+	 * standards more closely, this can be revisited.
+	 */
+	test("a||", "%.s|%.0s|%.*s", "a", "b", 0, "c");
+	test("a  |   |   ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");
+}
+
+static void __init
+plain(void)
+{
+	test(PTR1_ZEROES PTR1_STR " " PTR2_STR, "%p %p", PTR1, PTR2);
+	/*
+	 * The field width is overloaded for some %p extensions to
+	 * pass another piece of information. For plain pointers, the
+	 * behaviour is slightly odd: One cannot pass either the 0
+	 * flag nor a precision to %p without gcc complaining, and if
+	 * one explicitly gives a field width, the number is no longer
+	 * zero-padded.
+	 */
+	test("|" PTR1_STR PTR1_SPACES "  |  " PTR1_SPACES PTR1_STR "|",
+	     "|%-*p|%*p|", PTR_WIDTH+2, PTR1, PTR_WIDTH+2, PTR1);
+	test("|" PTR2_STR "  |  " PTR2_STR "|",
+	     "|%-*p|%*p|", PTR_WIDTH+2, PTR2, PTR_WIDTH+2, PTR2);
+
+	/*
+	 * Unrecognized %p extensions are treated as plain %p, but the
+	 * alphanumeric suffix is ignored (that is, does not occur in
+	 * the output.)
+	 */
+	test("|"PTR1_ZEROES PTR1_STR"|", "|%p0y|", PTR1);
+	test("|"PTR2_STR"|", "|%p0y|", PTR2);
+}
+
+static void __init
+symbol_ptr(void)
+{
+}
+
+static void __init
+kernel_ptr(void)
+{
+}
+
+static void __init
+struct_resource(void)
+{
+}
+
+static void __init
+addr(void)
+{
+}
+
+static void __init
+escaped_str(void)
+{
+}
+
+static void __init
+hex_string(void)
+{
+	const char buf[3] = {0xc0, 0xff, 0xee};
+
+	test("c0 ff ee|c0:ff:ee|c0-ff-ee|c0ffee",
+	     "%3ph|%3phC|%3phD|%3phN", buf, buf, buf, buf);
+	test("c0 ff ee|c0:ff:ee|c0-ff-ee|c0ffee",
+	     "%*ph|%*phC|%*phD|%*phN", 3, buf, 3, buf, 3, buf, 3, buf);
+}
+
+static void __init
+mac(void)
+{
+	const u8 addr[6] = {0x2d, 0x48, 0xd6, 0xfc, 0x7a, 0x05};
+
+	test("2d:48:d6:fc:7a:05", "%pM", addr);
+	test("05:7a:fc:d6:48:2d", "%pMR", addr);
+	test("2d-48-d6-fc-7a-05", "%pMF", addr);
+	test("2d48d6fc7a05", "%pm", addr);
+	test("057afcd6482d", "%pmR", addr);
+}
+
+static void __init
+ip4(void)
+{
+	struct sockaddr_in sa;
+
+	sa.sin_family = AF_INET;
+	sa.sin_port = cpu_to_be16(12345);
+	sa.sin_addr.s_addr = cpu_to_be32(0x7f000001);
+
+	test("127.000.000.001|127.0.0.1", "%pi4|%pI4", &sa.sin_addr, &sa.sin_addr);
+	test("127.000.000.001|127.0.0.1", "%piS|%pIS", &sa, &sa);
+	sa.sin_addr.s_addr = cpu_to_be32(0x01020304);
+	test("001.002.003.004:12345|1.2.3.4:12345", "%piSp|%pISp", &sa, &sa);
+}
+
+static void __init
+ip6(void)
+{
+}
+
+static void __init
+ip(void)
+{
+	ip4();
+	ip6();
+}
+
+static void __init
+uuid(void)
+{
+	const char uuid[16] = {0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7,
+			       0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf};
+
+	test("00010203-0405-0607-0809-0a0b0c0d0e0f", "%pUb", uuid);
+	test("00010203-0405-0607-0809-0A0B0C0D0E0F", "%pUB", uuid);
+	test("03020100-0504-0706-0809-0a0b0c0d0e0f", "%pUl", uuid);
+	test("03020100-0504-0706-0809-0A0B0C0D0E0F", "%pUL", uuid);
+}
+
+static void __init
+dentry(void)
+{
+}
+
+static void __init
+struct_va_format(void)
+{
+}
+
+static void __init
+struct_clk(void)
+{
+}
+
+static void __init
+bitmap(void)
+{
+	DECLARE_BITMAP(bits, 20);
+	const int primes[] = {2,3,5,7,11,13,17,19};
+	int i;
+
+	bitmap_zero(bits, 20);
+	test("00000|00000", "%20pb|%*pb", bits, 20, bits);
+	test("|", "%20pbl|%*pbl", bits, 20, bits);
+
+	for (i = 0; i < ARRAY_SIZE(primes); ++i)
+		set_bit(primes[i], bits);
+	test("a28ac|a28ac", "%20pb|%*pb", bits, 20, bits);
+	test("2-3,5,7,11,13,17,19|2-3,5,7,11,13,17,19", "%20pbl|%*pbl", bits, 20, bits);
+
+	bitmap_fill(bits, 20);
+	test("fffff|fffff", "%20pb|%*pb", bits, 20, bits);
+	test("0-19|0-19", "%20pbl|%*pbl", bits, 20, bits);
+}
+
+static void __init
+netdev_features(void)
+{
+}
+
+static void __init
+test_pointer(void)
+{
+	plain();
+	symbol_ptr();
+	kernel_ptr();
+	struct_resource();
+	addr();
+	escaped_str();
+	hex_string();
+	mac();
+	ip();
+	uuid();
+	dentry();
+	struct_va_format();
+	struct_clk();
+	bitmap();
+	netdev_features();
+}
+
+static int __init
+test_printf_init(void)
+{
+	test_buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
+	if (!test_buffer)
+		return -ENOMEM;
+
+	test_basic();
+	test_number();
+	test_string();
+	test_pointer();
+
+	kfree(test_buffer);
+
+	if (failed_tests == 0)
+		pr_info("all %u tests passed\n", total_tests);
+	else
+		pr_warn("failed %u out of %u tests\n", failed_tests, total_tests);
+
+	return failed_tests ? -EINVAL : 0;
+}
+
+module_init(test_printf_init);
+
+MODULE_AUTHOR("Rasmus Villemoes <linux@rasmusvillemoes.dk>");
+MODULE_LICENSE("GPL");