diff --git a/lib/test_printf.c b/lib/test_printf.c
new file mode 100644
index 0000000..53527ea
--- /dev/null
+++ b/lib/test_printf.c
@@ -0,0 +1,564 @@
+/*
+ * 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/bitmap.h>
+#include <linux/dcache.h>
+#include <linux/socket.h>
+#include <linux/in.h>
+
+#include <linux/gfp.h>
+#include <linux/mm.h>
+
+#define BUF_SIZE 256
+#define PAD_SIZE 16
+#define FILL_CHAR '$'
+
+static unsigned total_tests __initdata;
+static unsigned failed_tests __initdata;
+static char *test_buffer __initdata;
+static char *alloced_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(alloced_buffer, FILL_CHAR, BUF_SIZE + 2*PAD_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 (memchr_inv(alloced_buffer, FILL_CHAR, PAD_SIZE)) {
+		pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote before buffer\n", bufsize, fmt);
+		return 1;
+	}
+
+	if (!bufsize) {
+		if (memchr_inv(test_buffer, FILL_CHAR, BUF_SIZE + PAD_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 (memchr_inv(test_buffer + written + 1, FILL_CHAR, BUF_SIZE + PAD_SIZE - (written + 1))) {
+		pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond the nul-terminator\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;
+
+	if (elen >= BUF_SIZE) {
+		pr_err("error in test suite: expected output length %d too long. Format was '%s'.\n",
+		       elen, fmt);
+		failed_tests++;
+		return;
+	}
+
+	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) {
+		total_tests++;
+		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);
+	test("0|1|1|128|255", "%hhu|%hhu|%hhu|%hhu|%hhu", 0, 1, 257, 128, -1);
+	test("0|1|1|-128|-1", "%hhd|%hhd|%hhd|%hhd|%hhd", 0, 1, 257, 128, -1);
+	test("2015122420151225", "%ho%ho%#ho", 1037, 5282, -11627);
+	/*
+	 * POSIX/C99: »The result of converting zero with an explicit
+	 * precision of zero shall be no characters.« Hence the output
+	 * from the below test should really be "00|0||| ". However,
+	 * the kernel's printf also produces a single 0 in that
+	 * case. This test case simply documents the current
+	 * behaviour.
+	 */
+	test("00|0|0|0|0", "%.2d|%.1d|%.0d|%.*d|%1.0d", 0, 0, 0, 0, 0, 0);
+#ifndef __CHAR_UNSIGNED__
+	{
+		/*
+		 * Passing a 'char' to a %02x specifier doesn't do
+		 * what was presumably the intention when char is
+		 * signed and the value is negative. One must either &
+		 * with 0xff or cast to u8.
+		 */
+		char val = -16;
+		test("0xfffffff0|0xf0|0xf0", "%#02x|%#02x|%#02x", val, val & 0xff, (u8)val);
+	}
+#endif
+}
+
+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");
+	test("1234      ", "%-10.4s", "123456");
+	test("      1234", "%10.4s", "123456");
+	/*
+	 * POSIX and C99 say that a negative precision (which is only
+	 * possible to pass via a * argument) should be treated as if
+	 * the precision wasn't present, and that if the precision is
+	 * omitted (as in %.s), the precision should be taken to be
+	 * 0. However, the kernel's printf behave exactly opposite,
+	 * treating a negative precision as 0 and treating an omitted
+	 * precision specifier as if no precision was given.
+	 *
+	 * These test cases document the current behaviour; should
+	 * anyone ever feel the need to follow the standards more
+	 * closely, this can be revisited.
+	 */
+	test("    ", "%4.*s", -5, "123456");
+	test("123456", "%.s", "123456");
+	test("a||", "%.s|%.0s|%.*s", "a", "b", 0, "c");
+	test("a  |   |   ", "%-3.s|%-3.0s|%-3.*s", "a", "b", 0, "c");
+}
+
+#define PLAIN_BUF_SIZE 64	/* leave some space so we don't oops */
+
+#if BITS_PER_LONG == 64
+
+#define PTR_WIDTH 16
+#define PTR ((void *)0xffff0123456789abUL)
+#define PTR_STR "ffff0123456789ab"
+#define PTR_VAL_NO_CRNG "(____ptrval____)"
+#define ZEROS "00000000"	/* hex 32 zero bits */
+
+static int __init
+plain_format(void)
+{
+	char buf[PLAIN_BUF_SIZE];
+	int nchars;
+
+	nchars = snprintf(buf, PLAIN_BUF_SIZE, "%p", PTR);
+
+	if (nchars != PTR_WIDTH)
+		return -1;
+
+	if (strncmp(buf, PTR_VAL_NO_CRNG, PTR_WIDTH) == 0) {
+		pr_warn("crng possibly not yet initialized. plain 'p' buffer contains \"%s\"",
+			PTR_VAL_NO_CRNG);
+		return 0;
+	}
+
+	if (strncmp(buf, ZEROS, strlen(ZEROS)) != 0)
+		return -1;
+
+	return 0;
+}
+
+#else
+
+#define PTR_WIDTH 8
+#define PTR ((void *)0x456789ab)
+#define PTR_STR "456789ab"
+#define PTR_VAL_NO_CRNG "(ptrval)"
+
+static int __init
+plain_format(void)
+{
+	/* Format is implicitly tested for 32 bit machines by plain_hash() */
+	return 0;
+}
+
+#endif	/* BITS_PER_LONG == 64 */
+
+static int __init
+plain_hash(void)
+{
+	char buf[PLAIN_BUF_SIZE];
+	int nchars;
+
+	nchars = snprintf(buf, PLAIN_BUF_SIZE, "%p", PTR);
+
+	if (nchars != PTR_WIDTH)
+		return -1;
+
+	if (strncmp(buf, PTR_VAL_NO_CRNG, PTR_WIDTH) == 0) {
+		pr_warn("crng possibly not yet initialized. plain 'p' buffer contains \"%s\"",
+			PTR_VAL_NO_CRNG);
+		return 0;
+	}
+
+	if (strncmp(buf, PTR_STR, PTR_WIDTH) == 0)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * We can't use test() to test %p because we don't know what output to expect
+ * after an address is hashed.
+ */
+static void __init
+plain(void)
+{
+	int err;
+
+	err = plain_hash();
+	if (err) {
+		pr_warn("plain 'p' does not appear to be hashed\n");
+		failed_tests++;
+		return;
+	}
+
+	err = plain_format();
+	if (err) {
+		pr_warn("hashing plain 'p' has unexpected format\n");
+		failed_tests++;
+	}
+}
+
+static void __init
+symbol_ptr(void)
+{
+}
+
+static void __init
+kernel_ptr(void)
+{
+	/* We can't test this without access to kptr_restrict. */
+}
+
+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 struct dentry test_dentry[4] __initdata = {
+	{ .d_parent = &test_dentry[0],
+	  .d_name = QSTR_INIT(test_dentry[0].d_iname, 3),
+	  .d_iname = "foo" },
+	{ .d_parent = &test_dentry[0],
+	  .d_name = QSTR_INIT(test_dentry[1].d_iname, 5),
+	  .d_iname = "bravo" },
+	{ .d_parent = &test_dentry[1],
+	  .d_name = QSTR_INIT(test_dentry[2].d_iname, 4),
+	  .d_iname = "alfa" },
+	{ .d_parent = &test_dentry[2],
+	  .d_name = QSTR_INIT(test_dentry[3].d_iname, 5),
+	  .d_iname = "romeo" },
+};
+
+static void __init
+dentry(void)
+{
+	test("foo", "%pd", &test_dentry[0]);
+	test("foo", "%pd2", &test_dentry[0]);
+
+	test("romeo", "%pd", &test_dentry[3]);
+	test("alfa/romeo", "%pd2", &test_dentry[3]);
+	test("bravo/alfa/romeo", "%pd3", &test_dentry[3]);
+	test("/bravo/alfa/romeo", "%pd4", &test_dentry[3]);
+	test("/bravo/alfa", "%pd4", &test_dentry[2]);
+
+	test("bravo/alfa  |bravo/alfa  ", "%-12pd2|%*pd2", &test_dentry[2], -12, &test_dentry[2]);
+	test("  bravo/alfa|  bravo/alfa", "%12pd2|%*pd2", &test_dentry[2], 12, &test_dentry[2]);
+}
+
+static void __init
+struct_va_format(void)
+{
+}
+
+static void __init
+struct_clk(void)
+{
+}
+
+static void __init
+large_bitmap(void)
+{
+	const int nbits = 1 << 16;
+	unsigned long *bits = kcalloc(BITS_TO_LONGS(nbits), sizeof(long), GFP_KERNEL);
+	if (!bits)
+		return;
+
+	bitmap_set(bits, 1, 20);
+	bitmap_set(bits, 60000, 15);
+	test("1-20,60000-60014", "%*pbl", nbits, bits);
+	kfree(bits);
+}
+
+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);
+
+	large_bitmap();
+}
+
+static void __init
+netdev_features(void)
+{
+}
+
+static void __init
+flags(void)
+{
+	unsigned long flags;
+	gfp_t gfp;
+	char *cmp_buffer;
+
+	flags = 0;
+	test("", "%pGp", &flags);
+
+	/* Page flags should filter the zone id */
+	flags = 1UL << NR_PAGEFLAGS;
+	test("", "%pGp", &flags);
+
+	flags |= 1UL << PG_uptodate | 1UL << PG_dirty | 1UL << PG_lru
+		| 1UL << PG_active | 1UL << PG_swapbacked;
+	test("uptodate|dirty|lru|active|swapbacked", "%pGp", &flags);
+
+
+	flags = VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC
+			| VM_DENYWRITE;
+	test("read|exec|mayread|maywrite|mayexec|denywrite", "%pGv", &flags);
+
+	gfp = GFP_TRANSHUGE;
+	test("GFP_TRANSHUGE", "%pGg", &gfp);
+
+	gfp = GFP_ATOMIC|__GFP_DMA;
+	test("GFP_ATOMIC|GFP_DMA", "%pGg", &gfp);
+
+	gfp = __GFP_ATOMIC;
+	test("__GFP_ATOMIC", "%pGg", &gfp);
+
+	cmp_buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
+	if (!cmp_buffer)
+		return;
+
+	/* Any flags not translated by the table should remain numeric */
+	gfp = ~__GFP_BITS_MASK;
+	snprintf(cmp_buffer, BUF_SIZE, "%#lx", (unsigned long) gfp);
+	test(cmp_buffer, "%pGg", &gfp);
+
+	snprintf(cmp_buffer, BUF_SIZE, "__GFP_ATOMIC|%#lx",
+							(unsigned long) gfp);
+	gfp |= __GFP_ATOMIC;
+	test(cmp_buffer, "%pGg", &gfp);
+
+	kfree(cmp_buffer);
+}
+
+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();
+	flags();
+}
+
+static int __init
+test_printf_init(void)
+{
+	alloced_buffer = kmalloc(BUF_SIZE + 2*PAD_SIZE, GFP_KERNEL);
+	if (!alloced_buffer)
+		return -ENOMEM;
+	test_buffer = alloced_buffer + PAD_SIZE;
+
+	test_basic();
+	test_number();
+	test_string();
+	test_pointer();
+
+	kfree(alloced_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");