<linux/hash.h>: Add support for architecture-specific functions

This is just the infrastructure; there are no users yet.

This is modelled on CONFIG_ARCH_RANDOM; a CONFIG_ symbol declares
the existence of <asm/hash.h>.

That file may define its own versions of various functions, and define
HAVE_* symbols (no CONFIG_ prefix!) to suppress the generic ones.

Included is a self-test (in lib/test_hash.c) that verifies the basics.
It is NOT in general required that the arch-specific functions compute
the same thing as the generic, but if a HAVE_* symbol is defined with
the value 1, then equality is tested.

Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Cc: Philippe De Muyter <phdm@macq.eu>
Cc: linux-m68k@lists.linux-m68k.org
Cc: Alistair Francis <alistai@xilinx.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: uclinux-h8-devel@lists.sourceforge.jp

3 files changed, 262 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1e9a607534ca..18ec69ba8eb6 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1815,6 +1815,17 @@ config TEST_RHASHTABLE
 
           If unsure, say N.
 
+config TEST_HASH
+        tristate "Perform selftest on hash functions"
+        default n
+        help
+          Enable this option to test the kernel's integer (<linux/hash,h>)
+          and string (<linux/stringhash.h>) hash functions on boot
+          (or module load).
+
+          This is intended to help people writing architecture-specific
+          optimized versions.  If unsure, say N.
+
 endmenu # runtime tests
 
 config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index 7bd6fd436c97..f80b1a1b3afd 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -48,6 +48,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
 obj-y += kstrtox.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
 obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
+obj-$(CONFIG_TEST_HASH) += test_hash.o
 obj-$(CONFIG_TEST_KASAN) += test_kasan.o
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_LKM) += test_module.o
diff --git a/lib/test_hash.c b/lib/test_hash.c
new file mode 100644
index 000000000000..c9549c8b4909
--- /dev/null
+++ b/lib/test_hash.c
@@ -0,0 +1,250 @@
+/*
+ * Test cases for <linux/hash.h> and <linux/stringhash.h>
+ * This just verifies that various ways of computing a hash
+ * produce the same thing and, for cases where a k-bit hash
+ * value is requested, is of the requested size.
+ *
+ * We fill a buffer with a 255-byte null-terminated string,
+ * and use both full_name_hash() and hashlen_string() to hash the
+ * substrings from i to j, where 0 <= i < j < 256.
+ *
+ * The returned values are used to check that __hash_32() and
+ * __hash_32_generic() compute the same thing.  Likewise hash_32()
+ * and hash_64().
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt "\n"
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/hash.h>
+#include <linux/stringhash.h>
+#include <linux/printk.h>
+
+/* 32-bit XORSHIFT generator.  Seed must not be zero. */
+static u32 __init __attribute_const__
+xorshift(u32 seed)
+{
+        seed ^= seed << 13;
+        seed ^= seed >> 17;
+        seed ^= seed << 5;
+        return seed;
+}
+
+/* Given a non-zero x, returns a non-zero byte. */
+static u8 __init __attribute_const__
+mod255(u32 x)
+{
+        x = (x & 0xffff) + (x >> 16);   /* 1 <= x <= 0x1fffe */
+        x = (x & 0xff) + (x >> 8);      /* 1 <= x <= 0x2fd */
+        x = (x & 0xff) + (x >> 8);      /* 1 <= x <= 0x100 */
+        x = (x & 0xff) + (x >> 8);      /* 1 <= x <= 0xff */
+        return x;
+}
+
+/* Fill the buffer with non-zero bytes. */
+static void __init
+fill_buf(char *buf, size_t len, u32 seed)
+{
+        size_t i;
+
+        for (i = 0; i < len; i++) {
+                seed = xorshift(seed);
+                buf[i] = mod255(seed);
+        }
+}
+
+/*
+ * Test the various integer hash functions.  h64 (or its low-order bits)
+ * is the integer to hash.  hash_or accumulates the OR of the hash values,
+ * which are later checked to see that they cover all the requested bits.
+ *
+ * Because these functions (as opposed to the string hashes) are all
+ * inline, the code being tested is actually in the module, and you can
+ * recompile and re-test the module without rebooting.
+ */
+static bool __init
+test_int_hash(unsigned long long h64, u32 hash_or[2][33])
+{
+        int k;
+        u32 h0 = (u32)h64, h1, h2;
+
+        /* Test __hash32 */
+        hash_or[0][0] |= h1 = __hash_32(h0);
+#ifdef HAVE_ARCH__HASH_32
+        hash_or[1][0] |= h2 = __hash_32_generic(h0);
+#if HAVE_ARCH__HASH_32 == 1
+        if (h1 != h2) {
+                pr_err("__hash_32(%#x) = %#x != __hash_32_generic() = %#x",
+                        h0, h1, h2);
+                return false;
+        }
+#endif
+#endif
+
+        /* Test k = 1..32 bits */
+        for (k = 1; k <= 32; k++) {
+                u32 const m = ((u32)2 << (k-1)) - 1;    /* Low k bits set */
+
+                /* Test hash_32 */
+                hash_or[0][k] |= h1 = hash_32(h0, k);
+                if (h1 > m) {
+                        pr_err("hash_32(%#x, %d) = %#x > %#x", h0, k, h1, m);
+                        return false;
+                }
+#ifdef HAVE_ARCH_HASH_32
+                h2 = hash_32_generic(h0, k);
+#if HAVE_ARCH_HASH_32 == 1
+                if (h1 != h2) {
+                        pr_err("hash_32(%#x, %d) = %#x != hash_32_generic() "
+                                " = %#x", h0, k, h1, h2);
+                        return false;
+                }
+#else
+                if (h2 > m) {
+                        pr_err("hash_32_generic(%#x, %d) = %#x > %#x",
+                                h0, k, h1, m);
+                        return false;
+                }
+#endif
+#endif
+                /* Test hash_64 */
+                hash_or[1][k] |= h1 = hash_64(h64, k);
+                if (h1 > m) {
+                        pr_err("hash_64(%#llx, %d) = %#x > %#x", h64, k, h1, m);
+                        return false;
+                }
+#ifdef HAVE_ARCH_HASH_64
+                h2 = hash_64_generic(h64, k);
+#if HAVE_ARCH_HASH_64 == 1
+                if (h1 != h2) {
+                        pr_err("hash_64(%#llx, %d) = %#x != hash_64_generic() "
+                                "= %#x", h64, k, h1, h2);
+                        return false;
+                }
+#else
+                if (h2 > m) {
+                        pr_err("hash_64_generic(%#llx, %d) = %#x > %#x",
+                                h64, k, h1, m);
+                        return false;
+                }
+#endif
+#endif
+        }
+
+        (void)h2;       /* Suppress unused variable warning */
+        return true;
+}
+
+#define SIZE 256        /* Run time is cubic in SIZE */
+
+static int __init
+test_hash_init(void)
+{
+        char buf[SIZE+1];
+        u32 string_or = 0, hash_or[2][33] = { 0 };
+        unsigned tests = 0;
+        unsigned long long h64 = 0;
+        int i, j;
+
+        fill_buf(buf, SIZE, 1);
+
+        /* Test every possible non-empty substring in the buffer. */
+        for (j = SIZE; j > 0; --j) {
+                buf[j] = '\0';
+
+                for (i = 0; i <= j; i++) {
+                        u64 hashlen = hashlen_string(buf+i);
+                        u32 h0 = full_name_hash(buf+i, j-i);
+
+                        /* Check that hashlen_string gets the length right */
+                        if (hashlen_len(hashlen) != j-i) {
+                                pr_err("hashlen_string(%d..%d) returned length"
+                                        " %u, expected %d",
+                                        i, j, hashlen_len(hashlen), j-i);
+                                return -EINVAL;
+                        }
+                        /* Check that the hashes match */
+                        if (hashlen_hash(hashlen) != h0) {
+                                pr_err("hashlen_string(%d..%d) = %08x != "
+                                        "full_name_hash() = %08x",
+                                        i, j, hashlen_hash(hashlen), h0);
+                                return -EINVAL;
+                        }
+
+                        string_or |= h0;
+                        h64 = h64 << 32 | h0;   /* For use with hash_64 */
+                        if (!test_int_hash(h64, hash_or))
+                                return -EINVAL;
+                        tests++;
+                } /* i */
+        } /* j */
+
+        /* The OR of all the hash values should cover all the bits */
+        if (~string_or) {
+                pr_err("OR of all string hash results = %#x != %#x",
+                        string_or, -1u);
+                return -EINVAL;
+        }
+        if (~hash_or[0][0]) {
+                pr_err("OR of all __hash_32 results = %#x != %#x",
+                        hash_or[0][0], -1u);
+                return -EINVAL;
+        }
+#ifdef HAVE_ARCH__HASH_32
+#if HAVE_ARCH__HASH_32 != 1     /* Test is pointless if results match */
+        if (~hash_or[1][0]) {
+                pr_err("OR of all __hash_32_generic results = %#x != %#x",
+                        hash_or[1][0], -1u);
+                return -EINVAL;
+        }
+#endif
+#endif
+
+        /* Likewise for all the i-bit hash values */
+        for (i = 1; i <= 32; i++) {
+                u32 const m = ((u32)2 << (i-1)) - 1;    /* Low i bits set */
+
+                if (hash_or[0][i] != m) {
+                        pr_err("OR of all hash_32(%d) results = %#x "
+                                "(%#x expected)", i, hash_or[0][i], m);
+                        return -EINVAL;
+                }
+                if (hash_or[1][i] != m) {
+                        pr_err("OR of all hash_64(%d) results = %#x "
+                                "(%#x expected)", i, hash_or[1][i], m);
+                        return -EINVAL;
+                }
+        }
+
+        /* Issue notices about skipped tests. */
+#ifndef HAVE_ARCH__HASH_32
+        pr_info("__hash_32() has no arch implementation to test.");
+#elif HAVE_ARCH__HASH_32 != 1
+        pr_info("__hash_32() is arch-specific; not compared to generic.");
+#endif
+#ifndef HAVE_ARCH_HASH_32
+        pr_info("hash_32() has no arch implementation to test.");
+#elif HAVE_ARCH_HASH_32 != 1
+        pr_info("hash_32() is arch-specific; not compared to generic.");
+#endif
+#ifndef HAVE_ARCH_HASH_64
+        pr_info("hash_64() has no arch implementation to test.");
+#elif HAVE_ARCH_HASH_64 != 1
+        pr_info("hash_64() is arch-specific; not compared to generic.");
+#endif
+
+        pr_notice("%u tests passed.", tests);
+
+        return 0;
+}
+
+static void __exit test_hash_exit(void)
+{
+}
+
+module_init(test_hash_init);    /* Does everything */
+module_exit(test_hash_exit);    /* Does nothing */
+
+MODULE_LICENSE("GPL");