root/lib/test_hash.c

DEFINITIONS

1. xorshift
2. mod255
3. fill_buf
4. test_int_hash
5. test_hash_init
6. test_hash_exit

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Test cases for <linux/hash.h> and <linux/stringhash.h>
   4  * This just verifies that various ways of computing a hash
   5  * produce the same thing and, for cases where a k-bit hash
   6  * value is requested, is of the requested size.
   7  *
   8  * We fill a buffer with a 255-byte null-terminated string,
   9  * and use both full_name_hash() and hashlen_string() to hash the
  10  * substrings from i to j, where 0 <= i < j < 256.
  11  *
  12  * The returned values are used to check that __hash_32() and
  13  * __hash_32_generic() compute the same thing.  Likewise hash_32()
  14  * and hash_64().
  15  */
  16 
  17 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt "\n"
  18 
  19 #include <linux/compiler.h>
  20 #include <linux/types.h>
  21 #include <linux/module.h>
  22 #include <linux/hash.h>
  23 #include <linux/stringhash.h>
  24 #include <linux/printk.h>
  25 
  26 /* 32-bit XORSHIFT generator.  Seed must not be zero. */
  27 static u32 __init __attribute_const__
  28 xorshift(u32 seed)
  29 {
  30         seed ^= seed << 13;
  31         seed ^= seed >> 17;
  32         seed ^= seed << 5;
  33         return seed;
  34 }
  35 
  36 /* Given a non-zero x, returns a non-zero byte. */
  37 static u8 __init __attribute_const__
  38 mod255(u32 x)
  39 {
  40         x = (x & 0xffff) + (x >> 16);   /* 1 <= x <= 0x1fffe */
  41         x = (x & 0xff) + (x >> 8);      /* 1 <= x <= 0x2fd */
  42         x = (x & 0xff) + (x >> 8);      /* 1 <= x <= 0x100 */
  43         x = (x & 0xff) + (x >> 8);      /* 1 <= x <= 0xff */
  44         return x;
  45 }
  46 
  47 /* Fill the buffer with non-zero bytes. */
  48 static void __init
  49 fill_buf(char *buf, size_t len, u32 seed)
  50 {
  51         size_t i;
  52 
  53         for (i = 0; i < len; i++) {
  54                 seed = xorshift(seed);
  55                 buf[i] = mod255(seed);
  56         }
  57 }
  58 
  59 /*
  60  * Test the various integer hash functions.  h64 (or its low-order bits)
  61  * is the integer to hash.  hash_or accumulates the OR of the hash values,
  62  * which are later checked to see that they cover all the requested bits.
  63  *
  64  * Because these functions (as opposed to the string hashes) are all
  65  * inline, the code being tested is actually in the module, and you can
  66  * recompile and re-test the module without rebooting.
  67  */
  68 static bool __init
  69 test_int_hash(unsigned long long h64, u32 hash_or[2][33])
  70 {
  71         int k;
  72         u32 h0 = (u32)h64, h1, h2;
  73 
  74         /* Test __hash32 */
  75         hash_or[0][0] |= h1 = __hash_32(h0);
  76 #ifdef HAVE_ARCH__HASH_32
  77         hash_or[1][0] |= h2 = __hash_32_generic(h0);
  78 #if HAVE_ARCH__HASH_32 == 1
  79         if (h1 != h2) {
  80                 pr_err("__hash_32(%#x) = %#x != __hash_32_generic() = %#x",
  81                         h0, h1, h2);
  82                 return false;
  83         }
  84 #endif
  85 #endif
  86 
  87         /* Test k = 1..32 bits */
  88         for (k = 1; k <= 32; k++) {
  89                 u32 const m = ((u32)2 << (k-1)) - 1;    /* Low k bits set */
  90 
  91                 /* Test hash_32 */
  92                 hash_or[0][k] |= h1 = hash_32(h0, k);
  93                 if (h1 > m) {
  94                         pr_err("hash_32(%#x, %d) = %#x > %#x", h0, k, h1, m);
  95                         return false;
  96                 }
  97 #ifdef HAVE_ARCH_HASH_32
  98                 h2 = hash_32_generic(h0, k);
  99 #if HAVE_ARCH_HASH_32 == 1
 100                 if (h1 != h2) {
 101                         pr_err("hash_32(%#x, %d) = %#x != hash_32_generic() "
 102                                 " = %#x", h0, k, h1, h2);
 103                         return false;
 104                 }
 105 #else
 106                 if (h2 > m) {
 107                         pr_err("hash_32_generic(%#x, %d) = %#x > %#x",
 108                                 h0, k, h1, m);
 109                         return false;
 110                 }
 111 #endif
 112 #endif
 113                 /* Test hash_64 */
 114                 hash_or[1][k] |= h1 = hash_64(h64, k);
 115                 if (h1 > m) {
 116                         pr_err("hash_64(%#llx, %d) = %#x > %#x", h64, k, h1, m);
 117                         return false;
 118                 }
 119 #ifdef HAVE_ARCH_HASH_64
 120                 h2 = hash_64_generic(h64, k);
 121 #if HAVE_ARCH_HASH_64 == 1
 122                 if (h1 != h2) {
 123                         pr_err("hash_64(%#llx, %d) = %#x != hash_64_generic() "
 124                                 "= %#x", h64, k, h1, h2);
 125                         return false;
 126                 }
 127 #else
 128                 if (h2 > m) {
 129                         pr_err("hash_64_generic(%#llx, %d) = %#x > %#x",
 130                                 h64, k, h1, m);
 131                         return false;
 132                 }
 133 #endif
 134 #endif
 135         }
 136 
 137         (void)h2;       /* Suppress unused variable warning */
 138         return true;
 139 }
 140 
 141 #define SIZE 256        /* Run time is cubic in SIZE */
 142 
 143 static int __init
 144 test_hash_init(void)
 145 {
 146         char buf[SIZE+1];
 147         u32 string_or = 0, hash_or[2][33] = { { 0, } };
 148         unsigned tests = 0;
 149         unsigned long long h64 = 0;
 150         int i, j;
 151 
 152         fill_buf(buf, SIZE, 1);
 153 
 154         /* Test every possible non-empty substring in the buffer. */
 155         for (j = SIZE; j > 0; --j) {
 156                 buf[j] = '\0';
 157 
 158                 for (i = 0; i <= j; i++) {
 159                         u64 hashlen = hashlen_string(buf+i, buf+i);
 160                         u32 h0 = full_name_hash(buf+i, buf+i, j-i);
 161 
 162                         /* Check that hashlen_string gets the length right */
 163                         if (hashlen_len(hashlen) != j-i) {
 164                                 pr_err("hashlen_string(%d..%d) returned length"
 165                                         " %u, expected %d",
 166                                         i, j, hashlen_len(hashlen), j-i);
 167                                 return -EINVAL;
 168                         }
 169                         /* Check that the hashes match */
 170                         if (hashlen_hash(hashlen) != h0) {
 171                                 pr_err("hashlen_string(%d..%d) = %08x != "
 172                                         "full_name_hash() = %08x",
 173                                         i, j, hashlen_hash(hashlen), h0);
 174                                 return -EINVAL;
 175                         }
 176 
 177                         string_or |= h0;
 178                         h64 = h64 << 32 | h0;   /* For use with hash_64 */
 179                         if (!test_int_hash(h64, hash_or))
 180                                 return -EINVAL;
 181                         tests++;
 182                 } /* i */
 183         } /* j */
 184 
 185         /* The OR of all the hash values should cover all the bits */
 186         if (~string_or) {
 187                 pr_err("OR of all string hash results = %#x != %#x",
 188                         string_or, -1u);
 189                 return -EINVAL;
 190         }
 191         if (~hash_or[0][0]) {
 192                 pr_err("OR of all __hash_32 results = %#x != %#x",
 193                         hash_or[0][0], -1u);
 194                 return -EINVAL;
 195         }
 196 #ifdef HAVE_ARCH__HASH_32
 197 #if HAVE_ARCH__HASH_32 != 1     /* Test is pointless if results match */
 198         if (~hash_or[1][0]) {
 199                 pr_err("OR of all __hash_32_generic results = %#x != %#x",
 200                         hash_or[1][0], -1u);
 201                 return -EINVAL;
 202         }
 203 #endif
 204 #endif
 205 
 206         /* Likewise for all the i-bit hash values */
 207         for (i = 1; i <= 32; i++) {
 208                 u32 const m = ((u32)2 << (i-1)) - 1;    /* Low i bits set */
 209 
 210                 if (hash_or[0][i] != m) {
 211                         pr_err("OR of all hash_32(%d) results = %#x "
 212                                 "(%#x expected)", i, hash_or[0][i], m);
 213                         return -EINVAL;
 214                 }
 215                 if (hash_or[1][i] != m) {
 216                         pr_err("OR of all hash_64(%d) results = %#x "
 217                                 "(%#x expected)", i, hash_or[1][i], m);
 218                         return -EINVAL;
 219                 }
 220         }
 221 
 222         /* Issue notices about skipped tests. */
 223 #ifdef HAVE_ARCH__HASH_32
 224 #if HAVE_ARCH__HASH_32 != 1
 225         pr_info("__hash_32() is arch-specific; not compared to generic.");
 226 #endif
 227 #else
 228         pr_info("__hash_32() has no arch implementation to test.");
 229 #endif
 230 #ifdef HAVE_ARCH_HASH_32
 231 #if HAVE_ARCH_HASH_32 != 1
 232         pr_info("hash_32() is arch-specific; not compared to generic.");
 233 #endif
 234 #else
 235         pr_info("hash_32() has no arch implementation to test.");
 236 #endif
 237 #ifdef HAVE_ARCH_HASH_64
 238 #if HAVE_ARCH_HASH_64 != 1
 239         pr_info("hash_64() is arch-specific; not compared to generic.");
 240 #endif
 241 #else
 242         pr_info("hash_64() has no arch implementation to test.");
 243 #endif
 244 
 245         pr_notice("%u tests passed.", tests);
 246 
 247         return 0;
 248 }
 249 
 250 static void __exit test_hash_exit(void)
 251 {
 252 }
 253 
 254 module_init(test_hash_init);    /* Does everything */
 255 module_exit(test_hash_exit);    /* Does nothing */
 256 
 257 MODULE_LICENSE("GPL");