src/malloc/malloc.c

   1 #define _GNU_SOURCE
   2 #include <stdlib.h>
   3 #include <string.h>
   4 #include <limits.h>
   5 #include <stdint.h>
   6 #include <errno.h>
   7 #include <sys/mman.h>
   8 #include "libc.h"
   9 #include "atomic.h"
  10 #include "pthread_impl.h"
  11 #include "malloc_impl.h"
  12
  13 #if defined(__GNUC__) && defined(__PIC__)
  14 #define inline inline __attribute__((always_inline))
  15 #endif
  16
  17 static struct {
  18         volatile uint64_t binmap;
  19         struct bin bins[64];
  20         volatile int split_merge_lock[2];
  21 } mal;
  22
  23 int __malloc_replaced;
  24
  25 /* Synchronization tools */
  26
  27 static inline void lock(volatile int *lk)
  28 {
  29         int need_locks = libc.need_locks;
  30         if (need_locks) {
  31                 while(a_swap(lk, 1)) __wait(lk, lk+1, 1, 1);
  32                 if (need_locks < 0) libc.need_locks = 0;
  33         }
  34 }
  35
  36 static inline void unlock(volatile int *lk)
  37 {
  38         if (lk[0]) {
  39                 a_store(lk, 0);
  40                 if (lk[1]) __wake(lk, 1, 1);
  41         }
  42 }
  43
  44 static inline void lock_bin(int i)
  45 {
  46         lock(mal.bins[i].lock);
  47         if (!mal.bins[i].head)
  48                 mal.bins[i].head = mal.bins[i].tail = BIN_TO_CHUNK(i);
  49 }
  50
  51 static inline void unlock_bin(int i)
  52 {
  53         unlock(mal.bins[i].lock);
  54 }
  55
  56 static int first_set(uint64_t x)
  57 {
  58 #if 1
  59         return a_ctz_64(x);
  60 #else
  61         static const char debruijn64[64] = {
  62                 0, 1, 2, 53, 3, 7, 54, 27, 4, 38, 41, 8, 34, 55, 48, 28,
  63                 62, 5, 39, 46, 44, 42, 22, 9, 24, 35, 59, 56, 49, 18, 29, 11,
  64                 63, 52, 6, 26, 37, 40, 33, 47, 61, 45, 43, 21, 23, 58, 17, 10,
  65                 51, 25, 36, 32, 60, 20, 57, 16, 50, 31, 19, 15, 30, 14, 13, 12
  66         };
  67         static const char debruijn32[32] = {
  68                 0, 1, 23, 2, 29, 24, 19, 3, 30, 27, 25, 11, 20, 8, 4, 13,
  69                 31, 22, 28, 18, 26, 10, 7, 12, 21, 17, 9, 6, 16, 5, 15, 14
  70         };
  71         if (sizeof(long) < 8) {
  72                 uint32_t y = x;
  73                 if (!y) {
  74                         y = x>>32;
  75                         return 32 + debruijn32[(y&-y)*0x076be629 >> 27];
  76                 }
  77                 return debruijn32[(y&-y)*0x076be629 >> 27];
  78         }
  79         return debruijn64[(x&-x)*0x022fdd63cc95386dull >> 58];
  80 #endif
  81 }
  82
  83 static const unsigned char bin_tab[60] = {
  84                     32,33,34,35,36,36,37,37,38,38,39,39,
  85         40,40,40,40,41,41,41,41,42,42,42,42,43,43,43,43,
  86         44,44,44,44,44,44,44,44,45,45,45,45,45,45,45,45,
  87         46,46,46,46,46,46,46,46,47,47,47,47,47,47,47,47,
  88 };
  89
  90 static int bin_index(size_t x)
  91 {
  92         x = x / SIZE_ALIGN - 1;
  93         if (x <= 32) return x;
  94         if (x < 512) return bin_tab[x/8-4];
  95         if (x > 0x1c00) return 63;
  96         return bin_tab[x/128-4] + 16;
  97 }
  98
  99 static int bin_index_up(size_t x)
 100 {
 101         x = x / SIZE_ALIGN - 1;
 102         if (x <= 32) return x;
 103         x--;
 104         if (x < 512) return bin_tab[x/8-4] + 1;
 105         return bin_tab[x/128-4] + 17;
 106 }
 107
 108 #if 0
 109 void __dump_heap(int x)
 110 {
 111         struct chunk *c;
 112         int i;
 113         for (c = (void *)mal.heap; CHUNK_SIZE(c); c = NEXT_CHUNK(c))
 114                 fprintf(stderr, "base %p size %zu (%d) flags %d/%d\n",
 115                         c, CHUNK_SIZE(c), bin_index(CHUNK_SIZE(c)),
 116                         c->csize & 15,
 117                         NEXT_CHUNK(c)->psize & 15);
 118         for (i=0; i<64; i++) {
 119                 if (mal.bins[i].head != BIN_TO_CHUNK(i) && mal.bins[i].head) {
 120                         fprintf(stderr, "bin %d: %p\n", i, mal.bins[i].head);
 121                         if (!(mal.binmap & 1ULL<<i))
 122                                 fprintf(stderr, "missing from binmap!\n");
 123                 } else if (mal.binmap & 1ULL<<i)
 124                         fprintf(stderr, "binmap wrongly contains %d!\n", i);
 125         }
 126 }
 127 #endif
 128
 129 /* This function returns true if the interval [old,new]
 130  * intersects the 'len'-sized interval below &libc.auxv
 131  * (interpreted as the main-thread stack) or below &b
 132  * (the current stack). It is used to defend against
 133  * buggy brk implementations that can cross the stack. */
 134
 135 static int traverses_stack_p(uintptr_t old, uintptr_t new)
 136 {
 137         const uintptr_t len = 8<<20;
 138         uintptr_t a, b;
 139
 140         b = (uintptr_t)libc.auxv;
 141         a = b > len ? b-len : 0;
 142         if (new>a && old<b) return 1;
 143
 144         b = (uintptr_t)&b;
 145         a = b > len ? b-len : 0;
 146         if (new>a && old<b) return 1;
 147
 148         return 0;
 149 }
 150
 151 /* Expand the heap in-place if brk can be used, or otherwise via mmap,
 152  * using an exponential lower bound on growth by mmap to make
 153  * fragmentation asymptotically irrelevant. The size argument is both
 154  * an input and an output, since the caller needs to know the size
 155  * allocated, which will be larger than requested due to page alignment
 156  * and mmap minimum size rules. The caller is responsible for locking
 157  * to prevent concurrent calls. */
 158
 159 static void *__expand_heap(size_t *pn)
 160 {
 161         static uintptr_t brk;
 162         static unsigned mmap_step;
 163         size_t n = *pn;
 164
 165         if (n > SIZE_MAX/2 - PAGE_SIZE) {
 166                 errno = ENOMEM;
 167                 return 0;
 168         }
 169         n += -n & PAGE_SIZE-1;
 170
 171         if (!brk) {
 172                 brk = __syscall(SYS_brk, 0);
 173                 brk += -brk & PAGE_SIZE-1;
 174         }
 175
 176         if (n < SIZE_MAX-brk && !traverses_stack_p(brk, brk+n)
 177             && __syscall(SYS_brk, brk+n)==brk+n) {
 178                 *pn = n;
 179                 brk += n;
 180                 return (void *)(brk-n);
 181         }
 182
 183         size_t min = (size_t)PAGE_SIZE << mmap_step/2;
 184         if (n < min) n = min;
 185         void *area = __mmap(0, n, PROT_READ|PROT_WRITE,
 186                 MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
 187         if (area == MAP_FAILED) return 0;
 188         *pn = n;
 189         mmap_step++;
 190         return area;
 191 }
 192
 193 static struct chunk *expand_heap(size_t n)
 194 {
 195         static void *end;
 196         void *p;
 197         struct chunk *w;
 198
 199         /* The argument n already accounts for the caller's chunk
 200          * overhead needs, but if the heap can't be extended in-place,
 201          * we need room for an extra zero-sized sentinel chunk. */
 202         n += SIZE_ALIGN;
 203
 204         p = __expand_heap(&n);
 205         if (!p) return 0;
 206
 207         /* If not just expanding existing space, we need to make a
 208          * new sentinel chunk below the allocated space. */
 209         if (p != end) {
 210                 /* Valid/safe because of the prologue increment. */
 211                 n -= SIZE_ALIGN;
 212                 p = (char *)p + SIZE_ALIGN;
 213                 w = MEM_TO_CHUNK(p);
 214                 w->psize = 0 | C_INUSE;
 215         }
 216
 217         /* Record new heap end and fill in footer. */
 218         end = (char *)p + n;
 219         w = MEM_TO_CHUNK(end);
 220         w->psize = n | C_INUSE;
 221         w->csize = 0 | C_INUSE;
 222
 223         /* Fill in header, which may be new or may be replacing a
 224          * zero-size sentinel header at the old end-of-heap. */
 225         w = MEM_TO_CHUNK(p);
 226         w->csize = n | C_INUSE;
 227
 228         return w;
 229 }
 230
 231 static int adjust_size(size_t *n)
 232 {
 233         /* Result of pointer difference must fit in ptrdiff_t. */
 234         if (*n-1 > PTRDIFF_MAX - SIZE_ALIGN - PAGE_SIZE) {
 235                 if (*n) {
 236                         errno = ENOMEM;
 237                         return -1;
 238                 } else {
 239                         *n = SIZE_ALIGN;
 240                         return 0;
 241                 }
 242         }
 243         *n = (*n + OVERHEAD + SIZE_ALIGN - 1) & SIZE_MASK;
 244         return 0;
 245 }
 246
 247 static void unbin(struct chunk *c, int i)
 248 {
 249         if (c->prev == c->next)
 250                 a_and_64(&mal.binmap, ~(1ULL<<i));
 251         c->prev->next = c->next;
 252         c->next->prev = c->prev;
 253         c->csize |= C_INUSE;
 254         NEXT_CHUNK(c)->psize |= C_INUSE;
 255 }
 256
 257 static void bin_chunk(struct chunk *self, int i)
 258 {
 259         self->next = BIN_TO_CHUNK(i);
 260         self->prev = mal.bins[i].tail;
 261         self->next->prev = self;
 262         self->prev->next = self;
 263         if (self->prev == BIN_TO_CHUNK(i))
 264                 a_or_64(&mal.binmap, 1ULL<<i);
 265 }
 266
 267 static void trim(struct chunk *self, size_t n)
 268 {
 269         size_t n1 = CHUNK_SIZE(self);
 270         struct chunk *next, *split;
 271
 272         if (n >= n1 - DONTCARE) return;
 273
 274         next = NEXT_CHUNK(self);
 275         split = (void *)((char *)self + n);
 276
 277         split->psize = n | C_INUSE;
 278         split->csize = n1-n;
 279         next->psize = n1-n;
 280         self->csize = n | C_INUSE;
 281
 282         int i = bin_index(n1-n);
 283         lock_bin(i);
 284
 285         bin_chunk(split, i);
 286
 287         unlock_bin(i);
 288 }
 289
 290 void *malloc(size_t n)
 291 {
 292         struct chunk *c;
 293         int i, j;
 294         uint64_t mask;
 295
 296         if (adjust_size(&n) < 0) return 0;
 297
 298         if (n > MMAP_THRESHOLD) {
 299                 size_t len = n + OVERHEAD + PAGE_SIZE - 1 & -PAGE_SIZE;
 300                 char *base = __mmap(0, len, PROT_READ|PROT_WRITE,
 301                         MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
 302                 if (base == (void *)-1) return 0;
 303                 c = (void *)(base + SIZE_ALIGN - OVERHEAD);
 304                 c->csize = len - (SIZE_ALIGN - OVERHEAD);
 305                 c->psize = SIZE_ALIGN - OVERHEAD;
 306                 return CHUNK_TO_MEM(c);
 307         }
 308
 309         i = bin_index_up(n);
 310         if (i<63 && (mal.binmap & (1ULL<<i))) {
 311                 lock_bin(i);
 312                 c = mal.bins[i].head;
 313                 if (c != BIN_TO_CHUNK(i) && CHUNK_SIZE(c)-n <= DONTCARE) {
 314                         unbin(c, i);
 315                         unlock_bin(i);
 316                         return CHUNK_TO_MEM(c);
 317                 }
 318                 unlock_bin(i);
 319         }
 320         lock(mal.split_merge_lock);
 321         for (mask = mal.binmap & -(1ULL<<i); mask; mask -= (mask&-mask)) {
 322                 j = first_set(mask);
 323                 lock_bin(j);
 324                 c = mal.bins[j].head;
 325                 if (c != BIN_TO_CHUNK(j)) {
 326                         unbin(c, j);
 327                         unlock_bin(j);
 328                         break;
 329                 }
 330                 unlock_bin(j);
 331         }
 332         if (!mask) {
 333                 c = expand_heap(n);
 334                 if (!c) {
 335                         unlock(mal.split_merge_lock);
 336                         return 0;
 337                 }
 338         }
 339         trim(c, n);
 340         unlock(mal.split_merge_lock);
 341         return CHUNK_TO_MEM(c);
 342 }
 343
 344 static size_t mal0_clear(char *p, size_t pagesz, size_t n)
 345 {
 346 #ifdef __GNUC__
 347         typedef uint64_t __attribute__((__may_alias__)) T;
 348 #else
 349         typedef unsigned char T;
 350 #endif
 351         char *pp = p + n;
 352         size_t i = (uintptr_t)pp & (pagesz - 1);
 353         for (;;) {
 354                 pp = memset(pp - i, 0, i);
 355                 if (pp - p < pagesz) return pp - p;
 356                 for (i = pagesz; i; i -= 2*sizeof(T), pp -= 2*sizeof(T))
 357                         if (((T *)pp)[-1] | ((T *)pp)[-2])
 358                                 break;
 359         }
 360 }
 361
 362 void *calloc(size_t m, size_t n)
 363 {
 364         if (n && m > (size_t)-1/n) {
 365                 errno = ENOMEM;
 366                 return 0;
 367         }
 368         n *= m;
 369         void *p = malloc(n);
 370         if (!p) return p;
 371         if (!__malloc_replaced) {
 372                 if (IS_MMAPPED(MEM_TO_CHUNK(p)))
 373                         return p;
 374                 if (n >= PAGE_SIZE)
 375                         n = mal0_clear(p, PAGE_SIZE, n);
 376         }
 377         return memset(p, 0, n);
 378 }
 379
 380 void *realloc(void *p, size_t n)
 381 {
 382         struct chunk *self, *next;
 383         size_t n0, n1;
 384         void *new;
 385
 386         if (!p) return malloc(n);
 387
 388         if (adjust_size(&n) < 0) return 0;
 389
 390         self = MEM_TO_CHUNK(p);
 391         n1 = n0 = CHUNK_SIZE(self);
 392
 393         if (n<=n0 && n0-n<=DONTCARE) return p;
 394
 395         if (IS_MMAPPED(self)) {
 396                 size_t extra = self->psize;
 397                 char *base = (char *)self - extra;
 398                 size_t oldlen = n0 + extra;
 399                 size_t newlen = n + extra;
 400                 /* Crash on realloc of freed chunk */
 401                 if (extra & 1) a_crash();
 402                 if (newlen < PAGE_SIZE && (new = malloc(n-OVERHEAD))) {
 403                         n0 = n;
 404                         goto copy_free_ret;
 405                 }
 406                 newlen = (newlen + PAGE_SIZE-1) & -PAGE_SIZE;
 407                 if (oldlen == newlen) return p;
 408                 base = __mremap(base, oldlen, newlen, MREMAP_MAYMOVE);
 409                 if (base == (void *)-1)
 410                         goto copy_realloc;
 411                 self = (void *)(base + extra);
 412                 self->csize = newlen - extra;
 413                 return CHUNK_TO_MEM(self);
 414         }
 415
 416         next = NEXT_CHUNK(self);
 417
 418         /* Crash on corrupted footer (likely from buffer overflow) */
 419         if (next->psize != self->csize) a_crash();
 420
 421         lock(mal.split_merge_lock);
 422
 423         size_t nsize = next->csize & C_INUSE ? 0 : CHUNK_SIZE(next);
 424         if (n0+nsize >= n) {
 425                 int i = bin_index(nsize);
 426                 lock_bin(i);
 427                 if (!(next->csize & C_INUSE)) {
 428                         unbin(next, i);
 429                         unlock_bin(i);
 430                         next = NEXT_CHUNK(next);
 431                         self->csize = next->psize = n0+nsize | C_INUSE;
 432                         trim(self, n);
 433                         unlock(mal.split_merge_lock);
 434                         return CHUNK_TO_MEM(self);
 435                 }
 436                 unlock_bin(i);
 437         }
 438         unlock(mal.split_merge_lock);
 439
 440 copy_realloc:
 441         /* As a last resort, allocate a new chunk and copy to it. */
 442         new = malloc(n-OVERHEAD);
 443         if (!new) return 0;
 444 copy_free_ret:
 445         memcpy(new, p, n0-OVERHEAD);
 446         free(CHUNK_TO_MEM(self));
 447         return new;
 448 }
 449
 450 void __bin_chunk(struct chunk *self)
 451 {
 452         struct chunk *next = NEXT_CHUNK(self);
 453
 454         /* Crash on corrupted footer (likely from buffer overflow) */
 455         if (next->psize != self->csize) a_crash();
 456
 457         lock(mal.split_merge_lock);
 458
 459         size_t osize = CHUNK_SIZE(self), size = osize;
 460
 461         /* Since we hold split_merge_lock, only transition from free to
 462          * in-use can race; in-use to free is impossible */
 463         size_t psize = self->psize & C_INUSE ? 0 : CHUNK_PSIZE(self);
 464         size_t nsize = next->csize & C_INUSE ? 0 : CHUNK_SIZE(next);
 465
 466         if (psize) {
 467                 int i = bin_index(psize);
 468                 lock_bin(i);
 469                 if (!(self->psize & C_INUSE)) {
 470                         struct chunk *prev = PREV_CHUNK(self);
 471                         unbin(prev, i);
 472                         self = prev;
 473                         size += psize;
 474                 }
 475                 unlock_bin(i);
 476         }
 477         if (nsize) {
 478                 int i = bin_index(nsize);
 479                 lock_bin(i);
 480                 if (!(next->csize & C_INUSE)) {
 481                         unbin(next, i);
 482                         next = NEXT_CHUNK(next);
 483                         size += nsize;
 484                 }
 485                 unlock_bin(i);
 486         }
 487
 488         int i = bin_index(size);
 489         lock_bin(i);
 490
 491         self->csize = size;
 492         next->psize = size;
 493         bin_chunk(self, i);
 494         unlock(mal.split_merge_lock);
 495
 496         /* Replace middle of large chunks with fresh zero pages */
 497         if (size > RECLAIM && (size^(size-osize)) > size-osize) {
 498                 uintptr_t a = (uintptr_t)self + SIZE_ALIGN+PAGE_SIZE-1 & -PAGE_SIZE;
 499                 uintptr_t b = (uintptr_t)next - SIZE_ALIGN & -PAGE_SIZE;
 500 #if 1
 501                 __madvise((void *)a, b-a, MADV_DONTNEED);
 502 #else
 503                 __mmap((void *)a, b-a, PROT_READ|PROT_WRITE,
 504                         MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0);
 505 #endif
 506         }
 507
 508         unlock_bin(i);
 509 }
 510
 511 static void unmap_chunk(struct chunk *self)
 512 {
 513         size_t extra = self->psize;
 514         char *base = (char *)self - extra;
 515         size_t len = CHUNK_SIZE(self) + extra;
 516         /* Crash on double free */
 517         if (extra & 1) a_crash();
 518         __munmap(base, len);
 519 }
 520
 521 void free(void *p)
 522 {
 523         if (!p) return;
 524
 525         struct chunk *self = MEM_TO_CHUNK(p);
 526
 527         if (IS_MMAPPED(self))
 528                 unmap_chunk(self);
 529         else
 530                 __bin_chunk(self);
 531 }
 532
 533 void __malloc_donate(char *start, char *end)
 534 {
 535         size_t align_start_up = (SIZE_ALIGN-1) & (-(uintptr_t)start - OVERHEAD);
 536         size_t align_end_down = (SIZE_ALIGN-1) & (uintptr_t)end;
 537
 538         /* Getting past this condition ensures that the padding for alignment
 539          * and header overhead will not overflow and will leave a nonzero
 540          * multiple of SIZE_ALIGN bytes between start and end. */
 541         if (end - start <= OVERHEAD + align_start_up + align_end_down)
 542                 return;
 543         start += align_start_up + OVERHEAD;
 544         end   -= align_end_down;
 545
 546         struct chunk *c = MEM_TO_CHUNK(start), *n = MEM_TO_CHUNK(end);
 547         c->psize = n->csize = C_INUSE;
 548         c->csize = n->psize = C_INUSE | (end-start);
 549         __bin_chunk(c);
 550 }