src/util/ralloc.c

   1 /*
   2  * Copyright © 2010 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 #include <assert.h>
  25 #include <stdlib.h>
  26 #include <stdarg.h>
  27 #include <stdio.h>
  28 #include <string.h>
  29 #include <stdint.h>
  30
  31 /* Android defines SIZE_MAX in limits.h, instead of the standard stdint.h */
  32 #ifdef ANDROID
  33 #include <limits.h>
  34 #endif
  35
  36 /* Some versions of MinGW are missing _vscprintf's declaration, although they
  37  * still provide the symbol in the import library. */
  38 #ifdef __MINGW32__
  39 _CRTIMP int _vscprintf(const char *format, va_list argptr);
  40 #endif
  41
  42 #include "ralloc.h"
  43
  44 #ifndef va_copy
  45 #ifdef __va_copy
  46 #define va_copy(dest, src) __va_copy((dest), (src))
  47 #else
  48 #define va_copy(dest, src) (dest) = (src)
  49 #endif
  50 #endif
  51
  52 #define CANARY 0x5A1106
  53
  54 struct ralloc_header
  55 {
  56 #ifdef DEBUG
  57    /* A canary value used to determine whether a pointer is ralloc'd. */
  58    unsigned canary;
  59 #endif
  60
  61    struct ralloc_header *parent;
  62
  63    /* The first child (head of a linked list) */
  64    struct ralloc_header *child;
  65
  66    /* Linked list of siblings */
  67    struct ralloc_header *prev;
  68    struct ralloc_header *next;
  69
  70    void (*destructor)(void *);
  71 };
  72
  73 typedef struct ralloc_header ralloc_header;
  74
  75 static void unlink_block(ralloc_header *info);
  76 static void unsafe_free(ralloc_header *info);
  77
  78 static ralloc_header *
  79 get_header(const void *ptr)
  80 {
  81    ralloc_header *info = (ralloc_header *) (((char *) ptr) -
  82                                             sizeof(ralloc_header));
  83 #ifdef DEBUG
  84    assert(info->canary == CANARY);
  85 #endif
  86    return info;
  87 }
  88
  89 #define PTR_FROM_HEADER(info) (((char *) info) + sizeof(ralloc_header))
  90
  91 static void
  92 add_child(ralloc_header *parent, ralloc_header *info)
  93 {
  94    if (parent != NULL) {
  95       info->parent = parent;
  96       info->next = parent->child;
  97       parent->child = info;
  98
  99       if (info->next != NULL)
 100          info->next->prev = info;
 101    }
 102 }
 103
 104 void *
 105 ralloc_context(const void *ctx)
 106 {
 107    return ralloc_size(ctx, 0);
 108 }
 109
 110 void *
 111 ralloc_size(const void *ctx, size_t size)
 112 {
 113    void *block = malloc(size + sizeof(ralloc_header));
 114    ralloc_header *info;
 115    ralloc_header *parent;
 116
 117    if (unlikely(block == NULL))
 118       return NULL;
 119
 120    info = (ralloc_header *) block;
 121    /* measurements have shown that calloc is slower (because of
 122     * the multiplication overflow checking?), so clear things
 123     * manually
 124     */
 125    info->parent = NULL;
 126    info->child = NULL;
 127    info->prev = NULL;
 128    info->next = NULL;
 129    info->destructor = NULL;
 130
 131    parent = ctx != NULL ? get_header(ctx) : NULL;
 132
 133    add_child(parent, info);
 134
 135 #ifdef DEBUG
 136    info->canary = CANARY;
 137 #endif
 138
 139    return PTR_FROM_HEADER(info);
 140 }
 141
 142 void *
 143 rzalloc_size(const void *ctx, size_t size)
 144 {
 145    void *ptr = ralloc_size(ctx, size);
 146
 147    if (likely(ptr))
 148       memset(ptr, 0, size);
 149
 150    return ptr;
 151 }
 152
 153 /* helper function - assumes ptr != NULL */
 154 static void *
 155 resize(void *ptr, size_t size)
 156 {
 157    ralloc_header *child, *old, *info;
 158
 159    old = get_header(ptr);
 160    info = realloc(old, size + sizeof(ralloc_header));
 161
 162    if (info == NULL)
 163       return NULL;
 164
 165    /* Update parent and sibling's links to the reallocated node. */
 166    if (info != old && info->parent != NULL) {
 167       if (info->parent->child == old)
 168          info->parent->child = info;
 169
 170       if (info->prev != NULL)
 171          info->prev->next = info;
 172
 173       if (info->next != NULL)
 174          info->next->prev = info;
 175    }
 176
 177    /* Update child->parent links for all children */
 178    for (child = info->child; child != NULL; child = child->next)
 179       child->parent = info;
 180
 181    return PTR_FROM_HEADER(info);
 182 }
 183
 184 void *
 185 reralloc_size(const void *ctx, void *ptr, size_t size)
 186 {
 187    if (unlikely(ptr == NULL))
 188       return ralloc_size(ctx, size);
 189
 190    assert(ralloc_parent(ptr) == ctx);
 191    return resize(ptr, size);
 192 }
 193
 194 void *
 195 ralloc_array_size(const void *ctx, size_t size, unsigned count)
 196 {
 197    if (count > SIZE_MAX/size)
 198       return NULL;
 199
 200    return ralloc_size(ctx, size * count);
 201 }
 202
 203 void *
 204 rzalloc_array_size(const void *ctx, size_t size, unsigned count)
 205 {
 206    if (count > SIZE_MAX/size)
 207       return NULL;
 208
 209    return rzalloc_size(ctx, size * count);
 210 }
 211
 212 void *
 213 reralloc_array_size(const void *ctx, void *ptr, size_t size, unsigned count)
 214 {
 215    if (count > SIZE_MAX/size)
 216       return NULL;
 217
 218    return reralloc_size(ctx, ptr, size * count);
 219 }
 220
 221 void
 222 ralloc_free(void *ptr)
 223 {
 224    ralloc_header *info;
 225
 226    if (ptr == NULL)
 227       return;
 228
 229    info = get_header(ptr);
 230    unlink_block(info);
 231    unsafe_free(info);
 232 }
 233
 234 static void
 235 unlink_block(ralloc_header *info)
 236 {
 237    /* Unlink from parent & siblings */
 238    if (info->parent != NULL) {
 239       if (info->parent->child == info)
 240          info->parent->child = info->next;
 241
 242       if (info->prev != NULL)
 243          info->prev->next = info->next;
 244
 245       if (info->next != NULL)
 246          info->next->prev = info->prev;
 247    }
 248    info->parent = NULL;
 249    info->prev = NULL;
 250    info->next = NULL;
 251 }
 252
 253 static void
 254 unsafe_free(ralloc_header *info)
 255 {
 256    /* Recursively free any children...don't waste time unlinking them. */
 257    ralloc_header *temp;
 258    while (info->child != NULL) {
 259       temp = info->child;
 260       info->child = temp->next;
 261       unsafe_free(temp);
 262    }
 263
 264    /* Free the block itself.  Call the destructor first, if any. */
 265    if (info->destructor != NULL)
 266       info->destructor(PTR_FROM_HEADER(info));
 267
 268    free(info);
 269 }
 270
 271 void
 272 ralloc_steal(const void *new_ctx, void *ptr)
 273 {
 274    ralloc_header *info, *parent;
 275
 276    if (unlikely(ptr == NULL))
 277       return;
 278
 279    info = get_header(ptr);
 280    parent = get_header(new_ctx);
 281
 282    unlink_block(info);
 283
 284    add_child(parent, info);
 285 }
 286
 287 void
 288 ralloc_adopt(const void *new_ctx, void *old_ctx)
 289 {
 290    ralloc_header *new_info, *old_info, *child;
 291
 292    if (unlikely(old_ctx == NULL))
 293       return;
 294
 295    old_info = get_header(old_ctx);
 296    new_info = get_header(new_ctx);
 297
 298    /* If there are no children, bail. */
 299    if (unlikely(old_info->child == NULL))
 300       return;
 301
 302    /* Set all the children's parent to new_ctx; get a pointer to the last child. */
 303    for (child = old_info->child; child->next != NULL; child = child->next) {
 304       child->parent = new_info;
 305    }
 306
 307    /* Connect the two lists together; parent them to new_ctx; make old_ctx empty. */
 308    child->next = new_info->child;
 309    child->parent = new_info;
 310    new_info->child = old_info->child;
 311    old_info->child = NULL;
 312 }
 313
 314 void *
 315 ralloc_parent(const void *ptr)
 316 {
 317    ralloc_header *info;
 318
 319    if (unlikely(ptr == NULL))
 320       return NULL;
 321
 322    info = get_header(ptr);
 323    return info->parent ? PTR_FROM_HEADER(info->parent) : NULL;
 324 }
 325
 326 static void *autofree_context = NULL;
 327
 328 static void
 329 autofree(void)
 330 {
 331    ralloc_free(autofree_context);
 332 }
 333
 334 void *
 335 ralloc_autofree_context(void)
 336 {
 337    if (unlikely(autofree_context == NULL)) {
 338       autofree_context = ralloc_context(NULL);
 339       atexit(autofree);
 340    }
 341    return autofree_context;
 342 }
 343
 344 void
 345 ralloc_set_destructor(const void *ptr, void(*destructor)(void *))
 346 {
 347    ralloc_header *info = get_header(ptr);
 348    info->destructor = destructor;
 349 }
 350
 351 char *
 352 ralloc_strdup(const void *ctx, const char *str)
 353 {
 354    size_t n;
 355    char *ptr;
 356
 357    if (unlikely(str == NULL))
 358       return NULL;
 359
 360    n = strlen(str);
 361    ptr = ralloc_array(ctx, char, n + 1);
 362    memcpy(ptr, str, n);
 363    ptr[n] = '\0';
 364    return ptr;
 365 }
 366
 367 char *
 368 ralloc_strndup(const void *ctx, const char *str, size_t max)
 369 {
 370    size_t n;
 371    char *ptr;
 372
 373    if (unlikely(str == NULL))
 374       return NULL;
 375
 376    n = strnlen(str, max);
 377    ptr = ralloc_array(ctx, char, n + 1);
 378    memcpy(ptr, str, n);
 379    ptr[n] = '\0';
 380    return ptr;
 381 }
 382
 383 /* helper routine for strcat/strncat - n is the exact amount to copy */
 384 static bool
 385 cat(char **dest, const char *str, size_t n)
 386 {
 387    char *both;
 388    size_t existing_length;
 389    assert(dest != NULL && *dest != NULL);
 390
 391    existing_length = strlen(*dest);
 392    both = resize(*dest, existing_length + n + 1);
 393    if (unlikely(both == NULL))
 394       return false;
 395
 396    memcpy(both + existing_length, str, n);
 397    both[existing_length + n] = '\0';
 398
 399    *dest = both;
 400    return true;
 401 }
 402
 403
 404 bool
 405 ralloc_strcat(char **dest, const char *str)
 406 {
 407    return cat(dest, str, strlen(str));
 408 }
 409
 410 bool
 411 ralloc_strncat(char **dest, const char *str, size_t n)
 412 {
 413    /* Clamp n to the string length */
 414    size_t str_length = strlen(str);
 415    if (str_length < n)
 416       n = str_length;
 417
 418    return cat(dest, str, n);
 419 }
 420
 421 char *
 422 ralloc_asprintf(const void *ctx, const char *fmt, ...)
 423 {
 424    char *ptr;
 425    va_list args;
 426    va_start(args, fmt);
 427    ptr = ralloc_vasprintf(ctx, fmt, args);
 428    va_end(args);
 429    return ptr;
 430 }
 431
 432 /* Return the length of the string that would be generated by a printf-style
 433  * format and argument list, not including the \0 byte.
 434  */
 435 static size_t
 436 printf_length(const char *fmt, va_list untouched_args)
 437 {
 438    int size;
 439    char junk;
 440
 441    /* Make a copy of the va_list so the original caller can still use it */
 442    va_list args;
 443    va_copy(args, untouched_args);
 444
 445 #ifdef _WIN32
 446    /* We need to use _vcsprintf to calculate the size as vsnprintf returns -1
 447     * if the number of characters to write is greater than count.
 448     */
 449    size = _vscprintf(fmt, args);
 450    (void)junk;
 451 #else
 452    size = vsnprintf(&junk, 1, fmt, args);
 453 #endif
 454    assert(size >= 0);
 455
 456    va_end(args);
 457
 458    return size;
 459 }
 460
 461 char *
 462 ralloc_vasprintf(const void *ctx, const char *fmt, va_list args)
 463 {
 464    size_t size = printf_length(fmt, args) + 1;
 465
 466    char *ptr = ralloc_size(ctx, size);
 467    if (ptr != NULL)
 468       vsnprintf(ptr, size, fmt, args);
 469
 470    return ptr;
 471 }
 472
 473 bool
 474 ralloc_asprintf_append(char **str, const char *fmt, ...)
 475 {
 476    bool success;
 477    va_list args;
 478    va_start(args, fmt);
 479    success = ralloc_vasprintf_append(str, fmt, args);
 480    va_end(args);
 481    return success;
 482 }
 483
 484 bool
 485 ralloc_vasprintf_append(char **str, const char *fmt, va_list args)
 486 {
 487    size_t existing_length;
 488    assert(str != NULL);
 489    existing_length = *str ? strlen(*str) : 0;
 490    return ralloc_vasprintf_rewrite_tail(str, &existing_length, fmt, args);
 491 }
 492
 493 bool
 494 ralloc_asprintf_rewrite_tail(char **str, size_t *start, const char *fmt, ...)
 495 {
 496    bool success;
 497    va_list args;
 498    va_start(args, fmt);
 499    success = ralloc_vasprintf_rewrite_tail(str, start, fmt, args);
 500    va_end(args);
 501    return success;
 502 }
 503
 504 bool
 505 ralloc_vasprintf_rewrite_tail(char **str, size_t *start, const char *fmt,
 506                               va_list args)
 507 {
 508    size_t new_length;
 509    char *ptr;
 510
 511    assert(str != NULL);
 512
 513    if (unlikely(*str == NULL)) {
 514       // Assuming a NULL context is probably bad, but it's expected behavior.
 515       *str = ralloc_vasprintf(NULL, fmt, args);
 516       *start = strlen(*str);
 517       return true;
 518    }
 519
 520    new_length = printf_length(fmt, args);
 521
 522    ptr = resize(*str, *start + new_length + 1);
 523    if (unlikely(ptr == NULL))
 524       return false;
 525
 526    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 527    *str = ptr;
 528    *start += new_length;
 529    return true;
 530 }
 531
 532 /***************************************************************************
 533  * Linear allocator for short-lived allocations.
 534  ***************************************************************************
 535  *
 536  * The allocator consists of a parent node (2K buffer), which requires
 537  * a ralloc parent, and child nodes (allocations). Child nodes can't be freed
 538  * directly, because the parent doesn't track them. You have to release
 539  * the parent node in order to release all its children.
 540  *
 541  * The allocator uses a fixed-sized buffer with a monotonically increasing
 542  * offset after each allocation. If the buffer is all used, another buffer
 543  * is allocated, sharing the same ralloc parent, so all buffers are at
 544  * the same level in the ralloc hierarchy.
 545  *
 546  * The linear parent node is always the first buffer and keeps track of all
 547  * other buffers.
 548  */
 549
 550 #define ALIGN_POT(x, y) (((x) + (y) - 1) & ~((y) - 1))
 551
 552 #define MIN_LINEAR_BUFSIZE 2048
 553 #define SUBALLOC_ALIGNMENT sizeof(uintptr_t)
 554 #define LMAGIC 0x87b9c7d3
 555
 556 struct linear_header {
 557 #ifdef DEBUG
 558    unsigned magic;   /* for debugging */
 559 #endif
 560    unsigned offset;  /* points to the first unused byte in the buffer */
 561    unsigned size;    /* size of the buffer */
 562    void *ralloc_parent;          /* new buffers will use this */
 563    struct linear_header *next;   /* next buffer if we have more */
 564    struct linear_header *latest; /* the only buffer that has free space */
 565
 566    /* After this structure, the buffer begins.
 567     * Each suballocation consists of linear_size_chunk as its header followed
 568     * by the suballocation, so it goes:
 569     *
 570     * - linear_size_chunk
 571     * - allocated space
 572     * - linear_size_chunk
 573     * - allocated space
 574     * etc.
 575     *
 576     * linear_size_chunk is only needed by linear_realloc.
 577     */
 578 };
 579
 580 struct linear_size_chunk {
 581    unsigned size; /* for realloc */
 582    unsigned _padding;
 583 };
 584
 585 typedef struct linear_header linear_header;
 586 typedef struct linear_size_chunk linear_size_chunk;
 587
 588 #define LINEAR_PARENT_TO_HEADER(parent) \
 589    (linear_header*) \
 590    ((char*)(parent) - sizeof(linear_size_chunk) - sizeof(linear_header))
 591
 592 /* Allocate the linear buffer with its header. */
 593 static linear_header *
 594 create_linear_node(void *ralloc_ctx, unsigned min_size)
 595 {
 596    linear_header *node;
 597
 598    min_size += sizeof(linear_size_chunk);
 599
 600    if (likely(min_size < MIN_LINEAR_BUFSIZE))
 601       min_size = MIN_LINEAR_BUFSIZE;
 602
 603    node = ralloc_size(ralloc_ctx, sizeof(linear_header) + min_size);
 604    if (unlikely(!node))
 605       return NULL;
 606
 607 #ifdef DEBUG
 608    node->magic = LMAGIC;
 609 #endif
 610    node->offset = 0;
 611    node->size = min_size;
 612    node->ralloc_parent = ralloc_ctx;
 613    node->next = NULL;
 614    node->latest = node;
 615    return node;
 616 }
 617
 618 void *
 619 linear_alloc_child(void *parent, unsigned size)
 620 {
 621    linear_header *first = LINEAR_PARENT_TO_HEADER(parent);
 622    linear_header *latest = first->latest;
 623    linear_header *new_node;
 624    linear_size_chunk *ptr;
 625    unsigned full_size;
 626
 627    assert(first->magic == LMAGIC);
 628    assert(!latest->next);
 629
 630    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 631    full_size = sizeof(linear_size_chunk) + size;
 632
 633    if (unlikely(latest->offset + full_size > latest->size)) {
 634       /* allocate a new node */
 635       new_node = create_linear_node(latest->ralloc_parent, size);
 636       if (unlikely(!new_node))
 637          return NULL;
 638
 639       first->latest = new_node;
 640       latest->latest = new_node;
 641       latest->next = new_node;
 642       latest = new_node;
 643    }
 644
 645    ptr = (linear_size_chunk *)((char*)&latest[1] + latest->offset);
 646    ptr->size = size;
 647    latest->offset += full_size;
 648    return &ptr[1];
 649 }
 650
 651 void *
 652 linear_alloc_parent(void *ralloc_ctx, unsigned size)
 653 {
 654    linear_header *node;
 655
 656    if (unlikely(!ralloc_ctx))
 657       return NULL;
 658
 659    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 660
 661    node = create_linear_node(ralloc_ctx, size);
 662    if (unlikely(!node))
 663       return NULL;
 664
 665    return linear_alloc_child((char*)node +
 666                              sizeof(linear_header) +
 667                              sizeof(linear_size_chunk), size);
 668 }
 669
 670 void *
 671 linear_zalloc_child(void *parent, unsigned size)
 672 {
 673    void *ptr = linear_alloc_child(parent, size);
 674
 675    if (likely(ptr))
 676       memset(ptr, 0, size);
 677    return ptr;
 678 }
 679
 680 void *
 681 linear_zalloc_parent(void *parent, unsigned size)
 682 {
 683    void *ptr = linear_alloc_parent(parent, size);
 684
 685    if (likely(ptr))
 686       memset(ptr, 0, size);
 687    return ptr;
 688 }
 689
 690 void
 691 linear_free_parent(void *ptr)
 692 {
 693    linear_header *node;
 694
 695    if (unlikely(!ptr))
 696       return;
 697
 698    node = LINEAR_PARENT_TO_HEADER(ptr);
 699    assert(node->magic == LMAGIC);
 700
 701    while (node) {
 702       void *ptr = node;
 703
 704       node = node->next;
 705       ralloc_free(ptr);
 706    }
 707 }
 708
 709 void
 710 ralloc_steal_linear_parent(void *new_ralloc_ctx, void *ptr)
 711 {
 712    linear_header *node;
 713
 714    if (unlikely(!ptr))
 715       return;
 716
 717    node = LINEAR_PARENT_TO_HEADER(ptr);
 718    assert(node->magic == LMAGIC);
 719
 720    while (node) {
 721       ralloc_steal(new_ralloc_ctx, node);
 722       node->ralloc_parent = new_ralloc_ctx;
 723       node = node->next;
 724    }
 725 }
 726
 727 void *
 728 ralloc_parent_of_linear_parent(void *ptr)
 729 {
 730    linear_header *node = LINEAR_PARENT_TO_HEADER(ptr);
 731    assert(node->magic == LMAGIC);
 732    return node->ralloc_parent;
 733 }
 734
 735 void *
 736 linear_realloc(void *parent, void *old, unsigned new_size)
 737 {
 738    unsigned old_size = 0;
 739    ralloc_header *new_ptr;
 740
 741    new_ptr = linear_alloc_child(parent, new_size);
 742
 743    if (unlikely(!old))
 744       return new_ptr;
 745
 746    old_size = ((linear_size_chunk*)old)[-1].size;
 747
 748    if (likely(new_ptr && old_size))
 749       memcpy(new_ptr, old, MIN2(old_size, new_size));
 750
 751    return new_ptr;
 752 }
 753
 754 /* All code below is pretty much copied from ralloc and only the alloc
 755  * calls are different.
 756  */
 757
 758 char *
 759 linear_strdup(void *parent, const char *str)
 760 {
 761    unsigned n;
 762    char *ptr;
 763
 764    if (unlikely(!str))
 765       return NULL;
 766
 767    n = strlen(str);
 768    ptr = linear_alloc_child(parent, n + 1);
 769    if (unlikely(!ptr))
 770       return NULL;
 771
 772    memcpy(ptr, str, n);
 773    ptr[n] = '\0';
 774    return ptr;
 775 }
 776
 777 char *
 778 linear_asprintf(void *parent, const char *fmt, ...)
 779 {
 780    char *ptr;
 781    va_list args;
 782    va_start(args, fmt);
 783    ptr = linear_vasprintf(parent, fmt, args);
 784    va_end(args);
 785    return ptr;
 786 }
 787
 788 char *
 789 linear_vasprintf(void *parent, const char *fmt, va_list args)
 790 {
 791    unsigned size = printf_length(fmt, args) + 1;
 792
 793    char *ptr = linear_alloc_child(parent, size);
 794    if (ptr != NULL)
 795       vsnprintf(ptr, size, fmt, args);
 796
 797    return ptr;
 798 }
 799
 800 bool
 801 linear_asprintf_append(void *parent, char **str, const char *fmt, ...)
 802 {
 803    bool success;
 804    va_list args;
 805    va_start(args, fmt);
 806    success = linear_vasprintf_append(parent, str, fmt, args);
 807    va_end(args);
 808    return success;
 809 }
 810
 811 bool
 812 linear_vasprintf_append(void *parent, char **str, const char *fmt, va_list args)
 813 {
 814    size_t existing_length;
 815    assert(str != NULL);
 816    existing_length = *str ? strlen(*str) : 0;
 817    return linear_vasprintf_rewrite_tail(parent, str, &existing_length, fmt, args);
 818 }
 819
 820 bool
 821 linear_asprintf_rewrite_tail(void *parent, char **str, size_t *start,
 822                              const char *fmt, ...)
 823 {
 824    bool success;
 825    va_list args;
 826    va_start(args, fmt);
 827    success = linear_vasprintf_rewrite_tail(parent, str, start, fmt, args);
 828    va_end(args);
 829    return success;
 830 }
 831
 832 bool
 833 linear_vasprintf_rewrite_tail(void *parent, char **str, size_t *start,
 834                               const char *fmt, va_list args)
 835 {
 836    size_t new_length;
 837    char *ptr;
 838
 839    assert(str != NULL);
 840
 841    if (unlikely(*str == NULL)) {
 842       *str = linear_vasprintf(parent, fmt, args);
 843       *start = strlen(*str);
 844       return true;
 845    }
 846
 847    new_length = printf_length(fmt, args);
 848
 849    ptr = linear_realloc(parent, *str, *start + new_length + 1);
 850    if (unlikely(ptr == NULL))
 851       return false;
 852
 853    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 854    *str = ptr;
 855    *start += new_length;
 856    return true;
 857 }
 858
 859 /* helper routine for strcat/strncat - n is the exact amount to copy */
 860 static bool
 861 linear_cat(void *parent, char **dest, const char *str, unsigned n)
 862 {
 863    char *both;
 864    unsigned existing_length;
 865    assert(dest != NULL && *dest != NULL);
 866
 867    existing_length = strlen(*dest);
 868    both = linear_realloc(parent, *dest, existing_length + n + 1);
 869    if (unlikely(both == NULL))
 870       return false;
 871
 872    memcpy(both + existing_length, str, n);
 873    both[existing_length + n] = '\0';
 874
 875    *dest = both;
 876    return true;
 877 }
 878
 879 bool
 880 linear_strcat(void *parent, char **dest, const char *str)
 881 {
 882    return linear_cat(parent, dest, str, strlen(str));
 883 }