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 /* Align the header's size so that ralloc() allocations will return with the
  55  * same alignment as a libc malloc would have (8 on 32-bit GLIBC, 16 on
  56  * 64-bit), avoiding performance penalities on x86 and alignment faults on
  57  * ARM.
  58  */
  59 struct
  60 #ifdef _MSC_VER
  61  __declspec(align(8))
  62 #else
  63  __attribute__((aligned))
  64 #endif
  65    ralloc_header
  66 {
  67 #ifdef DEBUG
  68    /* A canary value used to determine whether a pointer is ralloc'd. */
  69    unsigned canary;
  70 #endif
  71
  72    struct ralloc_header *parent;
  73
  74    /* The first child (head of a linked list) */
  75    struct ralloc_header *child;
  76
  77    /* Linked list of siblings */
  78    struct ralloc_header *prev;
  79    struct ralloc_header *next;
  80
  81    void (*destructor)(void *);
  82 };
  83
  84 typedef struct ralloc_header ralloc_header;
  85
  86 static void unlink_block(ralloc_header *info);
  87 static void unsafe_free(ralloc_header *info);
  88
  89 static ralloc_header *
  90 get_header(const void *ptr)
  91 {
  92    ralloc_header *info = (ralloc_header *) (((char *) ptr) -
  93                                             sizeof(ralloc_header));
  94 #ifdef DEBUG
  95    assert(info->canary == CANARY);
  96 #endif
  97    return info;
  98 }
  99
 100 #define PTR_FROM_HEADER(info) (((char *) info) + sizeof(ralloc_header))
 101
 102 static void
 103 add_child(ralloc_header *parent, ralloc_header *info)
 104 {
 105    if (parent != NULL) {
 106       info->parent = parent;
 107       info->next = parent->child;
 108       parent->child = info;
 109
 110       if (info->next != NULL)
 111          info->next->prev = info;
 112    }
 113 }
 114
 115 void *
 116 ralloc_context(const void *ctx)
 117 {
 118    return ralloc_size(ctx, 0);
 119 }
 120
 121 void *
 122 ralloc_size(const void *ctx, size_t size)
 123 {
 124    void *block = malloc(size + sizeof(ralloc_header));
 125    ralloc_header *info;
 126    ralloc_header *parent;
 127
 128    if (unlikely(block == NULL))
 129       return NULL;
 130
 131    info = (ralloc_header *) block;
 132    /* measurements have shown that calloc is slower (because of
 133     * the multiplication overflow checking?), so clear things
 134     * manually
 135     */
 136    info->parent = NULL;
 137    info->child = NULL;
 138    info->prev = NULL;
 139    info->next = NULL;
 140    info->destructor = NULL;
 141
 142    parent = ctx != NULL ? get_header(ctx) : NULL;
 143
 144    add_child(parent, info);
 145
 146 #ifdef DEBUG
 147    info->canary = CANARY;
 148 #endif
 149
 150    return PTR_FROM_HEADER(info);
 151 }
 152
 153 void *
 154 rzalloc_size(const void *ctx, size_t size)
 155 {
 156    void *ptr = ralloc_size(ctx, size);
 157
 158    if (likely(ptr))
 159       memset(ptr, 0, size);
 160
 161    return ptr;
 162 }
 163
 164 /* helper function - assumes ptr != NULL */
 165 static void *
 166 resize(void *ptr, size_t size)
 167 {
 168    ralloc_header *child, *old, *info;
 169
 170    old = get_header(ptr);
 171    info = realloc(old, size + sizeof(ralloc_header));
 172
 173    if (info == NULL)
 174       return NULL;
 175
 176    /* Update parent and sibling's links to the reallocated node. */
 177    if (info != old && info->parent != NULL) {
 178       if (info->parent->child == old)
 179          info->parent->child = info;
 180
 181       if (info->prev != NULL)
 182          info->prev->next = info;
 183
 184       if (info->next != NULL)
 185          info->next->prev = info;
 186    }
 187
 188    /* Update child->parent links for all children */
 189    for (child = info->child; child != NULL; child = child->next)
 190       child->parent = info;
 191
 192    return PTR_FROM_HEADER(info);
 193 }
 194
 195 void *
 196 reralloc_size(const void *ctx, void *ptr, size_t size)
 197 {
 198    if (unlikely(ptr == NULL))
 199       return ralloc_size(ctx, size);
 200
 201    assert(ralloc_parent(ptr) == ctx);
 202    return resize(ptr, size);
 203 }
 204
 205 void *
 206 ralloc_array_size(const void *ctx, size_t size, unsigned count)
 207 {
 208    if (count > SIZE_MAX/size)
 209       return NULL;
 210
 211    return ralloc_size(ctx, size * count);
 212 }
 213
 214 void *
 215 rzalloc_array_size(const void *ctx, size_t size, unsigned count)
 216 {
 217    if (count > SIZE_MAX/size)
 218       return NULL;
 219
 220    return rzalloc_size(ctx, size * count);
 221 }
 222
 223 void *
 224 reralloc_array_size(const void *ctx, void *ptr, size_t size, unsigned count)
 225 {
 226    if (count > SIZE_MAX/size)
 227       return NULL;
 228
 229    return reralloc_size(ctx, ptr, size * count);
 230 }
 231
 232 void
 233 ralloc_free(void *ptr)
 234 {
 235    ralloc_header *info;
 236
 237    if (ptr == NULL)
 238       return;
 239
 240    info = get_header(ptr);
 241    unlink_block(info);
 242    unsafe_free(info);
 243 }
 244
 245 static void
 246 unlink_block(ralloc_header *info)
 247 {
 248    /* Unlink from parent & siblings */
 249    if (info->parent != NULL) {
 250       if (info->parent->child == info)
 251          info->parent->child = info->next;
 252
 253       if (info->prev != NULL)
 254          info->prev->next = info->next;
 255
 256       if (info->next != NULL)
 257          info->next->prev = info->prev;
 258    }
 259    info->parent = NULL;
 260    info->prev = NULL;
 261    info->next = NULL;
 262 }
 263
 264 static void
 265 unsafe_free(ralloc_header *info)
 266 {
 267    /* Recursively free any children...don't waste time unlinking them. */
 268    ralloc_header *temp;
 269    while (info->child != NULL) {
 270       temp = info->child;
 271       info->child = temp->next;
 272       unsafe_free(temp);
 273    }
 274
 275    /* Free the block itself.  Call the destructor first, if any. */
 276    if (info->destructor != NULL)
 277       info->destructor(PTR_FROM_HEADER(info));
 278
 279    free(info);
 280 }
 281
 282 void
 283 ralloc_steal(const void *new_ctx, void *ptr)
 284 {
 285    ralloc_header *info, *parent;
 286
 287    if (unlikely(ptr == NULL))
 288       return;
 289
 290    info = get_header(ptr);
 291    parent = get_header(new_ctx);
 292
 293    unlink_block(info);
 294
 295    add_child(parent, info);
 296 }
 297
 298 void
 299 ralloc_adopt(const void *new_ctx, void *old_ctx)
 300 {
 301    ralloc_header *new_info, *old_info, *child;
 302
 303    if (unlikely(old_ctx == NULL))
 304       return;
 305
 306    old_info = get_header(old_ctx);
 307    new_info = get_header(new_ctx);
 308
 309    /* If there are no children, bail. */
 310    if (unlikely(old_info->child == NULL))
 311       return;
 312
 313    /* Set all the children's parent to new_ctx; get a pointer to the last child. */
 314    for (child = old_info->child; child->next != NULL; child = child->next) {
 315       child->parent = new_info;
 316    }
 317
 318    /* Connect the two lists together; parent them to new_ctx; make old_ctx empty. */
 319    child->next = new_info->child;
 320    child->parent = new_info;
 321    new_info->child = old_info->child;
 322    old_info->child = NULL;
 323 }
 324
 325 void *
 326 ralloc_parent(const void *ptr)
 327 {
 328    ralloc_header *info;
 329
 330    if (unlikely(ptr == NULL))
 331       return NULL;
 332
 333    info = get_header(ptr);
 334    return info->parent ? PTR_FROM_HEADER(info->parent) : NULL;
 335 }
 336
 337 void
 338 ralloc_set_destructor(const void *ptr, void(*destructor)(void *))
 339 {
 340    ralloc_header *info = get_header(ptr);
 341    info->destructor = destructor;
 342 }
 343
 344 char *
 345 ralloc_strdup(const void *ctx, const char *str)
 346 {
 347    size_t n;
 348    char *ptr;
 349
 350    if (unlikely(str == NULL))
 351       return NULL;
 352
 353    n = strlen(str);
 354    ptr = ralloc_array(ctx, char, n + 1);
 355    memcpy(ptr, str, n);
 356    ptr[n] = '\0';
 357    return ptr;
 358 }
 359
 360 char *
 361 ralloc_strndup(const void *ctx, const char *str, size_t max)
 362 {
 363    size_t n;
 364    char *ptr;
 365
 366    if (unlikely(str == NULL))
 367       return NULL;
 368
 369    n = strnlen(str, max);
 370    ptr = ralloc_array(ctx, char, n + 1);
 371    memcpy(ptr, str, n);
 372    ptr[n] = '\0';
 373    return ptr;
 374 }
 375
 376 /* helper routine for strcat/strncat - n is the exact amount to copy */
 377 static bool
 378 cat(char **dest, const char *str, size_t n)
 379 {
 380    char *both;
 381    size_t existing_length;
 382    assert(dest != NULL && *dest != NULL);
 383
 384    existing_length = strlen(*dest);
 385    both = resize(*dest, existing_length + n + 1);
 386    if (unlikely(both == NULL))
 387       return false;
 388
 389    memcpy(both + existing_length, str, n);
 390    both[existing_length + n] = '\0';
 391
 392    *dest = both;
 393    return true;
 394 }
 395
 396
 397 bool
 398 ralloc_strcat(char **dest, const char *str)
 399 {
 400    return cat(dest, str, strlen(str));
 401 }
 402
 403 bool
 404 ralloc_strncat(char **dest, const char *str, size_t n)
 405 {
 406    /* Clamp n to the string length */
 407    size_t str_length = strlen(str);
 408    if (str_length < n)
 409       n = str_length;
 410
 411    return cat(dest, str, n);
 412 }
 413
 414 char *
 415 ralloc_asprintf(const void *ctx, const char *fmt, ...)
 416 {
 417    char *ptr;
 418    va_list args;
 419    va_start(args, fmt);
 420    ptr = ralloc_vasprintf(ctx, fmt, args);
 421    va_end(args);
 422    return ptr;
 423 }
 424
 425 /* Return the length of the string that would be generated by a printf-style
 426  * format and argument list, not including the \0 byte.
 427  */
 428 static size_t
 429 printf_length(const char *fmt, va_list untouched_args)
 430 {
 431    int size;
 432    char junk;
 433
 434    /* Make a copy of the va_list so the original caller can still use it */
 435    va_list args;
 436    va_copy(args, untouched_args);
 437
 438 #ifdef _WIN32
 439    /* We need to use _vcsprintf to calculate the size as vsnprintf returns -1
 440     * if the number of characters to write is greater than count.
 441     */
 442    size = _vscprintf(fmt, args);
 443    (void)junk;
 444 #else
 445    size = vsnprintf(&junk, 1, fmt, args);
 446 #endif
 447    assert(size >= 0);
 448
 449    va_end(args);
 450
 451    return size;
 452 }
 453
 454 char *
 455 ralloc_vasprintf(const void *ctx, const char *fmt, va_list args)
 456 {
 457    size_t size = printf_length(fmt, args) + 1;
 458
 459    char *ptr = ralloc_size(ctx, size);
 460    if (ptr != NULL)
 461       vsnprintf(ptr, size, fmt, args);
 462
 463    return ptr;
 464 }
 465
 466 bool
 467 ralloc_asprintf_append(char **str, const char *fmt, ...)
 468 {
 469    bool success;
 470    va_list args;
 471    va_start(args, fmt);
 472    success = ralloc_vasprintf_append(str, fmt, args);
 473    va_end(args);
 474    return success;
 475 }
 476
 477 bool
 478 ralloc_vasprintf_append(char **str, const char *fmt, va_list args)
 479 {
 480    size_t existing_length;
 481    assert(str != NULL);
 482    existing_length = *str ? strlen(*str) : 0;
 483    return ralloc_vasprintf_rewrite_tail(str, &existing_length, fmt, args);
 484 }
 485
 486 bool
 487 ralloc_asprintf_rewrite_tail(char **str, size_t *start, const char *fmt, ...)
 488 {
 489    bool success;
 490    va_list args;
 491    va_start(args, fmt);
 492    success = ralloc_vasprintf_rewrite_tail(str, start, fmt, args);
 493    va_end(args);
 494    return success;
 495 }
 496
 497 bool
 498 ralloc_vasprintf_rewrite_tail(char **str, size_t *start, const char *fmt,
 499                               va_list args)
 500 {
 501    size_t new_length;
 502    char *ptr;
 503
 504    assert(str != NULL);
 505
 506    if (unlikely(*str == NULL)) {
 507       // Assuming a NULL context is probably bad, but it's expected behavior.
 508       *str = ralloc_vasprintf(NULL, fmt, args);
 509       *start = strlen(*str);
 510       return true;
 511    }
 512
 513    new_length = printf_length(fmt, args);
 514
 515    ptr = resize(*str, *start + new_length + 1);
 516    if (unlikely(ptr == NULL))
 517       return false;
 518
 519    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 520    *str = ptr;
 521    *start += new_length;
 522    return true;
 523 }
 524
 525 /***************************************************************************
 526  * Linear allocator for short-lived allocations.
 527  ***************************************************************************
 528  *
 529  * The allocator consists of a parent node (2K buffer), which requires
 530  * a ralloc parent, and child nodes (allocations). Child nodes can't be freed
 531  * directly, because the parent doesn't track them. You have to release
 532  * the parent node in order to release all its children.
 533  *
 534  * The allocator uses a fixed-sized buffer with a monotonically increasing
 535  * offset after each allocation. If the buffer is all used, another buffer
 536  * is allocated, sharing the same ralloc parent, so all buffers are at
 537  * the same level in the ralloc hierarchy.
 538  *
 539  * The linear parent node is always the first buffer and keeps track of all
 540  * other buffers.
 541  */
 542
 543 #define ALIGN_POT(x, y) (((x) + (y) - 1) & ~((y) - 1))
 544
 545 #define MIN_LINEAR_BUFSIZE 2048
 546 #define SUBALLOC_ALIGNMENT sizeof(uintptr_t)
 547 #define LMAGIC 0x87b9c7d3
 548
 549 struct linear_header {
 550 #ifdef DEBUG
 551    unsigned magic;   /* for debugging */
 552 #endif
 553    unsigned offset;  /* points to the first unused byte in the buffer */
 554    unsigned size;    /* size of the buffer */
 555    void *ralloc_parent;          /* new buffers will use this */
 556    struct linear_header *next;   /* next buffer if we have more */
 557    struct linear_header *latest; /* the only buffer that has free space */
 558
 559    /* After this structure, the buffer begins.
 560     * Each suballocation consists of linear_size_chunk as its header followed
 561     * by the suballocation, so it goes:
 562     *
 563     * - linear_size_chunk
 564     * - allocated space
 565     * - linear_size_chunk
 566     * - allocated space
 567     * etc.
 568     *
 569     * linear_size_chunk is only needed by linear_realloc.
 570     */
 571 };
 572
 573 struct linear_size_chunk {
 574    unsigned size; /* for realloc */
 575    unsigned _padding;
 576 };
 577
 578 typedef struct linear_header linear_header;
 579 typedef struct linear_size_chunk linear_size_chunk;
 580
 581 #define LINEAR_PARENT_TO_HEADER(parent) \
 582    (linear_header*) \
 583    ((char*)(parent) - sizeof(linear_size_chunk) - sizeof(linear_header))
 584
 585 /* Allocate the linear buffer with its header. */
 586 static linear_header *
 587 create_linear_node(void *ralloc_ctx, unsigned min_size)
 588 {
 589    linear_header *node;
 590
 591    min_size += sizeof(linear_size_chunk);
 592
 593    if (likely(min_size < MIN_LINEAR_BUFSIZE))
 594       min_size = MIN_LINEAR_BUFSIZE;
 595
 596    node = ralloc_size(ralloc_ctx, sizeof(linear_header) + min_size);
 597    if (unlikely(!node))
 598       return NULL;
 599
 600 #ifdef DEBUG
 601    node->magic = LMAGIC;
 602 #endif
 603    node->offset = 0;
 604    node->size = min_size;
 605    node->ralloc_parent = ralloc_ctx;
 606    node->next = NULL;
 607    node->latest = node;
 608    return node;
 609 }
 610
 611 void *
 612 linear_alloc_child(void *parent, unsigned size)
 613 {
 614    linear_header *first = LINEAR_PARENT_TO_HEADER(parent);
 615    linear_header *latest = first->latest;
 616    linear_header *new_node;
 617    linear_size_chunk *ptr;
 618    unsigned full_size;
 619
 620    assert(first->magic == LMAGIC);
 621    assert(!latest->next);
 622
 623    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 624    full_size = sizeof(linear_size_chunk) + size;
 625
 626    if (unlikely(latest->offset + full_size > latest->size)) {
 627       /* allocate a new node */
 628       new_node = create_linear_node(latest->ralloc_parent, size);
 629       if (unlikely(!new_node))
 630          return NULL;
 631
 632       first->latest = new_node;
 633       latest->latest = new_node;
 634       latest->next = new_node;
 635       latest = new_node;
 636    }
 637
 638    ptr = (linear_size_chunk *)((char*)&latest[1] + latest->offset);
 639    ptr->size = size;
 640    latest->offset += full_size;
 641    return &ptr[1];
 642 }
 643
 644 void *
 645 linear_alloc_parent(void *ralloc_ctx, unsigned size)
 646 {
 647    linear_header *node;
 648
 649    if (unlikely(!ralloc_ctx))
 650       return NULL;
 651
 652    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 653
 654    node = create_linear_node(ralloc_ctx, size);
 655    if (unlikely(!node))
 656       return NULL;
 657
 658    return linear_alloc_child((char*)node +
 659                              sizeof(linear_header) +
 660                              sizeof(linear_size_chunk), size);
 661 }
 662
 663 void *
 664 linear_zalloc_child(void *parent, unsigned size)
 665 {
 666    void *ptr = linear_alloc_child(parent, size);
 667
 668    if (likely(ptr))
 669       memset(ptr, 0, size);
 670    return ptr;
 671 }
 672
 673 void *
 674 linear_zalloc_parent(void *parent, unsigned size)
 675 {
 676    void *ptr = linear_alloc_parent(parent, size);
 677
 678    if (likely(ptr))
 679       memset(ptr, 0, size);
 680    return ptr;
 681 }
 682
 683 void
 684 linear_free_parent(void *ptr)
 685 {
 686    linear_header *node;
 687
 688    if (unlikely(!ptr))
 689       return;
 690
 691    node = LINEAR_PARENT_TO_HEADER(ptr);
 692    assert(node->magic == LMAGIC);
 693
 694    while (node) {
 695       void *ptr = node;
 696
 697       node = node->next;
 698       ralloc_free(ptr);
 699    }
 700 }
 701
 702 void
 703 ralloc_steal_linear_parent(void *new_ralloc_ctx, void *ptr)
 704 {
 705    linear_header *node;
 706
 707    if (unlikely(!ptr))
 708       return;
 709
 710    node = LINEAR_PARENT_TO_HEADER(ptr);
 711    assert(node->magic == LMAGIC);
 712
 713    while (node) {
 714       ralloc_steal(new_ralloc_ctx, node);
 715       node->ralloc_parent = new_ralloc_ctx;
 716       node = node->next;
 717    }
 718 }
 719
 720 void *
 721 ralloc_parent_of_linear_parent(void *ptr)
 722 {
 723    linear_header *node = LINEAR_PARENT_TO_HEADER(ptr);
 724    assert(node->magic == LMAGIC);
 725    return node->ralloc_parent;
 726 }
 727
 728 void *
 729 linear_realloc(void *parent, void *old, unsigned new_size)
 730 {
 731    unsigned old_size = 0;
 732    ralloc_header *new_ptr;
 733
 734    new_ptr = linear_alloc_child(parent, new_size);
 735
 736    if (unlikely(!old))
 737       return new_ptr;
 738
 739    old_size = ((linear_size_chunk*)old)[-1].size;
 740
 741    if (likely(new_ptr && old_size))
 742       memcpy(new_ptr, old, MIN2(old_size, new_size));
 743
 744    return new_ptr;
 745 }
 746
 747 /* All code below is pretty much copied from ralloc and only the alloc
 748  * calls are different.
 749  */
 750
 751 char *
 752 linear_strdup(void *parent, const char *str)
 753 {
 754    unsigned n;
 755    char *ptr;
 756
 757    if (unlikely(!str))
 758       return NULL;
 759
 760    n = strlen(str);
 761    ptr = linear_alloc_child(parent, n + 1);
 762    if (unlikely(!ptr))
 763       return NULL;
 764
 765    memcpy(ptr, str, n);
 766    ptr[n] = '\0';
 767    return ptr;
 768 }
 769
 770 char *
 771 linear_asprintf(void *parent, const char *fmt, ...)
 772 {
 773    char *ptr;
 774    va_list args;
 775    va_start(args, fmt);
 776    ptr = linear_vasprintf(parent, fmt, args);
 777    va_end(args);
 778    return ptr;
 779 }
 780
 781 char *
 782 linear_vasprintf(void *parent, const char *fmt, va_list args)
 783 {
 784    unsigned size = printf_length(fmt, args) + 1;
 785
 786    char *ptr = linear_alloc_child(parent, size);
 787    if (ptr != NULL)
 788       vsnprintf(ptr, size, fmt, args);
 789
 790    return ptr;
 791 }
 792
 793 bool
 794 linear_asprintf_append(void *parent, char **str, const char *fmt, ...)
 795 {
 796    bool success;
 797    va_list args;
 798    va_start(args, fmt);
 799    success = linear_vasprintf_append(parent, str, fmt, args);
 800    va_end(args);
 801    return success;
 802 }
 803
 804 bool
 805 linear_vasprintf_append(void *parent, char **str, const char *fmt, va_list args)
 806 {
 807    size_t existing_length;
 808    assert(str != NULL);
 809    existing_length = *str ? strlen(*str) : 0;
 810    return linear_vasprintf_rewrite_tail(parent, str, &existing_length, fmt, args);
 811 }
 812
 813 bool
 814 linear_asprintf_rewrite_tail(void *parent, char **str, size_t *start,
 815                              const char *fmt, ...)
 816 {
 817    bool success;
 818    va_list args;
 819    va_start(args, fmt);
 820    success = linear_vasprintf_rewrite_tail(parent, str, start, fmt, args);
 821    va_end(args);
 822    return success;
 823 }
 824
 825 bool
 826 linear_vasprintf_rewrite_tail(void *parent, char **str, size_t *start,
 827                               const char *fmt, va_list args)
 828 {
 829    size_t new_length;
 830    char *ptr;
 831
 832    assert(str != NULL);
 833
 834    if (unlikely(*str == NULL)) {
 835       *str = linear_vasprintf(parent, fmt, args);
 836       *start = strlen(*str);
 837       return true;
 838    }
 839
 840    new_length = printf_length(fmt, args);
 841
 842    ptr = linear_realloc(parent, *str, *start + new_length + 1);
 843    if (unlikely(ptr == NULL))
 844       return false;
 845
 846    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 847    *str = ptr;
 848    *start += new_length;
 849    return true;
 850 }
 851
 852 /* helper routine for strcat/strncat - n is the exact amount to copy */
 853 static bool
 854 linear_cat(void *parent, char **dest, const char *str, unsigned n)
 855 {
 856    char *both;
 857    unsigned existing_length;
 858    assert(dest != NULL && *dest != NULL);
 859
 860    existing_length = strlen(*dest);
 861    both = linear_realloc(parent, *dest, existing_length + n + 1);
 862    if (unlikely(both == NULL))
 863       return false;
 864
 865    memcpy(both + existing_length, str, n);
 866    both[existing_length + n] = '\0';
 867
 868    *dest = both;
 869    return true;
 870 }
 871
 872 bool
 873 linear_strcat(void *parent, char **dest, const char *str)
 874 {
 875    return linear_cat(parent, dest, str, strlen(str));
 876 }