brk.cpp revision 738b0cc5e95a9a650e9621603f4dd8dd16b07568 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <errno.h>
30#include <unistd.h>
31
32#if __LP64__
33static void* __bionic_brk;
34#else
35void* __bionic_brk; // Accidentally exported by the NDK.
36#endif
37
38int brk(void* end_data) {
39  __bionic_brk = __brk(end_data);
40  if (__bionic_brk < end_data) {
41    errno = ENOMEM;
42    return -1;
43  }
44  return 0;
45}
46
47void* sbrk(ptrdiff_t increment) {
48  // Initialize __bionic_brk if necessary.
49  if (__bionic_brk == NULL) {
50    __bionic_brk = __brk(NULL);
51  }
52
53  // Don't ask the kernel if we already know the answer.
54  if (increment == 0) {
55    return __bionic_brk;
56  }
57
58  // Avoid overflow.
59  uintptr_t old_brk = reinterpret_cast<uintptr_t>(__bionic_brk);
60  if ((increment > 0 && static_cast<uintptr_t>(increment) > (UINTPTR_MAX - old_brk)) ||
61      (increment < 0 && static_cast<uintptr_t>(-increment) > old_brk)) {
62    errno = ENOMEM;
63    return reinterpret_cast<void*>(-1);
64  }
65
66  void* desired_brk = reinterpret_cast<void*>(old_brk + increment);
67  __bionic_brk = __brk(desired_brk);
68  if (__bionic_brk < desired_brk) {
69    errno = ENOMEM;
70    return reinterpret_cast<void*>(-1);
71  }
72
73  return reinterpret_cast<void*>(old_brk);
74}
75