1/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18/* Mark symbols hidden in static PIE for early self relocation to work. */
19#if BUILD_PIE_DEFAULT
20# pragma GCC visibility push(hidden)
21#endif
22#include <errno.h>
23#include <libc-internal.h>
24#include <stdbool.h>
25#include <stdint.h>
26#include <unistd.h>
27
28/* Defined in brk.c. */
29extern void *__curbrk;
30extern int __brk (void *addr);
31
32/* Extend the process's data space by INCREMENT.
33 If INCREMENT is negative, shrink data space by - INCREMENT.
34 Return start of new space allocated, or -1 for errors. */
35void *
36__sbrk (intptr_t increment)
37{
38 /* Controls whether __brk (0) is called to read the brk value from
39 the kernel. */
40 bool update_brk = __curbrk == NULL;
41
42#if defined (SHARED) && ! IS_IN (rtld)
43 if (!__libc_initial)
44 {
45 if (increment != 0)
46 {
47 /* Do not allow changing the brk from an inner libc because
48 it cannot be synchronized with the outer libc's brk. */
49 __set_errno (ENOMEM);
50 return (void *) -1;
51 }
52 /* Querying the kernel's brk value from an inner namespace is
53 fine. */
54 update_brk = true;
55 }
56#endif
57
58 if (update_brk)
59 if (__brk (0) < 0) /* Initialize the break. */
60 return (void *) -1;
61
62 if (increment == 0)
63 return __curbrk;
64
65 void *oldbrk = __curbrk;
66 if (increment > 0
67 ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
68 : ((uintptr_t) oldbrk < (uintptr_t) -increment))
69 {
70 __set_errno (ENOMEM);
71 return (void *) -1;
72 }
73
74 if (__brk (oldbrk + increment) < 0)
75 return (void *) -1;
76
77 return oldbrk;
78}
79libc_hidden_def (__sbrk)
80weak_alias (__sbrk, sbrk)
81

source code of glibc/misc/sbrk.c