misc/sbrk.c

   1 /* Copyright (C) 1991-2020 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 #include <errno.h>
  19 #include <stdint.h>
  20 #include <unistd.h>
  21 #include <libc-internal.h>
  22
  23 /* Defined in brk.c.  */
  24 extern void *__curbrk;
  25 extern int __brk (void *addr);
  26
  27 /* Extend the process's data space by INCREMENT.
  28    If INCREMENT is negative, shrink data space by - INCREMENT.
  29    Return start of new space allocated, or -1 for errors.  */
  30 void *
  31 __sbrk (intptr_t increment)
  32 {
  33   void *oldbrk;
  34
  35   /* If this is not part of the dynamic library or the library is used
  36      via dynamic loading in a statically linked program update
  37      __curbrk from the kernel's brk value.  That way two separate
  38      instances of __brk and __sbrk can share the heap, returning
  39      interleaved pieces of it.  */
  40   if (__curbrk == NULL || __libc_multiple_libcs)
  41     if (__brk (0) < 0)          /* Initialize the break.  */
  42       return (void *) -1;
  43
  44   if (increment == 0)
  45     return __curbrk;
  46
  47   oldbrk = __curbrk;
  48   if (increment > 0
  49       ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
  50       : ((uintptr_t) oldbrk < (uintptr_t) -increment))
  51     {
  52       __set_errno (ENOMEM);
  53       return (void *) -1;
  54     }
  55
  56   if (__brk (oldbrk + increment) < 0)
  57     return (void *) -1;
  58
  59   return oldbrk;
  60 }
  61 libc_hidden_def (__sbrk)
  62 weak_alias (__sbrk, sbrk)