misc/sbrk.c

   1 /* Copyright (C) 1991-2014 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    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <stdint.h>
  20 #include <unistd.h>
  21
  22 /* Defined in brk.c.  */
  23 extern void *__curbrk;
  24 extern int __brk (void *addr);
  25
  26 /* Defined in init-first.c.  */
  27 extern int __libc_multiple_libcs attribute_hidden;
  28
  29 /* Extend the process's data space by INCREMENT.
  30    If INCREMENT is negative, shrink data space by - INCREMENT.
  31    Return start of new space allocated, or -1 for errors.  */
  32 void *
  33 __sbrk (intptr_t increment)
  34 {
  35   void *oldbrk;
  36
  37   /* If this is not part of the dynamic library or the library is used
  38      via dynamic loading in a statically linked program update
  39      __curbrk from the kernel's brk value.  That way two separate
  40      instances of __brk and __sbrk can share the heap, returning
  41      interleaved pieces of it.  */
  42   if (__curbrk == NULL || __libc_multiple_libcs)
  43     if (__brk (0) < 0)          /* Initialize the break.  */
  44       return (void *) -1;
  45
  46   if (increment == 0)
  47     return __curbrk;
  48
  49   oldbrk = __curbrk;
  50   if ((increment > 0
  51        ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
  52        : ((uintptr_t) oldbrk < (uintptr_t) -increment))
  53       || __brk (oldbrk + increment) < 0)
  54     return (void *) -1;
  55
  56   return oldbrk;
  57 }
  58 libc_hidden_def (__sbrk)
  59 weak_alias (__sbrk, sbrk)