sysdeps/generic/sbrk.c

   1 /* Copyright (C) 1991, 1995, 1996 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 modify
   5 it under the terms of the GNU General Public License as published by
   6 the Free Software Foundation; either version 2, or (at your option)
   7 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
  12 GNU General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with the GNU C Library; see the file COPYING.  If not, write to
  16 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  17
  18 #include <unistd.h>
  19 #include <errno.h>
  20
  21 /* Defined in brk.c.  */
  22 extern void *__curbrk;
  23 extern int __brk (void *addr);
  24
  25 extern int __libc_multiple_libcs;       /* Defined in init-first.c.  */
  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 (ptrdiff_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 (__brk (oldbrk + increment) < 0)
  49     return (void *) -1;
  50
  51   return oldbrk;
  52 }
  53
  54 weak_alias (__sbrk, sbrk)