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 /* Extend the process's data space by INCREMENT.
  26    If INCREMENT is negative, shrink data space by - INCREMENT.
  27    Return start of new space allocated, or -1 for errors.  */
  28 void *
  29 __sbrk (ptrdiff_t increment)
  30 {
  31   void *oldbrk;
  32
  33   /* Always update __curbrk from the kernel's brk value.  That way two
  34      separate instances of __brk and __sbrk can share the heap, returning
  35      interleaved pieces of it.  This happens when libc.so is loaded by
  36      dlopen in a statically-linked program that already uses __brk.  */
  37   if (__brk (0) < 0)
  38     return (void *) -1;
  39
  40   if (increment == 0)
  41     return __curbrk;
  42
  43   oldbrk = __curbrk;
  44   if (__brk (oldbrk + increment) < 0)
  45     return (void *) -1;
  46
  47   return oldbrk;
  48 }
  49
  50 weak_alias (__sbrk, sbrk)