misc/sbrk.c

   1 /* Copyright (C) 1991,1995-1997,2000,2002,2009 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <errno.h>
  20 #include <stdint.h>
  21 #include <unistd.h>
  22
  23 /* Defined in brk.c.  */
  24 extern void *__curbrk;
  25 extern int __brk (void *addr);
  26
  27 /* Defined in init-first.c.  */
  28 extern int __libc_multiple_libcs attribute_hidden;
  29
  30 /* Extend the process's data space by INCREMENT.
  31    If INCREMENT is negative, shrink data space by - INCREMENT.
  32    Return start of new space allocated, or -1 for errors.  */
  33 void *
  34 __sbrk (intptr_t increment)
  35 {
  36   void *oldbrk;
  37
  38   /* If this is not part of the dynamic library or the library is used
  39      via dynamic loading in a statically linked program update
  40      __curbrk from the kernel's brk value.  That way two separate
  41      instances of __brk and __sbrk can share the heap, returning
  42      interleaved pieces of it.  */
  43   if (__curbrk == NULL || __libc_multiple_libcs)
  44     if (__brk (0) < 0)          /* Initialize the break.  */
  45       return (void *) -1;
  46
  47   if (increment == 0)
  48     return __curbrk;
  49
  50   oldbrk = __curbrk;
  51   if ((increment > 0
  52        ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
  53        : ((uintptr_t) oldbrk < (uintptr_t) -increment))
  54       || __brk (oldbrk + increment) < 0)
  55     return (void *) -1;
  56
  57   return oldbrk;
  58 }
  59 libc_hidden_def (__sbrk)
  60 weak_alias (__sbrk, sbrk)