sysdeps/nacl/brk.c

   1 /* brk -- Adjust the "break" at the end of initial data.  NaCl version.
   2    Copyright (C) 2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <libc-internal.h>
  21 #include <stdint.h>
  22 #include <sys/mman.h>
  23 #include <sys/param.h>
  24 #include <unistd.h>
  25
  26 /* sbrk.c expects this.  */
  27 void *__curbrk;
  28
  29 static uintptr_t
  30 page_above (void *addr)
  31 {
  32   return ALIGN_UP ((uintptr_t) addr, EXEC_PAGESIZE);
  33 }
  34
  35 /* Set the end of the process's data space to ADDR.
  36    Return 0 if successful, -1 if not.  */
  37 int
  38 __brk (void *addr)
  39 {
  40   /* The NaCl sysbrk call is deprecated, so we do not use it here.  Other
  41      libc code expects that __sbrk can be used at least a little bit, so
  42      rather than a plain stub we have a minimal __brk implementation here.
  43      It just uses mmap/munmap to grow or shrink the break area, punting as
  44      soon as mmap fails to use the same contiguous area.  */
  45
  46   if (__glibc_unlikely (__curbrk == NULL))
  47     {
  48       /* This is the first call.  We must initialize the record
  49          of the current position.  It starts out at the end of the
  50          main program's data segment.  */
  51
  52       /* XXX dynamic case??? */
  53       extern char _end[];
  54       __curbrk = _end;
  55     }
  56
  57   if (__glibc_unlikely (addr == NULL))
  58     /* This is a call just to ensure that __curbrk is set up.  */
  59     return 0;
  60
  61   uintptr_t old_limit = page_above (__curbrk);
  62   uintptr_t new_limit = page_above (addr);
  63
  64   if (old_limit > new_limit)
  65     {
  66       /* We're shrinking the old heap enough to release some pages.  */
  67       if (__munmap ((void *) new_limit, old_limit - new_limit) != 0)
  68         return -1;
  69     }
  70   else if (old_limit < new_limit)
  71     {
  72       /* We're growing the old heap enough to need some more pages.
  73          See if they are available.  */
  74       void *new_space = __mmap ((void *) old_limit, new_limit - old_limit,
  75                                 PROT_READ | PROT_WRITE, MAP_ANON, -1, 0);
  76       if (new_space != (void *) old_limit)
  77         {
  78           if (new_space != MAP_FAILED)
  79             {
  80               /* mmap chose some different place for the pages
  81                  because the contiguous area was not available.
  82                  Oh well.  We can't use that.  */
  83               __munmap (new_space, new_limit - old_limit);
  84               __set_errno (ENOMEM);
  85             }
  86           return -1;
  87         }
  88     }
  89
  90   __curbrk = addr;
  91   return 0;
  92 }
  93 weak_alias (__brk, brk)