sysdeps/unix/sysv/linux/dl-sysdep.c

   1 /* Dynamic linker system dependencies for Linux.
   2    Copyright (C) 1995,1997,2001,2004,2005,2006 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 /* Linux needs some special initialization, but otherwise uses
  21    the generic dynamic linker system interface code.  */
  22
  23 #include <unistd.h>
  24 #include <ldsodefs.h>
  25 #include <kernel-features.h>
  26
  27 #define DL_SYSDEP_INIT frob_brk ()
  28
  29 static inline void
  30 frob_brk (void)
  31 {
  32   __brk (0);                    /* Initialize the break.  */
  33
  34 #if ! __ASSUME_BRK_PAGE_ROUNDED
  35   /* If the dynamic linker was executed as a program, then the break may
  36      start immediately after our data segment.  However, dl-minimal.c has
  37      already stolen the remainder of the page for internal allocations.
  38      If we don't adjust the break location recorded by the kernel, the
  39      normal program startup will inquire, find the value at our &_end,
  40      and start allocating its own data there, clobbering dynamic linker
  41      data structures allocated there during startup.
  42
  43      Later Linux kernels have changed this behavior so that the initial
  44      break value is rounded up to the page boundary before we start.  */
  45
  46   extern void *__curbrk attribute_hidden;
  47   extern void _end attribute_hidden;
  48   void *const endpage = (void *) 0 + (((__curbrk - (void *) 0)
  49                                        + GLRO(dl_pagesize) - 1)
  50                                       & -GLRO(dl_pagesize));
  51   if (__builtin_expect (__curbrk >= &_end && __curbrk < endpage, 0))
  52     __brk (endpage);
  53 #endif
  54 }
  55
  56 #include <elf/dl-sysdep.c>