elf/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995-1999, 2000 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #ifndef _LINK_H
  22 #define _LINK_H 1
  23
  24 #include <features.h>
  25 #include <elf.h>
  26 #include <dlfcn.h>
  27 #include <sys/types.h>
  28
  29 /* We use this macro to refer to ELF types independent of the native wordsize.
  30    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  31 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, type)
  32 #define _ElfW(e,w,t)    _ElfW_1 (e, w, _##t)
  33 #define _ElfW_1(e,w,t)  e##w##t
  34
  35 #include <bits/elfclass.h>              /* Defines __ELF_NATIVE_CLASS.  */
  36
  37 /* Rendezvous structure used by the run-time dynamic linker to communicate
  38    details of shared object loading to the debugger.  If the executable's
  39    dynamic section has a DT_DEBUG element, the run-time linker sets that
  40    element's value to the address where this structure can be found.  */
  41
  42 struct r_debug
  43   {
  44     int r_version;              /* Version number for this protocol.  */
  45
  46     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  47
  48     /* This is the address of a function internal to the run-time linker,
  49        that will always be called when the linker begins to map in a
  50        library or unmap it, and again when the mapping change is complete.
  51        The debugger can set a breakpoint at this address if it wants to
  52        notice shared object mapping changes.  */
  53     ElfW(Addr) r_brk;
  54     enum
  55       {
  56         /* This state value describes the mapping change taking place when
  57            the `r_brk' address is called.  */
  58         RT_CONSISTENT,          /* Mapping change is complete.  */
  59         RT_ADD,                 /* Beginning to add a new object.  */
  60         RT_DELETE               /* Beginning to remove an object mapping.  */
  61       } r_state;
  62
  63     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  64   };
  65
  66 /* This is the instance of that structure used by the dynamic linker.  */
  67 extern struct r_debug _r_debug;
  68
  69 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  70    of whatever module refers to `_DYNAMIC'.  So, to find its own
  71    `struct r_debug', a program could do:
  72      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
  73        if (dyn->d_tag == DT_DEBUG)
  74          r_debug = (struct r_debug *) dyn->d_un.d_ptr;
  75    */
  76 extern ElfW(Dyn) _DYNAMIC[];
  77
  78 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  79    members form a chain of all the shared objects loaded at startup.
  80
  81    These data structures exist in space used by the run-time dynamic linker;
  82    modifying them may have disastrous results.  */
  83
  84 struct link_map
  85   {
  86     /* These first few members are part of the protocol with the debugger.
  87        This is the same format used in SVR4.  */
  88
  89     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
  90     char *l_name;               /* Absolute file name object was found in.  */
  91     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
  92     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
  93   };
  94
  95 #endif /* link.h */