elf/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995, 1996, 1997, 1998, 1999 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)
  73        if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
  74    */
  75 extern ElfW(Dyn) _DYNAMIC[];
  76
  77
  78 /* Some internal data structures of the dynamic linker used in the
  79    linker map.  We only provide forward declarations.  */
  80 struct libname_list;
  81 struct r_found_version;
  82 struct r_search_path_elem;
  83
  84 /* Forward declaration.  */
  85 struct link_map;
  86
  87 /* Structure to describe a single list of scope elements.  The lookup
  88    functions get passed an array of pointers to such structures.  */
  89 struct r_scope_elem
  90 {
  91   /* Array of maps for the scope.  */
  92   struct link_map **r_list;
  93   /* Number of entries in the scope.  */
  94   unsigned int r_nlist;
  95
  96   /* Array of maps which also includes duplicates.  */
  97   struct link_map **r_duplist;
  98   /* Number of elements in this list.  */
  99   unsigned int r_nduplist;
 100 };
 101
 102
 103 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 104    members form a chain of all the shared objects loaded at startup.
 105
 106    These data structures exist in space used by the run-time dynamic linker;
 107    modifying them may have disastrous results.
 108
 109    This data structure might change in future, if necessary.  User-level
 110    programs must avoid defining objects of this type.  */
 111
 112 struct link_map
 113   {
 114     /* These first few members are part of the protocol with the debugger.
 115        This is the same format used in SVR4.  */
 116
 117     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 118     char *l_name;               /* Absolute file name object was found in.  */
 119     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 120     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 121
 122     /* All following members are internal to the dynamic linker.
 123        They may change without notice.  */
 124
 125     struct libname_list *l_libname;
 126     /* Indexed pointers to dynamic section.
 127        [0,DT_NUM) are indexed by the processor-independent tags.
 128        [DT_NUM,DT_NUM+DT_PROCNUM) are indexed by the tag minus DT_LOPROC.
 129        [DT_NUM+DT_PROCNUM,DT_NUM+DT_PROCNUM+DT_EXTRANUM) are indexed
 130        by DT_EXTRATAGIDX(tagvalue) and
 131        [DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM,
 132         DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 133        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 134
 135     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM];
 136     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 137     ElfW(Addr) l_entry;         /* Entry point location.  */
 138     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 139
 140     /* Array of DT_NEEDED dependencies and their dependencies, in
 141        dependency order for symbol lookup (with and without
 142        duplicates).  There is no entry before the dependencies have
 143        been loaded.  */
 144     struct r_scope_elem l_searchlist;
 145
 146     /* We need a special searchlist to process objects marked with
 147        DT_SYMBOLIC.  */
 148     struct r_scope_elem l_symbolic_searchlist;
 149
 150     /* Dependent object that first caused this object to be loaded.  */
 151     struct link_map *l_loader;
 152
 153     /* Symbol hash table.  */
 154     ElfW(Symndx) l_nbuckets;
 155     const ElfW(Symndx) *l_buckets, *l_chain;
 156
 157     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 158     enum                        /* Where this object came from.  */
 159       {
 160         lt_executable,          /* The main executable program.  */
 161         lt_library,             /* Library needed by main executable.  */
 162         lt_loaded               /* Extra run-time loaded shared object.  */
 163       } l_type:2;
 164     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 165     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 166     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 167     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 168     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 169
 170     /* Array with version names.  */
 171     unsigned int l_nversions;
 172     struct r_found_version *l_versions;
 173
 174     /* Collected information about own RPATH directories.  */
 175     struct r_search_path_elem **l_rpath_dirs;
 176
 177     /* Collected results of relocation while profiling.  */
 178     ElfW(Addr) *l_reloc_result;
 179
 180     /* Pointer to the version information if available.  */
 181     ElfW(Half) *l_versyms;
 182
 183     /* String specifying the path where this object was found.  */
 184     const char *l_origin;
 185
 186     /* Start and finish of memory map for this object.  l_map_start
 187        need not be the same as l_addr.  */
 188     ElfW(Addr) l_map_start, l_map_end;
 189
 190     /* This is an array defining the lookup scope for this link map.
 191      There are at most three different scope lists.  */
 192     struct r_scope_elem *l_scope[4];
 193
 194     /* A similar array, this time only with the local scope.  This is
 195        used occasionally.  */
 196     struct r_scope_elem *l_local_scope[2];
 197
 198     /* This information is kept to check for sure whether a shared
 199        object is the same as one already loaded.  */
 200     dev_t l_dev;
 201     ino_t l_ino;
 202
 203     /* Nonzero if the data structure pointed to by `l_phdr' is allocated.  */
 204     int l_phdr_allocated;
 205   };
 206
 207 #endif /* link.h */