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
  79 /* Some internal data structures of the dynamic linker used in the
  80    linker map.  We only provide forward declarations.  */
  81 struct libname_list;
  82 struct r_found_version;
  83 struct r_search_path_elem;
  84
  85 /* Forward declaration.  */
  86 struct link_map;
  87
  88 /* Structure to describe a single list of scope elements.  The lookup
  89    functions get passed an array of pointers to such structures.  */
  90 struct r_scope_elem
  91 {
  92   /* Array of maps for the scope.  */
  93   struct link_map **r_list;
  94   /* Number of entries in the scope.  */
  95   unsigned int r_nlist;
  96
  97   /* Array of maps which also includes duplicates.  */
  98   struct link_map **r_duplist;
  99   /* Number of elements in this list.  */
 100   unsigned int r_nduplist;
 101 };
 102
 103
 104 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 105    members form a chain of all the shared objects loaded at startup.
 106
 107    These data structures exist in space used by the run-time dynamic linker;
 108    modifying them may have disastrous results.
 109
 110    This data structure might change in future, if necessary.  User-level
 111    programs must avoid defining objects of this type.  */
 112
 113 struct link_map
 114   {
 115     /* These first few members are part of the protocol with the debugger.
 116        This is the same format used in SVR4.  */
 117
 118     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 119     char *l_name;               /* Absolute file name object was found in.  */
 120     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 121     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 122
 123     /* All following members are internal to the dynamic linker.
 124        They may change without notice.  */
 125
 126     struct libname_list *l_libname;
 127     /* Indexed pointers to dynamic section.
 128        [0,DT_NUM) are indexed by the processor-independent tags.
 129        [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
 130        [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_EXTRANUM) are indexed
 131        by DT_EXTRATAGIDX(tagvalue) and
 132        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 133         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 134        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 135
 136     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 137                      + DT_EXTRANUM];
 138     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 139     ElfW(Addr) l_entry;         /* Entry point location.  */
 140     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 141     ElfW(Half) l_ldnum; /* Number of dynamic segment entries.  */
 142
 143     /* Array of DT_NEEDED dependencies and their dependencies, in
 144        dependency order for symbol lookup (with and without
 145        duplicates).  There is no entry before the dependencies have
 146        been loaded.  */
 147     struct r_scope_elem l_searchlist;
 148
 149     /* We need a special searchlist to process objects marked with
 150        DT_SYMBOLIC.  */
 151     struct r_scope_elem l_symbolic_searchlist;
 152
 153     /* Dependent object that first caused this object to be loaded.  */
 154     struct link_map *l_loader;
 155
 156     /* Symbol hash table.  */
 157     Elf_Symndx l_nbuckets;
 158     const Elf_Symndx *l_buckets, *l_chain;
 159
 160     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 161     enum                        /* Where this object came from.  */
 162       {
 163         lt_executable,          /* The main executable program.  */
 164         lt_library,             /* Library needed by main executable.  */
 165         lt_loaded               /* Extra run-time loaded shared object.  */
 166       } l_type:2;
 167     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 168     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 169     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 170     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 171     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 172                                         to by `l_phdr' is allocated.  */
 173
 174     /* Array with version names.  */
 175     unsigned int l_nversions;
 176     struct r_found_version *l_versions;
 177
 178     /* Collected information about own RPATH directories.  */
 179     struct r_search_path_elem **l_rpath_dirs;
 180
 181     /* Collected results of relocation while profiling.  */
 182     ElfW(Addr) *l_reloc_result;
 183
 184     /* Pointer to the version information if available.  */
 185     ElfW(Versym) *l_versyms;
 186
 187     /* String specifying the path where this object was found.  */
 188     const char *l_origin;
 189
 190     /* Start and finish of memory map for this object.  l_map_start
 191        need not be the same as l_addr.  */
 192     ElfW(Addr) l_map_start, l_map_end;
 193
 194     /* This is an array defining the lookup scope for this link map.
 195      There are at most three different scope lists.  */
 196     struct r_scope_elem *l_scope[4];
 197
 198     /* A similar array, this time only with the local scope.  This is
 199        used occasionally.  */
 200     struct r_scope_elem *l_local_scope[2];
 201
 202     /* This information is kept to check for sure whether a shared
 203        object is the same as one already loaded.  */
 204     dev_t l_dev;
 205     ino_t l_ino;
 206
 207     /* Collected information about own RUNPATH directories.  */
 208     struct r_search_path_elem **l_runpath_dirs;
 209
 210     /* List of object in order of the init and fini calls.  */
 211     struct link_map **l_initfini;
 212
 213     /* List of the dependencies introduced through symbol binding.  */
 214     unsigned int l_reldepsmax;
 215     unsigned int l_reldepsact;
 216     struct link_map **l_reldeps;
 217   };
 218
 219 #endif /* link.h */