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 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
  28 /* We use this macro to refer to ELF types independent of the native wordsize.
  29    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  30 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, type)
  31 #define _ElfW(e,w,t)    _ElfW_1 (e, w, _##t)
  32 #define _ElfW_1(e,w,t)  e##w##t
  33
  34 #include <bits/elfclass.h>              /* Defines __ELF_NATIVE_CLASS.  */
  35
  36 /* Rendezvous structure used by the run-time dynamic linker to communicate
  37    details of shared object loading to the debugger.  If the executable's
  38    dynamic section has a DT_DEBUG element, the run-time linker sets that
  39    element's value to the address where this structure can be found.  */
  40
  41 struct r_debug
  42   {
  43     int r_version;              /* Version number for this protocol.  */
  44
  45     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  46
  47     /* This is the address of a function internal to the run-time linker,
  48        that will always be called when the linker begins to map in a
  49        library or unmap it, and again when the mapping change is complete.
  50        The debugger can set a breakpoint at this address if it wants to
  51        notice shared object mapping changes.  */
  52     ElfW(Addr) r_brk;
  53     enum
  54       {
  55         /* This state value describes the mapping change taking place when
  56            the `r_brk' address is called.  */
  57         RT_CONSISTENT,          /* Mapping change is complete.  */
  58         RT_ADD,                 /* Beginning to add a new object.  */
  59         RT_DELETE               /* Beginning to remove an object mapping.  */
  60       } r_state;
  61
  62     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  63   };
  64
  65 /* This is the instance of that structure used by the dynamic linker.  */
  66 extern struct r_debug _r_debug;
  67
  68 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  69    of whatever module refers to `_DYNAMIC'.  So, to find its own
  70    `struct r_debug', a program could do:
  71      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL)
  72        if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
  73    */
  74 extern ElfW(Dyn) _DYNAMIC[];
  75
  76
  77 /* Some internal data structures of the dynamic linker used in the
  78    linker map.  We only provide forward declarations.  */
  79 struct libname_list;
  80 struct r_found_version;
  81 struct r_search_path_elem;
  82
  83 /* Forward declaration.  */
  84 struct link_map;
  85
  86 /* Structure to describe a single list of scope elements.  The lookup
  87    functions get passed an array of pointers to such structures.  */
  88 struct r_scope_elem
  89 {
  90   /* Array of maps for the scope.  */
  91   struct link_map **r_list;
  92   /* Number of entries in the scope.  */
  93   unsigned int r_nlist;
  94
  95   /* Array of maps which also includes duplicates.  */
  96   struct link_map **r_duplist;
  97   /* Number of elements in this list.  */
  98   unsigned int r_nduplist;
  99 };
 100
 101
 102 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 103    members form a chain of all the shared objects loaded at startup.
 104
 105    These data structures exist in space used by the run-time dynamic linker;
 106    modifying them may have disastrous results.
 107
 108    This data structure might change in future, if necessary.  User-level
 109    programs must avoid defining objects of this type.  */
 110
 111 struct link_map
 112   {
 113     /* These first few members are part of the protocol with the debugger.
 114        This is the same format used in SVR4.  */
 115
 116     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 117     char *l_name;               /* Absolute file name object was found in.  */
 118     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 119     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 120
 121     /* All following members are internal to the dynamic linker.
 122        They may change without notice.  */
 123
 124     struct libname_list *l_libname;
 125     /* Indexed pointers to dynamic section.
 126        [0,DT_NUM) are indexed by the processor-independent tags.
 127        [DT_NUM,DT_NUM+DT_PROCNUM) are indexed by the tag minus DT_LOPROC.
 128        [DT_NUM+DT_PROCNUM,DT_NUM+DT_PROCNUM+DT_EXTRANUM) are indexed
 129        by DT_EXTRATAGIDX(tagvalue) and
 130        [DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM,
 131         DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 132        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 133
 134     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM];
 135     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 136     ElfW(Addr) l_entry;         /* Entry point location.  */
 137     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 138
 139     /* Array of DT_NEEDED dependencies and their dependencies, in
 140        dependency order for symbol lookup (with and without
 141        duplicates).  There is no entry before the dependencies have
 142        been loaded.  */
 143     struct r_scope_elem l_searchlist;
 144
 145     /* We need a special searchlist to process objects marked with
 146        DT_SYMBOLIC.  */
 147     struct r_scope_elem l_symbolic_searchlist;
 148
 149     /* Dependent object that first caused this object to be loaded.  */
 150     struct link_map *l_loader;
 151
 152     /* Symbol hash table.  */
 153     ElfW(Symndx) l_nbuckets;
 154     const ElfW(Symndx) *l_buckets, *l_chain;
 155
 156     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 157     enum                        /* Where this object came from.  */
 158       {
 159         lt_executable,          /* The main executable program.  */
 160         lt_library,             /* Library needed by main executable.  */
 161         lt_loaded               /* Extra run-time loaded shared object.  */
 162       } l_type:2;
 163     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 164     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 165     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 166     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 167     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 168
 169     /* Array with version names.  */
 170     unsigned int l_nversions;
 171     struct r_found_version *l_versions;
 172
 173     /* Collected information about own RPATH directories.  */
 174     struct r_search_path_elem **l_rpath_dirs;
 175
 176     /* Collected results of relocation while profiling.  */
 177     ElfW(Addr) *l_reloc_result;
 178
 179     /* Pointer to the version information if available.  */
 180     ElfW(Half) *l_versyms;
 181
 182     /* String specifying the path where this object was found.  */
 183     const char *l_origin;
 184
 185     /* Start and finish of memory map for this object.  l_map_start
 186        need not be the same as l_addr.  */
 187     ElfW(Addr) l_map_start, l_map_end;
 188
 189     /* This is an array defining the lookup scope for this link map.
 190      There are at most three different scope lists.  */
 191     struct r_scope_elem *l_scope[4];
 192
 193     /* A similar array, this time only with the local scope.  This is
 194        used occasionally.  */
 195     struct r_scope_elem *l_local_scope[2];
 196   };
 197
 198 #endif /* link.h */