include/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, 2001 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 Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the 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    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    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 #include <bits/link.h>
  37 #include <dl-lookupcfg.h>
  38
  39 /* Rendezvous structure used by the run-time dynamic linker to communicate
  40    details of shared object loading to the debugger.  If the executable's
  41    dynamic section has a DT_DEBUG element, the run-time linker sets that
  42    element's value to the address where this structure can be found.  */
  43
  44 struct r_debug
  45   {
  46     int r_version;              /* Version number for this protocol.  */
  47
  48     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  49
  50     /* This is the address of a function internal to the run-time linker,
  51        that will always be called when the linker begins to map in a
  52        library or unmap it, and again when the mapping change is complete.
  53        The debugger can set a breakpoint at this address if it wants to
  54        notice shared object mapping changes.  */
  55     ElfW(Addr) r_brk;
  56     enum
  57       {
  58         /* This state value describes the mapping change taking place when
  59            the `r_brk' address is called.  */
  60         RT_CONSISTENT,          /* Mapping change is complete.  */
  61         RT_ADD,                 /* Beginning to add a new object.  */
  62         RT_DELETE               /* Beginning to remove an object mapping.  */
  63       } r_state;
  64
  65     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  66   };
  67
  68 /* This is the instance of that structure used by the dynamic linker.  */
  69 extern struct r_debug _r_debug;
  70
  71 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  72    of whatever module refers to `_DYNAMIC'.  So, to find its own
  73    `struct r_debug', a program could do:
  74      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
  75        if (dyn->d_tag == DT_DEBUG)
  76          r_debug = (struct r_debug *) dyn->d_un.d_ptr;
  77    */
  78 extern ElfW(Dyn) _DYNAMIC[];
  79
  80
  81 /* Some internal data structures of the dynamic linker used in the
  82    linker map.  We only provide forward declarations.  */
  83 struct libname_list;
  84 struct r_found_version;
  85 struct r_search_path_elem;
  86
  87 /* Forward declaration.  */
  88 struct link_map;
  89
  90 /* Structure to describe a single list of scope elements.  The lookup
  91    functions get passed an array of pointers to such structures.  */
  92 struct r_scope_elem
  93 {
  94   /* Array of maps for the scope.  */
  95   struct link_map **r_list;
  96   /* Number of entries in the scope.  */
  97   unsigned int r_nlist;
  98 };
  99
 100
 101 /* Structure to record search path and allocation mechanism.  */
 102 struct r_search_path_struct
 103   {
 104     struct r_search_path_elem **dirs;
 105     int malloced;
 106   };
 107
 108
 109 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 110    members form a chain of all the shared objects loaded at startup.
 111
 112    These data structures exist in space used by the run-time dynamic linker;
 113    modifying them may have disastrous results.
 114
 115    This data structure might change in future, if necessary.  User-level
 116    programs must avoid defining objects of this type.  */
 117
 118 struct link_map
 119   {
 120     /* These first few members are part of the protocol with the debugger.
 121        This is the same format used in SVR4.  */
 122
 123     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 124     char *l_name;               /* Absolute file name object was found in.  */
 125     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 126     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 127
 128     /* All following members are internal to the dynamic linker.
 129        They may change without notice.  */
 130
 131     struct libname_list *l_libname;
 132     /* Indexed pointers to dynamic section.
 133        [0,DT_NUM) are indexed by the processor-independent tags.
 134        [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
 135        [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_EXTRANUM) are indexed
 136        by DT_EXTRATAGIDX(tagvalue) and
 137        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 138         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 139        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 140
 141     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 142                      + DT_EXTRANUM];
 143     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 144     ElfW(Addr) l_entry;         /* Entry point location.  */
 145     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 146     ElfW(Half) l_ldnum; /* Number of dynamic segment entries.  */
 147
 148     /* Array of DT_NEEDED dependencies and their dependencies, in
 149        dependency order for symbol lookup (with and without
 150        duplicates).  There is no entry before the dependencies have
 151        been loaded.  */
 152     struct r_scope_elem l_searchlist;
 153
 154     /* We need a special searchlist to process objects marked with
 155        DT_SYMBOLIC.  */
 156     struct r_scope_elem l_symbolic_searchlist;
 157
 158     /* Dependent object that first caused this object to be loaded.  */
 159     struct link_map *l_loader;
 160
 161     /* Symbol hash table.  */
 162     Elf_Symndx l_nbuckets;
 163     const Elf_Symndx *l_buckets, *l_chain;
 164
 165     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 166     enum                        /* Where this object came from.  */
 167       {
 168         lt_executable,          /* The main executable program.  */
 169         lt_library,             /* Library needed by main executable.  */
 170         lt_loaded               /* Extra run-time loaded shared object.  */
 171       } l_type:2;
 172     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 173     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 174     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 175     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 176     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 177                                         to by `l_phdr' is allocated.  */
 178     unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
 179                                       the l_libname list.  */
 180     unsigned int l_faked:1;     /* Nonzero if this is a faked descriptor
 181                                    without associated file.  */
 182
 183     /* Array with version names.  */
 184     unsigned int l_nversions;
 185     struct r_found_version *l_versions;
 186
 187     /* Collected information about own RPATH directories.  */
 188     struct r_search_path_struct l_rpath_dirs;
 189
 190     /* Collected results of relocation while profiling.  */
 191     ElfW(Addr) *l_reloc_result;
 192
 193     /* Pointer to the version information if available.  */
 194     ElfW(Versym) *l_versyms;
 195
 196     /* String specifying the path where this object was found.  */
 197     const char *l_origin;
 198
 199     /* Start and finish of memory map for this object.  l_map_start
 200        need not be the same as l_addr.  */
 201     ElfW(Addr) l_map_start, l_map_end;
 202
 203     /* Default array for 'l_scope'.  */
 204     struct r_scope_elem *l_scope_mem[4];
 205     /* Size of array allocated for 'l_scope'.  */
 206     size_t l_scope_max;
 207     /* This is an array defining the lookup scope for this link map.
 208        There are at most three different scope lists.  */
 209     struct r_scope_elem **l_scope;
 210
 211     /* A similar array, this time only with the local scope.  This is
 212        used occasionally.  */
 213     struct r_scope_elem *l_local_scope[2];
 214
 215     /* This information is kept to check for sure whether a shared
 216        object is the same as one already loaded.  */
 217     dev_t l_dev;
 218     ino64_t l_ino;
 219
 220     /* Collected information about own RUNPATH directories.  */
 221     struct r_search_path_struct l_runpath_dirs;
 222
 223     /* List of object in order of the init and fini calls.  */
 224     struct link_map **l_initfini;
 225
 226     /* List of the dependencies introduced through symbol binding.  */
 227     unsigned int l_reldepsmax;
 228     unsigned int l_reldepsact;
 229     struct link_map **l_reldeps;
 230
 231     /* Various flag words.  */
 232     ElfW(Word) l_feature_1;
 233     ElfW(Word) l_flags_1;
 234
 235     /* Temporarily used in `dl_close'.  */
 236     unsigned int l_idx;
 237
 238     struct link_map_machine l_mach;
 239
 240     struct
 241     {
 242       const ElfW(Sym) *sym;
 243       int type_class;
 244 #ifdef DL_LOOKUP_RETURNS_MAP
 245       struct link_map *value;
 246 #else
 247       ElfW(Addr) value;
 248 #endif
 249       const ElfW(Sym) *ret;
 250     } l_lookup_cache;
 251   };
 252
 253 struct dl_phdr_info
 254   {
 255     ElfW(Addr) dlpi_addr;
 256     const char *dlpi_name;
 257     const ElfW(Phdr) *dlpi_phdr;
 258     ElfW(Half) dlpi_phnum;
 259   };
 260
 261 extern int dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 262                                              size_t size, void *data),
 263                             void *data);
 264 extern int __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 265                                                size_t size, void *data),
 266                               void *data);
 267
 268 #endif /* link.h */