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, 2002 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 <elf.h>
  25 #include <dlfcn.h>
  26 #include <stddef.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_VERSIONTAGNUM) are
 136        indexed by DT_VERSIONTAGIDX(tagvalue).
 137        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 138         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM) are indexed by
 139        DT_EXTRATAGIDX(tagvalue).
 140        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM,
 141         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM) are
 142        indexed by DT_VALTAGIDX(tagvalue) and
 143        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM,
 144         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM+DT_ADDRNUM)
 145        are indexed by DT_ADDRTAGIDX(tagvalue), see <elf.h>.  */
 146
 147     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 148                      + DT_EXTRANUM + DT_VALNUM + DT_ADDRNUM];
 149     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 150     ElfW(Addr) l_entry;         /* Entry point location.  */
 151     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 152     ElfW(Half) l_ldnum; /* Number of dynamic segment entries.  */
 153
 154     /* Array of DT_NEEDED dependencies and their dependencies, in
 155        dependency order for symbol lookup (with and without
 156        duplicates).  There is no entry before the dependencies have
 157        been loaded.  */
 158     struct r_scope_elem l_searchlist;
 159
 160     /* We need a special searchlist to process objects marked with
 161        DT_SYMBOLIC.  */
 162     struct r_scope_elem l_symbolic_searchlist;
 163
 164     /* Dependent object that first caused this object to be loaded.  */
 165     struct link_map *l_loader;
 166
 167     /* Symbol hash table.  */
 168     Elf_Symndx l_nbuckets;
 169     const Elf_Symndx *l_buckets, *l_chain;
 170
 171     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 172     enum                        /* Where this object came from.  */
 173       {
 174         lt_executable,          /* The main executable program.  */
 175         lt_library,             /* Library needed by main executable.  */
 176         lt_loaded               /* Extra run-time loaded shared object.  */
 177       } l_type:2;
 178     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 179     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 180     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 181     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 182     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 183                                         to by `l_phdr' is allocated.  */
 184     unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
 185                                       the l_libname list.  */
 186     unsigned int l_faked:1;     /* Nonzero if this is a faked descriptor
 187                                    without associated file.  */
 188
 189     /* Array with version names.  */
 190     unsigned int l_nversions;
 191     struct r_found_version *l_versions;
 192
 193     /* Collected information about own RPATH directories.  */
 194     struct r_search_path_struct l_rpath_dirs;
 195
 196     /* Collected results of relocation while profiling.  */
 197     ElfW(Addr) *l_reloc_result;
 198
 199     /* Pointer to the version information if available.  */
 200     ElfW(Versym) *l_versyms;
 201
 202     /* String specifying the path where this object was found.  */
 203     const char *l_origin;
 204
 205     /* Start and finish of memory map for this object.  l_map_start
 206        need not be the same as l_addr.  */
 207     ElfW(Addr) l_map_start, l_map_end;
 208
 209     /* Default array for 'l_scope'.  */
 210     struct r_scope_elem *l_scope_mem[4];
 211     /* Size of array allocated for 'l_scope'.  */
 212     size_t l_scope_max;
 213     /* This is an array defining the lookup scope for this link map.
 214        There are at most three different scope lists.  */
 215     struct r_scope_elem **l_scope;
 216
 217     /* A similar array, this time only with the local scope.  This is
 218        used occasionally.  */
 219     struct r_scope_elem *l_local_scope[2];
 220
 221     /* This information is kept to check for sure whether a shared
 222        object is the same as one already loaded.  */
 223     dev_t l_dev;
 224     ino64_t l_ino;
 225
 226     /* Collected information about own RUNPATH directories.  */
 227     struct r_search_path_struct l_runpath_dirs;
 228
 229     /* List of object in order of the init and fini calls.  */
 230     struct link_map **l_initfini;
 231
 232     /* List of the dependencies introduced through symbol binding.  */
 233     unsigned int l_reldepsmax;
 234     unsigned int l_reldepsact;
 235     struct link_map **l_reldeps;
 236
 237     /* Various flag words.  */
 238     ElfW(Word) l_feature_1;
 239     ElfW(Word) l_flags_1;
 240
 241     /* Temporarily used in `dl_close'.  */
 242     unsigned int l_idx;
 243
 244     struct link_map_machine l_mach;
 245
 246     struct
 247     {
 248       const ElfW(Sym) *sym;
 249       int type_class;
 250 #ifdef DL_LOOKUP_RETURNS_MAP
 251       struct link_map *value;
 252 #else
 253       ElfW(Addr) value;
 254 #endif
 255       const ElfW(Sym) *ret;
 256     } l_lookup_cache;
 257
 258     /* Thread-local storage related info.  */
 259
 260     /* Next module in list of initialization images.  */
 261     struct link_map *l_tls_nextimage;
 262     /* Start of the initialization image.  */
 263     void *l_tls_initimage;
 264     /* Size of the initialization image.  */
 265     size_t l_tls_initimage_size;
 266     /* Size of the TLS block.  */
 267     size_t l_tls_blocksize;
 268     /* For objects present at startup time: offset in the static TLS block.  */
 269     ptrdiff_t l_tls_offset;
 270     /* Index of the module in the dtv array.  */
 271     size_t l_tls_modid;
 272   };
 273
 274 struct dl_phdr_info
 275   {
 276     ElfW(Addr) dlpi_addr;
 277     const char *dlpi_name;
 278     const ElfW(Phdr) *dlpi_phdr;
 279     ElfW(Half) dlpi_phnum;
 280   };
 281
 282 extern int dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 283                                              size_t size, void *data),
 284                             void *data);
 285 extern int __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 286                                                size_t size, void *data),
 287                               void *data);
 288
 289 #endif /* link.h */