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 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
  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
  98
  99 /* Structure to record search path and allocation mechanism.  */
 100 struct r_search_path_struct
 101   {
 102     struct r_search_path_elem **dirs;
 103     int malloced;
 104   };
 105
 106
 107 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 108    members form a chain of all the shared objects loaded at startup.
 109
 110    These data structures exist in space used by the run-time dynamic linker;
 111    modifying them may have disastrous results.
 112
 113    This data structure might change in future, if necessary.  User-level
 114    programs must avoid defining objects of this type.  */
 115
 116 struct link_map
 117   {
 118     /* These first few members are part of the protocol with the debugger.
 119        This is the same format used in SVR4.  */
 120
 121     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 122     char *l_name;               /* Absolute file name object was found in.  */
 123     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 124     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 125
 126     /* All following members are internal to the dynamic linker.
 127        They may change without notice.  */
 128
 129     struct libname_list *l_libname;
 130     /* Indexed pointers to dynamic section.
 131        [0,DT_NUM) are indexed by the processor-independent tags.
 132        [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
 133        [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_EXTRANUM) are indexed
 134        by DT_EXTRATAGIDX(tagvalue) and
 135        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 136         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 137        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 138
 139     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 140                      + DT_EXTRANUM];
 141     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 142     ElfW(Addr) l_entry;         /* Entry point location.  */
 143     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 144     ElfW(Half) l_ldnum; /* Number of dynamic segment entries.  */
 145
 146     /* Array of DT_NEEDED dependencies and their dependencies, in
 147        dependency order for symbol lookup (with and without
 148        duplicates).  There is no entry before the dependencies have
 149        been loaded.  */
 150     struct r_scope_elem l_searchlist;
 151
 152     /* We need a special searchlist to process objects marked with
 153        DT_SYMBOLIC.  */
 154     struct r_scope_elem l_symbolic_searchlist;
 155
 156     /* Dependent object that first caused this object to be loaded.  */
 157     struct link_map *l_loader;
 158
 159     /* Symbol hash table.  */
 160     Elf_Symndx l_nbuckets;
 161     const Elf_Symndx *l_buckets, *l_chain;
 162
 163     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 164     enum                        /* Where this object came from.  */
 165       {
 166         lt_executable,          /* The main executable program.  */
 167         lt_library,             /* Library needed by main executable.  */
 168         lt_loaded               /* Extra run-time loaded shared object.  */
 169       } l_type:2;
 170     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 171     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 172     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 173     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 174     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 175                                         to by `l_phdr' is allocated.  */
 176     unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
 177                                       the l_libname list.  */
 178     unsigned int l_faked:1;     /* Nonzero if this is a faked descriptor
 179                                    without associated file.  */
 180
 181     /* Array with version names.  */
 182     unsigned int l_nversions;
 183     struct r_found_version *l_versions;
 184
 185     /* Collected information about own RPATH directories.  */
 186     struct r_search_path_struct l_rpath_dirs;
 187
 188     /* Collected results of relocation while profiling.  */
 189     ElfW(Addr) *l_reloc_result;
 190
 191     /* Pointer to the version information if available.  */
 192     ElfW(Versym) *l_versyms;
 193
 194     /* String specifying the path where this object was found.  */
 195     const char *l_origin;
 196
 197     /* Start and finish of memory map for this object.  l_map_start
 198        need not be the same as l_addr.  */
 199     ElfW(Addr) l_map_start, l_map_end;
 200
 201     /* This is an array defining the lookup scope for this link map.
 202        There are at most three different scope lists.  */
 203     struct r_scope_elem *l_scope[4];
 204
 205     /* A similar array, this time only with the local scope.  This is
 206        used occasionally.  */
 207     struct r_scope_elem *l_local_scope[2];
 208
 209     /* This information is kept to check for sure whether a shared
 210        object is the same as one already loaded.  */
 211     dev_t l_dev;
 212     ino64_t l_ino;
 213
 214     /* Collected information about own RUNPATH directories.  */
 215     struct r_search_path_struct l_runpath_dirs;
 216
 217     /* List of object in order of the init and fini calls.  */
 218     struct link_map **l_initfini;
 219
 220     /* List of the dependencies introduced through symbol binding.  */
 221     unsigned int l_reldepsmax;
 222     unsigned int l_reldepsact;
 223     struct link_map **l_reldeps;
 224
 225     /* Various flag words.  */
 226     ElfW(Word) l_feature_1;
 227     ElfW(Word) l_flags_1;
 228
 229     /* Temporarily used in `dl_close'.  */
 230     unsigned int l_idx;
 231   };
 232
 233 #endif /* link.h */