include/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995-2002, 2003, 2004 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 #include <tls.h>                /* Defines USE_TLS.  */
  39
  40 /* Rendezvous structure used by the run-time dynamic linker to communicate
  41    details of shared object loading to the debugger.  If the executable's
  42    dynamic section has a DT_DEBUG element, the run-time linker sets that
  43    element's value to the address where this structure can be found.  */
  44
  45 struct r_debug
  46   {
  47     int r_version;              /* Version number for this protocol.  */
  48
  49     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  50
  51     /* This is the address of a function internal to the run-time linker,
  52        that will always be called when the linker begins to map in a
  53        library or unmap it, and again when the mapping change is complete.
  54        The debugger can set a breakpoint at this address if it wants to
  55        notice shared object mapping changes.  */
  56     ElfW(Addr) r_brk;
  57     enum
  58       {
  59         /* This state value describes the mapping change taking place when
  60            the `r_brk' address is called.  */
  61         RT_CONSISTENT,          /* Mapping change is complete.  */
  62         RT_ADD,                 /* Beginning to add a new object.  */
  63         RT_DELETE               /* Beginning to remove an object mapping.  */
  64       } r_state;
  65
  66     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  67   };
  68
  69 /* This is the instance of that structure used by the dynamic linker.  */
  70 extern struct r_debug _r_debug;
  71
  72 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  73    of whatever module refers to `_DYNAMIC'.  So, to find its own
  74    `struct r_debug', a program could do:
  75      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
  76        if (dyn->d_tag == DT_DEBUG)
  77          r_debug = (struct r_debug *) dyn->d_un.d_ptr;
  78    */
  79 extern ElfW(Dyn) _DYNAMIC[];
  80
  81
  82 /* Some internal data structures of the dynamic linker used in the
  83    linker map.  We only provide forward declarations.  */
  84 struct libname_list;
  85 struct r_found_version;
  86 struct r_search_path_elem;
  87
  88 /* Forward declaration.  */
  89 struct link_map;
  90
  91 /* Structure to describe a single list of scope elements.  The lookup
  92    functions get passed an array of pointers to such structures.  */
  93 struct r_scope_elem
  94 {
  95   /* Array of maps for the scope.  */
  96   struct link_map **r_list;
  97   /* Number of entries in the scope.  */
  98   unsigned int r_nlist;
  99 };
 100
 101
 102 /* Structure to record search path and allocation mechanism.  */
 103 struct r_search_path_struct
 104   {
 105     struct r_search_path_elem **dirs;
 106     int malloced;
 107   };
 108
 109
 110 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 111    members form a chain of all the shared objects loaded at startup.
 112
 113    These data structures exist in space used by the run-time dynamic linker;
 114    modifying them may have disastrous results.
 115
 116    This data structure might change in future, if necessary.  User-level
 117    programs must avoid defining objects of this type.  */
 118
 119 struct link_map
 120   {
 121     /* These first few members are part of the protocol with the debugger.
 122        This is the same format used in SVR4.  */
 123
 124     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 125     char *l_name;               /* Absolute file name object was found in.  */
 126     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 127     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 128
 129     /* All following members are internal to the dynamic linker.
 130        They may change without notice.  */
 131
 132     struct libname_list *l_libname;
 133     /* Indexed pointers to dynamic section.
 134        [0,DT_NUM) are indexed by the processor-independent tags.
 135        [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
 136        [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM) are
 137        indexed by DT_VERSIONTAGIDX(tagvalue).
 138        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 139         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM) are indexed by
 140        DT_EXTRATAGIDX(tagvalue).
 141        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM,
 142         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM) are
 143        indexed by DT_VALTAGIDX(tagvalue) and
 144        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM,
 145         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM+DT_ADDRNUM)
 146        are indexed by DT_ADDRTAGIDX(tagvalue), see <elf.h>.  */
 147
 148     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 149                      + DT_EXTRANUM + DT_VALNUM + DT_ADDRNUM];
 150     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 151     ElfW(Addr) l_entry;         /* Entry point location.  */
 152     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 153     ElfW(Half) l_ldnum; /* Number of dynamic segment entries.  */
 154
 155     /* Array of DT_NEEDED dependencies and their dependencies, in
 156        dependency order for symbol lookup (with and without
 157        duplicates).  There is no entry before the dependencies have
 158        been loaded.  */
 159     struct r_scope_elem l_searchlist;
 160
 161     /* We need a special searchlist to process objects marked with
 162        DT_SYMBOLIC.  */
 163     struct r_scope_elem l_symbolic_searchlist;
 164
 165     /* Dependent object that first caused this object to be loaded.  */
 166     struct link_map *l_loader;
 167
 168     /* Symbol hash table.  */
 169     Elf_Symndx l_nbuckets;
 170     const Elf_Symndx *l_buckets, *l_chain;
 171
 172     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 173     enum                        /* Where this object came from.  */
 174       {
 175         lt_executable,          /* The main executable program.  */
 176         lt_library,             /* Library needed by main executable.  */
 177         lt_loaded               /* Extra run-time loaded shared object.  */
 178       } l_type:2;
 179     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 180     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 181     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 182     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 183     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 184                                         to by `l_phdr' is allocated.  */
 185     unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
 186                                       the l_libname list.  */
 187     unsigned int l_faked:1;     /* Nonzero if this is a faked descriptor
 188                                    without associated file.  */
 189     unsigned int l_need_tls_init:1; /* Nonzero if GL(dl_init_static_tls)
 190                                        should be called on this link map
 191                                        when relocation finishes.  */
 192     unsigned int l_used:1;      /* Nonzero if the DSO is used.  */
 193     /* Array with version names.  */
 194     unsigned int l_nversions;
 195     struct r_found_version *l_versions;
 196
 197     /* Collected information about own RPATH directories.  */
 198     struct r_search_path_struct l_rpath_dirs;
 199
 200     /* Collected results of relocation while profiling.  */
 201     ElfW(Addr) *l_reloc_result;
 202
 203     /* Pointer to the version information if available.  */
 204     ElfW(Versym) *l_versyms;
 205
 206     /* String specifying the path where this object was found.  */
 207     const char *l_origin;
 208
 209     /* Start and finish of memory map for this object.  l_map_start
 210        need not be the same as l_addr.  */
 211     ElfW(Addr) l_map_start, l_map_end;
 212     /* End of the executable part of the mapping.  */
 213     ElfW(Addr) l_text_end;
 214
 215     /* Default array for 'l_scope'.  */
 216     struct r_scope_elem *l_scope_mem[4];
 217     /* Size of array allocated for 'l_scope'.  */
 218     size_t l_scope_max;
 219     /* This is an array defining the lookup scope for this link map.
 220        There are at most three different scope lists.  */
 221     struct r_scope_elem **l_scope;
 222
 223     /* A similar array, this time only with the local scope.  This is
 224        used occasionally.  */
 225     struct r_scope_elem *l_local_scope[2];
 226
 227     /* This information is kept to check for sure whether a shared
 228        object is the same as one already loaded.  */
 229     dev_t l_dev;
 230     ino64_t l_ino;
 231
 232     /* Collected information about own RUNPATH directories.  */
 233     struct r_search_path_struct l_runpath_dirs;
 234
 235     /* List of object in order of the init and fini calls.  */
 236     struct link_map **l_initfini;
 237
 238     /* List of the dependencies introduced through symbol binding.  */
 239     unsigned int l_reldepsmax;
 240     unsigned int l_reldepsact;
 241     struct link_map **l_reldeps;
 242
 243     /* Various flag words.  */
 244     ElfW(Word) l_feature_1;
 245     ElfW(Word) l_flags_1;
 246     ElfW(Word) l_flags;
 247
 248     /* Temporarily used in `dl_close'.  */
 249     unsigned int l_idx;
 250
 251     struct link_map_machine l_mach;
 252
 253     struct
 254     {
 255       const ElfW(Sym) *sym;
 256       int type_class;
 257 #ifdef DL_LOOKUP_RETURNS_MAP
 258       struct link_map *value;
 259 #else
 260       ElfW(Addr) value;
 261 #endif
 262       const ElfW(Sym) *ret;
 263     } l_lookup_cache;
 264
 265 #ifdef USE_TLS
 266     /* Thread-local storage related info.  */
 267
 268     /* Start of the initialization image.  */
 269     void *l_tls_initimage;
 270     /* Size of the initialization image.  */
 271     size_t l_tls_initimage_size;
 272     /* Size of the TLS block.  */
 273     size_t l_tls_blocksize;
 274     /* Alignment requirement of the TLS block.  */
 275     size_t l_tls_align;
 276     /* Offset of first byte module alignment.  */
 277     size_t l_tls_firstbyte_offset;
 278 # ifndef NO_TLS_OFFSET
 279 #  define NO_TLS_OFFSET 0
 280 # endif
 281     /* For objects present at startup time: offset in the static TLS block.  */
 282     ptrdiff_t l_tls_offset;
 283     /* Index of the module in the dtv array.  */
 284     size_t l_tls_modid;
 285 #endif
 286
 287     /* Information used to change permission after the relocations are
 288        done.  */
 289     ElfW(Addr) l_relro_addr;
 290     size_t l_relro_size;
 291   };
 292
 293 struct dl_phdr_info
 294   {
 295     ElfW(Addr) dlpi_addr;
 296     const char *dlpi_name;
 297     const ElfW(Phdr) *dlpi_phdr;
 298     ElfW(Half) dlpi_phnum;
 299
 300     unsigned long long int dlpi_adds;
 301     unsigned long long int dlpi_subs;
 302   };
 303
 304 extern int dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 305                                              size_t size, void *data),
 306                             void *data);
 307 extern int __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 308                                                size_t size, void *data),
 309                               void *data);
 310
 311 #endif /* link.h */