elf/link.h

   1 /* Run-time dynamic linker data structures for loaded ELF shared objects.
   2    Copyright (C) 1995, 1996, 1997, 1998 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #ifndef _LINK_H
  21 #define _LINK_H 1
  22
  23 #include <features.h>
  24
  25 #define __need_size_t
  26 #define __need_NULL
  27 #include <stddef.h>
  28
  29 #include <elf.h>
  30 #include <dlfcn.h>
  31
  32 __BEGIN_DECLS
  33
  34 /* We use this macro to refer to ELF types independent of the native wordsize.
  35    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  36 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, type)
  37 #define ELFW(type)      _ElfW (ELF, __ELF_NATIVE_CLASS, type)
  38 #define _ElfW(e,w,t)    _ElfW_1 (e, w, _##t)
  39 #define _ElfW_1(e,w,t)  e##w##t
  40
  41 #include <bits/elfclass.h>              /* Defines __ELF_NATIVE_CLASS.  */
  42
  43 /* Rendezvous structure used by the run-time dynamic linker to communicate
  44    details of shared object loading to the debugger.  If the executable's
  45    dynamic section has a DT_DEBUG element, the run-time linker sets that
  46    element's value to the address where this structure can be found.  */
  47
  48 struct r_debug
  49   {
  50     int r_version;              /* Version number for this protocol.  */
  51
  52     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  53
  54     /* This is the address of a function internal to the run-time linker,
  55        that will always be called when the linker begins to map in a
  56        library or unmap it, and again when the mapping change is complete.
  57        The debugger can set a breakpoint at this address if it wants to
  58        notice shared object mapping changes.  */
  59     ElfW(Addr) r_brk;
  60     enum
  61       {
  62         /* This state value describes the mapping change taking place when
  63            the `r_brk' address is called.  */
  64         RT_CONSISTENT,          /* Mapping change is complete.  */
  65         RT_ADD,                 /* Beginning to add a new object.  */
  66         RT_DELETE               /* Beginning to remove an object mapping.  */
  67       } r_state;
  68
  69     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  70   };
  71
  72 /* This is the instance of that structure used by the dynamic linker.  */
  73 extern struct r_debug _r_debug;
  74
  75 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  76    of whatever module refers to `_DYNAMIC'.  So, to find its own
  77    `struct r_debug', a program could do:
  78      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL)
  79        if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
  80    */
  81
  82 extern ElfW(Dyn) _DYNAMIC[];
  83
  84 /* For the version handling we need an array with only names and their
  85    hash values.  */
  86 struct r_found_version
  87   {
  88     const char *name;
  89     ElfW(Word) hash;
  90
  91     int hidden;
  92     const char *filename;
  93   };
  94
  95 /* We want to cache information about the searches for shared objects.  */
  96
  97 enum r_dir_status { unknown, nonexisting, existing };
  98
  99 struct r_search_path_elem
 100   {
 101     const char *dirname;
 102
 103     size_t dirnamelen;
 104     enum r_dir_status dirstatus;
 105
 106     size_t machdirnamelen;
 107     enum r_dir_status machdirstatus;
 108
 109     /* This link is only used in the `all_dirs' member of `r_search_path'.  */
 110     struct r_search_path_elem *next;
 111   };
 112
 113
 114 /* A data structure for a simple single linked list of strings.  */
 115 struct libname_list
 116   {
 117     const char *name;           /* Name requested (before search).  */
 118     struct libname_list *next;  /* Link to next name for this object.  */
 119   };
 120
 121
 122 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 123    members form a chain of all the shared objects loaded at startup.
 124
 125    These data structures exist in space used by the run-time dynamic linker;
 126    modifying them may have disastrous results.  */
 127
 128 struct link_map
 129   {
 130     /* These first few members are part of the protocol with the debugger.
 131        This is the same format used in SVR4.  */
 132
 133     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 134     char *l_name;               /* Absolute file name object was found in.  */
 135     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 136     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 137
 138     /* All following members are internal to the dynamic linker.
 139        They may change without notice.  */
 140
 141     struct libname_list  *l_libname;
 142     /* Indexed pointers to dynamic section.
 143        [0,DT_NUM) are indexed by the processor-independent tags.
 144        [DT_NUM,DT_NUM+DT_PROCNUM) are indexed by the tag minus DT_LOPROC.
 145        [DT_NUM+DT_PROCNUM,DT_NUM+DT_PROCNUM+DT_EXTRANUM) are indexed
 146        by DT_EXTRATAGIDX(tagvalue) and
 147        [DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM,
 148         DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 149        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 150
 151     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM];
 152     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 153     ElfW(Addr) l_entry;         /* Entry point location.  */
 154     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 155
 156     /* Array of DT_NEEDED dependencies and their dependencies, in
 157        dependency order for symbol lookup.  This is null before the
 158        dependencies have been loaded.  */
 159     struct link_map **l_searchlist;
 160     unsigned int l_nsearchlist;
 161
 162     /* We keep another list in which we keep duplicates.  This is
 163        needed in _dl_lookup_symbol_skip to implemented RTLD_NEXT.  */
 164     struct link_map **l_dupsearchlist;
 165     unsigned int l_ndupsearchlist;
 166
 167     /* Dependent object that first caused this object to be loaded.  */
 168     struct link_map *l_loader;
 169
 170     /* Symbol hash table.  */
 171     ElfW(Symndx) l_nbuckets;
 172     const ElfW(Symndx) *l_buckets, *l_chain;
 173
 174     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 175     enum                        /* Where this object came from.  */
 176       {
 177         lt_executable,          /* The main executable program.  */
 178         lt_library,             /* Library needed by main executable.  */
 179         lt_loaded               /* Extra run-time loaded shared object.  */
 180       } l_type:2;
 181     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 182     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 183     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 184     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 185     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 186
 187     /* Array with version names.  */
 188     unsigned int l_nversions;
 189     struct r_found_version *l_versions;
 190
 191     /* Collected information about own RPATH directories.  */
 192     struct r_search_path_elem **l_rpath_dirs;
 193   };
 194
 195
 196 /* Test whether given NAME matches any of the names of the given object.  */
 197 static __inline int
 198 __attribute__ ((unused))
 199 _dl_name_match_p (const char *__name, struct link_map *__map)
 200 {
 201   int __found = strcmp (__name, __map->l_name) == 0;
 202   struct libname_list *__runp = __map->l_libname;
 203
 204   while (! __found && __runp != NULL)
 205     if (strcmp (__name, __runp->name) == 0)
 206       __found = 1;
 207     else
 208       __runp = __runp->next;
 209
 210   return __found;
 211 }
 212
 213 /* Function used as argument for `_dl_receive_error' function.  The
 214    arguments are the error code, error string, and the objname the
 215    error occurred in.  */
 216 typedef void (*receiver_fct) (int, const char *, const char *);
 217 \f
 218 /* Internal functions of the run-time dynamic linker.
 219    These can be accessed if you link again the dynamic linker
 220    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 221    but are not normally of interest to user programs.
 222
 223    The `-ldl' library functions in <dlfcn.h> provide a simple
 224    user interface to run-time dynamic linking.  */
 225
 226
 227 /* Cached value of `getpagesize ()'.  */
 228 extern size_t _dl_pagesize;
 229
 230 /* File descriptor referring to the zero-fill device.  */
 231 extern int _dl_zerofd;
 232
 233 /* Name of the shared object to be profiled (if any).  */
 234 extern const char *_dl_profile;
 235 /* Map of shared object to be profiled.  */
 236 extern struct link_map *_dl_profile_map;
 237
 238 /* OS-dependent function to open the zero-fill device.  */
 239 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 240
 241 /* OS-dependent function to write a message on the standard output.
 242    All arguments are `const char *'; args until a null pointer
 243    are concatenated to form the message to print.  */
 244 extern void _dl_sysdep_message (const char *string, ...);
 245
 246 /* OS-dependent function to write a message on the standard error.
 247    All arguments are `const char *'; args until a null pointer
 248    are concatenated to form the message to print.  */
 249 extern void _dl_sysdep_error (const char *string, ...);
 250
 251 /* OS-dependent function to give a fatal error message and exit
 252    when the dynamic linker fails before the program is fully linked.
 253    All arguments are `const char *'; args until a null pointer
 254    are concatenated to form the message to print.  */
 255 extern void _dl_sysdep_fatal (const char *string, ...)
 256      __attribute__ ((__noreturn__));
 257
 258 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 259    This tells the dynamic linker to ignore environment variables.  */
 260 extern int _dl_secure;
 261
 262 /* This function is called by all the internal dynamic linker functions
 263    when they encounter an error.  ERRCODE is either an `errno' code or
 264    zero; OBJECT is the name of the problematical shared object, or null if
 265    it is a general problem; ERRSTRING is a string describing the specific
 266    problem.  */
 267 extern void _dl_signal_error (int errcode,
 268                               const char *object,
 269                               const char *errstring);
 270
 271 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 272    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 273    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 274    code passed is the return value.  ERRSTRING if nonzero points to a
 275    malloc'ed string which the caller has to free after use.
 276    ARGS is passed as argument to OPERATE.  */
 277 extern int _dl_catch_error (char **errstring,
 278                             const char **object,
 279                             void (*operate) (void *),
 280                             void *args);
 281
 282 /* Call OPERATE, receiving errors from `dl_signal_error'.  Unlike
 283    `_dl_catch_error' the operation is resumed after the OPERATE
 284    function returns.
 285    ARGS is passed as argument to OPERATE.  */
 286 extern void _dl_receive_error (receiver_fct fct, void (*operate) (void *),
 287                                void *args);
 288
 289
 290 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 291    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 292    arranges for `dlerror' to return the error details.
 293    ARGS is passed as argument to OPERATE.  */
 294 extern int _dlerror_run (void (*operate) (void *), void *args);
 295
 296
 297 /* Open the shared object NAME and map in its segments.
 298    LOADER's DT_RPATH is used in searching for NAME.
 299    If the object is already opened, returns its existing map.
 300    For preloaded shared objects PRELOADED is set to a non-zero
 301    value to allow additional security checks.  */
 302 extern struct link_map *_dl_map_object (struct link_map *loader,
 303                                         const char *name, int preloaded,
 304                                         int type, int trace_mode);
 305
 306 /* Call _dl_map_object on the dependencies of MAP, and set up
 307    MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
 308    loaded objects that will be inserted into MAP->l_searchlist after MAP
 309    but before its dependencies.  */
 310 extern void _dl_map_object_deps (struct link_map *map,
 311                                  struct link_map **preloads,
 312                                  unsigned int npreloads, int trace_mode);
 313
 314 /* Cache the locations of MAP's hash table.  */
 315 extern void _dl_setup_hash (struct link_map *map);
 316
 317
 318 /* Open the shared object NAME, relocate it, and run its initializer if it
 319    hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
 320    the object is already opened, returns its existing map.  */
 321 extern struct link_map *_dl_open (const char *name, int mode);
 322
 323 /* Close an object previously opened by _dl_open.  */
 324 extern void _dl_close (struct link_map *map);
 325
 326
 327 /* Search loaded objects' symbol tables for a definition of the symbol
 328    referred to by UNDEF.  *SYM is the symbol table entry containing the
 329    reference; it is replaced with the defining symbol, and the base load
 330    address of the defining object is returned.  SYMBOL_SCOPE is a
 331    null-terminated list of object scopes to search; each object's
 332    l_searchlist (i.e. the segment of the dependency tree starting at that
 333    object) is searched in turn.  REFERENCE_NAME should name the object
 334    containing the reference; it is used in error messages.
 335    RELOC_TYPE is a machine-dependent reloc type, which is passed to
 336    the `elf_machine_lookup_*_p' macros in dl-machine.h to affect which
 337    symbols can be chosen.  */
 338 extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
 339                                      const ElfW(Sym) **sym,
 340                                      struct link_map *symbol_scope[],
 341                                      const char *reference_name,
 342                                      int reloc_type);
 343
 344 /* Lookup versioned symbol.  */
 345 extern ElfW(Addr) _dl_lookup_versioned_symbol (const char *undef,
 346                                                const ElfW(Sym) **sym,
 347                                                struct link_map *symbol_scope[],
 348                                                const char *reference_name,
 349                                                const struct r_found_version *version,
 350                                                int reloc_type);
 351
 352 /* For handling RTLD_NEXT we must be able to skip shared objects.  */
 353 extern ElfW(Addr) _dl_lookup_symbol_skip (const char *undef,
 354                                           const ElfW(Sym) **sym,
 355                                           struct link_map *symbol_scope[],
 356                                           const char *reference_name,
 357                                           struct link_map *skip_this);
 358
 359 /* For handling RTLD_NEXT with versioned symbols we must be able to
 360    skip shared objects.  */
 361 extern ElfW(Addr) _dl_lookup_versioned_symbol_skip (const char *undef,
 362                                                     const ElfW(Sym) **sym,
 363                                                     struct link_map *symbol_scope[],
 364                                                     const char *reference_name,
 365                                                     const struct r_found_version *version,
 366                                                     struct link_map *skip_this);
 367
 368 /* Locate shared object containing the given address.  */
 369 extern int _dl_addr (const void *address, Dl_info *info);
 370
 371 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 372 extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);
 373
 374
 375 /* Structure describing the dynamic linker itself.  */
 376 extern struct link_map _dl_rtld_map;
 377
 378 /* The list of objects currently loaded is the third element of the
 379    `_dl_default_scope' array, and the fourth element is always null.
 380    This leaves two slots before it that are used when resolving
 381    DT_SYMBOLIC objects' references one after it for normal references
 382    (see below).  */
 383 #define _dl_loaded      (_dl_default_scope[2])
 384 extern struct link_map *_dl_default_scope[5];
 385
 386 /* Null-terminated list of objects in the dynamic `global scope'.  The
 387    list starts at [2]; i.e. &_dl_global_scope[2] is the argument
 388    passed to _dl_lookup_symbol to search the global scope.  To search
 389    a specific object and its dependencies in preference to the global
 390    scope, fill in the [1] slot and pass its address; for two specific
 391    object scopes, fill [0] and [1].  The list is double-terminated; to
 392    search the global scope and then a specific object and its
 393    dependencies, set *_dl_global_scope_end.  This variable initially
 394    points to _dl_default_scope, and _dl_loaded is always kept in [2]
 395    of this list.  A new list is malloc'd when new objects are loaded
 396    with RTLD_GLOBAL.  */
 397 extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
 398 extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */
 399
 400 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
 401    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
 402    references made in the object MAP's relocations.  */
 403 extern struct link_map **_dl_object_relocation_scope (struct link_map *map);
 404
 405
 406 /* Allocate a `struct link_map' for a new object being loaded,
 407    and enter it into the _dl_loaded list.  */
 408 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 409                                         int type);
 410
 411 /* Relocate the given object (if it hasn't already been).
 412    SCOPE is passed to _dl_lookup_symbol in symbol lookups.
 413    If LAZY is nonzero, don't relocate its PLT.  */
 414 extern void _dl_relocate_object (struct link_map *map,
 415                                  struct link_map *scope[],
 416                                  int lazy);
 417
 418 /* Check the version dependencies of all objects available through
 419    MAP.  If VERBOSE print some more diagnostics.  */
 420 extern int _dl_check_all_versions (struct link_map *map, int verbose);
 421
 422 /* Check the version dependencies for MAP.  If VERBOSE print some more
 423    diagnostics.  */
 424 extern int _dl_check_map_versions (struct link_map *map, int verbose);
 425
 426 /* Return the address of the next initializer function for MAP or one of
 427    its dependencies that has not yet been run.  When there are no more
 428    initializers to be run, this returns zero.  The functions are returned
 429    in the order they should be called.  */
 430 extern ElfW(Addr) _dl_init_next (struct link_map *map);
 431
 432 /* Call the finalizer functions of all shared objects whose
 433    initializer functions have completed.  */
 434 extern void _dl_fini (void);
 435
 436 /* The dynamic linker calls this function before and having changing
 437    any shared object mappings.  The `r_state' member of `struct r_debug'
 438    says what change is taking place.  This function's address is
 439    the value of the `r_brk' member.  */
 440 extern void _dl_debug_state (void);
 441
 442 /* Initialize `struct r_debug' if it has not already been done.  The
 443    argument is the run-time load address of the dynamic linker, to be put
 444    in the `r_ldbase' member.  Returns the address of the structure.  */
 445 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);
 446
 447 /* Initialize the basic data structure for the search paths.  */
 448 extern void _dl_init_paths (const char *library_path);
 449
 450 /* Gather the information needed to install the profiling tables and start
 451    the timers.  */
 452 extern void _dl_start_profile (struct link_map *map, const char *output_dir);
 453
 454 /* The actual functions used to keep book on the calls.  */
 455 extern void _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc);
 456
 457
 458 /* Show the members of the auxiliry aray passed up from the kernel.  */
 459 extern void _dl_show_auxv (void);
 460
 461 __END_DECLS
 462
 463 #endif /* link.h */