elf/link.h

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