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 #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 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 115    members form a chain of all the shared objects loaded at startup.
 116
 117    These data structures exist in space used by the run-time dynamic linker;
 118    modifying them may have disastrous results.  */
 119
 120 struct link_map
 121   {
 122     /* These first few members are part of the protocol with the debugger.
 123        This is the same format used in SVR4.  */
 124
 125     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 126     char *l_name;               /* Absolute file name object was found in.  */
 127     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 128     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 129
 130     /* All following members are internal to the dynamic linker.
 131        They may change without notice.  */
 132
 133     struct libname_list
 134       {
 135         const char *name;       /* Name requested (before search).  */
 136         struct libname_list *next; /* Link to next name for this object.  */
 137       } *l_libname;
 138     /* Indexed pointers to dynamic section.
 139        [0,DT_NUM) are indexed by the processor-independent tags.
 140        [DT_NUM,DT_NUM+DT_PROCNUM) are indexed by the tag minus DT_LOPROC.
 141        [DT_NUM+DT_PROCNUM,DT_NUM+DT_PROCNUM+DT_EXTRANUM) are indexed
 142        by DT_EXTRATAGIDX(tagvalue) and
 143        [DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM,
 144         DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 145        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 146
 147     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM];
 148     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 149     ElfW(Addr) l_entry;         /* Entry point location.  */
 150     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 151
 152     /* Array of DT_NEEDED dependencies and their dependencies, in
 153        dependency order for symbol lookup.  This is null before the
 154        dependencies have been loaded.  */
 155     struct link_map **l_searchlist;
 156     unsigned int l_nsearchlist;
 157
 158     /* We keep another list in which we keep duplicates.  This is
 159        needed in _dl_lookup_symbol_skip to implemented RTLD_NEXT.  */
 160     struct link_map **l_dupsearchlist;
 161     unsigned int l_ndupsearchlist;
 162
 163     /* Dependent object that first caused this object to be loaded.  */
 164     struct link_map *l_loader;
 165
 166     /* Symbol hash table.  */
 167     ElfW(Symndx) l_nbuckets;
 168     const ElfW(Symndx) *l_buckets, *l_chain;
 169
 170     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 171     enum                        /* Where this object came from.  */
 172       {
 173         lt_executable,          /* The main executable program.  */
 174         lt_library,             /* Library needed by main executable.  */
 175         lt_loaded               /* Extra run-time loaded shared object.  */
 176       } l_type:2;
 177     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 178     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 179     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 180     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 181     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 182
 183     /* Array with version names.  */
 184     unsigned int l_nversions;
 185     struct r_found_version *l_versions;
 186
 187     /* Collected information about own RPATH directories.  */
 188     struct r_search_path_elem **l_rpath_dirs;
 189   };
 190
 191
 192 /* Test whether given NAME matches any of the names of the given object.  */
 193 static __inline int
 194 __attribute__ ((unused))
 195 _dl_name_match_p (const char *__name, struct link_map *__map)
 196 {
 197   int __found = strcmp (__name, __map->l_name) == 0;
 198   struct libname_list *__runp = __map->l_libname;
 199
 200   while (! __found && __runp != NULL)
 201     if (strcmp (__name, __runp->name) == 0)
 202       __found = 1;
 203     else
 204       __runp = __runp->next;
 205
 206   return __found;
 207 }
 208
 209 /* Function used as argument for `_dl_receive_error' function.  The
 210    arguments are the error code, error string, and the objname the
 211    error occurred in.  */
 212 typedef void (*receiver_fct) (int, const char *, const char *);
 213 \f
 214 /* Internal functions of the run-time dynamic linker.
 215    These can be accessed if you link again the dynamic linker
 216    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 217    but are not normally of interest to user programs.
 218
 219    The `-ldl' library functions in <dlfcn.h> provide a simple
 220    user interface to run-time dynamic linking.  */
 221
 222
 223 /* Cached value of `getpagesize ()'.  */
 224 extern size_t _dl_pagesize;
 225
 226 /* File descriptor referring to the zero-fill device.  */
 227 extern int _dl_zerofd;
 228
 229 /* Name of the shared object to be profiled (if any).  */
 230 extern const char *_dl_profile;
 231 /* Map of shared object to be profiled.  */
 232 extern struct link_map *_dl_profile_map;
 233
 234 /* OS-dependent function to open the zero-fill device.  */
 235 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 236
 237 /* OS-dependent function to write a message on the standard output.
 238    All arguments are `const char *'; args until a null pointer
 239    are concatenated to form the message to print.  */
 240 extern void _dl_sysdep_message (const char *string, ...);
 241
 242 /* OS-dependent function to write a message on the standard error.
 243    All arguments are `const char *'; args until a null pointer
 244    are concatenated to form the message to print.  */
 245 extern void _dl_sysdep_error (const char *string, ...);
 246
 247 /* OS-dependent function to give a fatal error message and exit
 248    when the dynamic linker fails before the program is fully linked.
 249    All arguments are `const char *'; args until a null pointer
 250    are concatenated to form the message to print.  */
 251 extern void _dl_sysdep_fatal (const char *string, ...)
 252      __attribute__ ((__noreturn__));
 253
 254 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 255    This tells the dynamic linker to ignore environment variables.  */
 256 extern int _dl_secure;
 257
 258 /* This function is called by all the internal dynamic linker functions
 259    when they encounter an error.  ERRCODE is either an `errno' code or
 260    zero; OBJECT is the name of the problematical shared object, or null if
 261    it is a general problem; ERRSTRING is a string describing the specific
 262    problem.  */
 263 extern void _dl_signal_error (int errcode,
 264                               const char *object,
 265                               const char *errstring);
 266
 267 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 268    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 269    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 270    code passed is the return value.  ERRSTRING if nonzero points to a
 271    malloc'ed string which the caller has to free after use.
 272    ARGS is passed as argument to OPERATE.  */
 273 extern int _dl_catch_error (char **errstring,
 274                             const char **object,
 275                             void (*operate) (void *),
 276                             void *args);
 277
 278 /* Call OPERATE, receiving errors from `dl_signal_error'.  Unlike
 279    `_dl_catch_error' the operation is resumed after the OPERATE
 280    function returns.
 281    ARGS is passed as argument to OPERATE.  */
 282 extern void _dl_receive_error (receiver_fct fct, void (*operate) (void *),
 283                                void *args);
 284
 285
 286 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 287    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 288    arranges for `dlerror' to return the error details.
 289    ARGS is passed as argument to OPERATE.  */
 290 extern int _dlerror_run (void (*operate) (void *), void *args);
 291
 292
 293 /* Open the shared object NAME and map in its segments.
 294    LOADER's DT_RPATH is used in searching for NAME.
 295    If the object is already opened, returns its existing map.  */
 296 extern struct link_map *_dl_map_object (struct link_map *loader,
 297                                         const char *name, int type,
 298                                         int trace_mode);
 299
 300 /* Call _dl_map_object on the dependencies of MAP, and set up
 301    MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
 302    loaded objects that will be inserted into MAP->l_searchlist after MAP
 303    but before its dependencies.  */
 304 extern void _dl_map_object_deps (struct link_map *map,
 305                                  struct link_map **preloads,
 306                                  unsigned int npreloads, int trace_mode);
 307
 308 /* Cache the locations of MAP's hash table.  */
 309 extern void _dl_setup_hash (struct link_map *map);
 310
 311
 312 /* Open the shared object NAME, relocate it, and run its initializer if it
 313    hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
 314    the object is already opened, returns its existing map.  */
 315 extern struct link_map *_dl_open (const char *name, int mode);
 316
 317 /* Close an object previously opened by _dl_open.  */
 318 extern void _dl_close (struct link_map *map);
 319
 320
 321 /* Search loaded objects' symbol tables for a definition of the symbol
 322    referred to by UNDEF.  *SYM is the symbol table entry containing the
 323    reference; it is replaced with the defining symbol, and the base load
 324    address of the defining object is returned.  SYMBOL_SCOPE is a
 325    null-terminated list of object scopes to search; each object's
 326    l_searchlist (i.e. the segment of the dependency tree starting at that
 327    object) is searched in turn.  REFERENCE_NAME should name the object
 328    containing the reference; it is used in error messages.
 329    RELOC_TYPE is a machine-dependent reloc type, which is passed to
 330    the `elf_machine_lookup_*_p' macros in dl-machine.h to affect which
 331    symbols can be chosen.  */
 332 extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
 333                                      const ElfW(Sym) **sym,
 334                                      struct link_map *symbol_scope[],
 335                                      const char *reference_name,
 336                                      int reloc_type);
 337
 338 /* Lookup versioned symbol.  */
 339 extern ElfW(Addr) _dl_lookup_versioned_symbol (const char *undef,
 340                                                const ElfW(Sym) **sym,
 341                                                struct link_map *symbol_scope[],
 342                                                const char *reference_name,
 343                                                const struct r_found_version *version,
 344                                                int reloc_type);
 345
 346 /* For handling RTLD_NEXT we must be able to skip shared objects.  */
 347 extern ElfW(Addr) _dl_lookup_symbol_skip (const char *undef,
 348                                           const ElfW(Sym) **sym,
 349                                           struct link_map *symbol_scope[],
 350                                           const char *reference_name,
 351                                           struct link_map *skip_this);
 352
 353 /* For handling RTLD_NEXT with versioned symbols we must be able to
 354    skip shared objects.  */
 355 extern ElfW(Addr) _dl_lookup_versioned_symbol_skip (const char *undef,
 356                                                     const ElfW(Sym) **sym,
 357                                                     struct link_map *symbol_scope[],
 358                                                     const char *reference_name,
 359                                                     const struct r_found_version *version,
 360                                                     struct link_map *skip_this);
 361
 362 /* Locate shared object containing the given address.  */
 363 extern int _dl_addr (const void *address, Dl_info *info);
 364
 365 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 366 extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);
 367
 368
 369 /* Structure describing the dynamic linker itself.  */
 370 extern struct link_map _dl_rtld_map;
 371
 372 /* The list of objects currently loaded is the third element of the
 373    `_dl_default_scope' array, and the fourth element is always null.
 374    This leaves two slots before it that are used when resolving
 375    DT_SYMBOLIC objects' references one after it for normal references
 376    (see below).  */
 377 #define _dl_loaded      (_dl_default_scope[2])
 378 extern struct link_map *_dl_default_scope[5];
 379
 380 /* Null-terminated list of objects in the dynamic `global scope'.  The
 381    list starts at [2]; i.e. &_dl_global_scope[2] is the argument
 382    passed to _dl_lookup_symbol to search the global scope.  To search
 383    a specific object and its dependencies in preference to the global
 384    scope, fill in the [1] slot and pass its address; for two specific
 385    object scopes, fill [0] and [1].  The list is double-terminated; to
 386    search the global scope and then a specific object and its
 387    dependencies, set *_dl_global_scope_end.  This variable initially
 388    points to _dl_default_scope, and _dl_loaded is always kept in [2]
 389    of this list.  A new list is malloc'd when new objects are loaded
 390    with RTLD_GLOBAL.  */
 391 extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
 392 extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */
 393
 394 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
 395    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
 396    references made in the object MAP's relocations.  */
 397 extern struct link_map **_dl_object_relocation_scope (struct link_map *map);
 398
 399
 400 /* Allocate a `struct link_map' for a new object being loaded,
 401    and enter it into the _dl_loaded list.  */
 402 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 403                                         int type);
 404
 405 /* Relocate the given object (if it hasn't already been).
 406    SCOPE is passed to _dl_lookup_symbol in symbol lookups.
 407    If LAZY is nonzero, don't relocate its PLT.  */
 408 extern void _dl_relocate_object (struct link_map *map,
 409                                  struct link_map *scope[],
 410                                  int lazy);
 411
 412 /* Check the version dependencies of all objects available through
 413    MAP.  If VERBOSE print some more diagnostics.  */
 414 extern int _dl_check_all_versions (struct link_map *map, int verbose);
 415
 416 /* Check the version dependencies for MAP.  If VERBOSE print some more
 417    diagnostics.  */
 418 extern int _dl_check_map_versions (struct link_map *map, int verbose);
 419
 420 /* Return the address of the next initializer function for MAP or one of
 421    its dependencies that has not yet been run.  When there are no more
 422    initializers to be run, this returns zero.  The functions are returned
 423    in the order they should be called.  */
 424 extern ElfW(Addr) _dl_init_next (struct link_map *map);
 425
 426 /* Call the finalizer functions of all shared objects whose
 427    initializer functions have completed.  */
 428 extern void _dl_fini (void);
 429
 430 /* The dynamic linker calls this function before and having changing
 431    any shared object mappings.  The `r_state' member of `struct r_debug'
 432    says what change is taking place.  This function's address is
 433    the value of the `r_brk' member.  */
 434 extern void _dl_debug_state (void);
 435
 436 /* Initialize `struct r_debug' if it has not already been done.  The
 437    argument is the run-time load address of the dynamic linker, to be put
 438    in the `r_ldbase' member.  Returns the address of the structure.  */
 439 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);
 440
 441 /* Initialize the basic data structure for the search paths.  */
 442 extern void _dl_init_paths (void);
 443
 444 /* Gather the information needed to install the profiling tables and start
 445    the timers.  */
 446 extern void _dl_start_profile (struct link_map *map, const char *output_dir);
 447
 448 /* The actual functions used to keep book on the calls.  */
 449 extern void _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc);
 450
 451
 452 /* Show the member of the auxiliry aray passed up from the kernel.  */
 453 extern void _dl_show_auxv (void);
 454
 455 __END_DECLS
 456
 457 #endif /* link.h */