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
  22 #define _LINK_H 1
  23 #include <features.h>
  24
  25 #define __need_size_t
  26 #include <stddef.h>
  27
  28 #include <elf.h>
  29
  30 __BEGIN_DECLS
  31
  32 /* We use this macro to refer to ELF types independent of the native wordsize.
  33    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  34 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, type)
  35 #define ELFW(type)      _ElfW (ELF, __ELF_NATIVE_CLASS, type)
  36 #define _ElfW(e,w,t)    _ElfW_1 (e, w, _##t)
  37 #define _ElfW_1(e,w,t)  e##w##t
  38 #include <elfclass.h>           /* Defines __ELF_NATIVE_CLASS.  */
  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)
  76        if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
  77    */
  78
  79 extern ElfW(Dyn) _DYNAMIC[];
  80
  81
  82 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  83    members form a chain of all the shared objects loaded at startup.
  84
  85    These data structures exist in space used by the run-time dynamic linker;
  86    modifying them may have disastrous results.  */
  87
  88 struct link_map
  89   {
  90     /* These first few members are part of the protocol with the debugger.
  91        This is the same format used in SVR4.  */
  92
  93     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
  94     char *l_name;               /* Absolute file name object was found in.  */
  95     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
  96     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
  97
  98     /* All following members are internal to the dynamic linker.
  99        They may change without notice.  */
 100
 101     const char *l_libname;      /* Name requested (before search).  */
 102     /* Indexed pointers to dynamic section.
 103        [0,DT_NUM) are indexed by the processor-independent tags.
 104        [DT_NUM,DT_NUM+DT_PROCNUM) are indexed by the tag minus DT_LOPROC.
 105        [DT_NUM+DT_PROCNUM,DT_NUM+DT_PROCNUM+DT_EXTRANUM) are indexed
 106        by DT_EXTRATAGIDX(tagvalue) and
 107        [DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM,
 108         DT_NUM+DT_PROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM)
 109        are indexed by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 110
 111     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM];
 112     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 113     ElfW(Addr) l_entry;         /* Entry point location.  */
 114     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 115
 116     /* Array of DT_NEEDED dependencies and their dependencies, in
 117        dependency order for symbol lookup.  This is null before the
 118        dependencies have been loaded.  */
 119     struct link_map **l_searchlist;
 120     unsigned int l_nsearchlist;
 121
 122     /* We keep another list in which we keep duplicates.  This is
 123        needed in _dl_lookup_symbol_skip to implemented RTLD_NEXT.  */
 124     struct link_map **l_dupsearchlist;
 125     unsigned int l_ndupsearchlist;
 126
 127     /* Dependent object that first caused this object to be loaded.  */
 128     struct link_map *l_loader;
 129
 130     /* Symbol hash table.  */
 131     ElfW(Symndx) l_nbuckets;
 132     const ElfW(Symndx) *l_buckets, *l_chain;
 133
 134     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 135     enum                        /* Where this object came from.  */
 136       {
 137         lt_executable,          /* The main executable program.  */
 138         lt_library,             /* Library needed by main executable.  */
 139         lt_loaded,              /* Extra run-time loaded shared object.  */
 140       } l_type:2;
 141     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 142     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 143     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 144     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 145     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 146   };
 147
 148
 149 /* Function used as argument for `_dl_receive_error' function.  The
 150    arguments are the error string and the objname the error occurred
 151    in.  */
 152 typedef void (*receiver_fct) (const char *, const char *);
 153 \f
 154 /* Internal functions of the run-time dynamic linker.
 155    These can be accessed if you link again the dynamic linker
 156    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 157    but are not normally of interest to user programs.
 158
 159    The `-ldl' library functions in <dlfcn.h> provide a simple
 160    user interface to run-time dynamic linking.  */
 161
 162
 163 /* Cached value of `getpagesize ()'.  */
 164 extern size_t _dl_pagesize;
 165
 166 /* File descriptor referring to the zero-fill device.  */
 167 extern int _dl_zerofd;
 168
 169 /* OS-dependent function to open the zero-fill device.  */
 170 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 171
 172 /* OS-dependent function to write a message on the standard output.
 173    All arguments are `const char *'; args until a null pointer
 174    are concatenated to form the message to print.  */
 175 extern void _dl_sysdep_message (const char *string, ...);
 176
 177 /* OS-dependent function to write a message on the standard error.
 178    All arguments are `const char *'; args until a null pointer
 179    are concatenated to form the message to print.  */
 180 extern void _dl_sysdep_error (const char *string, ...);
 181
 182 /* OS-dependent function to give a fatal error message and exit
 183    when the dynamic linker fails before the program is fully linked.
 184    All arguments are `const char *'; args until a null pointer
 185    are concatenated to form the message to print.  */
 186 extern void _dl_sysdep_fatal (const char *string, ...)
 187      __attribute__ ((__noreturn__));
 188
 189 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 190    This tells the dynamic linker to ignore environment variables.  */
 191 extern int _dl_secure;
 192
 193 /* This function is called by all the internal dynamic linker functions
 194    when they encounter an error.  ERRCODE is either an `errno' code or
 195    zero; OBJECT is the name of the problematical shared object, or null if
 196    it is a general problem; ERRSTRING is a string describing the specific
 197    problem.  */
 198 extern void _dl_signal_error (int errcode,
 199                               const char *object,
 200                               const char *errstring);
 201
 202 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 203    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 204    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 205    code passed is the return value.  ERRSTRING if nonzero points to a
 206    malloc'ed string which the caller has to free after use.  */
 207 extern int _dl_catch_error (char **errstring,
 208                             const char **object,
 209                             void (*operate) (void));
 210
 211 /* Call OPERATE, receiving errors from `dl_signal_error'.  Unlike
 212    `_dl_catch_error' the operation is resumed after the OPERATE
 213    function returns.  */
 214 extern void _dl_receive_error (receiver_fct fct, void (*operate) (void));
 215
 216
 217 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 218    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 219    arranges for `dlerror' to return the error details.  */
 220 extern int _dlerror_run (void (*operate) (void));
 221
 222
 223 /* Open the shared object NAME and map in its segments.
 224    LOADER's DT_RPATH is used in searching for NAME.
 225    If the object is already opened, returns its existing map.  */
 226 extern struct link_map *_dl_map_object (struct link_map *loader,
 227                                         const char *name, int type,
 228                                         int trace_mode);
 229
 230 /* Call _dl_map_object on the dependencies of MAP, and set up
 231    MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
 232    loaded objects that will be inserted into MAP->l_searchlist after MAP
 233    but before its dependencies.  */
 234 extern void _dl_map_object_deps (struct link_map *map,
 235                                  struct link_map **preloads,
 236                                  unsigned int npreloads, int trace_mode);
 237
 238 /* Cache the locations of MAP's hash table.  */
 239 extern void _dl_setup_hash (struct link_map *map);
 240
 241
 242 /* Open the shared object NAME, relocate it, and run its initializer if it
 243    hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
 244    the object is already opened, returns its existing map.  */
 245 extern struct link_map *_dl_open (const char *name, int mode);
 246
 247 /* Close an object previously opened by _dl_open.  */
 248 extern void _dl_close (struct link_map *map);
 249
 250
 251 /* Search loaded objects' symbol tables for a definition of the symbol
 252    referred to by UNDEF.  *SYM is the symbol table entry containing the
 253    reference; it is replaced with the defining symbol, and the base load
 254    address of the defining object is returned.  SYMBOL_SCOPE is a
 255    null-terminated list of object scopes to search; each object's
 256    l_searchlist (i.e. the segment of the dependency tree starting at that
 257    object) is searched in turn.  REFERENCE_NAME should name the object
 258    containing the reference; it is used in error messages.  FLAGS is a
 259    set of flags:  */
 260 #define DL_LOOKUP_NOEXEC 1      /* Don't search the executable for a
 261                                    definition; this is used for copy
 262                                    relocs. */
 263 #define DL_LOOKUP_NOPLT 2       /* The reference must not be resolved
 264                                    to a PLT entry.  */
 265 extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
 266                                      const ElfW(Sym) **sym,
 267                                      struct link_map *symbol_scope[],
 268                                      const char *reference_name,
 269                                      int flags);
 270
 271 /* For handling RTLD_NEXT we must be able to skip shared objects.  */
 272 extern ElfW(Addr) _dl_lookup_symbol_skip (const char *undef,
 273                                           const ElfW(Sym) **sym,
 274                                           struct link_map *symbol_scope[],
 275                                           const char *reference_name,
 276                                           struct link_map *skip_this,
 277                                           int flags);
 278
 279 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 280 extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);
 281
 282
 283 /* Structure describing the dynamic linker itself.  */
 284 extern struct link_map _dl_rtld_map;
 285
 286 /* The list of objects currently loaded is the third element of the
 287    `_dl_default_scope' array, and the fourth element is always null.
 288    This leaves two slots before it that are used when resolving
 289    DT_SYMBOLIC objects' references one after it for normal references
 290    (see below).  */
 291 #define _dl_loaded      (_dl_default_scope[2])
 292 extern struct link_map *_dl_default_scope[5];
 293
 294 /* Null-terminated list of objects in the dynamic `global scope'.  The
 295    list starts at [2]; i.e. &_dl_global_scope[2] is the argument
 296    passed to _dl_lookup_symbol to search the global scope.  To search
 297    a specific object and its dependencies in preference to the global
 298    scope, fill in the [1] slot and pass its address; for two specific
 299    object scopes, fill [0] and [1].  The list is double-terminated; to
 300    search the global scope and then a specific object and its
 301    dependencies, set *_dl_global_scope_end.  This variable initially
 302    points to _dl_default_scope, and _dl_loaded is always kept in [2]
 303    of this list.  A new list is malloc'd when new objects are loaded
 304    with RTLD_GLOBAL.  */
 305 extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
 306 extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */
 307
 308 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
 309    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
 310    references made in the object MAP's relocations.  */
 311 extern struct link_map **_dl_object_relocation_scope (struct link_map *map);
 312
 313
 314 /* Allocate a `struct link_map' for a new object being loaded,
 315    and enter it into the _dl_loaded list.  */
 316 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 317                                         int type);
 318
 319 /* Relocate the given object (if it hasn't already been).
 320    SCOPE is passed to _dl_lookup_symbol in symbol lookups.
 321    If LAZY is nonzero, don't relocate its PLT.  */
 322 extern void _dl_relocate_object (struct link_map *map,
 323                                  struct link_map *scope[],
 324                                  int lazy);
 325
 326 /* Return the address of the next initializer function for MAP or one of
 327    its dependencies that has not yet been run.  When there are no more
 328    initializers to be run, this returns zero.  The functions are returned
 329    in the order they should be called.  */
 330 extern ElfW(Addr) _dl_init_next (struct link_map *map);
 331
 332 /* Call the finalizer functions of all shared objects whose
 333    initializer functions have completed.  */
 334 extern void _dl_fini (void);
 335
 336 /* The dynamic linker calls this function before and having changing
 337    any shared object mappings.  The `r_state' member of `struct r_debug'
 338    says what change is taking place.  This function's address is
 339    the value of the `r_brk' member.  */
 340 extern void _dl_debug_state (void);
 341
 342 /* Initialize `struct r_debug' if it has not already been done.  The
 343    argument is the run-time load address of the dynamic linker, to be put
 344    in the `r_ldbase' member.  Returns the address of the structure.  */
 345 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);
 346
 347 __END_DECLS
 348
 349 #endif /* link.h */