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 #define __need_size_t
  24 #include <stddef.h>
  25
  26 #include <elf.h>
  27
  28 /* We use this macro to refer to ELF types independent of the native wordsize.
  29    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  30 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, 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 #include <elfclass.h>           /* Defines __ELF_NATIVE_CLASS.  */
  35
  36 /* Rendezvous structure used by the run-time dynamic linker to communicate
  37    details of shared object loading to the debugger.  If the executable's
  38    dynamic section has a DT_DEBUG element, the run-time linker sets that
  39    element's value to the address where this structure can be found.  */
  40
  41 struct r_debug
  42   {
  43     int r_version;              /* Version number for this protocol.  */
  44
  45     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  46
  47     /* This is the address of a function internal to the run-time linker,
  48        that will always be called when the linker begins to map in a
  49        library or unmap it, and again when the mapping change is complete.
  50        The debugger can set a breakpoint at this address if it wants to
  51        notice shared object mapping changes.  */
  52     ElfW(Addr) r_brk;
  53     enum
  54       {
  55         /* This state value describes the mapping change taking place when
  56            the `r_brk' address is called.  */
  57         RT_CONSISTENT,          /* Mapping change is complete.  */
  58         RT_ADD,                 /* Beginning to add a new object.  */
  59         RT_DELETE,              /* Beginning to remove an object mapping.  */
  60       } r_state;
  61
  62     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  63   };
  64
  65 /* This is the instance of that structure used by the dynamic linker.  */
  66 extern struct r_debug _r_debug;
  67
  68 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  69    of whatever module refers to `_DYNAMIC'.  So, to find its own
  70    `struct r_debug', a program could do:
  71      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL)
  72        if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
  73    */
  74
  75 extern ElfW(Dyn) _DYNAMIC[];
  76
  77
  78 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  79    members form a chain of all the shared objects loaded at startup.
  80
  81    These data structures exist in space used by the run-time dynamic linker;
  82    modifying them may have disastrous results.  */
  83
  84 struct link_map
  85   {
  86     /* These first few members are part of the protocol with the debugger.
  87        This is the same format used in SVR4.  */
  88
  89     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
  90     char *l_name;               /* Absolute file name object was found in.  */
  91     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
  92     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
  93
  94     /* All following members are internal to the dynamic linker.
  95        They may change without notice.  */
  96
  97     const char *l_libname;      /* Name requested (before search).  */
  98     /* Indexed pointers to dynamic section.
  99        [0,DT_NUM) are indexed by the processor-independent tags.
 100        [DT_NUM,DT_NUM+DT_PROCNUM) are indexed by the tag minus DT_LOPROC.
 101        [DT_NUM+DT_PROCNUM,DT_NUM+DT_PROCNUM+DT_EXTRANUM) are indexed
 102        by DT_EXTRATAGIDX(tagvalue) (see <elf.h>).  */
 103
 104     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM + DT_EXTRANUM];
 105     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 106     ElfW(Addr) l_entry;         /* Entry point location.  */
 107     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 108
 109     /* Array of DT_NEEDED dependencies and their dependencies, in
 110        dependency order for symbol lookup.  This is null before the
 111        dependencies have been loaded.  */
 112     struct link_map **l_searchlist;
 113     unsigned int l_nsearchlist;
 114
 115     /* We keep another list in which we keep duplicates.  This is
 116        needed in _dl_lookup_symbol_skip to implemented RTLD_NEXT.  */
 117     struct link_map **l_dupsearchlist;
 118     unsigned int l_ndupsearchlist;
 119
 120     /* Dependent object that first caused this object to be loaded.  */
 121     struct link_map *l_loader;
 122
 123     /* Symbol hash table.  */
 124     ElfW(Symndx) l_nbuckets;
 125     const ElfW(Symndx) *l_buckets, *l_chain;
 126
 127     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 128     enum                        /* Where this object came from.  */
 129       {
 130         lt_executable,          /* The main executable program.  */
 131         lt_library,             /* Library needed by main executable.  */
 132         lt_loaded,              /* Extra run-time loaded shared object.  */
 133       } l_type:2;
 134     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 135     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 136     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 137     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 138     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 139   };
 140 \f
 141 /* Internal functions of the run-time dynamic linker.
 142    These can be accessed if you link again the dynamic linker
 143    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 144    but are not normally of interest to user programs.
 145
 146    The `-ldl' library functions in <dlfcn.h> provide a simple
 147    user interface to run-time dynamic linking.  */
 148
 149
 150 /* Cached value of `getpagesize ()'.  */
 151 extern size_t _dl_pagesize;
 152
 153 /* File descriptor referring to the zero-fill device.  */
 154 extern int _dl_zerofd;
 155
 156 /* OS-dependent function to open the zero-fill device.  */
 157 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 158
 159 /* OS-dependent function to write a message on the standard output.
 160    All arguments are `const char *'; args until a null pointer
 161    are concatenated to form the message to print.  */
 162 extern void _dl_sysdep_message (const char *string, ...);
 163
 164 /* OS-dependent function to give a fatal error message and exit
 165    when the dynamic linker fails before the program is fully linked.
 166    All arguments are `const char *'; args until a null pointer
 167    are concatenated to form the message to print.  */
 168 extern void _dl_sysdep_fatal (const char *string, ...)
 169      __attribute__ ((__noreturn__));
 170
 171 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 172    This tells the dynamic linker to ignore environment variables.  */
 173 extern int _dl_secure;
 174
 175 /* This function is called by all the internal dynamic linker functions
 176    when they encounter an error.  ERRCODE is either an `errno' code or
 177    zero; OBJECT is the name of the problematical shared object, or null if
 178    it is a general problem; ERRSTRING is a string describing the specific
 179    problem.  */
 180
 181 extern void _dl_signal_error (int errcode,
 182                               const char *object,
 183                               const char *errstring)
 184      __attribute__ ((__noreturn__));
 185
 186 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 187    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 188    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 189    code passed is the return value.  ERRSTRING if nonzero points to a
 190    malloc'ed string which the caller has to free after use.  */
 191 extern int _dl_catch_error (char **errstring,
 192                             const char **object,
 193                             void (*operate) (void));
 194
 195
 196 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 197    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 198    arranges for `dlerror' to return the error details.  */
 199 extern int _dlerror_run (void (*operate) (void));
 200
 201
 202 /* Open the shared object NAME and map in its segments.
 203    LOADER's DT_RPATH is used in searching for NAME.
 204    If the object is already opened, returns its existing map.  */
 205 extern struct link_map *_dl_map_object (struct link_map *loader,
 206                                         const char *name, int type,
 207                                         int trace_mode);
 208
 209 /* Call _dl_map_object on the dependencies of MAP, and set up
 210    MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
 211    loaded objects that will be inserted into MAP->l_searchlist after MAP
 212    but before its dependencies.  */
 213 extern void _dl_map_object_deps (struct link_map *map,
 214                                  struct link_map **preloads,
 215                                  unsigned int npreloads, int trace_mode);
 216
 217 /* Cache the locations of MAP's hash table.  */
 218 extern void _dl_setup_hash (struct link_map *map);
 219
 220
 221 /* Open the shared object NAME, relocate it, and run its initializer if it
 222    hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
 223    the object is already opened, returns its existing map.  */
 224 extern struct link_map *_dl_open (const char *name, int mode);
 225
 226 /* Close an object previously opened by _dl_open.  */
 227 extern void _dl_close (struct link_map *map);
 228
 229
 230 /* Search loaded objects' symbol tables for a definition of the symbol
 231    referred to by UNDEF.  *SYM is the symbol table entry containing the
 232    reference; it is replaced with the defining symbol, and the base load
 233    address of the defining object is returned.  SYMBOL_SCOPE is a
 234    null-terminated list of object scopes to search; each object's
 235    l_searchlist (i.e. the segment of the dependency tree starting at that
 236    object) is searched in turn.  REFERENCE_NAME should name the object
 237    containing the reference; it is used in error messages.  FLAGS is a
 238    set of flags:  */
 239 #define DL_LOOKUP_NOEXEC 1      /* Don't search the executable for a
 240                                    definition; this is used for copy
 241                                    relocs. */
 242 #define DL_LOOKUP_NOPLT 2       /* The reference must not be resolved
 243                                    to a PLT entry.  */
 244 extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
 245                                      const ElfW(Sym) **sym,
 246                                      struct link_map *symbol_scope[],
 247                                      const char *reference_name,
 248                                      int flags);
 249
 250 /* For handling RTLD_NEXT we must be able to skip shared objects.  */
 251 extern ElfW(Addr) _dl_lookup_symbol_skip (const char *undef,
 252                                           const ElfW(Sym) **sym,
 253                                           struct link_map *symbol_scope[],
 254                                           const char *reference_name,
 255                                           struct link_map *skip_this,
 256                                           int flags);
 257
 258 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 259 extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);
 260
 261
 262 /* Structure describing the dynamic linker itself.  */
 263 extern struct link_map _dl_rtld_map;
 264
 265 /* The list of objects currently loaded is the third element of the
 266    `_dl_default_scope' array, and the fourth element is always null.
 267    This leaves two slots before it that are used when resolving
 268    DT_SYMBOLIC objects' references one after it for normal references
 269    (see below).  */
 270 #define _dl_loaded      (_dl_default_scope[2])
 271 extern struct link_map *_dl_default_scope[5];
 272
 273 /* Null-terminated list of objects in the dynamic `global scope'.  The
 274    list starts at [2]; i.e. &_dl_global_scope[2] is the argument
 275    passed to _dl_lookup_symbol to search the global scope.  To search
 276    a specific object and its dependencies in preference to the global
 277    scope, fill in the [1] slot and pass its address; for two specific
 278    object scopes, fill [0] and [1].  The list is double-terminated; to
 279    search the global scope and then a specific object and its
 280    dependencies, set *_dl_global_scope_end.  This variable initially
 281    points to _dl_default_scope, and _dl_loaded is always kept in [2]
 282    of this list.  A new list is malloc'd when new objects are loaded
 283    with RTLD_GLOBAL.  */
 284 extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
 285 extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */
 286
 287 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
 288    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
 289    references made in the object MAP's relocations.  */
 290 extern struct link_map **_dl_object_relocation_scope (struct link_map *map);
 291
 292
 293 /* Allocate a `struct link_map' for a new object being loaded,
 294    and enter it into the _dl_loaded list.  */
 295 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 296                                         int type);
 297
 298 /* Relocate the given object (if it hasn't already been).
 299    SCOPE is passed to _dl_lookup_symbol in symbol lookups.
 300    If LAZY is nonzero, don't relocate its PLT.  */
 301 extern void _dl_relocate_object (struct link_map *map,
 302                                  struct link_map *scope[],
 303                                  int lazy);
 304
 305 /* Return the address of the next initializer function for MAP or one of
 306    its dependencies that has not yet been run.  When there are no more
 307    initializers to be run, this returns zero.  The functions are returned
 308    in the order they should be called.  */
 309 extern ElfW(Addr) _dl_init_next (struct link_map *map);
 310
 311 /* Call the finalizer functions of all shared objects whose
 312    initializer functions have completed.  */
 313 extern void _dl_fini (void);
 314
 315 /* The dynamic linker calls this function before and having changing
 316    any shared object mappings.  The `r_state' member of `struct r_debug'
 317    says what change is taking place.  This function's address is
 318    the value of the `r_brk' member.  */
 319 extern void _dl_debug_state (void);
 320
 321 /* Initialize `struct r_debug' if it has not already been done.  The
 322    argument is the run-time load address of the dynamic linker, to be put
 323    in the `r_ldbase' member.  Returns the address of the structure.  */
 324 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);
 325
 326
 327 #endif /* link.h */