elf/link.h

   1 /* Run-time dynamic linker data structures for loaded ELF shared objects.
   2 Copyright (C) 1995, 1996 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
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, 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     ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM];
 102     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 103     ElfW(Addr) l_entry;         /* Entry point location.  */
 104     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 105
 106     /* Array of DT_NEEDED dependencies and their dependencies, in
 107        dependency order for symbol lookup.  This is null before the
 108        dependencies have been loaded.  */
 109     struct link_map **l_searchlist;
 110     unsigned int l_nsearchlist;
 111
 112     /* Dependent object that first caused this object to be loaded.  */
 113     struct link_map *l_loader;
 114
 115     /* Symbol hash table.  */
 116     ElfW(Symndx) l_nbuckets;
 117     const ElfW(Symndx) *l_buckets, *l_chain;
 118
 119     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 120     enum                        /* Where this object came from.  */
 121       {
 122         lt_executable,          /* The main executable program.  */
 123         lt_library,             /* Library needed by main executable.  */
 124         lt_loaded,              /* Extra run-time loaded shared object.  */
 125       } l_type:2;
 126     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 127     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 128     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 129     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 130     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 131   };
 132 \f
 133 /* Internal functions of the run-time dynamic linker.
 134    These can be accessed if you link again the dynamic linker
 135    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 136    but are not normally of interest to user programs.
 137
 138    The `-ldl' library functions in <dlfcn.h> provide a simple
 139    user interface to run-time dynamic linking.  */
 140
 141
 142 /* Cached value of `getpagesize ()'.  */
 143 extern size_t _dl_pagesize;
 144
 145 /* File descriptor referring to the zero-fill device.  */
 146 extern int _dl_zerofd;
 147
 148 /* OS-dependent function to open the zero-fill device.  */
 149 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 150
 151 /* OS-dependent function to write a message on the standard output.
 152    All arguments are `const char *'; args until a null pointer
 153    are concatenated to form the message to print.  */
 154 extern void _dl_sysdep_message (const char *string, ...);
 155
 156 /* OS-dependent function to give a fatal error message and exit
 157    when the dynamic linker fails before the program is fully linked.
 158    All arguments are `const char *'; args until a null pointer
 159    are concatenated to form the message to print.  */
 160 extern void _dl_sysdep_fatal (const char *string, ...)
 161      __attribute__ ((__noreturn__));
 162
 163 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 164    This tells the dynamic linker to ignore environment variables.  */
 165 extern int _dl_secure;
 166
 167 /* This function is called by all the internal dynamic linker functions
 168    when they encounter an error.  ERRCODE is either an `errno' code or
 169    zero; OBJECT is the name of the problematical shared object, or null if
 170    it is a general problem; ERRSTRING is a string describing the specific
 171    problem.  */
 172
 173 extern void _dl_signal_error (int errcode,
 174                               const char *object,
 175                               const char *errstring)
 176      __attribute__ ((__noreturn__));
 177
 178 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 179    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 180    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 181    code passed is the return value.  ERRSTRING if nonzero points to a
 182    malloc'ed string which the caller has to free after use.  */
 183 extern int _dl_catch_error (char **errstring,
 184                             const char **object,
 185                             void (*operate) (void));
 186
 187
 188 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 189    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 190    arranges for `dlerror' to return the error details.  */
 191 extern int _dlerror_run (void (*operate) (void));
 192
 193
 194 /* Open the shared object NAME and map in its segments.
 195    LOADER's DT_RPATH is used in searching for NAME.
 196    If the object is already opened, returns its existing map.  */
 197 extern struct link_map *_dl_map_object (struct link_map *loader,
 198                                         const char *name, int type);
 199
 200 /* Call _dl_map_object on the dependencies of MAP, and set up
 201    MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
 202    loaded objects that will be inserted into MAP->l_searchlist after MAP
 203    but before its dependencies.  */
 204 extern void _dl_map_object_deps (struct link_map *map,
 205                                  struct link_map **preloads,
 206                                  unsigned int npreloads);
 207
 208 /* Cache the locations of MAP's hash table.  */
 209 extern void _dl_setup_hash (struct link_map *map);
 210
 211
 212 /* Open the shared object NAME, relocate it, and run its initializer if it
 213    hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
 214    the object is already opened, returns its existing map.  */
 215 extern struct link_map *_dl_open (const char *name, int mode);
 216
 217 /* Close an object previously opened by _dl_open.  */
 218 extern void _dl_close (struct link_map *map);
 219
 220
 221 /* Search loaded objects' symbol tables for a definition of the symbol
 222    referred to by UNDEF.  *SYM is the symbol table entry containing the
 223    reference; it is replaced with the defining symbol, and the base load
 224    address of the defining object is returned.  SYMBOL_SCOPE is a
 225    null-terminated list of object scopes to search; each object's
 226    l_searchlist (i.e. the segment of the dependency tree starting at that
 227    object) is searched in turn.  REFERENCE_NAME should name the object
 228    containing the reference; it is used in error messages.  FLAGS is a
 229    set of flags:  */
 230 #define DL_LOOKUP_NOEXEC 1      /* Don't search the executable for a
 231                                    definition; this is used for copy
 232                                    relocs. */
 233 #define DL_LOOKUP_NOPLT 2       /* The reference must not be resolved
 234                                    to a PLT entry.  */
 235 extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
 236                                      const ElfW(Sym) **sym,
 237                                      struct link_map *symbol_scope[],
 238                                      const char *reference_name,
 239                                      int flags);
 240
 241 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 242 extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);
 243
 244
 245 /* Structure describing the dynamic linker itself.  */
 246 extern struct link_map _dl_rtld_map;
 247
 248 /* The list of objects currently loaded is the third element of the
 249    `_dl_default_scope' array, and the fourth element is always null.
 250    This leaves two slots before it that are used when resolving
 251    DT_SYMBOLIC objects' references one after it for normal references
 252    (see below).  */
 253 #define _dl_loaded      (_dl_default_scope[2])
 254 extern struct link_map *_dl_default_scope[5];
 255
 256 /* Null-terminated list of objects in the dynamic `global scope'.  The
 257    list starts at [2]; i.e. &_dl_global_scope[2] is the argument
 258    passed to _dl_lookup_symbol to search the global scope.  To search
 259    a specific object and its dependencies in preference to the global
 260    scope, fill in the [1] slot and pass its address; for two specific
 261    object scopes, fill [0] and [1].  The list is double-terminated; to
 262    search the global scope and then a specific object and its
 263    dependencies, set *_dl_global_scope_end.  This variable initially
 264    points to _dl_default_scope, and _dl_loaded is always kept in [2]
 265    of this list.  A new list is malloc'd when new objects are loaded
 266    with RTLD_GLOBAL.  */
 267 extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
 268 extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */
 269
 270 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
 271    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
 272    references made in the object MAP's relocations.  */
 273 extern struct link_map **_dl_object_relocation_scope (struct link_map *map);
 274
 275
 276 /* Allocate a `struct link_map' for a new object being loaded,
 277    and enter it into the _dl_loaded list.  */
 278 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 279                                         int type);
 280
 281 /* Relocate the given object (if it hasn't already been).
 282    SCOPE is passed to _dl_lookup_symbol in symbol lookups.
 283    If LAZY is nonzero, don't relocate its PLT.  */
 284 extern void _dl_relocate_object (struct link_map *map,
 285                                  struct link_map *scope[],
 286                                  int lazy);
 287
 288 /* Return the address of the next initializer function for MAP or one of
 289    its dependencies that has not yet been run.  When there are no more
 290    initializers to be run, this returns zero.  The functions are returned
 291    in the order they should be called.  */
 292 extern ElfW(Addr) _dl_init_next (struct link_map *map);
 293
 294 /* Call the finalizer functions of all shared objects whose
 295    initializer functions have completed.  */
 296 extern void _dl_fini (void);
 297
 298 /* The dynamic linker calls this function before and having changing
 299    any shared object mappings.  The `r_state' member of `struct r_debug'
 300    says what change is taking place.  This function's address is
 301    the value of the `r_brk' member.  */
 302 extern void _dl_debug_state (void);
 303
 304 /* Initialize `struct r_debug' if it has not already been done.  The
 305    argument is the run-time load address of the dynamic linker, to be put
 306    in the `r_ldbase' member.  Returns the address of the structure.  */
 307 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);
 308
 309
 310 #endif /* link.h */