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 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     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     /* We keep another list in which we keep duplicates.  This is
 113        needed in _dl_lookup_symbol_skip to implemented RTLD_NEXT.  */
 114     struct link_map **l_dupsearchlist;
 115     unsigned int l_ndupsearchlist;
 116
 117     /* Dependent object that first caused this object to be loaded.  */
 118     struct link_map *l_loader;
 119
 120     /* Symbol hash table.  */
 121     ElfW(Symndx) l_nbuckets;
 122     const ElfW(Symndx) *l_buckets, *l_chain;
 123
 124     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 125     enum                        /* Where this object came from.  */
 126       {
 127         lt_executable,          /* The main executable program.  */
 128         lt_library,             /* Library needed by main executable.  */
 129         lt_loaded,              /* Extra run-time loaded shared object.  */
 130       } l_type:2;
 131     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 132     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 133     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 134     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 135     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 136   };
 137 \f
 138 /* Internal functions of the run-time dynamic linker.
 139    These can be accessed if you link again the dynamic linker
 140    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 141    but are not normally of interest to user programs.
 142
 143    The `-ldl' library functions in <dlfcn.h> provide a simple
 144    user interface to run-time dynamic linking.  */
 145
 146
 147 /* Cached value of `getpagesize ()'.  */
 148 extern size_t _dl_pagesize;
 149
 150 /* File descriptor referring to the zero-fill device.  */
 151 extern int _dl_zerofd;
 152
 153 /* OS-dependent function to open the zero-fill device.  */
 154 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 155
 156 /* OS-dependent function to write a message on the standard output.
 157    All arguments are `const char *'; args until a null pointer
 158    are concatenated to form the message to print.  */
 159 extern void _dl_sysdep_message (const char *string, ...);
 160
 161 /* OS-dependent function to give a fatal error message and exit
 162    when the dynamic linker fails before the program is fully linked.
 163    All arguments are `const char *'; args until a null pointer
 164    are concatenated to form the message to print.  */
 165 extern void _dl_sysdep_fatal (const char *string, ...)
 166      __attribute__ ((__noreturn__));
 167
 168 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 169    This tells the dynamic linker to ignore environment variables.  */
 170 extern int _dl_secure;
 171
 172 /* This function is called by all the internal dynamic linker functions
 173    when they encounter an error.  ERRCODE is either an `errno' code or
 174    zero; OBJECT is the name of the problematical shared object, or null if
 175    it is a general problem; ERRSTRING is a string describing the specific
 176    problem.  */
 177
 178 extern void _dl_signal_error (int errcode,
 179                               const char *object,
 180                               const char *errstring)
 181      __attribute__ ((__noreturn__));
 182
 183 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 184    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 185    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 186    code passed is the return value.  ERRSTRING if nonzero points to a
 187    malloc'ed string which the caller has to free after use.  */
 188 extern int _dl_catch_error (char **errstring,
 189                             const char **object,
 190                             void (*operate) (void));
 191
 192
 193 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 194    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 195    arranges for `dlerror' to return the error details.  */
 196 extern int _dlerror_run (void (*operate) (void));
 197
 198
 199 /* Open the shared object NAME and map in its segments.
 200    LOADER's DT_RPATH is used in searching for NAME.
 201    If the object is already opened, returns its existing map.  */
 202 extern struct link_map *_dl_map_object (struct link_map *loader,
 203                                         const char *name, int type,
 204                                         int trace_mode);
 205
 206 /* Call _dl_map_object on the dependencies of MAP, and set up
 207    MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
 208    loaded objects that will be inserted into MAP->l_searchlist after MAP
 209    but before its dependencies.  */
 210 extern void _dl_map_object_deps (struct link_map *map,
 211                                  struct link_map **preloads,
 212                                  unsigned int npreloads, int trace_mode);
 213
 214 /* Cache the locations of MAP's hash table.  */
 215 extern void _dl_setup_hash (struct link_map *map);
 216
 217
 218 /* Open the shared object NAME, relocate it, and run its initializer if it
 219    hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
 220    the object is already opened, returns its existing map.  */
 221 extern struct link_map *_dl_open (const char *name, int mode);
 222
 223 /* Close an object previously opened by _dl_open.  */
 224 extern void _dl_close (struct link_map *map);
 225
 226
 227 /* Search loaded objects' symbol tables for a definition of the symbol
 228    referred to by UNDEF.  *SYM is the symbol table entry containing the
 229    reference; it is replaced with the defining symbol, and the base load
 230    address of the defining object is returned.  SYMBOL_SCOPE is a
 231    null-terminated list of object scopes to search; each object's
 232    l_searchlist (i.e. the segment of the dependency tree starting at that
 233    object) is searched in turn.  REFERENCE_NAME should name the object
 234    containing the reference; it is used in error messages.  FLAGS is a
 235    set of flags:  */
 236 #define DL_LOOKUP_NOEXEC 1      /* Don't search the executable for a
 237                                    definition; this is used for copy
 238                                    relocs. */
 239 #define DL_LOOKUP_NOPLT 2       /* The reference must not be resolved
 240                                    to a PLT entry.  */
 241 extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
 242                                      const ElfW(Sym) **sym,
 243                                      struct link_map *symbol_scope[],
 244                                      const char *reference_name,
 245                                      int flags);
 246
 247 /* For handling RTLD_NEXT we must be able to skip shared objects.  */
 248 extern ElfW(Addr) _dl_lookup_symbol_skip (const char *undef,
 249                                           const ElfW(Sym) **sym,
 250                                           struct link_map *symbol_scope[],
 251                                           const char *reference_name,
 252                                           struct link_map *skip_this,
 253                                           int flags);
 254
 255 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 256 extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);
 257
 258
 259 /* Structure describing the dynamic linker itself.  */
 260 extern struct link_map _dl_rtld_map;
 261
 262 /* The list of objects currently loaded is the third element of the
 263    `_dl_default_scope' array, and the fourth element is always null.
 264    This leaves two slots before it that are used when resolving
 265    DT_SYMBOLIC objects' references one after it for normal references
 266    (see below).  */
 267 #define _dl_loaded      (_dl_default_scope[2])
 268 extern struct link_map *_dl_default_scope[5];
 269
 270 /* Null-terminated list of objects in the dynamic `global scope'.  The
 271    list starts at [2]; i.e. &_dl_global_scope[2] is the argument
 272    passed to _dl_lookup_symbol to search the global scope.  To search
 273    a specific object and its dependencies in preference to the global
 274    scope, fill in the [1] slot and pass its address; for two specific
 275    object scopes, fill [0] and [1].  The list is double-terminated; to
 276    search the global scope and then a specific object and its
 277    dependencies, set *_dl_global_scope_end.  This variable initially
 278    points to _dl_default_scope, and _dl_loaded is always kept in [2]
 279    of this list.  A new list is malloc'd when new objects are loaded
 280    with RTLD_GLOBAL.  */
 281 extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
 282 extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */
 283
 284 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
 285    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
 286    references made in the object MAP's relocations.  */
 287 extern struct link_map **_dl_object_relocation_scope (struct link_map *map);
 288
 289
 290 /* Allocate a `struct link_map' for a new object being loaded,
 291    and enter it into the _dl_loaded list.  */
 292 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 293                                         int type);
 294
 295 /* Relocate the given object (if it hasn't already been).
 296    SCOPE is passed to _dl_lookup_symbol in symbol lookups.
 297    If LAZY is nonzero, don't relocate its PLT.  */
 298 extern void _dl_relocate_object (struct link_map *map,
 299                                  struct link_map *scope[],
 300                                  int lazy);
 301
 302 /* Return the address of the next initializer function for MAP or one of
 303    its dependencies that has not yet been run.  When there are no more
 304    initializers to be run, this returns zero.  The functions are returned
 305    in the order they should be called.  */
 306 extern ElfW(Addr) _dl_init_next (struct link_map *map);
 307
 308 /* Call the finalizer functions of all shared objects whose
 309    initializer functions have completed.  */
 310 extern void _dl_fini (void);
 311
 312 /* The dynamic linker calls this function before and having changing
 313    any shared object mappings.  The `r_state' member of `struct r_debug'
 314    says what change is taking place.  This function's address is
 315    the value of the `r_brk' member.  */
 316 extern void _dl_debug_state (void);
 317
 318 /* Initialize `struct r_debug' if it has not already been done.  The
 319    argument is the run-time load address of the dynamic linker, to be put
 320    in the `r_ldbase' member.  Returns the address of the structure.  */
 321 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);
 322
 323
 324 #endif /* link.h */