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 #include <elf.h>
  24
  25
  26 /* Rendezvous structure used by the run-time dynamic linker to communicate
  27    details of shared object loading to the debugger.  If the executable's
  28    dynamic section has a DT_DEBUG element, the run-time linker sets that
  29    element's value to the address where this structure can be found.  */
  30
  31 struct r_debug
  32   {
  33     int r_version;              /* Version number for this protocol.  */
  34
  35     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  36
  37     /* This is the address of a function internal to the run-time linker,
  38        that will always be called when the linker begins to map in a
  39        library or unmap it, and again when the mapping change is complete.
  40        The debugger can set a breakpoint at this address if it wants to
  41        notice shared object mapping changes.  */
  42     Elf32_Addr r_brk;
  43     enum
  44       {
  45         /* This state value describes the mapping change taking place when
  46            the `r_brk' address is called.  */
  47         RT_CONSISTENT,          /* Mapping change is complete.  */
  48         RT_ADD,                 /* Beginning to add a new object.  */
  49         RT_DELETE,              /* Beginning to remove an object mapping.  */
  50       } r_state;
  51
  52     Elf32_Addr r_ldbase;        /* Base address the linker is loaded at.  */
  53   };
  54
  55 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  56    of whatever module refers to `_DYNAMIC'.  So, to find its own
  57    `struct r_debug', a program could do:
  58      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL)
  59        if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
  60    */
  61
  62 extern Elf32_Dyn _DYNAMIC[];
  63
  64
  65 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  66    members form a chain of all the shared objects loaded at startup.
  67
  68    These data structures exist in space used by the run-time dynamic linker;
  69    modifying them may have disastrous results.  */
  70
  71 struct link_map
  72   {
  73     /* These first few members are part of the protocol with the debugger.
  74        This is the same format used in SVR4.  */
  75
  76     Elf32_Addr l_addr;          /* Base address shared object is loaded at.  */
  77     char *l_name;               /* Absolute file name object was found in.  */
  78     Elf32_Dyn *l_ld;            /* Dynamic section of the shared object.  */
  79     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
  80
  81     /* All following members are internal to the dynamic linker.
  82        They may change without notice.  */
  83
  84     const char *l_libname;      /* Name requested (before search).  */
  85     /* Indexed pointers to dynamic section.
  86        [0,DT_NUM) are indexed by the processor-independent tags.
  87        [DT_NUM,DT_NUM+DT_PROCNUM] are indexed by the tag minus DT_LOPROC.  */
  88     Elf32_Dyn *l_info[DT_NUM + DT_PROCNUM];
  89     const Elf32_Phdr *l_phdr;   /* Pointer to program header table in core.  */
  90     Elf32_Word l_phnum;         /* Number of program header entries.  */
  91     Elf32_Addr l_entry;         /* Entry point location.  */
  92
  93     /* Array of DT_NEEDED dependencies and their dependencies, in
  94        dependency order for symbol lookup.  This is null before the
  95        dependencies have been loaded.  */
  96     struct link_map **l_searchlist;
  97     unsigned int l_nsearchlist;
  98
  99     /* Symbol hash table.  */
 100     Elf32_Word l_nbuckets;
 101     const Elf32_Word *l_buckets, *l_chain;
 102
 103     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
 104     enum                        /* Where this object came from.  */
 105       {
 106         lt_executable,          /* The main executable program.  */
 107         lt_interpreter,         /* The interpreter: the dynamic linker.  */
 108         lt_library,             /* Library needed by main executable.  */
 109         lt_loaded,              /* Extra run-time loaded shared object.  */
 110       } l_type:2;
 111     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 112     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 113     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 114     unsigned int l_reserved:3;  /* Reserved for internal use.  */
 115   };
 116 \f
 117 /* Internal functions of the run-time dynamic linker.
 118    These can be accessed if you link again the dynamic linker
 119    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 120    but are not normally of interest to user programs.
 121
 122    The `-ldl' library functions in <dlfcn.h> provide a simple
 123    user interface to run-time dynamic linking.  */
 124
 125
 126 /* File descriptor referring to the zero-fill device.  */
 127 extern int _dl_zerofd;
 128
 129 /* OS-dependent function to open the zero-fill device.  */
 130 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 131
 132 /* OS-dependent function to write a message on the standard output.
 133    All arguments are `const char *'; args until a null pointer
 134    are concatenated to form the message to print.  */
 135 extern void _dl_sysdep_message (const char *string, ...);
 136
 137 /* OS-dependent function to give a fatal error message and exit
 138    when the dynamic linker fails before the program is fully linked.
 139    All arguments are `const char *'; args until a null pointer
 140    are concatenated to form the message to print.  */
 141 extern void _dl_sysdep_fatal (const char *string, ...)
 142      __attribute__ ((__noreturn__));
 143
 144 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 145    This tells the dynamic linker to ignore environment variables.  */
 146 extern int _dl_secure;
 147
 148 /* This function is called by all the internal dynamic linker functions
 149    when they encounter an error.  ERRCODE is either an `errno' code or
 150    zero; OBJECT is the name of the problematical shared object, or null if
 151    it is a general problem; ERRSTRING is a string describing the specific
 152    problem.  */
 153
 154 extern void _dl_signal_error (int errcode,
 155                               const char *object,
 156                               const char *errstring)
 157      __attribute__ ((__noreturn__));
 158
 159 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 160    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 161    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 162    code passed is the return value.  */
 163 extern int _dl_catch_error (const char **errstring,
 164                             const char **object,
 165                             void (*operate) (void));
 166
 167
 168 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 169    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 170    arranges for `dlerror' to return the error details.  */
 171 extern int _dlerror_run (void (*operate) (void));
 172
 173
 174 /* Open the shared object NAME and map in its segments.
 175    LOADER's DT_RPATH is used in searching for NAME.
 176    If the object is already opened, returns its existing map.  */
 177 extern struct link_map *_dl_map_object (struct link_map *loader,
 178                                         const char *name);
 179
 180 /* Similar, but file found at REALNAME and opened on FD.
 181    REALNAME must malloc'd storage and is used in internal data structures.  */
 182 extern struct link_map *_dl_map_object_from_fd (const char *name,
 183                                                 int fd, char *realname);
 184
 185 /* Call _dl_map_object on the dependencies of MAP, and
 186    set up MAP->l_searchlist.  */
 187 extern void _dl_map_object_deps (struct link_map *map);
 188
 189 /* Cache the locations of MAP's hash table.  */
 190 extern void _dl_setup_hash (struct link_map *map);
 191
 192
 193 /* Open the shared object NAME, relocate it, and run its initializer if it
 194    hasn't already been run.  LOADER's DT_RPATH is used in searching for
 195    NAME.  MODE is as for `dlopen' (see <dlfcn.h>).  If the object is
 196    already opened, returns its existing map.  */
 197 extern struct link_map *_dl_open (struct link_map *loader,
 198                                   const char *name, int mode);
 199
 200
 201
 202 /* Search loaded objects' symbol tables for a definition of the symbol
 203    referred to by UNDEF.  *SYM is the symbol table entry containing the
 204    reference; it is replaced with the defining symbol, and the base load
 205    address of the defining object is returned.  Each of SYMBOL_SCOPE[0] and
 206    SYMBOL_SCOPE[1] that is not null and their dependencies are searched to
 207    resolve the name.  REFERENCE_NAME should name the object containing the
 208    reference; it is used in error messages.  RELOC_ADDR is the address
 209    being fixed up and the chosen symbol cannot be one with this value.  If
 210    NOPLT is nonzero, then the reference must not be resolved to a PLT
 211    entry.  */
 212 extern Elf32_Addr _dl_lookup_symbol (const char *undef,
 213                                      const Elf32_Sym **sym,
 214                                      struct link_map *symbol_scope[2],
 215                                      const char *reference_name,
 216                                      Elf32_Addr reloc_addr,
 217                                      int noplt);
 218
 219 /* Look up symbol NAME in MAP's scope and return its run-time address.  */
 220 extern Elf32_Addr _dl_symbol_value (struct link_map *map, const char *name);
 221
 222
 223 /* Structure describing the dynamic linker itself.  */
 224 extern struct link_map _dl_rtld_map;
 225
 226 /* List of objects currently loaded.  */
 227 extern struct link_map *_dl_loaded;
 228
 229 /* Tail of that list which were loaded at startup.  */
 230 extern struct link_map *_dl_startup_loaded;
 231
 232 /* Allocate a `struct link_map' for a new object being loaded,
 233    and enter it into the _dl_loaded list.  */
 234 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 235                                         int type);
 236
 237 /* Relocate the given object (if it hasn't already been).
 238    If LAZY is nonzero, don't relocate its PLT.  */
 239 extern void _dl_relocate_object (struct link_map *map, int lazy);
 240
 241 /* Return the address of the next initializer function for MAP or one of
 242    its dependencies that has not yet been run.  When there are no more
 243    initializers to be run, this returns zero.  The functions are returned
 244    in the order they should be called.  */
 245 extern Elf32_Addr _dl_init_next (struct link_map *map);
 246
 247 /* Call the finalizer functions of all shared objects whose
 248    initializer functions have completed.  */
 249 extern void _dl_fini (void);
 250
 251 /* The dynamic linker calls this function before and having changing
 252    any shared object mappings.  The `r_state' member of `struct r_debug'
 253    says what change is taking place.  This function's address is
 254    the value of the `r_brk' member.  */
 255 extern void _dl_r_debug_state (void);
 256
 257
 258 #endif /* link.h */