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     /* Symbol hash table.  */
  94     Elf32_Word l_nbuckets;
  95     const Elf32_Word *l_buckets, *l_chain;
  96
  97     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
  98     enum                        /* Where this object came from.  */
  99       {
 100         lt_executable,          /* The main executable program.  */
 101         lt_interpreter,         /* The interpreter: the dynamic linker.  */
 102         lt_library,             /* Library needed by main executable.  */
 103         lt_loaded,              /* Extra run-time loaded shared object.  */
 104       } l_type:2;
 105     unsigned int l_deps_loaded:1; /* Nonzero if DT_NEEDED items loaded.  */
 106     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 107     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 108     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 109   };
 110 \f
 111 /* Internal functions of the run-time dynamic linker.
 112    These can be accessed if you link again the dynamic linker
 113    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 114    but are not normally of interest to user programs.
 115
 116    The `-ldl' library functions in <dlfcn.h> provide a simple
 117    user interface to run-time dynamic linking.  */
 118
 119
 120 /* File descriptor referring to the zero-fill device.  */
 121 extern int _dl_zerofd;
 122
 123 /* OS-dependent function to open the zero-fill device.  */
 124 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 125
 126 /* OS-dependent function to write a message on the standard output.
 127    All arguments are `const char *'; args until a null pointer
 128    are concatenated to form the message to print.  */
 129 extern void _dl_sysdep_message (const char *string, ...);
 130
 131 /* OS-dependent function to give a fatal error message and exit
 132    when the dynamic linker fails before the program is fully linked.
 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_fatal (const char *string, ...)
 136      __attribute__ ((__noreturn__));
 137
 138 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 139    This tells the dynamic linker to ignore environment variables.  */
 140 extern int _dl_secure;
 141
 142 /* This function is called by all the internal dynamic linker functions
 143    when they encounter an error.  ERRCODE is either an `errno' code or
 144    zero; OBJECT is the name of the problematical shared object, or null if
 145    it is a general problem; ERRSTRING is a string describing the specific
 146    problem.  */
 147
 148 extern void _dl_signal_error (int errcode,
 149                               const char *object,
 150                               const char *errstring)
 151      __attribute__ ((__noreturn__));
 152
 153 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 154    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 155    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 156    code passed is the return value.  */
 157 extern int _dl_catch_error (const char **errstring,
 158                             const char **object,
 159                             void (*operate) (void));
 160
 161
 162 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 163    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 164    arranges for `dlerror' to return the error details.  */
 165 extern int _dlerror_run (void (*operate) (void));
 166
 167
 168 /* Open the shared object NAME and map in its segments.
 169    LOADER's DT_RPATH is used in searching for NAME.
 170    If the object is already opened, returns its existing map.  */
 171 extern struct link_map *_dl_map_object (struct link_map *loader,
 172                                         const char *name);
 173
 174 /* Similar, but file found at REALNAME and opened on FD.
 175    REALNAME must malloc'd storage and is used in internal data structures.  */
 176 extern struct link_map *_dl_map_object_from_fd (const char *name,
 177                                                 int fd, char *realname);
 178
 179 /* Cache the locations of MAP's hash table.  */
 180 extern void _dl_setup_hash (struct link_map *map);
 181
 182
 183 /* Search loaded objects' symbol tables for a definition of the symbol
 184    referred to by UNDEF.  *SYM is the symbol table entry containing the
 185    reference; it is replaced with the defining symbol, and the base load
 186    address of the defining object is returned.  SYMBOL_SCOPE is the head of
 187    the chain used for searching.  REFERENCE_NAME should name the object
 188    containing the reference; it is used in error messages.  If NOPLT is
 189    nonzero, then the reference must not be resolved to a PLT entry.  */
 190 extern Elf32_Addr _dl_lookup_symbol (const char *undef,
 191                                      const Elf32_Sym **sym,
 192                                      struct link_map *symbol_scope,
 193                                      const char *reference_name,
 194                                      int noplt);
 195
 196
 197 /* List of objects currently loaded.  */
 198 extern struct link_map *_dl_loaded;
 199
 200 /* Tail of that list which were loaded at startup.  */
 201 extern struct link_map *_dl_startup_loaded;
 202
 203 /* Allocate a `struct link_map' for a new object being loaded,
 204    and enter it into the _dl_loaded list.  */
 205 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 206                                         int type);
 207
 208 /* Relocate the given object (if it hasn't already been).
 209    If LAZY is nonzero, don't relocate its PLT.  */
 210 extern void _dl_relocate_object (struct link_map *map, int lazy);
 211
 212 /* Return the address of the next initializer function not yet run.
 213    When there are no more initializers to be run, this returns zero.
 214    The functions are returned in the order they should be called.  */
 215 extern Elf32_Addr _dl_init_next (void);
 216
 217 /* Call the finalizer functions of all shared objects whose
 218    initializer functions have completed.  */
 219 extern void _dl_fini (void);
 220
 221 /* The dynamic linker calls this function before and having changing
 222    any shared object mappings.  The `r_state' member of `struct r_debug'
 223    says what change is taking place.  This function's address is
 224    the value of the `r_brk' member.  */
 225 extern void _dl_r_debug_state (void);
 226
 227
 228 #endif /* link.h */