elf/link.h

   1 /* Run-time dynamic linker data structures for loaded ELF shared objects.
   2 Copyright (C) 1995 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     Elf32_Dyn *l_info[DT_NUM];  /* Indexed pointers to dynamic section.  */
  86     const Elf32_Phdr *l_phdr;   /* Pointer to program header table in core.  */
  87     Elf32_Word l_phnum;         /* Number of program header entries.  */
  88     Elf32_Addr l_entry;         /* Entry point location.  */
  89
  90     /* Symbol hash table.  */
  91     Elf32_Word l_nbuckets;
  92     const Elf32_Word *l_buckets, *l_chain;
  93
  94     unsigned int l_opencount;   /* Reference count for dlopen/dlclose.  */
  95     enum                        /* Where this object came from.  */
  96       {
  97         lt_executable,          /* The main executable program.  */
  98         lt_interpreter,         /* The interpreter: the dynamic linker.  */
  99         lt_library,             /* Library needed by main executable.  */
 100         lt_loaded,              /* Extra run-time loaded shared object.  */
 101       } l_type:2;
 102     unsigned int l_deps_loaded:1; /* Nonzero if DT_NEEDED items loaded.  */
 103     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 104     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 105     unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
 106   };
 107 \f
 108 /* Internal functions of the run-time dynamic linker.
 109    These can be accessed if you link again the dynamic linker
 110    as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
 111    but are not normally of interest to user programs.
 112
 113    The `-ldl' library functions in <dlfcn.h> provide a simple
 114    user interface to run-time dynamic linking.  */
 115
 116
 117 /* File descriptor referring to the zero-fill device.  */
 118 extern int _dl_zerofd;
 119
 120 /* OS-dependent function to open the zero-fill device.  */
 121 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
 122
 123 /* OS-dependent function to write a message on the standard output.
 124    All arguments are `const char *'; args until a null pointer
 125    are concatenated to form the message to print.  */
 126 extern void _dl_sysdep_message (const char *string, ...);
 127
 128 /* OS-dependent function to give a fatal error message and exit
 129    when the dynamic linker fails before the program is fully linked.
 130    All arguments are `const char *'; args until a null pointer
 131    are concatenated to form the message to print.  */
 132 extern void _dl_sysdep_fatal (const char *string, ...)
 133      __attribute__ ((__noreturn__));
 134
 135 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
 136    This tells the dynamic linker to ignore environment variables.  */
 137 extern int _dl_secure;
 138
 139 /* This function is called by all the internal dynamic linker functions
 140    when they encounter an error.  ERRCODE is either an `errno' code or
 141    zero; OBJECT is the name of the problematical shared object, or null if
 142    it is a general problem; ERRSTRING is a string describing the specific
 143    problem.  */
 144
 145 extern void _dl_signal_error (int errcode,
 146                               const char *object,
 147                               const char *errstring)
 148      __attribute__ ((__noreturn__));
 149
 150 /* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
 151    error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
 152    *OBJECT are set to the strings passed to _dl_signal_error, and the error
 153    code passed is the return value.  */
 154 extern int _dl_catch_error (const char **errstring,
 155                             const char **object,
 156                             void (*operate) (void));
 157
 158
 159 /* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
 160    _dl_catch_error.  Returns zero for success, nonzero for failure; and
 161    arranges for `dlerror' to return the error details.  */
 162 extern int _dlerror_run (void (*operate) (void));
 163
 164
 165 /* Open the shared object NAME and map in its segments.
 166    LOADER's DT_RPATH is used in searching for NAME.
 167    If the object is already opened, returns its existing map.  */
 168 extern struct link_map *_dl_map_object (struct link_map *loader,
 169                                         const char *name);
 170
 171 /* Similar, but file found at REALNAME and opened on FD.
 172    REALNAME must malloc'd storage and is used in internal data structures.  */
 173 extern struct link_map *_dl_map_object_from_fd (const char *name,
 174                                                 int fd, char *realname);
 175
 176 /* Cache the locations of MAP's hash table.  */
 177 extern void _dl_setup_hash (struct link_map *map);
 178
 179
 180 /* Search loaded objects' symbol tables for a definition of the symbol
 181    referred to by UNDEF.  *SYM is the symbol table entry containing the
 182    reference; it is replaced with the defining symbol, and the base load
 183    address of the defining object is returned.  SYMBOL_SCOPE is the head of
 184    the chain used for searching.  REFERENCE_NAME should name the object
 185    containing the reference; it is used in error messages.  If NOSELF is
 186    nonzero, them *SYM itself cannot define the value; another binding must
 187    be found.  */
 188 extern Elf32_Addr _dl_lookup_symbol (const char *undef,
 189                                      const Elf32_Sym **sym,
 190                                      struct link_map *symbol_scope,
 191                                      const char *reference_name,
 192                                      int noself);
 193
 194
 195 /* List of objects currently loaded.  */
 196 extern struct link_map *_dl_loaded;
 197
 198 /* Tail of that list which were loaded at startup.  */
 199 extern struct link_map *_dl_startup_loaded;
 200
 201 /* Allocate a `struct link_map' for a new object being loaded,
 202    and enter it into the _dl_loaded list.  */
 203 extern struct link_map *_dl_new_object (char *realname, const char *libname,
 204                                         int type);
 205
 206 /* Relocate the given object (if it hasn't already been).
 207    If LAZY is nonzero, don't relocate its PLT.  */
 208 extern void _dl_relocate_object (struct link_map *map, int lazy);
 209
 210 /* Return the address of the next initializer function not yet run.
 211    When there are no more initializers to be run, this returns zero.
 212    The functions are returned in the order they should be called.  */
 213 extern Elf32_Addr _dl_init_next (void);
 214
 215 /* Call the finalizer functions of all shared objects whose
 216    initializer functions have completed.  */
 217 extern void _dl_fini (void);
 218
 219 /* The dynamic linker calls this function before and having changing
 220    any shared object mappings.  The `r_state' member of `struct r_debug'
 221    says what change is taking place.  This function's address is
 222    the value of the `r_brk' member.  */
 223 extern void _dl_r_debug_state (void);
 224
 225
 226 #endif /* link.h */