glibc/elf/link.h

/* Run-time dynamic linker data structures for loaded ELF shared objects.
Copyright (C) 1995, 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#ifndef	_LINK_H
#define	_LINK_H	1

#define __need_size_t
#include <stddef.h>

#include <elf.h>

/* We use this macro to refer to ELF types independent of the native wordsize.
   `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
#define ElfW(type)	_ElfW (Elf, __ELF_NATIVE_CLASS, type)
#define ELFW(type)	_ElfW (ELF, __ELF_NATIVE_CLASS, type)
#define _ElfW(e,w,t)	_ElfW_1 (e, w, _##t)
#define _ElfW_1(e,w,t)	e##w##t
#include <elfclass.h>		/* Defines __ELF_NATIVE_CLASS.  */

/* Rendezvous structure used by the run-time dynamic linker to communicate
   details of shared object loading to the debugger.  If the executable's
   dynamic section has a DT_DEBUG element, the run-time linker sets that
   element's value to the address where this structure can be found.  */

struct r_debug
  {
    int r_version;		/* Version number for this protocol.  */

    struct link_map *r_map;	/* Head of the chain of loaded objects.  */

    /* This is the address of a function internal to the run-time linker,
       that will always be called when the linker begins to map in a
       library or unmap it, and again when the mapping change is complete.
       The debugger can set a breakpoint at this address if it wants to
       notice shared object mapping changes.  */
    ElfW(Addr) r_brk;
    enum
      {
	/* This state value describes the mapping change taking place when
	   the `r_brk' address is called.  */
	RT_CONSISTENT,		/* Mapping change is complete.  */
	RT_ADD,			/* Beginning to add a new object.  */
	RT_DELETE,		/* Beginning to remove an object mapping.  */
      } r_state;

    ElfW(Addr) r_ldbase;	/* Base address the linker is loaded at.  */
  };

/* This is the instance of that structure used by the dynamic linker.  */
extern struct r_debug _r_debug;

/* This symbol refers to the "dynamic structure" in the `.dynamic' section
   of whatever module refers to `_DYNAMIC'.  So, to find its own
   `struct r_debug', a program could do:
     for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL)
       if (dyn->d_tag == DT_DEBUG) r_debug = (struct r_debug) dyn->d_un.d_ptr;
   */

extern ElfW(Dyn) _DYNAMIC[];


/* Structure describing a loaded shared object.  The `l_next' and `l_prev'
   members form a chain of all the shared objects loaded at startup.

   These data structures exist in space used by the run-time dynamic linker;
   modifying them may have disastrous results.  */

struct link_map
  {
    /* These first few members are part of the protocol with the debugger.
       This is the same format used in SVR4.  */

    ElfW(Addr) l_addr;		/* Base address shared object is loaded at.  */
    char *l_name;		/* Absolute file name object was found in.  */
    ElfW(Dyn) *l_ld;		/* Dynamic section of the shared object.  */
    struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */

    /* All following members are internal to the dynamic linker.
       They may change without notice.  */

    const char *l_libname;	/* Name requested (before search).  */
    /* Indexed pointers to dynamic section.
       [0,DT_NUM) are indexed by the processor-independent tags.
       [DT_NUM,DT_NUM+DT_PROCNUM] are indexed by the tag minus DT_LOPROC.  */
    ElfW(Dyn) *l_info[DT_NUM + DT_PROCNUM];
    const ElfW(Phdr) *l_phdr;	/* Pointer to program header table in core.  */
    ElfW(Addr) l_entry;		/* Entry point location.  */
    ElfW(Half) l_phnum;		/* Number of program header entries.  */

    /* Array of DT_NEEDED dependencies and their dependencies, in
       dependency order for symbol lookup.  This is null before the
       dependencies have been loaded.  */
    struct link_map **l_searchlist;
    unsigned int l_nsearchlist;

    /* Dependent object that first caused this object to be loaded.  */
    struct link_map *l_loader;

    /* Symbol hash table.  */
    ElfW(Symndx) l_nbuckets;
    const ElfW(Symndx) *l_buckets, *l_chain;

    unsigned int l_opencount;	/* Reference count for dlopen/dlclose.  */
    enum			/* Where this object came from.  */
      {
	lt_executable,		/* The main executable program.  */
	lt_library,		/* Library needed by main executable.  */
	lt_loaded,		/* Extra run-time loaded shared object.  */
      } l_type:2;
    unsigned int l_relocated:1;	/* Nonzero if object's relocations done.  */
    unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
    unsigned int l_init_running:1; /* Nonzero while DT_INIT function runs.  */
    unsigned int l_global:1;	/* Nonzero if object in _dl_global_scope.  */
    unsigned int l_reserved:2;	/* Reserved for internal use.  */
  };

/* Internal functions of the run-time dynamic linker.
   These can be accessed if you link again the dynamic linker
   as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
   but are not normally of interest to user programs.

   The `-ldl' library functions in <dlfcn.h> provide a simple
   user interface to run-time dynamic linking.  */


/* Cached value of `getpagesize ()'.  */
extern size_t _dl_pagesize;

/* File descriptor referring to the zero-fill device.  */
extern int _dl_zerofd;

/* OS-dependent function to open the zero-fill device.  */
extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */

/* OS-dependent function to write a message on the standard output.
   All arguments are `const char *'; args until a null pointer
   are concatenated to form the message to print.  */
extern void _dl_sysdep_message (const char *string, ...);

/* OS-dependent function to give a fatal error message and exit
   when the dynamic linker fails before the program is fully linked.
   All arguments are `const char *'; args until a null pointer
   are concatenated to form the message to print.  */
extern void _dl_sysdep_fatal (const char *string, ...)
     __attribute__ ((__noreturn__));

/* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
   This tells the dynamic linker to ignore environment variables.  */
extern int _dl_secure;

/* This function is called by all the internal dynamic linker functions
   when they encounter an error.  ERRCODE is either an `errno' code or
   zero; OBJECT is the name of the problematical shared object, or null if
   it is a general problem; ERRSTRING is a string describing the specific
   problem.  */

extern void _dl_signal_error (int errcode,
			      const char *object,
			      const char *errstring)
     __attribute__ ((__noreturn__));

/* Call OPERATE, catching errors from `dl_signal_error'.  If there is no
   error, *ERRSTRING is set to null.  If there is an error, *ERRSTRING and
   *OBJECT are set to the strings passed to _dl_signal_error, and the error
   code passed is the return value.  ERRSTRING if nonzero points to a
   malloc'ed string which the caller has to free after use.  */
extern int _dl_catch_error (char **errstring,
			    const char **object,
			    void (*operate) (void));


/* Helper function for <dlfcn.h> functions.  Runs the OPERATE function via
   _dl_catch_error.  Returns zero for success, nonzero for failure; and
   arranges for `dlerror' to return the error details.  */
extern int _dlerror_run (void (*operate) (void));


/* Open the shared object NAME and map in its segments.
   LOADER's DT_RPATH is used in searching for NAME.
   If the object is already opened, returns its existing map.  */
extern struct link_map *_dl_map_object (struct link_map *loader,
					const char *name, int type);

/* Call _dl_map_object on the dependencies of MAP, and set up
   MAP->l_searchlist.  PRELOADS points to a vector of NPRELOADS previously
   loaded objects that will be inserted into MAP->l_searchlist after MAP
   but before its dependencies.  */
extern void _dl_map_object_deps (struct link_map *map,
				 struct link_map **preloads,
				 unsigned int npreloads);

/* Cache the locations of MAP's hash table.  */
extern void _dl_setup_hash (struct link_map *map);


/* Open the shared object NAME, relocate it, and run its initializer if it
   hasn't already been run.  MODE is as for `dlopen' (see <dlfcn.h>).  If
   the object is already opened, returns its existing map.  */
extern struct link_map *_dl_open (const char *name, int mode);

/* Close an object previously opened by _dl_open.  */
extern void _dl_close (struct link_map *map);


/* Search loaded objects' symbol tables for a definition of the symbol
   referred to by UNDEF.  *SYM is the symbol table entry containing the
   reference; it is replaced with the defining symbol, and the base load
   address of the defining object is returned.  SYMBOL_SCOPE is a
   null-terminated list of object scopes to search; each object's
   l_searchlist (i.e. the segment of the dependency tree starting at that
   object) is searched in turn.  REFERENCE_NAME should name the object
   containing the reference; it is used in error messages.  FLAGS is a
   set of flags:  */
#define DL_LOOKUP_NOEXEC 1	/* Don't search the executable for a
				   definition; this is used for copy
				   relocs. */
#define DL_LOOKUP_NOPLT 2	/* The reference must not be resolved
				   to a PLT entry.  */
extern ElfW(Addr) _dl_lookup_symbol (const char *undef,
				     const ElfW(Sym) **sym,
				     struct link_map *symbol_scope[],
				     const char *reference_name,
				     int flags);

/* Look up symbol NAME in MAP's scope and return its run-time address.  */
extern ElfW(Addr) _dl_symbol_value (struct link_map *map, const char *name);


/* Structure describing the dynamic linker itself.  */
extern struct link_map _dl_rtld_map;

/* The list of objects currently loaded is the third element of the
   `_dl_default_scope' array, and the fourth element is always null.
   This leaves two slots before it that are used when resolving
   DT_SYMBOLIC objects' references one after it for normal references
   (see below).  */
#define _dl_loaded	(_dl_default_scope[2])
extern struct link_map *_dl_default_scope[5];

/* Null-terminated list of objects in the dynamic `global scope'.  The
   list starts at [2]; i.e. &_dl_global_scope[2] is the argument
   passed to _dl_lookup_symbol to search the global scope.  To search
   a specific object and its dependencies in preference to the global
   scope, fill in the [1] slot and pass its address; for two specific
   object scopes, fill [0] and [1].  The list is double-terminated; to
   search the global scope and then a specific object and its
   dependencies, set *_dl_global_scope_end.  This variable initially
   points to _dl_default_scope, and _dl_loaded is always kept in [2]
   of this list.  A new list is malloc'd when new objects are loaded
   with RTLD_GLOBAL.  */
extern struct link_map **_dl_global_scope, **_dl_global_scope_end;
extern size_t _dl_global_scope_alloc; /* Number of slots malloc'd.  */

/* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
   _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
   references made in the object MAP's relocations.  */
extern struct link_map **_dl_object_relocation_scope (struct link_map *map);


/* Allocate a `struct link_map' for a new object being loaded,
   and enter it into the _dl_loaded list.  */
extern struct link_map *_dl_new_object (char *realname, const char *libname,
					int type);

/* Relocate the given object (if it hasn't already been).
   SCOPE is passed to _dl_lookup_symbol in symbol lookups.
   If LAZY is nonzero, don't relocate its PLT.  */
extern void _dl_relocate_object (struct link_map *map,
				 struct link_map *scope[],
				 int lazy);

/* Return the address of the next initializer function for MAP or one of
   its dependencies that has not yet been run.  When there are no more
   initializers to be run, this returns zero.  The functions are returned
   in the order they should be called.  */
extern ElfW(Addr) _dl_init_next (struct link_map *map);

/* Call the finalizer functions of all shared objects whose
   initializer functions have completed.  */
extern void _dl_fini (void);

/* The dynamic linker calls this function before and having changing
   any shared object mappings.  The `r_state' member of `struct r_debug'
   says what change is taking place.  This function's address is
   the value of the `r_brk' member.  */
extern void _dl_debug_state (void);

/* Initialize `struct r_debug' if it has not already been done.  The
   argument is the run-time load address of the dynamic linker, to be put
   in the `r_ldbase' member.  Returns the address of the structure.  */
extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase);


#endif /* link.h */