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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.
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.
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.
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. */
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. */
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. */
43 int r_version
; /* Version number for this protocol. */
45 struct link_map
*r_map
; /* Head of the chain of loaded objects. */
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. */
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. */
62 ElfW(Addr
) r_ldbase
; /* Base address the linker is loaded at. */
65 /* This is the instance of that structure used by the dynamic linker. */
66 extern struct r_debug _r_debug
;
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;
75 extern ElfW(Dyn
) _DYNAMIC
[];
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.
81 These data structures exist in space used by the run-time dynamic linker;
82 modifying them may have disastrous results. */
86 /* These first few members are part of the protocol with the debugger.
87 This is the same format used in SVR4. */
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. */
94 /* All following members are internal to the dynamic linker.
95 They may change without notice. */
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. */
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
;
112 /* Dependent object that first caused this object to be loaded. */
113 struct link_map
*l_loader
;
115 /* Symbol hash table. */
116 ElfW(Symndx
) l_nbuckets
;
117 const ElfW(Symndx
) *l_buckets
, *l_chain
;
119 unsigned int l_opencount
; /* Reference count for dlopen/dlclose. */
120 enum /* Where this object came from. */
122 lt_executable
, /* The main executable program. */
123 lt_library
, /* Library needed by main executable. */
124 lt_loaded
, /* Extra run-time loaded shared object. */
126 unsigned int l_relocated
:1; /* Nonzero if object's relocations done. */
127 unsigned int l_init_called
:1; /* Nonzero if DT_INIT function called. */
128 unsigned int l_init_running
:1; /* Nonzero while DT_INIT function runs. */
129 unsigned int l_global
:1; /* Nonzero if object in _dl_global_scope. */
130 unsigned int l_reserved
:2; /* Reserved for internal use. */
133 /* Internal functions of the run-time dynamic linker.
134 These can be accessed if you link again the dynamic linker
135 as a shared library, as in `-lld' or `/lib/ld.so' explicitly;
136 but are not normally of interest to user programs.
138 The `-ldl' library functions in <dlfcn.h> provide a simple
139 user interface to run-time dynamic linking. */
142 /* Cached value of `getpagesize ()'. */
143 extern size_t _dl_pagesize
;
145 /* File descriptor referring to the zero-fill device. */
146 extern int _dl_zerofd
;
148 /* OS-dependent function to open the zero-fill device. */
149 extern int _dl_sysdep_open_zero_fill (void); /* dl-sysdep.c */
151 /* OS-dependent function to write a message on the standard output.
152 All arguments are `const char *'; args until a null pointer
153 are concatenated to form the message to print. */
154 extern void _dl_sysdep_message (const char *string
, ...);
156 /* OS-dependent function to give a fatal error message and exit
157 when the dynamic linker fails before the program is fully linked.
158 All arguments are `const char *'; args until a null pointer
159 are concatenated to form the message to print. */
160 extern void _dl_sysdep_fatal (const char *string
, ...)
161 __attribute__ ((__noreturn__
));
163 /* Nonzero if the program should be "secure" (i.e. it's setuid or somesuch).
164 This tells the dynamic linker to ignore environment variables. */
165 extern int _dl_secure
;
167 /* This function is called by all the internal dynamic linker functions
168 when they encounter an error. ERRCODE is either an `errno' code or
169 zero; OBJECT is the name of the problematical shared object, or null if
170 it is a general problem; ERRSTRING is a string describing the specific
173 extern void _dl_signal_error (int errcode
,
175 const char *errstring
)
176 __attribute__ ((__noreturn__
));
178 /* Call OPERATE, catching errors from `dl_signal_error'. If there is no
179 error, *ERRSTRING is set to null. If there is an error, *ERRSTRING and
180 *OBJECT are set to the strings passed to _dl_signal_error, and the error
181 code passed is the return value. */
182 extern int _dl_catch_error (const char **errstring
,
184 void (*operate
) (void));
187 /* Helper function for <dlfcn.h> functions. Runs the OPERATE function via
188 _dl_catch_error. Returns zero for success, nonzero for failure; and
189 arranges for `dlerror' to return the error details. */
190 extern int _dlerror_run (void (*operate
) (void));
193 /* Open the shared object NAME and map in its segments.
194 LOADER's DT_RPATH is used in searching for NAME.
195 If the object is already opened, returns its existing map. */
196 extern struct link_map
*_dl_map_object (struct link_map
*loader
,
197 const char *name
, int type
);
199 /* Call _dl_map_object on the dependencies of MAP, and
200 set up MAP->l_searchlist. */
201 extern void _dl_map_object_deps (struct link_map
*map
);
203 /* Cache the locations of MAP's hash table. */
204 extern void _dl_setup_hash (struct link_map
*map
);
207 /* Open the shared object NAME, relocate it, and run its initializer if it
208 hasn't already been run. LOADER's DT_RPATH is used in searching for
209 NAME. MODE is as for `dlopen' (see <dlfcn.h>). If the object is
210 already opened, returns its existing map. */
211 extern struct link_map
*_dl_open (struct link_map
*loader
,
212 const char *name
, int mode
);
214 /* Close an object previously opened by _dl_open. */
215 extern void _dl_close (struct link_map
*map
);
218 /* Search loaded objects' symbol tables for a definition of the symbol
219 referred to by UNDEF. *SYM is the symbol table entry containing the
220 reference; it is replaced with the defining symbol, and the base load
221 address of the defining object is returned. SYMBOL_SCOPE is a
222 null-terminated list of object scopes to search; each object's
223 l_searchlist (i.e. the segment of the dependency tree starting at that
224 object) is searched in turn. REFERENCE_NAME should name the object
225 containing the reference; it is used in error messages. RELOC_ADDR is
226 the address being fixed up and the chosen symbol cannot be one with this
227 value. If NOPLT is nonzero, then the reference must not be resolved to
229 extern ElfW(Addr
) _dl_lookup_symbol (const char *undef
,
230 const ElfW(Sym
) **sym
,
231 struct link_map
*symbol_scope
[],
232 const char *reference_name
,
233 ElfW(Addr
) reloc_addr
,
236 /* Look up symbol NAME in MAP's scope and return its run-time address. */
237 extern ElfW(Addr
) _dl_symbol_value (struct link_map
*map
, const char *name
);
240 /* Structure describing the dynamic linker itself. */
241 extern struct link_map _dl_rtld_map
;
243 /* The list of objects currently loaded is the third element of the
244 `_dl_default_scope' array, and the fourth element is always null.
245 This leaves two slots before it that are used when resolving
246 DT_SYMBOLIC objects' references one after it for normal references
248 #define _dl_loaded (_dl_default_scope[2])
249 extern struct link_map
*_dl_default_scope
[5];
251 /* Null-terminated list of objects in the dynamic `global scope'. The
252 list starts at [2]; i.e. &_dl_global_scope[2] is the argument
253 passed to _dl_lookup_symbol to search the global scope. To search
254 a specific object and its dependencies in preference to the global
255 scope, fill in the [1] slot and pass its address; for two specific
256 object scopes, fill [0] and [1]. The list is double-terminated; to
257 search the global scope and then a specific object and its
258 dependencies, set *_dl_global_scope_end. This variable initially
259 points to _dl_default_scope, and _dl_loaded is always kept in [2]
260 of this list. A new list is malloc'd when new objects are loaded
262 extern struct link_map
**_dl_global_scope
, **_dl_global_scope_end
;
263 extern size_t _dl_global_scope_alloc
; /* Number of slots malloc'd. */
265 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
266 _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
267 references made in the object MAP's relocations. */
268 extern struct link_map
**_dl_object_relocation_scope (struct link_map
*map
);
271 /* Allocate a `struct link_map' for a new object being loaded,
272 and enter it into the _dl_loaded list. */
273 extern struct link_map
*_dl_new_object (char *realname
, const char *libname
,
276 /* Relocate the given object (if it hasn't already been).
277 SCOPE is passed to _dl_lookup_symbol in symbol lookups.
278 If LAZY is nonzero, don't relocate its PLT. */
279 extern void _dl_relocate_object (struct link_map
*map
,
280 struct link_map
*scope
[],
283 /* Return the address of the next initializer function for MAP or one of
284 its dependencies that has not yet been run. When there are no more
285 initializers to be run, this returns zero. The functions are returned
286 in the order they should be called. */
287 extern ElfW(Addr
) _dl_init_next (struct link_map
*map
);
289 /* Call the finalizer functions of all shared objects whose
290 initializer functions have completed. */
291 extern void _dl_fini (void);
293 /* The dynamic linker calls this function before and having changing
294 any shared object mappings. The `r_state' member of `struct r_debug'
295 says what change is taking place. This function's address is
296 the value of the `r_brk' member. */
297 extern void _dl_debug_state (void);
299 /* Initialize `struct r_debug' if it has not already been done. The
300 argument is the run-time load address of the dynamic linker, to be put
301 in the `r_ldbase' member. Returns the address of the structure. */
302 extern struct r_debug
*_dl_debug_initialize (ElfW(Addr
) ldbase
);
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