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1 /* Run time dynamic linker.
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. */
25 #include <sys/mman.h> /* Check if MAP_ANON is defined. */
26 #include "../stdio-common/_itoa.h"
28 #include "dynamic-link.h"
31 /* System-specific function to do initial startup for the dynamic linker.
32 After this, file access calls and getenv must work. This is responsible
33 for setting __libc_enable_secure if we need to be secure (e.g. setuid),
34 and for setting _dl_argc and _dl_argv, and then calling _dl_main. */
35 extern ElfW(Addr
) _dl_sysdep_start (void **start_argptr
,
36 void (*dl_main
) (const ElfW(Phdr
) *phdr
,
38 ElfW(Addr
) *user_entry
));
39 extern void _dl_sysdep_start_cleanup (void);
43 const char *_dl_rpath
;
45 static void dl_main (const ElfW(Phdr
) *phdr
,
47 ElfW(Addr
) *user_entry
);
49 struct link_map _dl_rtld_map
;
54 #error "sysdeps/MACHINE/dl-machine.h fails to define RTLD_START"
60 struct link_map bootstrap_map
;
62 /* This #define produces dynamic linking inline functions for
63 bootstrap relocation instead of general-purpose relocation. */
64 #define RTLD_BOOTSTRAP
65 #define RESOLVE(sym, flags) bootstrap_map.l_addr
66 #include "dynamic-link.h"
68 /* Figure out the run-time load address of the dynamic linker itself. */
69 bootstrap_map
.l_addr
= elf_machine_load_address ();
71 /* Read our own dynamic section and fill in the info array.
72 Conveniently, the first element of the GOT contains the
73 offset of _DYNAMIC relative to the run-time load address. */
74 bootstrap_map
.l_ld
= (void *) bootstrap_map
.l_addr
+ *elf_machine_got ();
75 elf_get_dynamic_info (bootstrap_map
.l_ld
, bootstrap_map
.l_info
);
77 #ifdef ELF_MACHINE_BEFORE_RTLD_RELOC
78 ELF_MACHINE_BEFORE_RTLD_RELOC (bootstrap_map
.l_info
);
81 /* Relocate ourselves so we can do normal function calls and
82 data access using the global offset table. */
84 ELF_DYNAMIC_RELOCATE (&bootstrap_map
, 0);
87 /* Now life is sane; we can call functions and access global data.
88 Set up to use the operating system facilities, and find out from
89 the operating system's program loader where to find the program
90 header table in core. */
93 /* Transfer data about ourselves to the permanent link_map structure. */
94 _dl_rtld_map
.l_addr
= bootstrap_map
.l_addr
;
95 _dl_rtld_map
.l_ld
= bootstrap_map
.l_ld
;
96 memcpy (_dl_rtld_map
.l_info
, bootstrap_map
.l_info
,
97 sizeof _dl_rtld_map
.l_info
);
98 _dl_setup_hash (&_dl_rtld_map
);
100 /* Cache the DT_RPATH stored in ld.so itself; this will be
101 the default search path. */
102 _dl_rpath
= (void *) (_dl_rtld_map
.l_addr
+
103 _dl_rtld_map
.l_info
[DT_STRTAB
]->d_un
.d_ptr
+
104 _dl_rtld_map
.l_info
[DT_RPATH
]->d_un
.d_val
);
106 /* Call the OS-dependent function to set up life so we can do things like
107 file access. It will call `dl_main' (below) to do all the real work
108 of the dynamic linker, and then unwind our frame and run the user
109 entry point on the same stack we entered on. */
110 return _dl_sysdep_start (arg
, &dl_main
);
114 /* Now life is peachy; we can do all normal operations.
115 On to the real work. */
119 unsigned int _dl_skip_args
; /* Nonzero if we were run directly. */
122 dl_main (const ElfW(Phdr
) *phdr
,
124 ElfW(Addr
) *user_entry
)
126 const ElfW(Phdr
) *ph
;
129 enum { normal
, list
, verify
} mode
= normal
;
130 struct link_map
**preloads
;
131 unsigned int npreloads
;
133 if (*user_entry
== (ElfW(Addr
)) &_start
)
135 /* Ho ho. We are not the program interpreter! We are the program
136 itself! This means someone ran ld.so as a command. Well, that
137 might be convenient to do sometimes. We support it by
138 interpreting the args like this:
140 ld.so PROGRAM ARGS...
142 The first argument is the name of a file containing an ELF
143 executable we will load and run with the following arguments.
144 To simplify life here, PROGRAM is searched for using the
145 normal rules for shared objects, rather than $PATH or anything
146 like that. We just load it and use its entry point; we don't
147 pay attention to its PT_INTERP command (we are the interpreter
148 ourselves). This is an easy way to test a new ld.so before
152 Usage: ld.so [--list|--verify] EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
153 You have invoked `ld.so', the helper program for shared library executables.\n\
154 This program usually lives in the file `/lib/ld.so', and special directives\n\
155 in executable files using ELF shared libraries tell the system's program\n\
156 loader to load the helper program from this file. This helper program loads\n\
157 the shared libraries needed by the program executable, prepares the program\n\
158 to run, and runs it. You may invoke this helper program directly from the\n\
159 command line to load and run an ELF executable file; this is like executing\n\
160 that file itself, but always uses this helper program from the file you\n\
161 specified, instead of the helper program file specified in the executable\n\
162 file you run. This is mostly of use for maintainers to test new versions\n\
163 of this helper program; chances are you did not intend to run this program.\n",
166 /* Note the place where the dynamic linker actually came from. */
167 _dl_rtld_map
.l_name
= _dl_argv
[0];
169 if (! strcmp (_dl_argv
[1], "--list"))
177 else if (! strcmp (_dl_argv
[1], "--verify"))
190 l
= _dl_map_object (NULL
, _dl_argv
[0], lt_library
);
193 l
->l_name
= (char *) "";
194 *user_entry
= l
->l_entry
;
198 /* Create a link_map for the executable itself.
199 This will be what dlopen on "" returns. */
200 l
= _dl_new_object ((char *) "", "", lt_library
);
203 l
->l_entry
= *user_entry
;
208 /* GDB assumes that the first element on the chain is the
209 link_map for the executable itself, and always skips it.
210 Make sure the first one is indeed that one. */
211 l
->l_prev
->l_next
= l
->l_next
;
213 l
->l_next
->l_prev
= l
->l_prev
;
215 l
->l_next
= _dl_loaded
;
216 _dl_loaded
->l_prev
= l
;
220 /* Scan the program header table for the dynamic section. */
221 for (ph
= phdr
; ph
< &phdr
[phent
]; ++ph
)
225 /* This tells us where to find the dynamic section,
226 which tells us everything we need to do. */
227 l
->l_ld
= (void *) l
->l_addr
+ ph
->p_vaddr
;
230 /* This "interpreter segment" was used by the program loader to
231 find the program interpreter, which is this program itself, the
232 dynamic linker. We note what name finds us, so that a future
233 dlopen call or DT_NEEDED entry, for something that wants to link
234 against the dynamic linker as a shared library, will know that
235 the shared object is already loaded. */
236 _dl_rtld_map
.l_libname
= (const char *) l
->l_addr
+ ph
->p_vaddr
;
239 if (! _dl_rtld_map
.l_libname
&& _dl_rtld_map
.l_name
)
240 /* We were invoked directly, so the program might not have a PT_INTERP. */
241 _dl_rtld_map
.l_libname
= _dl_rtld_map
.l_name
;
243 assert (_dl_rtld_map
.l_libname
); /* How else did we get here? */
246 /* We were called just to verify that this is a dynamic executable
247 using us as the program interpreter. */
248 _exit ((strcmp (_dl_rtld_map
.l_libname
, _dl_rtld_map
.l_name
) ||
250 ? EXIT_FAILURE
: EXIT_SUCCESS
);
252 /* Extract the contents of the dynamic section for easy access. */
253 elf_get_dynamic_info (l
->l_ld
, l
->l_info
);
254 if (l
->l_info
[DT_HASH
])
255 /* Set up our cache of pointers into the hash table. */
258 /* Put the link_map for ourselves on the chain so it can be found by
260 if (! _dl_rtld_map
.l_name
)
261 /* If not invoked directly, the dynamic linker shared object file was
262 found by the PT_INTERP name. */
263 _dl_rtld_map
.l_name
= (char *) _dl_rtld_map
.l_libname
;
264 _dl_rtld_map
.l_type
= lt_library
;
267 l
->l_next
= &_dl_rtld_map
;
268 _dl_rtld_map
.l_prev
= l
;
272 if (! __libc_enable_secure
)
274 const char *preloadlist
= getenv ("LD_PRELOAD");
277 /* The LD_PRELOAD environment variable gives a colon-separated
278 list of libraries that are loaded before the executable's
279 dependencies and prepended to the global scope list. */
280 char *list
= strdupa (preloadlist
);
282 while ((p
= strsep (&list
, ":")) != NULL
)
284 (void) _dl_map_object (NULL
, p
, lt_library
);
290 /* Set up PRELOADS with a vector of the preloaded libraries. */
293 preloads
= __alloca (npreloads
* sizeof preloads
[0]);
294 l
= _dl_rtld_map
.l_next
; /* End of the chain before preloads. */
301 assert (i
== npreloads
);
306 /* Load all the libraries specified by DT_NEEDED entries. If LD_PRELOAD
307 specified some libraries to load, these are inserted before the actual
308 dependencies in the executable's searchlist for symbol resolution. */
309 _dl_map_object_deps (l
, preloads
, npreloads
);
312 /* We are done mapping things, so close the zero-fill descriptor. */
313 __close (_dl_zerofd
);
317 /* Remove _dl_rtld_map from the chain. */
318 _dl_rtld_map
.l_prev
->l_next
= _dl_rtld_map
.l_next
;
319 if (_dl_rtld_map
.l_next
)
320 _dl_rtld_map
.l_next
->l_prev
= _dl_rtld_map
.l_prev
;
322 if (_dl_rtld_map
.l_opencount
)
324 /* Some DT_NEEDED entry referred to the interpreter object itself, so
325 put it back in the list of visible objects. We insert it into the
326 chain in symbol search order because gdb uses the chain's order as
327 its symbol search order. */
329 while (l
->l_searchlist
[i
] != &_dl_rtld_map
)
331 _dl_rtld_map
.l_prev
= l
->l_searchlist
[i
- 1];
332 _dl_rtld_map
.l_next
= (i
+ 1 < l
->l_nsearchlist
?
333 l
->l_searchlist
[i
+ 1] : NULL
);
334 assert (_dl_rtld_map
.l_prev
->l_next
== _dl_rtld_map
.l_next
);
335 _dl_rtld_map
.l_prev
->l_next
= &_dl_rtld_map
;
336 if (_dl_rtld_map
.l_next
)
338 assert (_dl_rtld_map
.l_next
->l_prev
== _dl_rtld_map
.l_prev
);
339 _dl_rtld_map
.l_next
->l_prev
= &_dl_rtld_map
;
343 if (mode
!= normal
|| getenv ("LD_TRACE_LOADED_OBJECTS") != NULL
)
345 /* We were run just to list the shared libraries. It is
346 important that we do this before real relocation, because the
347 functions we call below for output may no longer work properly
352 if (! _dl_loaded
->l_info
[DT_NEEDED
])
353 _dl_sysdep_message ("\t", "statically linked\n", NULL
);
355 for (l
= _dl_loaded
->l_next
; l
; l
= l
->l_next
)
358 buf
[sizeof buf
- 1] = '\0';
359 bp
= _itoa (l
->l_addr
, &buf
[sizeof buf
- 1], 16, 0);
360 while (&buf
[sizeof buf
- 1] - bp
< sizeof l
->l_addr
* 2)
362 _dl_sysdep_message ("\t", l
->l_libname
, " => ", l
->l_name
,
363 " (0x", bp
, ")\n", NULL
);
367 for (i
= 1; i
< _dl_argc
; ++i
)
369 const ElfW(Sym
) *ref
= NULL
;
370 ElfW(Addr
) loadbase
= _dl_lookup_symbol (_dl_argv
[i
], &ref
,
371 &_dl_default_scope
[2],
374 buf
[sizeof buf
- 1] = '\0';
375 bp
= _itoa (ref
->st_value
, &buf
[sizeof buf
- 1], 16, 0);
376 while (&buf
[sizeof buf
- 1] - bp
< sizeof loadbase
* 2)
378 _dl_sysdep_message (_dl_argv
[i
], " found at 0x", bp
, NULL
);
379 buf
[sizeof buf
- 1] = '\0';
380 bp
= _itoa (loadbase
, &buf
[sizeof buf
- 1], 16, 0);
381 while (&buf
[sizeof buf
- 1] - bp
< sizeof loadbase
* 2)
383 _dl_sysdep_message (" in object at 0x", bp
, "\n", NULL
);
389 lazy
= !__libc_enable_secure
&& *(getenv ("LD_BIND_NOW") ?: "") == '\0';
392 /* Now we have all the objects loaded. Relocate them all except for
393 the dynamic linker itself. We do this in reverse order so that copy
394 relocs of earlier objects overwrite the data written by later
395 objects. We do not re-relocate the dynamic linker itself in this
396 loop because that could result in the GOT entries for functions we
397 call being changed, and that would break us. It is safe to relocate
398 the dynamic linker out of order because it has no copy relocs (we
399 know that because it is self-contained). */
406 if (l
!= &_dl_rtld_map
)
408 _dl_relocate_object (l
, _dl_object_relocation_scope (l
), lazy
);
409 *_dl_global_scope_end
= NULL
;
414 /* Do any necessary cleanups for the startup OS interface code.
415 We do these now so that no calls are made after rtld re-relocation
416 which might be resolved to different functions than we expect.
417 We cannot do this before relocating the other objects because
418 _dl_relocate_object might need to call `mprotect' for DT_TEXTREL. */
419 _dl_sysdep_start_cleanup ();
421 if (_dl_rtld_map
.l_opencount
> 0)
422 /* There was an explicit ref to the dynamic linker as a shared lib.
423 Re-relocate ourselves with user-controlled symbol definitions. */
424 _dl_relocate_object (&_dl_rtld_map
, &_dl_default_scope
[2], 0);
428 /* Initialize _r_debug. */
429 struct r_debug
*r
= _dl_debug_initialize (_dl_rtld_map
.l_addr
);
433 #ifdef ELF_MACHINE_DEBUG_SETUP
435 /* Some machines (e.g. MIPS) don't use DT_DEBUG in this way. */
437 ELF_MACHINE_DEBUG_SETUP (l
, r
);
438 ELF_MACHINE_DEBUG_SETUP (&_dl_rtld_map
, r
);
442 if (l
->l_info
[DT_DEBUG
])
443 /* There is a DT_DEBUG entry in the dynamic section. Fill it in
444 with the run-time address of the r_debug structure */
445 l
->l_info
[DT_DEBUG
]->d_un
.d_ptr
= (ElfW(Addr
)) r
;
447 /* Fill in the pointer in the dynamic linker's own dynamic section, in
448 case you run gdb on the dynamic linker directly. */
449 if (_dl_rtld_map
.l_info
[DT_DEBUG
])
450 _dl_rtld_map
.l_info
[DT_DEBUG
]->d_un
.d_ptr
= (ElfW(Addr
)) r
;
454 /* Notify the debugger that all objects are now mapped in. */
459 if (_dl_rtld_map
.l_info
[DT_INIT
])
461 /* Call the initializer for the compatibility version of the
462 dynamic linker. There is no additional initialization
463 required for the ABI-compliant dynamic linker. */
465 (*(void (*) (void)) (_dl_rtld_map
.l_addr
+
466 _dl_rtld_map
.l_info
[DT_INIT
]->d_un
.d_ptr
)) ();
468 /* Clear the field so a future dlopen won't run it again. */
469 _dl_rtld_map
.l_info
[DT_INIT
] = NULL
;
472 /* Once we return, _dl_sysdep_start will invoke
473 the DT_INIT functions and then *USER_ENTRY. */