about summary refs log tree commit diff
path: root/elf/dl-load.c
blob: 7319602d813bdb71c969e5b5a74e86be417ae0b8 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
/* _dl_map_object -- Map in a shared object's segments from the file.
Copyright (C) 1995 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.  */

#include <link.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include "dynamic-link.h"


#include <endian.h>
#if BYTE_ORDER == BIG_ENDIAN
#define byteorder ELFDATA2MSB
#define byteorder_name "big-endian"
#elif BYTE_ORDER == LITTLE_ENDIAN
#define byteorder ELFDATA2LSB
#define byteorder_name "little-endian"
#else
#error "Unknown BYTE_ORDER " BYTE_ORDER
#define byteorder ELFDATANONE
#endif

#define STRING(x) #x

int _dl_zerofd = -1;


/* Try to open NAME in one of the directories in DIRPATH.
   Return the fd, or -1.  If successful, fill in *REALNAME
   with the malloc'd full directory name.  */

static int
open_path (const char *name, size_t namelen,
	   const char *dirpath,
	   char **realname)
{
  char *buf;
  const char *p;
  int fd;

  p = dirpath;
  if (p == NULL || *p == '\0')
    {
      errno = ENOENT;
      return -1;
    }

  buf = alloca (strlen (dirpath) + 1 + namelen);
  do
    {
      dirpath = p;
      p = strpbrk (dirpath, ":;");
      if (p == NULL)
	p = strchr (dirpath, '\0');

      if (p == dirpath)
	/* Two adjacent colons, or a colon at the beginning or the end of
	   the path means to search the current directory.  */
	(void) memcpy (buf, name, namelen);
      else
	{
	  /* Construct the pathname to try.  */
	  (void) memcpy (buf, dirpath, p - dirpath);
	  buf[p - dirpath] = '/';
	  (void) memcpy (&buf[(p - dirpath) + 1], name, namelen);
	}

      fd = open (buf, O_RDONLY);
      if (fd != -1)
	{
	  *realname = strdup (buf);
	  return fd;
	}
      if (errno != ENOENT && errno != EACCES)
	/* The file exists and is readable, but something went wrong.  */
	return -1;
    }
  while (*p++ != '\0');

  return -1;
}


/* Map in the shared object file NAME.  */

struct link_map *
_dl_map_object (struct link_map *loader, const char *name,
		Elf32_Addr *entry_point)
{
  int fd;
  char *realname;
  struct link_map *l;

  /* Look for this name among those already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    if (! strcmp (name, l->l_libname))
      {
	/* The object is already loaded.
	   Just bump its reference count and return it.  */
	++l->l_opencount;
	return l;
      }

  if (strchr (name, '/') == NULL)
    {
      /* Search for NAME in several places.  */

      size_t namelen = strlen (name) + 1;

      inline void trypath (const char *dirpath)
	{
	  fd = open_path (name, namelen, dirpath, &realname);
	}

      fd = -1;
      if (loader && loader->l_info[DT_RPATH])
	trypath ((const char *) (loader->l_addr +
				 loader->l_info[DT_STRTAB]->d_un.d_ptr +
				 loader->l_info[DT_RPATH]->d_un.d_val));
      if (fd == -1 && ! _dl_secure)
	trypath (getenv ("LD_LIBRARY_PATH"));
      if (fd == -1)
	trypath ("/lib:/usr/lib");
    }
  else
    {
      fd = open (name, O_RDONLY);
      if (fd != -1)
	realname = strdup (name);
    }

  if (fd == -1)
    _dl_signal_error (errno, name, "cannot open shared object file");

  return _dl_map_object_from_fd (name, fd, realname, entry_point);
}


/* Map in the shared object NAME, actually located in REALNAME, and already
   opened on FD.  */

struct link_map *
_dl_map_object_from_fd (const char *name, int fd, char *realname, 
			Elf32_Addr *entry_point)
{
  struct link_map *l = NULL;
  const size_t pagesize = getpagesize ();
  void *file_mapping = NULL;
  size_t mapping_size = 0;

  void lose (int code, const char *msg)
    {
      (void) close (fd);
      if (file_mapping)
	munmap (file_mapping, mapping_size);
      _dl_signal_error (code, l ? l->l_name : name, msg);
    }

  /* Make sure LOCATION is mapped in.  */
  void *map (off_t location, size_t size)
    {
      if ((off_t) mapping_size <= location + (off_t) size)
	{
	  void *result;
	  if (file_mapping)
	    munmap (file_mapping, mapping_size);
	  mapping_size = (location + size + 1 + pagesize - 1);
	  mapping_size &= ~(pagesize - 1);
	  result = mmap (file_mapping, mapping_size, PROT_READ,
			 MAP_COPY|MAP_FILE, fd, 0);
	  if (result == (void *) -1)
	    lose (errno, "cannot map file data");
	  file_mapping = result;
	}
      return file_mapping + location;
    }

  const Elf32_Ehdr *header;

  /* Look again to see if the real name matched another already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    if (! strcmp (realname, l->l_name))
      {
	/* The object is already loaded.
	   Just bump its reference count and return it.  */
	close (fd);
	free (realname);
	++l->l_opencount;
	return l;
      }

  /* Map in the first page to read the header.  */
  header = map (0, sizeof *header);

#undef LOSE
#define LOSE(s) lose (0, (s))
  /* Check the header for basic validity.  */
  if (*(Elf32_Word *) &header->e_ident != ((ELFMAG0 << (EI_MAG0 * 8)) |
					   (ELFMAG1 << (EI_MAG1 * 8)) |
					   (ELFMAG2 << (EI_MAG2 * 8)) |
					   (ELFMAG3 << (EI_MAG3 * 8))))
    LOSE ("invalid ELF header");
  if (header->e_ident[EI_CLASS] != ELFCLASS32)
    LOSE ("ELF file class not 32-bit");
  if (header->e_ident[EI_DATA] != byteorder)
    LOSE ("ELF file data encoding not " byteorder_name);
  if (header->e_ident[EI_VERSION] != EV_CURRENT)
    LOSE ("ELF file version ident not " STRING(EV_CURRENT));
  if (header->e_version != EV_CURRENT)
    LOSE ("ELF file version not " STRING(EV_CURRENT));
  if (! elf_machine_matches_host (header->e_machine))
    LOSE ("ELF file machine architecture not " ELF_MACHINE_NAME);
  if (header->e_phentsize != sizeof (Elf32_Phdr))
    LOSE ("ELF file's phentsize not the expected size");

  /* Enter the new object in the list of loaded objects.  */
  l = _dl_new_object (realname, name, lt_loaded);
  l->l_opencount = 1;

  if (_dl_zerofd == -1)
    {
      _dl_zerofd = _dl_sysdep_open_zero_fill ();
      if (_dl_zerofd == -1)
	_dl_signal_error (errno, NULL, "cannot open zero fill device");
    }

  {
    /* Copy the program header table into stack space so we can then unmap
       the headers.  */
    Elf32_Phdr phdr[header->e_phnum];
    const Elf32_Phdr *ph;
    int anywhere;

    ph = map (header->e_phoff, header->e_phnum * sizeof (Elf32_Phdr));
    memcpy (phdr, ph, sizeof phdr);
    l->l_phnum = header->e_phnum;

    anywhere = header->e_type == ET_DYN || header->e_type == ET_REL;

    if (entry_point)
      *entry_point = header->e_entry;

    /* We are done reading the file's headers now.  Unmap them.  */
    munmap (file_mapping, mapping_size);

    /* Scan the program header table, processing its load commands.  */
    l->l_addr = 0;
    l->l_ld = 0;
    for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
      switch (ph->p_type)
	{
	  /* These entries tell us where to find things once the file's
	     segments are mapped in.  We record the addresses it says
	     verbatim, and later correct for the run-time load address.  */
	case PT_DYNAMIC:
	  l->l_ld = (void *) ph->p_vaddr;
	  break;
	case PT_PHDR:
	  l->l_phdr = (void *) ph->p_vaddr;
	  break;

	case PT_LOAD:
	  /* A load command tells us to map in part of the file.  */
	  if (ph->p_align % pagesize != 0)
	    LOSE ("ELF load command alignment not page-aligned");
	  if ((ph->p_vaddr - ph->p_offset) % ph->p_align)
	    LOSE ("ELF load command address/offset not properly aligned");
	  {
	    Elf32_Addr mapstart = ph->p_vaddr & ~(ph->p_align - 1);
	    Elf32_Addr mapend = ((ph->p_vaddr + ph->p_filesz + ph->p_align - 1)
				 & ~(ph->p_align - 1));
	    off_t mapoff = ph->p_offset & ~(ph->p_align - 1);
	    caddr_t mapat;
	    int prot = 0;
	    if (ph->p_flags & PF_R)
	      prot |= PROT_READ;
	    if (ph->p_flags & PF_W)
	      prot |= PROT_WRITE;
	    if (ph->p_flags & PF_X)
	      prot |= PROT_EXEC;

	    if (anywhere)
	      {
		/* XXX this loses if the first segment mmap call puts
		   it someplace where the later segments cannot fit.  */
		mapat = mmap ((caddr_t) (l->l_addr + mapstart),
			      mapend - mapstart,
			      prot, MAP_COPY|MAP_FILE|MAP_INHERIT |
			      /* Let the system choose any convenient
				 location if this is the first segment.
				 Following segments must be contiguous in
				 virtual space with the first.  */
			      (l->l_addr == 0 ? 0 : MAP_FIXED),
			      fd, mapoff);
		if (l->l_addr == 0)
		  /* This was the first segment mapped, so MAPAT is
		     the address the system chose for us.  Record it.  */
		  l->l_addr = (Elf32_Addr) mapat - mapstart;
	      }
	    else
	      {
		mapat = mmap ((caddr_t) mapstart, mapend - mapstart,
			      prot, MAP_COPY|MAP_FILE|MAP_INHERIT|MAP_FIXED,
			      fd, mapoff);
		/* This file refers to absolute addresses.  So consider its
		   "load base" to be zero, since that is what we add to the
		   file's addresses to find them in our memory.  */
		l->l_addr = 0;
	      }
	    if (mapat == (caddr_t) -1)
	      lose (errno, "failed to map segment from shared object");

	    if (ph->p_memsz > ph->p_filesz)
	      {
		/* Extra zero pages should appear at the end of this segment,
		   after the data mapped from the file.   */
		caddr_t zero, zeroend, zeropage;

		mapat += ph->p_vaddr - mapstart;
		zero = mapat + ph->p_filesz;
		zeroend = mapat + ph->p_memsz;
		zeropage = (caddr_t) ((Elf32_Addr) (zero + pagesize - 1)
				      & ~(pagesize - 1));

		if (zeroend < zeropage)
		  /* All the extra data is in the last page of the segment.
		     We can just zero it.  */
		  zeropage = zeroend;
		if (zeropage > zero)
		  {
		    /* Zero the final part of the last page of the segment.  */
		    if ((prot & PROT_WRITE) == 0)
		      {
			/* Dag nab it.  */
			if (mprotect ((caddr_t) ((Elf32_Addr) zero
						 & ~(pagesize - 1)),
				      pagesize,
				      prot|PROT_WRITE) < 0)
			  lose (errno, "cannot change memory protections");
		      }
		    memset (zero, 0, zeropage - zero);
		    if ((prot & PROT_WRITE) == 0)
		      mprotect ((caddr_t) ((Elf32_Addr) zero
					   & ~(pagesize - 1)),
				pagesize, prot);
		  }

		if (zeroend > zeropage)
		  /* Map the remaining zero pages in from the zero fill FD.  */
		  mapat = mmap (zeropage, zeroend - zeropage, prot,
				MAP_ANON|MAP_PRIVATE|MAP_FIXED|MAP_INHERIT,
				_dl_zerofd, 0);
	      }
	  }
	}

    if (l->l_ld == 0)
      LOSE ("object file has no dynamic section");
    (Elf32_Addr) l->l_ld += l->l_addr;

    if (l->l_phdr == 0)
      l->l_phdr = (void *) ((const Elf32_Ehdr *) l->l_addr)->e_phoff;
    (Elf32_Addr) l->l_phdr += l->l_addr;
  }

  elf_get_dynamic_info (l->l_ld, l->l_info);
  if (l->l_info[DT_HASH])
    _dl_setup_hash (l);

  return l;
}