File: dl-fptr.c

package info (click to toggle)
glibc 2.24-11+deb9u4
  • links: PTS, VCS
  • area: main
  • in suites: stretch, stretch-proposed-updates
  • size: 225,852 kB
  • sloc: ansic: 996,505; asm: 261,827; sh: 10,484; makefile: 9,856; cpp: 4,169; python: 3,971; perl: 2,254; awk: 1,753; pascal: 1,521; yacc: 291; sed: 80
file content (396 lines) | stat: -rw-r--r-- 10,896 bytes parent folder | download | duplicates (4)
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
392
393
394
395
396
/* Manage function descriptors.  Generic version.
   Copyright (C) 1999-2016 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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <libintl.h>
#include <unistd.h>
#include <string.h>
#include <sys/param.h>
#include <sys/mman.h>
#include <link.h>
#include <ldsodefs.h>
#include <elf/dynamic-link.h>
#include <dl-fptr.h>
#include <dl-unmap-segments.h>
#include <atomic.h>
#include <libc-internal.h>

#ifndef ELF_MACHINE_BOOT_FPTR_TABLE_LEN
/* ELF_MACHINE_BOOT_FPTR_TABLE_LEN should be greater than the number of
   dynamic symbols in ld.so.  */
# define ELF_MACHINE_BOOT_FPTR_TABLE_LEN 256
#endif

#ifndef ELF_MACHINE_LOAD_ADDRESS
# error "ELF_MACHINE_LOAD_ADDRESS is not defined."
#endif

#ifndef COMPARE_AND_SWAP
# define COMPARE_AND_SWAP(ptr, old, new) \
  (catomic_compare_and_exchange_bool_acq (ptr, new, old) == 0)
#endif

ElfW(Addr) _dl_boot_fptr_table [ELF_MACHINE_BOOT_FPTR_TABLE_LEN];

static struct local
  {
    struct fdesc_table *root;
    struct fdesc *free_list;
    unsigned int npages;		/* # of pages to allocate */
    /* the next to members MUST be consecutive! */
    struct fdesc_table boot_table;
    struct fdesc boot_fdescs[1024];
  }
local =
  {
#ifdef SHARED
    /* Address of .boot_table is not known until runtime.  */
    .root = 0,
#else
    .root = &local.boot_table,
#endif
    .npages = 2,
    .boot_table =
      {
	.len = sizeof (local.boot_fdescs) / sizeof (local.boot_fdescs[0]),
	.first_unused = 0
      }
  };

/* Create a new fdesc table and return a pointer to the first fdesc
   entry.  The fdesc lock must have been acquired already.  */

static struct fdesc_table *
new_fdesc_table (struct local *l, size_t *size)
{
  size_t old_npages = l->npages;
  size_t new_npages = old_npages + old_npages;
  struct fdesc_table *new_table;

  /* If someone has just created a new table, we return NULL to tell
     the caller to use the new table.  */
  if (! COMPARE_AND_SWAP (&l->npages, old_npages, new_npages))
    return (struct fdesc_table *) NULL;

  *size = old_npages * GLRO(dl_pagesize);
  new_table = __mmap (NULL, *size,
		      PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
  if (new_table == MAP_FAILED)
    _dl_signal_error (errno, NULL, NULL,
		      N_("cannot map pages for fdesc table"));

  new_table->len
    = (*size - sizeof (*new_table)) / sizeof (struct fdesc);
  new_table->first_unused = 1;
  return new_table;
}

/* Must call _dl_fptr_init before using any other function.  */
void
_dl_fptr_init (void)
{
  struct local *l;

  ELF_MACHINE_LOAD_ADDRESS (l, local);
  l->root = &l->boot_table;
}

static ElfW(Addr)
make_fdesc (ElfW(Addr) ip, ElfW(Addr) gp)
{
  struct fdesc *fdesc = NULL;
  struct fdesc_table *root;
  unsigned int old;
  struct local *l;

  ELF_MACHINE_LOAD_ADDRESS (l, local);

 retry:
  root = l->root;
  while (1)
    {
      old = root->first_unused;
      if (old >= root->len)
	break;
      else if (COMPARE_AND_SWAP (&root->first_unused, old, old + 1))
	{
	  fdesc = &root->fdesc[old];
	  goto install;
	}
    }

  if (l->free_list)
    {
      /* Get it from free-list.  */
      do
	{
	  fdesc = l->free_list;
	  if (fdesc == NULL)
	    goto retry;
	}
      while (! COMPARE_AND_SWAP ((ElfW(Addr) *) &l->free_list,
				 (ElfW(Addr)) fdesc, fdesc->ip));
    }
  else
    {
      /* Create a new fdesc table.  */
      size_t size;
      struct fdesc_table *new_table = new_fdesc_table (l, &size);

      if (new_table == NULL)
	goto retry;

      new_table->next = root;
      if (! COMPARE_AND_SWAP ((ElfW(Addr) *) &l->root,
			      (ElfW(Addr)) root,
			      (ElfW(Addr)) new_table))
	{
	  /* Someone has just installed a new table. Return NULL to
	     tell the caller to use the new table.  */
	  __munmap (new_table, size);
	  goto retry;
	}

      /* Note that the first entry was reserved while allocating the
	 memory for the new page.  */
      fdesc = &new_table->fdesc[0];
    }

 install:
  fdesc->ip = ip;
  fdesc->gp = gp;

  return (ElfW(Addr)) fdesc;
}


static inline ElfW(Addr) * __attribute__ ((always_inline))
make_fptr_table (struct link_map *map)
{
  const ElfW(Sym) *symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
  const char *strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]);
  ElfW(Addr) *fptr_table;
  size_t size;
  size_t len;
  const ElfW(Sym) *symtabend;

  /* Determine the end of the dynamic symbol table using the hash.  */
  if (map->l_info[DT_HASH] != NULL)
    symtabend = (symtab + ((Elf_Symndx *) D_PTR (map, l_info[DT_HASH]))[1]);
  else
  /* There is no direct way to determine the number of symbols in the
     dynamic symbol table and no hash table is present.  The ELF
     binary is ill-formed but what shall we do?  Use the beginning of
     the string table which generally follows the symbol table.  */
    symtabend = (const ElfW(Sym) *) strtab;

  len = (((char *) symtabend - (char *) symtab)
	 / map->l_info[DT_SYMENT]->d_un.d_val);
  size = ALIGN_UP (len * sizeof (fptr_table[0]), GLRO(dl_pagesize));

  /* We don't support systems without MAP_ANON.  We avoid using malloc
     because this might get called before malloc is setup.  */
  fptr_table = __mmap (NULL, size,
		       PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE,
		       -1, 0);
  if (fptr_table == MAP_FAILED)
    _dl_signal_error (errno, NULL, NULL,
		      N_("cannot map pages for fptr table"));

  if (COMPARE_AND_SWAP ((ElfW(Addr) *) &map->l_mach.fptr_table,
			(ElfW(Addr)) NULL, (ElfW(Addr)) fptr_table))
    map->l_mach.fptr_table_len = len;
  else
    __munmap (fptr_table, len * sizeof (fptr_table[0]));

  return map->l_mach.fptr_table;
}


ElfW(Addr)
_dl_make_fptr (struct link_map *map, const ElfW(Sym) *sym,
	       ElfW(Addr) ip)
{
  ElfW(Addr) *ftab = map->l_mach.fptr_table;
  const ElfW(Sym) *symtab;
  Elf_Symndx symidx;
  struct local *l;

  if (__builtin_expect (ftab == NULL, 0))
    ftab = make_fptr_table (map);

  symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
  symidx = sym - symtab;

  if (symidx >= map->l_mach.fptr_table_len)
    _dl_signal_error (0, NULL, NULL,
		      N_("internal error: symidx out of range of fptr table"));

  while (ftab[symidx] == 0)
    {
      /* GOT has already been relocated in elf_get_dynamic_info -
	 don't try to relocate it again.  */
      ElfW(Addr) fdesc
	= make_fdesc (ip, map->l_info[DT_PLTGOT]->d_un.d_ptr);

      if (__builtin_expect (COMPARE_AND_SWAP (&ftab[symidx], (ElfW(Addr)) NULL,
					      fdesc), 1))
	{
	  /* Noone has updated the entry and the new function
	     descriptor has been installed.  */
#if 0
	  const char *strtab
	    = (const void *) D_PTR (map, l_info[DT_STRTAB]);

	  ELF_MACHINE_LOAD_ADDRESS (l, local);
	  if (l->root != &l->boot_table
	      || l->boot_table.first_unused > 20)
	    _dl_debug_printf ("created fdesc symbol `%s' at %lx\n",
			      strtab + sym->st_name, ftab[symidx]);
#endif
	  break;
	}
      else
	{
	  /* We created a duplicated function descriptor. We put it on
	     free-list.  */
	  struct fdesc *f = (struct fdesc *) fdesc;

	  ELF_MACHINE_LOAD_ADDRESS (l, local);

	  do
	    f->ip = (ElfW(Addr)) l->free_list;
	  while (! COMPARE_AND_SWAP ((ElfW(Addr) *) &l->free_list,
				     f->ip, fdesc));
	}
    }

  return ftab[symidx];
}


void
_dl_unmap (struct link_map *map)
{
  ElfW(Addr) *ftab = map->l_mach.fptr_table;
  struct fdesc *head = NULL, *tail = NULL;
  size_t i;

  _dl_unmap_segments (map);

  if (ftab == NULL)
    return;

  /* String together the fdesc structures that are being freed.  */
  for (i = 0; i < map->l_mach.fptr_table_len; ++i)
    {
      if (ftab[i])
	{
	  *(struct fdesc **) ftab[i] = head;
	  head = (struct fdesc *) ftab[i];
	  if (tail == NULL)
	    tail = head;
	}
    }

  /* Prepend the new list to the free_list: */
  if (tail)
    do
      tail->ip = (ElfW(Addr)) local.free_list;
    while (! COMPARE_AND_SWAP ((ElfW(Addr) *) &local.free_list,
			       tail->ip, (ElfW(Addr)) head));

  __munmap (ftab, (map->l_mach.fptr_table_len
		   * sizeof (map->l_mach.fptr_table[0])));

  map->l_mach.fptr_table = NULL;
}

extern ElfW(Addr) _dl_fixup (struct link_map *, ElfW(Word)) attribute_hidden;

static inline Elf32_Addr
elf_machine_resolve (void)
{
  Elf32_Addr addr;

  asm ("b,l     1f,%0\n"
"	depi	0,31,2,%0\n"
"1:	addil	L'_dl_runtime_resolve - ($PIC_pcrel$0 - 8),%0\n"
"	ldo	R'_dl_runtime_resolve - ($PIC_pcrel$0 - 12)(%%r1),%0\n"
       : "=r" (addr) : : "r1");

  return addr;
}

static inline int
_dl_read_access_allowed (unsigned int *addr)
{
  int result;

  asm ("proberi	(%1),3,%0" : "=r" (result) : "r" (addr) : );

  return result;
}

ElfW(Addr)
_dl_lookup_address (const void *address)
{
  ElfW(Addr) addr = (ElfW(Addr)) address;
  unsigned int *desc, *gptr;

  /* Return ADDR if the least-significant two bits of ADDR are not consistent
     with ADDR being a linker defined function pointer.  The normal value for
     a code address in a backtrace is 3.  */
  if (((unsigned int) addr & 3) != 2)
    return addr;

  /* Handle special case where ADDR points to page 0.  */
  if ((unsigned int) addr < 4096)
    return addr;

  /* Clear least-significant two bits from descriptor address.  */
  desc = (unsigned int *) ((unsigned int) addr & ~3);
  if (!_dl_read_access_allowed (desc))
    return addr;

  /* Load first word of candidate descriptor.  It should be a pointer
     with word alignment and point to memory that can be read.  */
  gptr = (unsigned int *) desc[0];
  if (((unsigned int) gptr & 3) != 0
      || !_dl_read_access_allowed (gptr))
    return addr;

  /* See if descriptor requires resolution.  The following trampoline is
     used in each global offset table for function resolution:

		ldw 0(r20),r22
		bv r0(r22)
		ldw 4(r20),r21
     tramp:	b,l .-12,r20
		depwi 0,31,2,r20
		.word _dl_runtime_resolve
		.word "_dl_runtime_resolve ltp"
     got:	.word _DYNAMIC
		.word "struct link map address" */
  if (gptr[0] == 0xea9f1fdd			/* b,l .-12,r20     */
      && gptr[1] == 0xd6801c1e			/* depwi 0,31,2,r20 */
      && (ElfW(Addr)) gptr[2] == elf_machine_resolve ())
    _dl_fixup ((struct link_map *) gptr[5], (ElfW(Word)) desc[1]);

  return (ElfW(Addr)) desc[0];
}