aboutsummaryrefslogtreecommitdiff
path: root/bfd/merge.c
blob: eeaa1a01fe3868549a8d34a7625208db5cc4ae5c (plain)
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
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
/* SEC_MERGE support.
   Copyright (C) 2001-2023 Free Software Foundation, Inc.
   Written by Jakub Jelinek <jakub@redhat.com>.

   This file is part of BFD, the Binary File Descriptor library.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
   MA 02110-1301, USA.  */


/* This file contains support for merging duplicate entities within sections,
   as used in ELF SHF_MERGE.  */

#include "sysdep.h"
#include <limits.h>
#include "bfd.h"
#include "elf-bfd.h"
#include "libbfd.h"
#include "objalloc.h"
#include "libiberty.h"

/* We partition all mergable input sections into sets of similar
   characteristics.  These sets are the unit of merging.  All content
   of the input sections is scanned and inserted into a hash table.
   We also remember an input-offset to entry mapping per input section, but
   the content itself is removed.  After everything is read in we assign
   output offsets to all hash entries, and when relocations are processed we
   lookup the given input offset per input-section, get the matching entry
   and its output offset (possibly adjusted for offset pointing into the
   middle of an entry).

   The input-offset-to-entry mapping (in map_ofs/map) is sorted, so in principle
   we could binary search it, but that's not cache-friendly and it's faster
   to add another lookup structure that gets us very near the correct
   entry in just one step (that's what ofstolowbound is for) and do a linear
   search from there.  */

/* An entry in the section merge hash table.  */

struct sec_merge_hash_entry
{
  /* Length of this entry.  This includes the zero terminator.  */
  unsigned int len;
  /* Start of this string needs to be aligned to
     alignment octets (not 1 << align).  */
  unsigned int alignment;
  union
  {
    /* Index within the merged section.  */
    bfd_size_type index;
    /* Entry this is a suffix of (if alignment is 0).  */
    struct sec_merge_hash_entry *suffix;
  } u;
  /* Next entity in the hash table (in order of entering).  */
  struct sec_merge_hash_entry *next;
  char str[1];
};

/* The section merge hash table.  */

struct sec_merge_hash
{
  struct bfd_hash_table table;
  /* Next available index.  */
  bfd_size_type size;
  /* First entity in the SEC_MERGE sections of this type.  */
  struct sec_merge_hash_entry *first;
  /* Last entity in the SEC_MERGE sections of this type.  */
  struct sec_merge_hash_entry *last;
  /* Entity size.  */
  unsigned int entsize;
  /* Are entries fixed size or zero terminated strings?  */
  bool strings;
  /* struct-of-array variant of all entries in the hash-table: */
  unsigned int nbuckets;
  /* We keep hash-code and length of entry together in a separate
     array in such a way that it can be checked with just a single memory
     reference.  In this way we don't need indirect access to the entries
     in the normal case.  keys_lens[i] is 'hashcode << 32) | len' for entry
     i (which is pointed to be values[i]).  */
  uint64_t *key_lens;
  struct sec_merge_hash_entry **values;
};

/* True when given NEWCOUNT and NBUCKETS indicate that the hash table needs
   resizing.  */
#define NEEDS_RESIZE(newcount, nbuckets) ((newcount) > (nbuckets) / 3 * 2)

struct sec_merge_sec_info;

/* Information per merged blob.  This is the unit of merging and is
   related to (multiple) input sections of similar characteristics
   (alignment, entity size, strings or blobs).  */
struct sec_merge_info
{
  /* Chain of sec_merge_infos.  */
  struct sec_merge_info *next;
  /* Chain of sec_merge_sec_infos.  This first one will be the representative
     section that conceptually collects all merged content.  */
  struct sec_merge_sec_info *chain;
  struct sec_merge_sec_info **last;
  /* A hash table used to hold section content.  */
  struct sec_merge_hash *htab;
};

/* Offset into input mergable sections are represented by this type.
   Note how doesn't support crazy large mergable sections.  */
typedef uint32_t mapofs_type;

/* Given a sec_merge_sec_info S this gives the input offset of the IDX's
   recorded entry.  */
#define MAP_OFS(S,IDX) (S)->map_ofs[IDX]
/* And this gives the output offset (in the merged blob representing
   this S.  */
#define MAP_IDX(S,IDX) (S)->map[IDX].idx
/* For quick lookup of output offset given an input offset we store
   an array mapping intput-offset / OFSDIV to entry index.
   16 is better than 8, 32 is roughly same as 16, but uses less memory, so
   we use that. */
#define OFSDIV 32

/* Information per input merge section.  */
struct sec_merge_sec_info
{
  /* Chain of sec_merge_sec_infos.  */
  struct sec_merge_sec_info *next;
  /* The corresponding section.  */
  asection *sec;
  /* Pointer to merge_info pointing to us.  */
  void **psecinfo;
  /* The merge entity this is a part of.  */
  struct sec_merge_info *sinfo;
  /* The section associated with sinfo (i.e. the representative section).
     Same as sinfo->chain->sec, but faster to access in the hot function.  */
  asection *reprsec;
  /* First string in this section.  */
  struct sec_merge_hash_entry *first_str;
  /* Sparse mapping from input offset to entry covering that offset:  */
  unsigned int noffsetmap;  /* Number of these mappings.  */
  mapofs_type *map_ofs;     /* Input offset.  */
  union {
      struct sec_merge_hash_entry *entry;  /* Covering hash entry ... */
      bfd_size_type idx;                   /* ... or destination offset.  */
  } *map;
  /* Quick access: index into map_ofs[].  ofstolowbound[o / OFSDIV]=I is
     such that map_ofs[I] is the smallest offset higher that
     rounddown(o, OFSDIV) (and hence I-1 is the largest entry whose offset is
     smaller or equal to o/OFSDIV*OFSDIV).  */
  unsigned int *ofstolowbound;
  int fast_state;
};


/* Given a merge hash table TABLE and a number of entries to be
   ADDED, possibly resize the table for this to fit without further
   resizing.  */

static bool
sec_merge_maybe_resize (struct sec_merge_hash *table, unsigned added)
{
  struct bfd_hash_table *bfdtab = &table->table;
  if (NEEDS_RESIZE (bfdtab->count + added, table->nbuckets))
    {
      unsigned i;
      unsigned long newnb = table->nbuckets * 2;
      struct sec_merge_hash_entry **newv;
      uint64_t *newl;
      unsigned long alloc;

      while (NEEDS_RESIZE (bfdtab->count + added, newnb))
	{
	  newnb *= 2;
	  if (!newnb)
	    return false;
	}

      alloc = newnb * sizeof (newl[0]);
      if (alloc / sizeof (newl[0]) != newnb)
	return false;
      newl = objalloc_alloc ((struct objalloc *) table->table.memory, alloc);
      if (newl == NULL)
	return false;
      memset (newl, 0, alloc);
      alloc = newnb * sizeof (newv[0]);
      if (alloc / sizeof (newv[0]) != newnb)
	return false;
      newv = objalloc_alloc ((struct objalloc *) table->table.memory, alloc);
      if (newv == NULL)
	return false;
      memset (newv, 0, alloc);

      for (i = 0; i < table->nbuckets; i++)
	{
	  struct sec_merge_hash_entry *v = table->values[i];
	  if (v)
	    {
	      uint32_t thishash = table->key_lens[i] >> 32;
	      unsigned idx = thishash & (newnb - 1);
	      while (newv[idx])
		idx = (idx + 1) & (newnb - 1);
	      newl[idx] = table->key_lens[i];
	      newv[idx] = v;
	    }
	}

      table->key_lens = newl;
      table->values = newv;
      table->nbuckets = newnb;
    }
  return true;
}

/* Insert STRING (actually a byte blob of length LEN, with pre-computed
   HASH and bucket _INDEX) into our hash TABLE.  */

static struct sec_merge_hash_entry *
sec_merge_hash_insert (struct sec_merge_hash *table,
		 const char *string,
		 uint64_t hash, unsigned int len, unsigned int _index)
{
  struct bfd_hash_table *bfdtab = &table->table;
  struct sec_merge_hash_entry *hashp;

  hashp = (struct sec_merge_hash_entry *)
      bfd_hash_allocate (bfdtab, len + sizeof (struct sec_merge_hash_entry));
  if (hashp == NULL)
    return NULL;

  memcpy (hashp->str, string, len);
  hashp->len = len;
  hashp->alignment = 0;
  hashp->u.suffix = NULL;
  hashp->next = NULL;
  // We must not need resizing, otherwise the estimation was wrong
  BFD_ASSERT (!NEEDS_RESIZE (bfdtab->count + 1, table->nbuckets));
  bfdtab->count++;
  table->key_lens[_index] = (hash << 32) | (uint32_t)len;
  table->values[_index] = hashp;

  return hashp;
}

/* Read four bytes from *STR, interpret it as 32bit unsigned little
   endian value and return that.  */

static inline uint32_t
hash_read32 (const char *str)
{
  uint32_t i;
  /* All reasonable compilers will inline this memcpy and generate optimal
     code on architectures that support unaligned (4-byte) accesses.  */
  memcpy(&i, str, 4);
#ifdef WORDS_BIGENDIAN
  i = (i << 24) | ((i & 0xff00) << 8) | ((i >> 8) & 0xff00) | (i >> 24);
#endif
  return i;
}

/* Calculate and return a hashvalue of the bytes at STR[0..LEN-1].
   All non-zero lengths and all alignments are supported.

   This is somewhat similar to xxh3 (of xxhash), but restricted to 32bit.
   On cc1 strings this has quite similar statistic properties, and we
   don't need to jump through hoops to get fast 64x64->128 mults,
   or 64bit arith on 32 bit hosts.  We also don't care for seeds
   or secrets.  They improve mixing very little.  */

static uint32_t
hash_blob (const char *str, unsigned int len)
{
  uint32_t ret = 0;
  uint32_t mul = (1 << 0) +  (1 << 2) + (1 << 3) + (1 << 5) + (1 << 7);
  mul += (1 << 11) + (1 << 13) + (1 << 17) + (0 << 19) + (1 << 23) + (1 << 29);
  mul += (1u << 31);
  if (len >= 8)
    {
      uint32_t acc = len * 0x9e3779b1;
      while (len >= 8)
	{
	  uint32_t i1 = hash_read32  (str) ^ (0x396cfeb8 + 1*len);
	  uint32_t i2 = hash_read32  (str + 4) ^ (0xbe4ba423 + 1*len);
	  str += 8;
	  len -= 8;
	  uint64_t m = (uint64_t)i1 * i2;
	  acc += (uint32_t)m ^ (uint32_t)(m >> 32);
	}
      acc = acc ^ (acc >> 7);
      uint64_t r = (uint64_t)mul * acc;
      ret = (uint32_t)r ^ (uint32_t)(r >> 32);
      if (len == 0)
	goto end;
    }
  if (len >= 4)
    {
      uint32_t i1 = hash_read32  (str);
      uint32_t i2 = hash_read32  (str + len - 4);
      i1 = ((i1 + len) ^ (i1 >> 7));
      i2 = i2 ^ (i2 >> 7);
      uint64_t r = (uint64_t)mul * i1 + i2;
      ret += r ^ (r >> 32);
    }
  else
    {
      /* Cleverly read in 1 to 3 bytes without further conditionals.  */
      unsigned char c1 = str[0];
      unsigned char c2 = str[len >> 1];
      unsigned char c3 = str[len - 1];
      uint32_t i1 = ((uint32_t)c1 << 16) | ((uint32_t)c2 << 24)
		     | ((uint32_t) c3) | (len << 8);
      i1 = i1 ^ (i1 >> 7);
      uint64_t r = (uint64_t)mul * i1;
      ret += r ^ (r >> 32);
    }
end:
  return ret;
}

/* Given a hash TABLE, return the hash of STRING (a blob described
   according to info in TABLE, either a character string, or some fixed
   size entity) and set *PLEN to the length of this blob.  */

static uint32_t
hashit (struct sec_merge_hash *table, const char *string, unsigned int *plen)
{
  const unsigned char *s;
  uint32_t hash;
  unsigned int len, i;

  s = (const unsigned char *) string;
  if (table->strings)
    {
      if (table->entsize == 1)
	len = strlen (string) + 1;
      else
	{
	  len = 0;
	  for (;;)
	    {
	      for (i = 0; i < table->entsize; ++i)
		if (s[i] != '\0')
		  break;
	      if (i == table->entsize)
		break;
	      s += table->entsize;
	      ++len;
	    }
	  len *= table->entsize;
	  len += table->entsize;
	}
    }
  else
    len = table->entsize;
  hash = hash_blob (string, len);
  *plen = len;
  return hash;
}

/* Lookup or insert a blob STRING (of length LEN, precomputed HASH and
   input ALIGNMENT) into TABLE.  Return the found or new hash table entry.  */

static struct sec_merge_hash_entry *
sec_merge_hash_lookup (struct sec_merge_hash *table, const char *string,
		       unsigned int len, uint64_t hash,
		       unsigned int alignment)
{
  struct sec_merge_hash_entry *hashp;
  unsigned int _index;

  /*printf ("YYY insert 0x%x into %u buckets (%s)\n",
	  (unsigned)hash, (unsigned)table->nbuckets, string);*/
  uint64_t *key_lens = table->key_lens;
  struct sec_merge_hash_entry **values = table->values;
  uint64_t hlen = (hash << 32) | (uint32_t)len;
  unsigned int nbuckets = table->nbuckets;
  _index = hash & (nbuckets - 1);
  while (1)
    {
      uint64_t candlen = key_lens[_index];
      if (candlen == hlen
	  && !memcmp (values[_index]->str, string, len))
	{
	  hashp = values[_index];
	  if (hashp->alignment < alignment)
	    hashp->alignment = alignment;
	  return hashp;
	}
      if (!(candlen & (uint32_t)-1))
	break;
      _index = (_index + 1) & (nbuckets - 1);
    }

  hashp = sec_merge_hash_insert (table, string, hash, len, _index);
  if (hashp == NULL)
    return NULL;
  hashp->alignment = alignment;

  table->size++;
  BFD_ASSERT (table->size == table->table.count);
  if (table->first == NULL)
    table->first = hashp;
  else
    table->last->next = hashp;
  table->last = hashp;

  return hashp;
}

/* Create a new hash table.  */

static struct sec_merge_hash *
sec_merge_init (unsigned int entsize, bool strings)
{
  struct sec_merge_hash *table;

  table = (struct sec_merge_hash *) bfd_malloc (sizeof (struct sec_merge_hash));
  if (table == NULL)
    return NULL;

  if (! bfd_hash_table_init_n (&table->table, NULL,
			       sizeof (struct sec_merge_hash_entry), 0x2000))
    {
      free (table);
      return NULL;
    }

  table->size = 0;
  table->first = NULL;
  table->last = NULL;
  table->entsize = entsize;
  table->strings = strings;

  table->nbuckets = 0x2000;
  table->key_lens = objalloc_alloc ((struct objalloc *) table->table.memory,
				table->nbuckets * sizeof (table->key_lens[0]));
  memset (table->key_lens, 0, table->nbuckets * sizeof (table->key_lens[0]));
  table->values = objalloc_alloc ((struct objalloc *) table->table.memory,
				table->nbuckets * sizeof (table->values[0]));
  memset (table->values, 0, table->nbuckets * sizeof (table->values[0]));

  return table;
}

/* Append the tuple of input-offset O corresponding
   to hash table ENTRY into SECINFO, such that we later may lookup the
   entry just by O.  */

static bool
append_offsetmap (struct sec_merge_sec_info *secinfo,
		  mapofs_type o,
		  struct sec_merge_hash_entry *entry)
{
  if ((secinfo->noffsetmap & 2047) == 0)
    {
      bfd_size_type amt;
      amt = (secinfo->noffsetmap + 2048);
      secinfo->map_ofs = bfd_realloc (secinfo->map_ofs,
				      amt * sizeof(secinfo->map_ofs[0]));
      if (!secinfo->map_ofs)
	return false;
      secinfo->map = bfd_realloc (secinfo->map, amt * sizeof(secinfo->map[0]));
      if (!secinfo->map)
	return false;
    }
  unsigned int i = secinfo->noffsetmap++;
  MAP_OFS(secinfo, i) = o;
  secinfo->map[i].entry = entry;
  return true;
}

/* Prepare the input-offset-to-entry tables after output offsets are
   determined.  */

static void
prepare_offsetmap (struct sec_merge_sec_info *secinfo)
{
  unsigned int noffsetmap = secinfo->noffsetmap;
  unsigned int i, lbi;
  bfd_size_type l, sz, amt;

  secinfo->fast_state = 1;

  for (i = 0; i < noffsetmap; i++)
    MAP_IDX(secinfo, i) = secinfo->map[i].entry->u.index;

  sz = secinfo->sec->rawsize;
  amt = (sz / OFSDIV + 1) * sizeof (secinfo->ofstolowbound[0]);
  secinfo->ofstolowbound = bfd_zmalloc (amt);
  if (!secinfo->ofstolowbound)
    return;
  for (l = lbi = 0; l < sz; l += OFSDIV)
    {
      /* No need for bounds checking on lbi, as we've added a sentinel that's
	 larger than any offset.  */
      while (MAP_OFS(secinfo, lbi) <= l)
	lbi++;
      //BFD_ASSERT ((l / OFSDIV) <= (i / OFSDIV));
      secinfo->ofstolowbound[l / OFSDIV] = lbi;
    }
  secinfo->fast_state = 2;
}

static bool
sec_merge_emit (bfd *abfd, struct sec_merge_sec_info *secinfo,
		unsigned char *contents)
{
  struct sec_merge_hash_entry *entry = secinfo->first_str;
  asection *sec = secinfo->sec;
  file_ptr offset = sec->output_offset;
  char *pad = NULL;
  bfd_size_type off = 0;
  unsigned int opb = bfd_octets_per_byte (abfd, sec);
  int alignment_power = sec->output_section->alignment_power * opb;
  bfd_size_type pad_len;  /* Octets.  */

  /* FIXME: If alignment_power is 0 then really we should scan the
     entry list for the largest required alignment and use that.  */
  pad_len = alignment_power ? ((bfd_size_type) 1 << alignment_power) : 16;

  pad = (char *) bfd_zmalloc (pad_len);
  if (pad == NULL)
    return false;

  for (; entry != NULL; entry = entry->next)
    {
      const char *str;
      bfd_size_type len;

      if (!entry->len)
	continue;
      BFD_ASSERT (entry->alignment);
      len = -off & (entry->alignment - 1);
      if (len != 0)
	{
	  BFD_ASSERT (len <= pad_len);
	  if (contents)
	    {
	      memcpy (contents + offset, pad, len);
	      offset += len;
	    }
	  else if (bfd_write (pad, len, abfd) != len)
	    goto err;
	  off += len;
	}

      str = entry->str;
      len = entry->len;

      if (contents)
	{
	  memcpy (contents + offset, str, len);
	  offset += len;
	}
      else if (bfd_write (str, len, abfd) != len)
	goto err;

      off += len;
    }
  BFD_ASSERT (!entry);

  /* Trailing alignment needed?  */
  off = sec->size - off;
  if (1 && off != 0)
    {
      BFD_ASSERT (off <= pad_len);
      if (contents)
	memcpy (contents + offset, pad, off);
      else if (bfd_write (pad, off, abfd) != off)
	goto err;
    }

  free (pad);
  return true;

 err:
  free (pad);
  return false;
}

/* Register a SEC_MERGE section as a candidate for merging.
   This function is called for all non-dynamic SEC_MERGE input sections.  */

bool
_bfd_add_merge_section (bfd *abfd, void **psinfo, asection *sec,
			void **psecinfo)
{
  struct sec_merge_info *sinfo;
  struct sec_merge_sec_info *secinfo;
  asection *repr;
  unsigned int alignment_power;  /* Octets.  */
  unsigned int align;            /* Octets.  */
  unsigned int opb = bfd_octets_per_byte (abfd, sec);

  if ((abfd->flags & DYNAMIC) != 0
      || (sec->flags & SEC_MERGE) == 0)
    abort ();

  if (sec->size == 0
      || (sec->flags & SEC_EXCLUDE) != 0
      || sec->entsize == 0)
    return true;

  if (sec->size % sec->entsize != 0)
    return true;

  if ((sec->flags & SEC_RELOC) != 0)
    {
      /* We aren't prepared to handle relocations in merged sections.  */
      return true;
    }

  if (sec->size > (mapofs_type)-1)
    {
      /* Input offsets must be representable by mapofs_type.  */
      return true;
    }

#ifndef CHAR_BIT
#define CHAR_BIT 8
#endif
  alignment_power = sec->alignment_power * opb;
  if (alignment_power >= sizeof (align) * CHAR_BIT)
    return true;

  align = 1u << alignment_power;
  if ((sec->entsize < align
       && ((sec->entsize & (sec->entsize - 1))
	   || !(sec->flags & SEC_STRINGS)))
      || (sec->entsize > align
	  && (sec->entsize & (align - 1))))
    {
      /* Sanity check.  If string character size is smaller than
	 alignment, then we require character size to be a power
	 of 2, otherwise character size must be integer multiple
	 of alignment.  For non-string constants, alignment must
	 be smaller than or equal to entity size and entity size
	 must be integer multiple of alignment.  */
      return true;
    }

  /* Initialize the descriptor for this input section.  */

  *psecinfo = secinfo = bfd_zalloc (abfd, sizeof (*secinfo));
  if (*psecinfo == NULL)
    goto error_return;

  secinfo->sec = sec;
  secinfo->psecinfo = psecinfo;

  /* Search for a matching output merged section.  */
  for (sinfo = (struct sec_merge_info *) *psinfo; sinfo; sinfo = sinfo->next)
    if (sinfo->chain
	&& (repr = sinfo->chain->sec)
	&& ! ((repr->flags ^ sec->flags) & (SEC_MERGE | SEC_STRINGS))
	&& repr->entsize == sec->entsize
	&& repr->alignment_power == sec->alignment_power
	&& repr->output_section == sec->output_section)
      break;

  if (sinfo == NULL)
    {
      /* Initialize the information we need to keep track of.  */
      sinfo = (struct sec_merge_info *)
	  bfd_alloc (abfd, sizeof (struct sec_merge_info));
      if (sinfo == NULL)
	goto error_return;
      sinfo->next = (struct sec_merge_info *) *psinfo;
      sinfo->chain = NULL;
      sinfo->last = &sinfo->chain;
      *psinfo = sinfo;
      sinfo->htab = sec_merge_init (sec->entsize, (sec->flags & SEC_STRINGS));
      if (sinfo->htab == NULL)
	goto error_return;
    }

  *sinfo->last = secinfo;
  sinfo->last = &secinfo->next;

  secinfo->sinfo = sinfo;
  secinfo->reprsec = sinfo->chain->sec;

  return true;

 error_return:
  *psecinfo = NULL;
  return false;
}

/* Record one whole input section (described by SECINFO) into the hash table
   SINFO.  */

static bool
record_section (struct sec_merge_info *sinfo,
		struct sec_merge_sec_info *secinfo)
{
  asection *sec = secinfo->sec;
  struct sec_merge_hash_entry *entry;
  unsigned char *p, *end;
  bfd_vma mask, eltalign;
  unsigned int align;
  bfd_size_type amt;
  bfd_byte *contents;
  void *tmpptr;

  amt = sec->size;
  if (sec->flags & SEC_STRINGS)
    /* Some versions of gcc may emit a string without a zero terminator.
       See http://gcc.gnu.org/ml/gcc-patches/2006-06/msg01004.html
       Allocate space for an extra zero.  */
    amt += sec->entsize;
  contents = bfd_malloc (amt);
  if (!contents)
    goto error_return;

  /* Slurp in all section contents (possibly decompressing it).  */
  sec->rawsize = sec->size;
  if (sec->flags & SEC_STRINGS)
    memset (contents + sec->size, 0, sec->entsize);
  if (! bfd_get_full_section_contents (sec->owner, sec, &contents))
    goto error_return;

  /* Now populate the hash table and offset mapping.  */

  /* Presize the hash table for what we're going to add.  We overestimate
     quite a bit, but if it turns out to be too much then other sections
     merged into this area will make use of that as well.  */
  if (!sec_merge_maybe_resize (sinfo->htab, 1 + sec->size / 2))
    {
      bfd_set_error (bfd_error_no_memory);
      goto error_return;
    }

  /* Walk through the contents, calculate hashes and length of all
     blobs (strings or fixed-size entries) we find and fill the
     hash and offset tables.  */
  align = sec->alignment_power;
  mask = ((bfd_vma) 1 << align) - 1;
  end = contents + sec->size;
  for (p = contents; p < end;)
    {
      unsigned len;
      uint32_t hash = hashit (sinfo->htab, (char*) p, &len);
      unsigned int ofs = p - contents;
      eltalign = ofs;
      eltalign = ((eltalign ^ (eltalign - 1)) + 1) >> 1;
      if (!eltalign || eltalign > mask)
	eltalign = mask + 1;
      entry = sec_merge_hash_lookup (sinfo->htab, (char *) p, len, hash,
				     (unsigned) eltalign);
      if (! entry)
	goto error_return;
      if (! append_offsetmap (secinfo, ofs, entry))
	goto error_return;
      p += len;
    }

  /* Add a sentinel element that's conceptually behind all others.  */
  append_offsetmap (secinfo, sec->size, NULL);
  /* But don't count it.  */
  secinfo->noffsetmap--;

  free (contents);
  contents = NULL;

  /* We allocate the ofsmap arrays in blocks of 2048 elements.
     In case we have very many small input files/sections,
     this might waste large amounts of memory, so reallocate these
     arrays here to their true size.  */
  amt = secinfo->noffsetmap + 1;
  tmpptr = bfd_realloc (secinfo->map, amt * sizeof(secinfo->map[0]));
  if (tmpptr)
    secinfo->map = tmpptr;
  tmpptr = bfd_realloc (secinfo->map_ofs, amt * sizeof(secinfo->map_ofs[0]));
  if (tmpptr)
    secinfo->map_ofs = tmpptr;

  /*printf ("ZZZ %s:%s %u entries\n", sec->owner->filename, sec->name,
	  (unsigned)secinfo->noffsetmap);*/

  return true;

 error_return:
  free (contents);
  contents = NULL;
  for (secinfo = sinfo->chain; secinfo; secinfo = secinfo->next)
    *secinfo->psecinfo = NULL;
  return false;
}

/* qsort comparison function.  Won't ever return zero as all entries
   differ, so there is no issue with qsort stability here.  */

static int
strrevcmp (const void *a, const void *b)
{
  struct sec_merge_hash_entry *A = *(struct sec_merge_hash_entry **) a;
  struct sec_merge_hash_entry *B = *(struct sec_merge_hash_entry **) b;
  unsigned int lenA = A->len;
  unsigned int lenB = B->len;
  const unsigned char *s = (const unsigned char *) A->str + lenA - 1;
  const unsigned char *t = (const unsigned char *) B->str + lenB - 1;
  int l = lenA < lenB ? lenA : lenB;

  while (l)
    {
      if (*s != *t)
	return (int) *s - (int) *t;
      s--;
      t--;
      l--;
    }
  return lenA - lenB;
}

/* Like strrevcmp, but for the case where all strings have the same
   alignment > entsize.  */

static int
strrevcmp_align (const void *a, const void *b)
{
  struct sec_merge_hash_entry *A = *(struct sec_merge_hash_entry **) a;
  struct sec_merge_hash_entry *B = *(struct sec_merge_hash_entry **) b;
  unsigned int lenA = A->len;
  unsigned int lenB = B->len;
  const unsigned char *s = (const unsigned char *) A->str + lenA - 1;
  const unsigned char *t = (const unsigned char *) B->str + lenB - 1;
  int l = lenA < lenB ? lenA : lenB;
  int tail_align = (lenA & (A->alignment - 1)) - (lenB & (A->alignment - 1));

  if (tail_align != 0)
    return tail_align;

  while (l)
    {
      if (*s != *t)
	return (int) *s - (int) *t;
      s--;
      t--;
      l--;
    }
  return lenA - lenB;
}

static inline int
is_suffix (const struct sec_merge_hash_entry *A,
	   const struct sec_merge_hash_entry *B)
{
  if (A->len <= B->len)
    /* B cannot be a suffix of A unless A is equal to B, which is guaranteed
       not to be equal by the hash table.  */
    return 0;

  return memcmp (A->str + (A->len - B->len),
		 B->str, B->len) == 0;
}

/* This is a helper function for _bfd_merge_sections.  It attempts to
   merge strings matching suffixes of longer strings.  */
static struct sec_merge_sec_info *
merge_strings (struct sec_merge_info *sinfo)
{
  struct sec_merge_hash_entry **array, **a, *e;
  struct sec_merge_sec_info *secinfo;
  bfd_size_type size, amt;
  unsigned int alignment = 0;

  /* Now sort the strings */
  amt = sinfo->htab->size * sizeof (struct sec_merge_hash_entry *);
  array = (struct sec_merge_hash_entry **) bfd_malloc (amt);
  if (array == NULL)
    return NULL;

  for (e = sinfo->htab->first, a = array; e; e = e->next)
    if (e->alignment)
      {
	*a++ = e;
	/* Adjust the length to not include the zero terminator.  */
	e->len -= sinfo->htab->entsize;
	if (alignment != e->alignment)
	  {
	    if (alignment == 0)
	      alignment = e->alignment;
	    else
	      alignment = (unsigned) -1;
	  }
      }

  sinfo->htab->size = a - array;
  if (sinfo->htab->size != 0)
    {
      qsort (array, (size_t) sinfo->htab->size,
	     sizeof (struct sec_merge_hash_entry *),
	     (alignment != (unsigned) -1 && alignment > sinfo->htab->entsize
	      ? strrevcmp_align : strrevcmp));

      /* Loop over the sorted array and merge suffixes */
      e = *--a;
      e->len += sinfo->htab->entsize;
      while (--a >= array)
	{
	  struct sec_merge_hash_entry *cmp = *a;

	  cmp->len += sinfo->htab->entsize;
	  if (e->alignment >= cmp->alignment
	      && !((e->len - cmp->len) & (cmp->alignment - 1))
	      && is_suffix (e, cmp))
	    {
	      cmp->u.suffix = e;
	      cmp->alignment = 0;
	    }
	  else
	    e = cmp;
	}
    }

  free (array);

  /* Now assign positions to the strings we want to keep.  */
  size = 0;
  secinfo = sinfo->chain;
  for (e = sinfo->htab->first; e; e = e->next)
    {
      if (e->alignment)
	{
	  size = (size + e->alignment - 1) & ~((bfd_vma) e->alignment - 1);
	  e->u.index = size;
	  size += e->len;
	}
    }
  secinfo->sec->size = size;

  /* And now adjust the rest, removing them from the chain (but not hashtable)
     at the same time.  */
  for (a = &sinfo->htab->first, e = *a; e; e = e->next)
    if (e->alignment)
      a = &e->next;
    else
      {
	*a = e->next;
	if (e->len)
	  {
	    e->alignment = e->u.suffix->alignment;
	    e->u.index = e->u.suffix->u.index + (e->u.suffix->len - e->len);
	  }
      }

  BFD_ASSERT (!secinfo->first_str);
  secinfo->first_str = sinfo->htab->first;

  return secinfo;
}

/* This function is called once after all SEC_MERGE sections are registered
   with _bfd_merge_section.  */

bool
_bfd_merge_sections (bfd *abfd,
		     struct bfd_link_info *info ATTRIBUTE_UNUSED,
		     void *xsinfo,
		     void (*remove_hook) (bfd *, asection *))
{
  struct sec_merge_info *sinfo;

  for (sinfo = (struct sec_merge_info *) xsinfo; sinfo; sinfo = sinfo->next)
    {
      struct sec_merge_sec_info *secinfo;
      bfd_size_type align;  /* Bytes.  */

      if (! sinfo->chain)
	continue;

      /* Record the sections into the hash table.  */
      align = 1;
      for (secinfo = sinfo->chain; secinfo; secinfo = secinfo->next)
	if (secinfo->sec->flags & SEC_EXCLUDE)
	  {
	    *secinfo->psecinfo = NULL;
	    if (remove_hook)
	      (*remove_hook) (abfd, secinfo->sec);
	  }
	else
	  {
	    if (!record_section (sinfo, secinfo))
	      return false;
	    if (align)
	      {
		unsigned int opb = bfd_octets_per_byte (abfd, secinfo->sec);

		align = (bfd_size_type) 1 << secinfo->sec->alignment_power;
		if (((secinfo->sec->size / opb) & (align - 1)) != 0)
		  align = 0;
	      }
	  }

      if (sinfo->htab->first == NULL)
	continue;

      if (sinfo->htab->strings)
	{
	  secinfo = merge_strings (sinfo);
	  if (!secinfo)
	    return false;
	}
      else
	{
	  struct sec_merge_hash_entry *e = sinfo->htab->first;
	  bfd_size_type size = 0;  /* Octets.  */

	  /* Things are much simpler for non-strings.
	     Just assign them slots in the section.  */
	  secinfo = sinfo->chain;
	  BFD_ASSERT (!secinfo->first_str);
	  secinfo->first_str = e;
	  for (e = sinfo->htab->first; e; e = e->next)
	    {
	      if (e->alignment)
		{
		  size = (size + e->alignment - 1)
			 & ~((bfd_vma) e->alignment - 1);
		  e->u.index = size;
		  size += e->len;
		}
	    }
	  secinfo->sec->size = size;
	}

      /* If the input sections were padded according to their alignments,
	 then pad the output too.  */
      if (align)
	secinfo->sec->size = (secinfo->sec->size + align - 1) & -align;

      /* Finally remove all input sections which have not made it into
	 the hash table at all.  */
      for (secinfo = sinfo->chain; secinfo; secinfo = secinfo->next)
	if (secinfo->first_str == NULL)
	  secinfo->sec->flags |= SEC_EXCLUDE | SEC_KEEP;
    }

  return true;
}

/* Write out the merged section.  */

bool
_bfd_write_merged_section (bfd *output_bfd, asection *sec, void *psecinfo)
{
  struct sec_merge_sec_info *secinfo;
  file_ptr pos;
  unsigned char *contents;
  Elf_Internal_Shdr *hdr;

  secinfo = (struct sec_merge_sec_info *) psecinfo;

  if (!secinfo)
    return false;

  if (secinfo->first_str == NULL)
    return true;

  /* FIXME: octets_per_byte.  */
  hdr = &elf_section_data (sec->output_section)->this_hdr;
  if (hdr->sh_offset == (file_ptr) -1)
    {
      /* We must compress this section.  Write output to the
	 buffer.  */
      contents = hdr->contents;
      if (contents == NULL)
	abort ();
    }
  else
    {
      contents = NULL;
      pos = sec->output_section->filepos + sec->output_offset;
      if (bfd_seek (output_bfd, pos, SEEK_SET) != 0)
	return false;
    }

  BFD_ASSERT (sec == secinfo->sec);
  BFD_ASSERT (secinfo == secinfo->sinfo->chain);
  if (! sec_merge_emit (output_bfd, secinfo, contents))
    return false;

  return true;
}

/* Adjust an address in the SEC_MERGE section.  Given OFFSET within
   *PSEC, this returns the new offset in the adjusted SEC_MERGE
   section and writes the new section back into *PSEC.  */

bfd_vma
_bfd_merged_section_offset (bfd *output_bfd ATTRIBUTE_UNUSED, asection **psec,
			    void *psecinfo, bfd_vma offset)
{
  struct sec_merge_sec_info *secinfo;
  asection *sec = *psec;

  secinfo = (struct sec_merge_sec_info *) psecinfo;

  if (!secinfo)
    return offset;

  if (offset >= sec->rawsize)
    {
      if (offset > sec->rawsize)
	_bfd_error_handler
	  /* xgettext:c-format */
	  (_("%pB: access beyond end of merged section (%" PRId64 ")"),
	   sec->owner, (int64_t) offset);
      return secinfo->first_str ? sec->size : 0;
    }

  if (secinfo->fast_state != 2)
    {
      if (!secinfo->fast_state)
	prepare_offsetmap (secinfo);
      if (secinfo->fast_state != 2)
	return offset;
    }

  long lb = secinfo->ofstolowbound[offset / OFSDIV];
  *psec = secinfo->reprsec;

  /* No need for bounds checking on lb, as we've added a sentinel that's
     larger than any offset.  */
  while (MAP_OFS(secinfo, lb) <= offset)
    lb++;
  lb--;

  /*printf ("YYY (%s:%s):%u -> (%s):%u\n",
	  sec->owner->filename, sec->name, (unsigned)offset,
	  (*psec)->name, (unsigned)lb);*/
  return MAP_IDX(secinfo, lb) + offset - MAP_OFS(secinfo, lb);
}

/* Tidy up when done.  */

void
_bfd_merge_sections_free (void *xsinfo)
{
  struct sec_merge_info *sinfo;

  for (sinfo = (struct sec_merge_info *) xsinfo; sinfo; sinfo = sinfo->next)
    {
      struct sec_merge_sec_info *secinfo;
      for (secinfo = sinfo->chain; secinfo; secinfo = secinfo->next)
	{
	  free (secinfo->ofstolowbound);
	  free (secinfo->map);
	  free (secinfo->map_ofs);
	}
      bfd_hash_table_free (&sinfo->htab->table);
      free (sinfo->htab);
    }
}