bfd/elf-strtab.c

   1 /* ELF strtab with GC and suffix merging support.
   2    Copyright (C) 2001-2020 Free Software Foundation, Inc.
   3    Written by Jakub Jelinek <jakub@redhat.com>.
   4
   5    This file is part of BFD, the Binary File Descriptor library.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  20    MA 02110-1301, USA.  */
  21
  22 #include "sysdep.h"
  23 #include "bfd.h"
  24 #include "libbfd.h"
  25 #include "elf-bfd.h"
  26 #include "hashtab.h"
  27 #include "libiberty.h"
  28
  29 /* An entry in the strtab hash table.  */
  30
  31 struct elf_strtab_hash_entry
  32 {
  33   struct bfd_hash_entry root;
  34   /* Length of this entry.  This includes the zero terminator.  */
  35   int len;
  36   unsigned int refcount;
  37   union {
  38     /* Index within the merged section.  */
  39     bfd_size_type index;
  40     /* Entry this is a suffix of (if len < 0).  */
  41     struct elf_strtab_hash_entry *suffix;
  42   } u;
  43 };
  44
  45 /* The strtab hash table.  */
  46
  47 struct elf_strtab_hash
  48 {
  49   struct bfd_hash_table table;
  50   /* Next available index.  */
  51   size_t size;
  52   /* Number of array entries alloced.  */
  53   size_t alloced;
  54   /* Final strtab size.  */
  55   bfd_size_type sec_size;
  56   /* Array of pointers to strtab entries.  */
  57   struct elf_strtab_hash_entry **array;
  58 };
  59
  60 /* Routine to create an entry in a section merge hashtab.  */
  61
  62 static struct bfd_hash_entry *
  63 elf_strtab_hash_newfunc (struct bfd_hash_entry *entry,
  64                          struct bfd_hash_table *table,
  65                          const char *string)
  66 {
  67   /* Allocate the structure if it has not already been allocated by a
  68      subclass.  */
  69   if (entry == NULL)
  70     entry = (struct bfd_hash_entry *)
  71         bfd_hash_allocate (table, sizeof (struct elf_strtab_hash_entry));
  72   if (entry == NULL)
  73     return NULL;
  74
  75   /* Call the allocation method of the superclass.  */
  76   entry = bfd_hash_newfunc (entry, table, string);
  77
  78   if (entry)
  79     {
  80       /* Initialize the local fields.  */
  81       struct elf_strtab_hash_entry *ret;
  82
  83       ret = (struct elf_strtab_hash_entry *) entry;
  84       ret->u.index = -1;
  85       ret->refcount = 0;
  86       ret->len = 0;
  87     }
  88
  89   return entry;
  90 }
  91
  92 /* Create a new hash table.  */
  93
  94 struct elf_strtab_hash *
  95 _bfd_elf_strtab_init (void)
  96 {
  97   struct elf_strtab_hash *table;
  98   size_t amt = sizeof (struct elf_strtab_hash);
  99
 100   table = (struct elf_strtab_hash *) bfd_malloc (amt);
 101   if (table == NULL)
 102     return NULL;
 103
 104   if (!bfd_hash_table_init (&table->table, elf_strtab_hash_newfunc,
 105                             sizeof (struct elf_strtab_hash_entry)))
 106     {
 107       free (table);
 108       return NULL;
 109     }
 110
 111   table->sec_size = 0;
 112   table->size = 1;
 113   table->alloced = 64;
 114   amt = sizeof (struct elf_strtab_hasn_entry *);
 115   table->array = ((struct elf_strtab_hash_entry **)
 116                   bfd_malloc (table->alloced * amt));
 117   if (table->array == NULL)
 118     {
 119       free (table);
 120       return NULL;
 121     }
 122
 123   table->array[0] = NULL;
 124
 125   return table;
 126 }
 127
 128 /* Free a strtab.  */
 129
 130 void
 131 _bfd_elf_strtab_free (struct elf_strtab_hash *tab)
 132 {
 133   bfd_hash_table_free (&tab->table);
 134   free (tab->array);
 135   free (tab);
 136 }
 137
 138 /* Get the index of an entity in a hash table, adding it if it is not
 139    already present.  */
 140
 141 size_t
 142 _bfd_elf_strtab_add (struct elf_strtab_hash *tab,
 143                      const char *str,
 144                      bfd_boolean copy)
 145 {
 146   register struct elf_strtab_hash_entry *entry;
 147
 148   /* We handle this specially, since we don't want to do refcounting
 149      on it.  */
 150   if (*str == '\0')
 151     return 0;
 152
 153   BFD_ASSERT (tab->sec_size == 0);
 154   entry = (struct elf_strtab_hash_entry *)
 155           bfd_hash_lookup (&tab->table, str, TRUE, copy);
 156
 157   if (entry == NULL)
 158     return (size_t) -1;
 159
 160   entry->refcount++;
 161   if (entry->len == 0)
 162     {
 163       entry->len = strlen (str) + 1;
 164       /* 2G strings lose.  */
 165       BFD_ASSERT (entry->len > 0);
 166       if (tab->size == tab->alloced)
 167         {
 168           bfd_size_type amt = sizeof (struct elf_strtab_hash_entry *);
 169           tab->alloced *= 2;
 170           tab->array = (struct elf_strtab_hash_entry **)
 171               bfd_realloc_or_free (tab->array, tab->alloced * amt);
 172           if (tab->array == NULL)
 173             return (size_t) -1;
 174         }
 175
 176       entry->u.index = tab->size++;
 177       tab->array[entry->u.index] = entry;
 178     }
 179   return entry->u.index;
 180 }
 181
 182 void
 183 _bfd_elf_strtab_addref (struct elf_strtab_hash *tab, size_t idx)
 184 {
 185   if (idx == 0 || idx == (size_t) -1)
 186     return;
 187   BFD_ASSERT (tab->sec_size == 0);
 188   BFD_ASSERT (idx < tab->size);
 189   ++tab->array[idx]->refcount;
 190 }
 191
 192 void
 193 _bfd_elf_strtab_delref (struct elf_strtab_hash *tab, size_t idx)
 194 {
 195   if (idx == 0 || idx == (size_t) -1)
 196     return;
 197   BFD_ASSERT (tab->sec_size == 0);
 198   BFD_ASSERT (idx < tab->size);
 199   BFD_ASSERT (tab->array[idx]->refcount > 0);
 200   --tab->array[idx]->refcount;
 201 }
 202
 203 unsigned int
 204 _bfd_elf_strtab_refcount (struct elf_strtab_hash *tab, size_t idx)
 205 {
 206   return tab->array[idx]->refcount;
 207 }
 208
 209 void
 210 _bfd_elf_strtab_clear_all_refs (struct elf_strtab_hash *tab)
 211 {
 212   size_t idx;
 213
 214   for (idx = 1; idx < tab->size; idx++)
 215     tab->array[idx]->refcount = 0;
 216 }
 217
 218 /* Save strtab refcounts prior to adding --as-needed library.  */
 219
 220 struct strtab_save
 221 {
 222   size_t size;
 223   unsigned int refcount[1];
 224 };
 225
 226 void *
 227 _bfd_elf_strtab_save (struct elf_strtab_hash *tab)
 228 {
 229   struct strtab_save *save;
 230   size_t idx, size;
 231
 232   size = sizeof (*save) + (tab->size - 1) * sizeof (save->refcount[0]);
 233   save = bfd_malloc (size);
 234   if (save == NULL)
 235     return save;
 236
 237   save->size = tab->size;
 238   for (idx = 1; idx < tab->size; idx++)
 239     save->refcount[idx] = tab->array[idx]->refcount;
 240   return save;
 241 }
 242
 243 /* Restore strtab refcounts on finding --as-needed library not needed.  */
 244
 245 void
 246 _bfd_elf_strtab_restore (struct elf_strtab_hash *tab, void *buf)
 247 {
 248   size_t idx, curr_size = tab->size, save_size;
 249   struct strtab_save *save = (struct strtab_save *) buf;
 250
 251   BFD_ASSERT (tab->sec_size == 0);
 252   save_size = 1;
 253   if (save != NULL)
 254     save_size = save->size;
 255   BFD_ASSERT (save_size <= curr_size);
 256   tab->size = save_size;
 257   for (idx = 1; idx < save_size; ++idx)
 258     tab->array[idx]->refcount = save->refcount[idx];
 259
 260   for (; idx < curr_size; ++idx)
 261     {
 262       /* We don't remove entries from the hash table, just set their
 263          REFCOUNT to zero.  Setting LEN zero will result in the size
 264          growing if the entry is added again.  See _bfd_elf_strtab_add.  */
 265       tab->array[idx]->refcount = 0;
 266       tab->array[idx]->len = 0;
 267     }
 268 }
 269
 270 bfd_size_type
 271 _bfd_elf_strtab_size (struct elf_strtab_hash *tab)
 272 {
 273   return tab->sec_size ? tab->sec_size : tab->size;
 274 }
 275
 276 bfd_size_type
 277 _bfd_elf_strtab_len (struct elf_strtab_hash *tab)
 278 {
 279   return tab->size;
 280 }
 281
 282 bfd_size_type
 283 _bfd_elf_strtab_offset (struct elf_strtab_hash *tab, size_t idx)
 284 {
 285   struct elf_strtab_hash_entry *entry;
 286
 287   if (idx == 0)
 288     return 0;
 289   BFD_ASSERT (idx < tab->size);
 290   BFD_ASSERT (tab->sec_size);
 291   entry = tab->array[idx];
 292   BFD_ASSERT (entry->refcount > 0);
 293   entry->refcount--;
 294   return tab->array[idx]->u.index;
 295 }
 296
 297 const char *
 298 _bfd_elf_strtab_str (struct elf_strtab_hash *tab, size_t idx,
 299                      bfd_size_type *offset)
 300 {
 301   if (idx == 0)
 302     return 0;
 303   BFD_ASSERT (idx < tab->size);
 304   BFD_ASSERT (tab->sec_size);
 305   if (offset)
 306     *offset = tab->array[idx]->u.index;
 307   return tab->array[idx]->root.string;
 308 }
 309
 310 bfd_boolean
 311 _bfd_elf_strtab_emit (register bfd *abfd, struct elf_strtab_hash *tab)
 312 {
 313   bfd_size_type off = 1;
 314   size_t i;
 315
 316   if (bfd_bwrite ("", 1, abfd) != 1)
 317     return FALSE;
 318
 319   for (i = 1; i < tab->size; ++i)
 320     {
 321       register const char *str;
 322       register unsigned int len;
 323
 324       BFD_ASSERT (tab->array[i]->refcount == 0);
 325       len = tab->array[i]->len;
 326       if ((int) len < 0)
 327         continue;
 328
 329       str = tab->array[i]->root.string;
 330       if (bfd_bwrite (str, len, abfd) != len)
 331         return FALSE;
 332
 333       off += len;
 334     }
 335
 336   BFD_ASSERT (off == tab->sec_size);
 337   return TRUE;
 338 }
 339
 340 /* Compare two elf_strtab_hash_entry structures.  Called via qsort.
 341    Won't ever return zero as all entries differ, so there is no issue
 342    with qsort stability here.  */
 343
 344 static int
 345 strrevcmp (const void *a, const void *b)
 346 {
 347   struct elf_strtab_hash_entry *A = *(struct elf_strtab_hash_entry **) a;
 348   struct elf_strtab_hash_entry *B = *(struct elf_strtab_hash_entry **) b;
 349   unsigned int lenA = A->len;
 350   unsigned int lenB = B->len;
 351   const unsigned char *s = (const unsigned char *) A->root.string + lenA - 1;
 352   const unsigned char *t = (const unsigned char *) B->root.string + lenB - 1;
 353   int l = lenA < lenB ? lenA : lenB;
 354
 355   while (l)
 356     {
 357       if (*s != *t)
 358         return (int) *s - (int) *t;
 359       s--;
 360       t--;
 361       l--;
 362     }
 363   return lenA - lenB;
 364 }
 365
 366 static inline int
 367 is_suffix (const struct elf_strtab_hash_entry *A,
 368            const struct elf_strtab_hash_entry *B)
 369 {
 370   if (A->len <= B->len)
 371     /* B cannot be a suffix of A unless A is equal to B, which is guaranteed
 372        not to be equal by the hash table.  */
 373     return 0;
 374
 375   return memcmp (A->root.string + (A->len - B->len),
 376                  B->root.string, B->len - 1) == 0;
 377 }
 378
 379 /* This function assigns final string table offsets for used strings,
 380    merging strings matching suffixes of longer strings if possible.  */
 381
 382 void
 383 _bfd_elf_strtab_finalize (struct elf_strtab_hash *tab)
 384 {
 385   struct elf_strtab_hash_entry **array, **a, *e;
 386   bfd_size_type amt, sec_size;
 387   size_t size, i;
 388
 389   /* Sort the strings by suffix and length.  */
 390   amt = tab->size;
 391   amt *= sizeof (struct elf_strtab_hash_entry *);
 392   array = (struct elf_strtab_hash_entry **) bfd_malloc (amt);
 393   if (array == NULL)
 394     goto alloc_failure;
 395
 396   for (i = 1, a = array; i < tab->size; ++i)
 397     {
 398       e = tab->array[i];
 399       if (e->refcount)
 400         {
 401           *a++ = e;
 402           /* Adjust the length to not include the zero terminator.  */
 403           e->len -= 1;
 404         }
 405       else
 406         e->len = 0;
 407     }
 408
 409   size = a - array;
 410   if (size != 0)
 411     {
 412       qsort (array, size, sizeof (struct elf_strtab_hash_entry *), strrevcmp);
 413
 414       /* Loop over the sorted array and merge suffixes.  Start from the
 415          end because we want eg.
 416
 417          s1 -> "d"
 418          s2 -> "bcd"
 419          s3 -> "abcd"
 420
 421          to end up as
 422
 423          s3 -> "abcd"
 424          s2 _____^
 425          s1 _______^
 426
 427          ie. we don't want s1 pointing into the old s2.  */
 428       e = *--a;
 429       e->len += 1;
 430       while (--a >= array)
 431         {
 432           struct elf_strtab_hash_entry *cmp = *a;
 433
 434           cmp->len += 1;
 435           if (is_suffix (e, cmp))
 436             {
 437               cmp->u.suffix = e;
 438               cmp->len = -cmp->len;
 439             }
 440           else
 441             e = cmp;
 442         }
 443     }
 444
 445  alloc_failure:
 446   free (array);
 447
 448   /* Assign positions to the strings we want to keep.  */
 449   sec_size = 1;
 450   for (i = 1; i < tab->size; ++i)
 451     {
 452       e = tab->array[i];
 453       if (e->refcount && e->len > 0)
 454         {
 455           e->u.index = sec_size;
 456           sec_size += e->len;
 457         }
 458     }
 459
 460   tab->sec_size = sec_size;
 461
 462   /* Adjust the rest.  */
 463   for (i = 1; i < tab->size; ++i)
 464     {
 465       e = tab->array[i];
 466       if (e->refcount && e->len < 0)
 467         e->u.index = e->u.suffix->u.index + (e->u.suffix->len + e->len);
 468     }
 469 }