bfd/elf-strtab.c

   1 /* ELF strtab with GC and suffix merging support.
   2    Copyright (C) 2001-2019 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   bfd_size_type 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;
 249   struct strtab_save *save = (struct strtab_save *) buf;
 250
 251   BFD_ASSERT (tab->sec_size == 0);
 252   BFD_ASSERT (save->size <= curr_size);
 253   tab->size = save->size;
 254   for (idx = 1; idx < save->size; ++idx)
 255     tab->array[idx]->refcount = save->refcount[idx];
 256
 257   for (; idx < curr_size; ++idx)
 258     {
 259       /* We don't remove entries from the hash table, just set their
 260          REFCOUNT to zero.  Setting LEN zero will result in the size
 261          growing if the entry is added again.  See _bfd_elf_strtab_add.  */
 262       tab->array[idx]->refcount = 0;
 263       tab->array[idx]->len = 0;
 264     }
 265 }
 266
 267 bfd_size_type
 268 _bfd_elf_strtab_size (struct elf_strtab_hash *tab)
 269 {
 270   return tab->sec_size ? tab->sec_size : tab->size;
 271 }
 272
 273 bfd_size_type
 274 _bfd_elf_strtab_len (struct elf_strtab_hash *tab)
 275 {
 276   return tab->size;
 277 }
 278
 279 bfd_size_type
 280 _bfd_elf_strtab_offset (struct elf_strtab_hash *tab, size_t idx)
 281 {
 282   struct elf_strtab_hash_entry *entry;
 283
 284   if (idx == 0)
 285     return 0;
 286   BFD_ASSERT (idx < tab->size);
 287   BFD_ASSERT (tab->sec_size);
 288   entry = tab->array[idx];
 289   BFD_ASSERT (entry->refcount > 0);
 290   entry->refcount--;
 291   return tab->array[idx]->u.index;
 292 }
 293
 294 const char *
 295 _bfd_elf_strtab_str (struct elf_strtab_hash *tab, size_t idx,
 296                      bfd_size_type *offset)
 297 {
 298   if (idx == 0)
 299     return 0;
 300   BFD_ASSERT (idx < tab->size);
 301   BFD_ASSERT (tab->sec_size);
 302   if (offset)
 303     *offset = tab->array[idx]->u.index;
 304   return tab->array[idx]->root.string;
 305 }
 306
 307 bfd_boolean
 308 _bfd_elf_strtab_emit (register bfd *abfd, struct elf_strtab_hash *tab)
 309 {
 310   bfd_size_type off = 1;
 311   size_t i;
 312
 313   if (bfd_bwrite ("", 1, abfd) != 1)
 314     return FALSE;
 315
 316   for (i = 1; i < tab->size; ++i)
 317     {
 318       register const char *str;
 319       register unsigned int len;
 320
 321       BFD_ASSERT (tab->array[i]->refcount == 0);
 322       len = tab->array[i]->len;
 323       if ((int) len < 0)
 324         continue;
 325
 326       str = tab->array[i]->root.string;
 327       if (bfd_bwrite (str, len, abfd) != len)
 328         return FALSE;
 329
 330       off += len;
 331     }
 332
 333   BFD_ASSERT (off == tab->sec_size);
 334   return TRUE;
 335 }
 336
 337 /* Compare two elf_strtab_hash_entry structures.  Called via qsort.  */
 338
 339 static int
 340 strrevcmp (const void *a, const void *b)
 341 {
 342   struct elf_strtab_hash_entry *A = *(struct elf_strtab_hash_entry **) a;
 343   struct elf_strtab_hash_entry *B = *(struct elf_strtab_hash_entry **) b;
 344   unsigned int lenA = A->len;
 345   unsigned int lenB = B->len;
 346   const unsigned char *s = (const unsigned char *) A->root.string + lenA - 1;
 347   const unsigned char *t = (const unsigned char *) B->root.string + lenB - 1;
 348   int l = lenA < lenB ? lenA : lenB;
 349
 350   while (l)
 351     {
 352       if (*s != *t)
 353         return (int) *s - (int) *t;
 354       s--;
 355       t--;
 356       l--;
 357     }
 358   return lenA - lenB;
 359 }
 360
 361 static inline int
 362 is_suffix (const struct elf_strtab_hash_entry *A,
 363            const struct elf_strtab_hash_entry *B)
 364 {
 365   if (A->len <= B->len)
 366     /* B cannot be a suffix of A unless A is equal to B, which is guaranteed
 367        not to be equal by the hash table.  */
 368     return 0;
 369
 370   return memcmp (A->root.string + (A->len - B->len),
 371                  B->root.string, B->len - 1) == 0;
 372 }
 373
 374 /* This function assigns final string table offsets for used strings,
 375    merging strings matching suffixes of longer strings if possible.  */
 376
 377 void
 378 _bfd_elf_strtab_finalize (struct elf_strtab_hash *tab)
 379 {
 380   struct elf_strtab_hash_entry **array, **a, *e;
 381   bfd_size_type amt, sec_size;
 382   size_t size, i;
 383
 384   /* Sort the strings by suffix and length.  */
 385   amt = tab->size;
 386   amt *= sizeof (struct elf_strtab_hash_entry *);
 387   array = (struct elf_strtab_hash_entry **) bfd_malloc (amt);
 388   if (array == NULL)
 389     goto alloc_failure;
 390
 391   for (i = 1, a = array; i < tab->size; ++i)
 392     {
 393       e = tab->array[i];
 394       if (e->refcount)
 395         {
 396           *a++ = e;
 397           /* Adjust the length to not include the zero terminator.  */
 398           e->len -= 1;
 399         }
 400       else
 401         e->len = 0;
 402     }
 403
 404   size = a - array;
 405   if (size != 0)
 406     {
 407       qsort (array, size, sizeof (struct elf_strtab_hash_entry *), strrevcmp);
 408
 409       /* Loop over the sorted array and merge suffixes.  Start from the
 410          end because we want eg.
 411
 412          s1 -> "d"
 413          s2 -> "bcd"
 414          s3 -> "abcd"
 415
 416          to end up as
 417
 418          s3 -> "abcd"
 419          s2 _____^
 420          s1 _______^
 421
 422          ie. we don't want s1 pointing into the old s2.  */
 423       e = *--a;
 424       e->len += 1;
 425       while (--a >= array)
 426         {
 427           struct elf_strtab_hash_entry *cmp = *a;
 428
 429           cmp->len += 1;
 430           if (is_suffix (e, cmp))
 431             {
 432               cmp->u.suffix = e;
 433               cmp->len = -cmp->len;
 434             }
 435           else
 436             e = cmp;
 437         }
 438     }
 439
 440 alloc_failure:
 441   if (array)
 442     free (array);
 443
 444   /* Assign positions to the strings we want to keep.  */
 445   sec_size = 1;
 446   for (i = 1; i < tab->size; ++i)
 447     {
 448       e = tab->array[i];
 449       if (e->refcount && e->len > 0)
 450         {
 451           e->u.index = sec_size;
 452           sec_size += e->len;
 453         }
 454     }
 455
 456   tab->sec_size = sec_size;
 457
 458   /* Adjust the rest.  */
 459   for (i = 1; i < tab->size; ++i)
 460     {
 461       e = tab->array[i];
 462       if (e->refcount && e->len < 0)
 463         e->u.index = e->u.suffix->u.index + (e->u.suffix->len + e->len);
 464     }
 465 }