bfd/hash.c

   1 /* hash.c -- hash table routines for BFD
   2    Copyright 1993, 1994, 1995, 1997, 1999, 2001, 2002, 2003, 2004, 2005,
   3    2006, 2007, 2009 Free Software Foundation, Inc.
   4    Written by Steve Chamberlain <sac@cygnus.com>
   5
   6    This file is part of BFD, the Binary File Descriptor library.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21    MA 02110-1301, USA.  */
  22
  23 #include "sysdep.h"
  24 #include "bfd.h"
  25 #include "libbfd.h"
  26 #include "objalloc.h"
  27 #include "libiberty.h"
  28
  29 /*
  30 SECTION
  31         Hash Tables
  32
  33 @cindex Hash tables
  34         BFD provides a simple set of hash table functions.  Routines
  35         are provided to initialize a hash table, to free a hash table,
  36         to look up a string in a hash table and optionally create an
  37         entry for it, and to traverse a hash table.  There is
  38         currently no routine to delete an string from a hash table.
  39
  40         The basic hash table does not permit any data to be stored
  41         with a string.  However, a hash table is designed to present a
  42         base class from which other types of hash tables may be
  43         derived.  These derived types may store additional information
  44         with the string.  Hash tables were implemented in this way,
  45         rather than simply providing a data pointer in a hash table
  46         entry, because they were designed for use by the linker back
  47         ends.  The linker may create thousands of hash table entries,
  48         and the overhead of allocating private data and storing and
  49         following pointers becomes noticeable.
  50
  51         The basic hash table code is in <<hash.c>>.
  52
  53 @menu
  54 @* Creating and Freeing a Hash Table::
  55 @* Looking Up or Entering a String::
  56 @* Traversing a Hash Table::
  57 @* Deriving a New Hash Table Type::
  58 @end menu
  59
  60 INODE
  61 Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
  62 SUBSECTION
  63         Creating and freeing a hash table
  64
  65 @findex bfd_hash_table_init
  66 @findex bfd_hash_table_init_n
  67         To create a hash table, create an instance of a <<struct
  68         bfd_hash_table>> (defined in <<bfd.h>>) and call
  69         <<bfd_hash_table_init>> (if you know approximately how many
  70         entries you will need, the function <<bfd_hash_table_init_n>>,
  71         which takes a @var{size} argument, may be used).
  72         <<bfd_hash_table_init>> returns <<FALSE>> if some sort of
  73         error occurs.
  74
  75 @findex bfd_hash_newfunc
  76         The function <<bfd_hash_table_init>> take as an argument a
  77         function to use to create new entries.  For a basic hash
  78         table, use the function <<bfd_hash_newfunc>>.  @xref{Deriving
  79         a New Hash Table Type}, for why you would want to use a
  80         different value for this argument.
  81
  82 @findex bfd_hash_allocate
  83         <<bfd_hash_table_init>> will create an objalloc which will be
  84         used to allocate new entries.  You may allocate memory on this
  85         objalloc using <<bfd_hash_allocate>>.
  86
  87 @findex bfd_hash_table_free
  88         Use <<bfd_hash_table_free>> to free up all the memory that has
  89         been allocated for a hash table.  This will not free up the
  90         <<struct bfd_hash_table>> itself, which you must provide.
  91
  92 @findex bfd_hash_set_default_size
  93         Use <<bfd_hash_set_default_size>> to set the default size of
  94         hash table to use.
  95
  96 INODE
  97 Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
  98 SUBSECTION
  99         Looking up or entering a string
 100
 101 @findex bfd_hash_lookup
 102         The function <<bfd_hash_lookup>> is used both to look up a
 103         string in the hash table and to create a new entry.
 104
 105         If the @var{create} argument is <<FALSE>>, <<bfd_hash_lookup>>
 106         will look up a string.  If the string is found, it will
 107         returns a pointer to a <<struct bfd_hash_entry>>.  If the
 108         string is not found in the table <<bfd_hash_lookup>> will
 109         return <<NULL>>.  You should not modify any of the fields in
 110         the returns <<struct bfd_hash_entry>>.
 111
 112         If the @var{create} argument is <<TRUE>>, the string will be
 113         entered into the hash table if it is not already there.
 114         Either way a pointer to a <<struct bfd_hash_entry>> will be
 115         returned, either to the existing structure or to a newly
 116         created one.  In this case, a <<NULL>> return means that an
 117         error occurred.
 118
 119         If the @var{create} argument is <<TRUE>>, and a new entry is
 120         created, the @var{copy} argument is used to decide whether to
 121         copy the string onto the hash table objalloc or not.  If
 122         @var{copy} is passed as <<FALSE>>, you must be careful not to
 123         deallocate or modify the string as long as the hash table
 124         exists.
 125
 126 INODE
 127 Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
 128 SUBSECTION
 129         Traversing a hash table
 130
 131 @findex bfd_hash_traverse
 132         The function <<bfd_hash_traverse>> may be used to traverse a
 133         hash table, calling a function on each element.  The traversal
 134         is done in a random order.
 135
 136         <<bfd_hash_traverse>> takes as arguments a function and a
 137         generic <<void *>> pointer.  The function is called with a
 138         hash table entry (a <<struct bfd_hash_entry *>>) and the
 139         generic pointer passed to <<bfd_hash_traverse>>.  The function
 140         must return a <<boolean>> value, which indicates whether to
 141         continue traversing the hash table.  If the function returns
 142         <<FALSE>>, <<bfd_hash_traverse>> will stop the traversal and
 143         return immediately.
 144
 145 INODE
 146 Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
 147 SUBSECTION
 148         Deriving a new hash table type
 149
 150         Many uses of hash tables want to store additional information
 151         which each entry in the hash table.  Some also find it
 152         convenient to store additional information with the hash table
 153         itself.  This may be done using a derived hash table.
 154
 155         Since C is not an object oriented language, creating a derived
 156         hash table requires sticking together some boilerplate
 157         routines with a few differences specific to the type of hash
 158         table you want to create.
 159
 160         An example of a derived hash table is the linker hash table.
 161         The structures for this are defined in <<bfdlink.h>>.  The
 162         functions are in <<linker.c>>.
 163
 164         You may also derive a hash table from an already derived hash
 165         table.  For example, the a.out linker backend code uses a hash
 166         table derived from the linker hash table.
 167
 168 @menu
 169 @* Define the Derived Structures::
 170 @* Write the Derived Creation Routine::
 171 @* Write Other Derived Routines::
 172 @end menu
 173
 174 INODE
 175 Define the Derived Structures, Write the Derived Creation Routine, Deriving a New Hash Table Type, Deriving a New Hash Table Type
 176 SUBSUBSECTION
 177         Define the derived structures
 178
 179         You must define a structure for an entry in the hash table,
 180         and a structure for the hash table itself.
 181
 182         The first field in the structure for an entry in the hash
 183         table must be of the type used for an entry in the hash table
 184         you are deriving from.  If you are deriving from a basic hash
 185         table this is <<struct bfd_hash_entry>>, which is defined in
 186         <<bfd.h>>.  The first field in the structure for the hash
 187         table itself must be of the type of the hash table you are
 188         deriving from itself.  If you are deriving from a basic hash
 189         table, this is <<struct bfd_hash_table>>.
 190
 191         For example, the linker hash table defines <<struct
 192         bfd_link_hash_entry>> (in <<bfdlink.h>>).  The first field,
 193         <<root>>, is of type <<struct bfd_hash_entry>>.  Similarly,
 194         the first field in <<struct bfd_link_hash_table>>, <<table>>,
 195         is of type <<struct bfd_hash_table>>.
 196
 197 INODE
 198 Write the Derived Creation Routine, Write Other Derived Routines, Define the Derived Structures, Deriving a New Hash Table Type
 199 SUBSUBSECTION
 200         Write the derived creation routine
 201
 202         You must write a routine which will create and initialize an
 203         entry in the hash table.  This routine is passed as the
 204         function argument to <<bfd_hash_table_init>>.
 205
 206         In order to permit other hash tables to be derived from the
 207         hash table you are creating, this routine must be written in a
 208         standard way.
 209
 210         The first argument to the creation routine is a pointer to a
 211         hash table entry.  This may be <<NULL>>, in which case the
 212         routine should allocate the right amount of space.  Otherwise
 213         the space has already been allocated by a hash table type
 214         derived from this one.
 215
 216         After allocating space, the creation routine must call the
 217         creation routine of the hash table type it is derived from,
 218         passing in a pointer to the space it just allocated.  This
 219         will initialize any fields used by the base hash table.
 220
 221         Finally the creation routine must initialize any local fields
 222         for the new hash table type.
 223
 224         Here is a boilerplate example of a creation routine.
 225         @var{function_name} is the name of the routine.
 226         @var{entry_type} is the type of an entry in the hash table you
 227         are creating.  @var{base_newfunc} is the name of the creation
 228         routine of the hash table type your hash table is derived
 229         from.
 230
 231 EXAMPLE
 232
 233 .struct bfd_hash_entry *
 234 .@var{function_name} (struct bfd_hash_entry *entry,
 235 .                     struct bfd_hash_table *table,
 236 .                     const char *string)
 237 .{
 238 .  struct @var{entry_type} *ret = (@var{entry_type} *) entry;
 239 .
 240 . {* Allocate the structure if it has not already been allocated by a
 241 .    derived class.  *}
 242 .  if (ret == NULL)
 243 .    {
 244 .      ret = bfd_hash_allocate (table, sizeof (* ret));
 245 .      if (ret == NULL)
 246 .        return NULL;
 247 .    }
 248 .
 249 . {* Call the allocation method of the base class.  *}
 250 .  ret = ((@var{entry_type} *)
 251 .        @var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
 252 .
 253 . {* Initialize the local fields here.  *}
 254 .
 255 .  return (struct bfd_hash_entry *) ret;
 256 .}
 257
 258 DESCRIPTION
 259         The creation routine for the linker hash table, which is in
 260         <<linker.c>>, looks just like this example.
 261         @var{function_name} is <<_bfd_link_hash_newfunc>>.
 262         @var{entry_type} is <<struct bfd_link_hash_entry>>.
 263         @var{base_newfunc} is <<bfd_hash_newfunc>>, the creation
 264         routine for a basic hash table.
 265
 266         <<_bfd_link_hash_newfunc>> also initializes the local fields
 267         in a linker hash table entry: <<type>>, <<written>> and
 268         <<next>>.
 269
 270 INODE
 271 Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
 272 SUBSUBSECTION
 273         Write other derived routines
 274
 275         You will want to write other routines for your new hash table,
 276         as well.
 277
 278         You will want an initialization routine which calls the
 279         initialization routine of the hash table you are deriving from
 280         and initializes any other local fields.  For the linker hash
 281         table, this is <<_bfd_link_hash_table_init>> in <<linker.c>>.
 282
 283         You will want a lookup routine which calls the lookup routine
 284         of the hash table you are deriving from and casts the result.
 285         The linker hash table uses <<bfd_link_hash_lookup>> in
 286         <<linker.c>> (this actually takes an additional argument which
 287         it uses to decide how to return the looked up value).
 288
 289         You may want a traversal routine.  This should just call the
 290         traversal routine of the hash table you are deriving from with
 291         appropriate casts.  The linker hash table uses
 292         <<bfd_link_hash_traverse>> in <<linker.c>>.
 293
 294         These routines may simply be defined as macros.  For example,
 295         the a.out backend linker hash table, which is derived from the
 296         linker hash table, uses macros for the lookup and traversal
 297         routines.  These are <<aout_link_hash_lookup>> and
 298         <<aout_link_hash_traverse>> in aoutx.h.
 299 */
 300
 301 /* The default number of entries to use when creating a hash table.  */
 302 #define DEFAULT_SIZE 4051
 303
 304 /* The following function returns a nearest prime number which is
 305    greater than N, and near a power of two.  Copied from libiberty.
 306    Returns zero for ridiculously large N to signify an error.  */
 307
 308 static unsigned long
 309 higher_prime_number (unsigned long n)
 310 {
 311   /* These are primes that are near, but slightly smaller than, a
 312      power of two.  */
 313   static const unsigned long primes[] = {
 314     (unsigned long) 127,
 315     (unsigned long) 2039,
 316     (unsigned long) 32749,
 317     (unsigned long) 65521,
 318     (unsigned long) 131071,
 319     (unsigned long) 262139,
 320     (unsigned long) 524287,
 321     (unsigned long) 1048573,
 322     (unsigned long) 2097143,
 323     (unsigned long) 4194301,
 324     (unsigned long) 8388593,
 325     (unsigned long) 16777213,
 326     (unsigned long) 33554393,
 327     (unsigned long) 67108859,
 328     (unsigned long) 134217689,
 329     (unsigned long) 268435399,
 330     (unsigned long) 536870909,
 331     (unsigned long) 1073741789,
 332     (unsigned long) 2147483647,
 333                                         /* 4294967291L */
 334     ((unsigned long) 2147483647) + ((unsigned long) 2147483644),
 335   };
 336
 337   const unsigned long *low = &primes[0];
 338   const unsigned long *high = &primes[sizeof (primes) / sizeof (primes[0])];
 339
 340   while (low != high)
 341     {
 342       const unsigned long *mid = low + (high - low) / 2;
 343       if (n >= *mid)
 344         low = mid + 1;
 345       else
 346         high = mid;
 347     }
 348
 349   if (n >= *low)
 350     return 0;
 351
 352   return *low;
 353 }
 354
 355 static size_t bfd_default_hash_table_size = DEFAULT_SIZE;
 356
 357 /* Create a new hash table, given a number of entries.  */
 358
 359 bfd_boolean
 360 bfd_hash_table_init_n (struct bfd_hash_table *table,
 361                        struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
 362                                                           struct bfd_hash_table *,
 363                                                           const char *),
 364                        unsigned int entsize,
 365                        unsigned int size)
 366 {
 367   unsigned int alloc;
 368
 369   alloc = size * sizeof (struct bfd_hash_entry *);
 370
 371   table->memory = (void *) objalloc_create ();
 372   if (table->memory == NULL)
 373     {
 374       bfd_set_error (bfd_error_no_memory);
 375       return FALSE;
 376     }
 377   table->table = (struct bfd_hash_entry **)
 378       objalloc_alloc ((struct objalloc *) table->memory, alloc);
 379   if (table->table == NULL)
 380     {
 381       bfd_set_error (bfd_error_no_memory);
 382       return FALSE;
 383     }
 384   memset ((void *) table->table, 0, alloc);
 385   table->size = size;
 386   table->entsize = entsize;
 387   table->count = 0;
 388   table->frozen = 0;
 389   table->newfunc = newfunc;
 390   return TRUE;
 391 }
 392
 393 /* Create a new hash table with the default number of entries.  */
 394
 395 bfd_boolean
 396 bfd_hash_table_init (struct bfd_hash_table *table,
 397                      struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
 398                                                         struct bfd_hash_table *,
 399                                                         const char *),
 400                      unsigned int entsize)
 401 {
 402   return bfd_hash_table_init_n (table, newfunc, entsize,
 403                                 bfd_default_hash_table_size);
 404 }
 405
 406 /* Free a hash table.  */
 407
 408 void
 409 bfd_hash_table_free (struct bfd_hash_table *table)
 410 {
 411   objalloc_free ((struct objalloc *) table->memory);
 412   table->memory = NULL;
 413 }
 414
 415 /* Look up a string in a hash table.  */
 416
 417 struct bfd_hash_entry *
 418 bfd_hash_lookup (struct bfd_hash_table *table,
 419                  const char *string,
 420                  bfd_boolean create,
 421                  bfd_boolean copy)
 422 {
 423   const unsigned char *s;
 424   unsigned long hash;
 425   unsigned int c;
 426   struct bfd_hash_entry *hashp;
 427   unsigned int len;
 428   unsigned int index;
 429
 430   hash = 0;
 431   len = 0;
 432   s = (const unsigned char *) string;
 433   while ((c = *s++) != '\0')
 434     {
 435       hash += c + (c << 17);
 436       hash ^= hash >> 2;
 437     }
 438   len = (s - (const unsigned char *) string) - 1;
 439   hash += len + (len << 17);
 440   hash ^= hash >> 2;
 441
 442   index = hash % table->size;
 443   for (hashp = table->table[index];
 444        hashp != NULL;
 445        hashp = hashp->next)
 446     {
 447       if (hashp->hash == hash
 448           && strcmp (hashp->string, string) == 0)
 449         return hashp;
 450     }
 451
 452   if (! create)
 453     return NULL;
 454
 455   if (copy)
 456     {
 457       char *new_string;
 458
 459       new_string = (char *) objalloc_alloc ((struct objalloc *) table->memory,
 460                                             len + 1);
 461       if (!new_string)
 462         {
 463           bfd_set_error (bfd_error_no_memory);
 464           return NULL;
 465         }
 466       memcpy (new_string, string, len + 1);
 467       string = new_string;
 468     }
 469
 470   return bfd_hash_insert (table, string, hash);
 471 }
 472
 473 /* Insert an entry in a hash table.  */
 474
 475 struct bfd_hash_entry *
 476 bfd_hash_insert (struct bfd_hash_table *table,
 477                  const char *string,
 478                  unsigned long hash)
 479 {
 480   struct bfd_hash_entry *hashp;
 481   unsigned int index;
 482
 483   hashp = (*table->newfunc) (NULL, table, string);
 484   if (hashp == NULL)
 485     return NULL;
 486   hashp->string = string;
 487   hashp->hash = hash;
 488   index = hash % table->size;
 489   hashp->next = table->table[index];
 490   table->table[index] = hashp;
 491   table->count++;
 492
 493   if (!table->frozen && table->count > table->size * 3 / 4)
 494     {
 495       unsigned long newsize = higher_prime_number (table->size);
 496       struct bfd_hash_entry **newtable;
 497       unsigned int hi;
 498       unsigned long alloc = newsize * sizeof (struct bfd_hash_entry *);
 499
 500       /* If we can't find a higher prime, or we can't possibly alloc
 501          that much memory, don't try to grow the table.  */
 502       if (newsize == 0 || alloc / sizeof (struct bfd_hash_entry *) != newsize)
 503         {
 504           table->frozen = 1;
 505           return hashp;
 506         }
 507
 508       newtable = ((struct bfd_hash_entry **)
 509                   objalloc_alloc ((struct objalloc *) table->memory, alloc));
 510       if (newtable == NULL)
 511         {
 512           table->frozen = 1;
 513           return hashp;
 514         }
 515       memset ((PTR) newtable, 0, alloc);
 516
 517       for (hi = 0; hi < table->size; hi ++)
 518         while (table->table[hi])
 519           {
 520             struct bfd_hash_entry *chain = table->table[hi];
 521             struct bfd_hash_entry *chain_end = chain;
 522
 523             while (chain_end->next && chain_end->next->hash == chain->hash)
 524               chain_end = chain_end->next;
 525
 526             table->table[hi] = chain_end->next;
 527             index = chain->hash % newsize;
 528             chain_end->next = newtable[index];
 529             newtable[index] = chain;
 530           }
 531       table->table = newtable;
 532       table->size = newsize;
 533     }
 534
 535   return hashp;
 536 }
 537
 538 /* Replace an entry in a hash table.  */
 539
 540 void
 541 bfd_hash_replace (struct bfd_hash_table *table,
 542                   struct bfd_hash_entry *old,
 543                   struct bfd_hash_entry *nw)
 544 {
 545   unsigned int index;
 546   struct bfd_hash_entry **pph;
 547
 548   index = old->hash % table->size;
 549   for (pph = &table->table[index];
 550        (*pph) != NULL;
 551        pph = &(*pph)->next)
 552     {
 553       if (*pph == old)
 554         {
 555           *pph = nw;
 556           return;
 557         }
 558     }
 559
 560   abort ();
 561 }
 562
 563 /* Allocate space in a hash table.  */
 564
 565 void *
 566 bfd_hash_allocate (struct bfd_hash_table *table,
 567                    unsigned int size)
 568 {
 569   void * ret;
 570
 571   ret = objalloc_alloc ((struct objalloc *) table->memory, size);
 572   if (ret == NULL && size != 0)
 573     bfd_set_error (bfd_error_no_memory);
 574   return ret;
 575 }
 576
 577 /* Base method for creating a new hash table entry.  */
 578
 579 struct bfd_hash_entry *
 580 bfd_hash_newfunc (struct bfd_hash_entry *entry,
 581                   struct bfd_hash_table *table,
 582                   const char *string ATTRIBUTE_UNUSED)
 583 {
 584   if (entry == NULL)
 585     entry = (struct bfd_hash_entry *) bfd_hash_allocate (table,
 586                                                          sizeof (* entry));
 587   return entry;
 588 }
 589
 590 /* Traverse a hash table.  */
 591
 592 void
 593 bfd_hash_traverse (struct bfd_hash_table *table,
 594                    bfd_boolean (*func) (struct bfd_hash_entry *, void *),
 595                    void * info)
 596 {
 597   unsigned int i;
 598
 599   table->frozen = 1;
 600   for (i = 0; i < table->size; i++)
 601     {
 602       struct bfd_hash_entry *p;
 603
 604       for (p = table->table[i]; p != NULL; p = p->next)
 605         if (! (*func) (p, info))
 606           goto out;
 607     }
 608  out:
 609   table->frozen = 0;
 610 }
 611 \f
 612 void
 613 bfd_hash_set_default_size (bfd_size_type hash_size)
 614 {
 615   /* Extend this prime list if you want more granularity of hash table size.  */
 616   static const bfd_size_type hash_size_primes[] =
 617     {
 618       251, 509, 1021, 2039, 4051, 8599, 16699, 32749
 619     };
 620   size_t index;
 621
 622   /* Work out best prime number near the hash_size.  */
 623   for (index = 0; index < ARRAY_SIZE (hash_size_primes) - 1; ++index)
 624     if (hash_size <= hash_size_primes[index])
 625       break;
 626
 627   bfd_default_hash_table_size = hash_size_primes[index];
 628 }
 629 \f
 630 /* A few different object file formats (a.out, COFF, ELF) use a string
 631    table.  These functions support adding strings to a string table,
 632    returning the byte offset, and writing out the table.
 633
 634    Possible improvements:
 635    + look for strings matching trailing substrings of other strings
 636    + better data structures?  balanced trees?
 637    + look at reducing memory use elsewhere -- maybe if we didn't have
 638      to construct the entire symbol table at once, we could get by
 639      with smaller amounts of VM?  (What effect does that have on the
 640      string table reductions?)  */
 641
 642 /* An entry in the strtab hash table.  */
 643
 644 struct strtab_hash_entry
 645 {
 646   struct bfd_hash_entry root;
 647   /* Index in string table.  */
 648   bfd_size_type index;
 649   /* Next string in strtab.  */
 650   struct strtab_hash_entry *next;
 651 };
 652
 653 /* The strtab hash table.  */
 654
 655 struct bfd_strtab_hash
 656 {
 657   struct bfd_hash_table table;
 658   /* Size of strtab--also next available index.  */
 659   bfd_size_type size;
 660   /* First string in strtab.  */
 661   struct strtab_hash_entry *first;
 662   /* Last string in strtab.  */
 663   struct strtab_hash_entry *last;
 664   /* Whether to precede strings with a two byte length, as in the
 665      XCOFF .debug section.  */
 666   bfd_boolean xcoff;
 667 };
 668
 669 /* Routine to create an entry in a strtab.  */
 670
 671 static struct bfd_hash_entry *
 672 strtab_hash_newfunc (struct bfd_hash_entry *entry,
 673                      struct bfd_hash_table *table,
 674                      const char *string)
 675 {
 676   struct strtab_hash_entry *ret = (struct strtab_hash_entry *) entry;
 677
 678   /* Allocate the structure if it has not already been allocated by a
 679      subclass.  */
 680   if (ret == NULL)
 681     ret = (struct strtab_hash_entry *) bfd_hash_allocate (table,
 682                                                           sizeof (* ret));
 683   if (ret == NULL)
 684     return NULL;
 685
 686   /* Call the allocation method of the superclass.  */
 687   ret = (struct strtab_hash_entry *)
 688          bfd_hash_newfunc ((struct bfd_hash_entry *) ret, table, string);
 689
 690   if (ret)
 691     {
 692       /* Initialize the local fields.  */
 693       ret->index = (bfd_size_type) -1;
 694       ret->next = NULL;
 695     }
 696
 697   return (struct bfd_hash_entry *) ret;
 698 }
 699
 700 /* Look up an entry in an strtab.  */
 701
 702 #define strtab_hash_lookup(t, string, create, copy) \
 703   ((struct strtab_hash_entry *) \
 704    bfd_hash_lookup (&(t)->table, (string), (create), (copy)))
 705
 706 /* Create a new strtab.  */
 707
 708 struct bfd_strtab_hash *
 709 _bfd_stringtab_init (void)
 710 {
 711   struct bfd_strtab_hash *table;
 712   bfd_size_type amt = sizeof (* table);
 713
 714   table = (struct bfd_strtab_hash *) bfd_malloc (amt);
 715   if (table == NULL)
 716     return NULL;
 717
 718   if (!bfd_hash_table_init (&table->table, strtab_hash_newfunc,
 719                             sizeof (struct strtab_hash_entry)))
 720     {
 721       free (table);
 722       return NULL;
 723     }
 724
 725   table->size = 0;
 726   table->first = NULL;
 727   table->last = NULL;
 728   table->xcoff = FALSE;
 729
 730   return table;
 731 }
 732
 733 /* Create a new strtab in which the strings are output in the format
 734    used in the XCOFF .debug section: a two byte length precedes each
 735    string.  */
 736
 737 struct bfd_strtab_hash *
 738 _bfd_xcoff_stringtab_init (void)
 739 {
 740   struct bfd_strtab_hash *ret;
 741
 742   ret = _bfd_stringtab_init ();
 743   if (ret != NULL)
 744     ret->xcoff = TRUE;
 745   return ret;
 746 }
 747
 748 /* Free a strtab.  */
 749
 750 void
 751 _bfd_stringtab_free (struct bfd_strtab_hash *table)
 752 {
 753   bfd_hash_table_free (&table->table);
 754   free (table);
 755 }
 756
 757 /* Get the index of a string in a strtab, adding it if it is not
 758    already present.  If HASH is FALSE, we don't really use the hash
 759    table, and we don't eliminate duplicate strings.  */
 760
 761 bfd_size_type
 762 _bfd_stringtab_add (struct bfd_strtab_hash *tab,
 763                     const char *str,
 764                     bfd_boolean hash,
 765                     bfd_boolean copy)
 766 {
 767   struct strtab_hash_entry *entry;
 768
 769   if (hash)
 770     {
 771       entry = strtab_hash_lookup (tab, str, TRUE, copy);
 772       if (entry == NULL)
 773         return (bfd_size_type) -1;
 774     }
 775   else
 776     {
 777       entry = (struct strtab_hash_entry *) bfd_hash_allocate (&tab->table,
 778                                                               sizeof (* entry));
 779       if (entry == NULL)
 780         return (bfd_size_type) -1;
 781       if (! copy)
 782         entry->root.string = str;
 783       else
 784         {
 785           char *n;
 786
 787           n = (char *) bfd_hash_allocate (&tab->table, strlen (str) + 1);
 788           if (n == NULL)
 789             return (bfd_size_type) -1;
 790           entry->root.string = n;
 791         }
 792       entry->index = (bfd_size_type) -1;
 793       entry->next = NULL;
 794     }
 795
 796   if (entry->index == (bfd_size_type) -1)
 797     {
 798       entry->index = tab->size;
 799       tab->size += strlen (str) + 1;
 800       if (tab->xcoff)
 801         {
 802           entry->index += 2;
 803           tab->size += 2;
 804         }
 805       if (tab->first == NULL)
 806         tab->first = entry;
 807       else
 808         tab->last->next = entry;
 809       tab->last = entry;
 810     }
 811
 812   return entry->index;
 813 }
 814
 815 /* Get the number of bytes in a strtab.  */
 816
 817 bfd_size_type
 818 _bfd_stringtab_size (struct bfd_strtab_hash *tab)
 819 {
 820   return tab->size;
 821 }
 822
 823 /* Write out a strtab.  ABFD must already be at the right location in
 824    the file.  */
 825
 826 bfd_boolean
 827 _bfd_stringtab_emit (bfd *abfd, struct bfd_strtab_hash *tab)
 828 {
 829   bfd_boolean xcoff;
 830   struct strtab_hash_entry *entry;
 831
 832   xcoff = tab->xcoff;
 833
 834   for (entry = tab->first; entry != NULL; entry = entry->next)
 835     {
 836       const char *str;
 837       size_t len;
 838
 839       str = entry->root.string;
 840       len = strlen (str) + 1;
 841
 842       if (xcoff)
 843         {
 844           bfd_byte buf[2];
 845
 846           /* The output length includes the null byte.  */
 847           bfd_put_16 (abfd, (bfd_vma) len, buf);
 848           if (bfd_bwrite ((void *) buf, (bfd_size_type) 2, abfd) != 2)
 849             return FALSE;
 850         }
 851
 852       if (bfd_bwrite ((void *) str, (bfd_size_type) len, abfd) != len)
 853         return FALSE;
 854     }
 855
 856   return TRUE;
 857 }