bfd/hash.c

   1 /* hash.c -- hash table routines for BFD
   2    Copyright (C) 1993-2017 Free Software Foundation, Inc.
   3    Written by Steve Chamberlain <sac@cygnus.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 "objalloc.h"
  26 #include "libiberty.h"
  27
  28 /*
  29 SECTION
  30         Hash Tables
  31
  32 @cindex Hash tables
  33         BFD provides a simple set of hash table functions.  Routines
  34         are provided to initialize a hash table, to free a hash table,
  35         to look up a string in a hash table and optionally create an
  36         entry for it, and to traverse a hash table.  There is
  37         currently no routine to delete an string from a hash table.
  38
  39         The basic hash table does not permit any data to be stored
  40         with a string.  However, a hash table is designed to present a
  41         base class from which other types of hash tables may be
  42         derived.  These derived types may store additional information
  43         with the string.  Hash tables were implemented in this way,
  44         rather than simply providing a data pointer in a hash table
  45         entry, because they were designed for use by the linker back
  46         ends.  The linker may create thousands of hash table entries,
  47         and the overhead of allocating private data and storing and
  48         following pointers becomes noticeable.
  49
  50         The basic hash table code is in <<hash.c>>.
  51
  52 @menu
  53 @* Creating and Freeing a Hash Table::
  54 @* Looking Up or Entering a String::
  55 @* Traversing a Hash Table::
  56 @* Deriving a New Hash Table Type::
  57 @end menu
  58
  59 INODE
  60 Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
  61 SUBSECTION
  62         Creating and freeing a hash table
  63
  64 @findex bfd_hash_table_init
  65 @findex bfd_hash_table_init_n
  66         To create a hash table, create an instance of a <<struct
  67         bfd_hash_table>> (defined in <<bfd.h>>) and call
  68         <<bfd_hash_table_init>> (if you know approximately how many
  69         entries you will need, the function <<bfd_hash_table_init_n>>,
  70         which takes a @var{size} argument, may be used).
  71         <<bfd_hash_table_init>> returns <<FALSE>> if some sort of
  72         error occurs.
  73
  74 @findex bfd_hash_newfunc
  75         The function <<bfd_hash_table_init>> take as an argument a
  76         function to use to create new entries.  For a basic hash
  77         table, use the function <<bfd_hash_newfunc>>.  @xref{Deriving
  78         a New Hash Table Type}, for why you would want to use a
  79         different value for this argument.
  80
  81 @findex bfd_hash_allocate
  82         <<bfd_hash_table_init>> will create an objalloc which will be
  83         used to allocate new entries.  You may allocate memory on this
  84         objalloc using <<bfd_hash_allocate>>.
  85
  86 @findex bfd_hash_table_free
  87         Use <<bfd_hash_table_free>> to free up all the memory that has
  88         been allocated for a hash table.  This will not free up the
  89         <<struct bfd_hash_table>> itself, which you must provide.
  90
  91 @findex bfd_hash_set_default_size
  92         Use <<bfd_hash_set_default_size>> to set the default size of
  93         hash table to use.
  94
  95 INODE
  96 Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
  97 SUBSECTION
  98         Looking up or entering a string
  99
 100 @findex bfd_hash_lookup
 101         The function <<bfd_hash_lookup>> is used both to look up a
 102         string in the hash table and to create a new entry.
 103
 104         If the @var{create} argument is <<FALSE>>, <<bfd_hash_lookup>>
 105         will look up a string.  If the string is found, it will
 106         returns a pointer to a <<struct bfd_hash_entry>>.  If the
 107         string is not found in the table <<bfd_hash_lookup>> will
 108         return <<NULL>>.  You should not modify any of the fields in
 109         the returns <<struct bfd_hash_entry>>.
 110
 111         If the @var{create} argument is <<TRUE>>, the string will be
 112         entered into the hash table if it is not already there.
 113         Either way a pointer to a <<struct bfd_hash_entry>> will be
 114         returned, either to the existing structure or to a newly
 115         created one.  In this case, a <<NULL>> return means that an
 116         error occurred.
 117
 118         If the @var{create} argument is <<TRUE>>, and a new entry is
 119         created, the @var{copy} argument is used to decide whether to
 120         copy the string onto the hash table objalloc or not.  If
 121         @var{copy} is passed as <<FALSE>>, you must be careful not to
 122         deallocate or modify the string as long as the hash table
 123         exists.
 124
 125 INODE
 126 Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
 127 SUBSECTION
 128         Traversing a hash table
 129
 130 @findex bfd_hash_traverse
 131         The function <<bfd_hash_traverse>> may be used to traverse a
 132         hash table, calling a function on each element.  The traversal
 133         is done in a random order.
 134
 135         <<bfd_hash_traverse>> takes as arguments a function and a
 136         generic <<void *>> pointer.  The function is called with a
 137         hash table entry (a <<struct bfd_hash_entry *>>) and the
 138         generic pointer passed to <<bfd_hash_traverse>>.  The function
 139         must return a <<boolean>> value, which indicates whether to
 140         continue traversing the hash table.  If the function returns
 141         <<FALSE>>, <<bfd_hash_traverse>> will stop the traversal and
 142         return immediately.
 143
 144 INODE
 145 Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
 146 SUBSECTION
 147         Deriving a new hash table type
 148
 149         Many uses of hash tables want to store additional information
 150         which each entry in the hash table.  Some also find it
 151         convenient to store additional information with the hash table
 152         itself.  This may be done using a derived hash table.
 153
 154         Since C is not an object oriented language, creating a derived
 155         hash table requires sticking together some boilerplate
 156         routines with a few differences specific to the type of hash
 157         table you want to create.
 158
 159         An example of a derived hash table is the linker hash table.
 160         The structures for this are defined in <<bfdlink.h>>.  The
 161         functions are in <<linker.c>>.
 162
 163         You may also derive a hash table from an already derived hash
 164         table.  For example, the a.out linker backend code uses a hash
 165         table derived from the linker hash table.
 166
 167 @menu
 168 @* Define the Derived Structures::
 169 @* Write the Derived Creation Routine::
 170 @* Write Other Derived Routines::
 171 @end menu
 172
 173 INODE
 174 Define the Derived Structures, Write the Derived Creation Routine, Deriving a New Hash Table Type, Deriving a New Hash Table Type
 175 SUBSUBSECTION
 176         Define the derived structures
 177
 178         You must define a structure for an entry in the hash table,
 179         and a structure for the hash table itself.
 180
 181         The first field in the structure for an entry in the hash
 182         table must be of the type used for an entry in the hash table
 183         you are deriving from.  If you are deriving from a basic hash
 184         table this is <<struct bfd_hash_entry>>, which is defined in
 185         <<bfd.h>>.  The first field in the structure for the hash
 186         table itself must be of the type of the hash table you are
 187         deriving from itself.  If you are deriving from a basic hash
 188         table, this is <<struct bfd_hash_table>>.
 189
 190         For example, the linker hash table defines <<struct
 191         bfd_link_hash_entry>> (in <<bfdlink.h>>).  The first field,
 192         <<root>>, is of type <<struct bfd_hash_entry>>.  Similarly,
 193         the first field in <<struct bfd_link_hash_table>>, <<table>>,
 194         is of type <<struct bfd_hash_table>>.
 195
 196 INODE
 197 Write the Derived Creation Routine, Write Other Derived Routines, Define the Derived Structures, Deriving a New Hash Table Type
 198 SUBSUBSECTION
 199         Write the derived creation routine
 200
 201         You must write a routine which will create and initialize an
 202         entry in the hash table.  This routine is passed as the
 203         function argument to <<bfd_hash_table_init>>.
 204
 205         In order to permit other hash tables to be derived from the
 206         hash table you are creating, this routine must be written in a
 207         standard way.
 208
 209         The first argument to the creation routine is a pointer to a
 210         hash table entry.  This may be <<NULL>>, in which case the
 211         routine should allocate the right amount of space.  Otherwise
 212         the space has already been allocated by a hash table type
 213         derived from this one.
 214
 215         After allocating space, the creation routine must call the
 216         creation routine of the hash table type it is derived from,
 217         passing in a pointer to the space it just allocated.  This
 218         will initialize any fields used by the base hash table.
 219
 220         Finally the creation routine must initialize any local fields
 221         for the new hash table type.
 222
 223         Here is a boilerplate example of a creation routine.
 224         @var{function_name} is the name of the routine.
 225         @var{entry_type} is the type of an entry in the hash table you
 226         are creating.  @var{base_newfunc} is the name of the creation
 227         routine of the hash table type your hash table is derived
 228         from.
 229
 230 EXAMPLE
 231
 232 .struct bfd_hash_entry *
 233 .@var{function_name} (struct bfd_hash_entry *entry,
 234 .                     struct bfd_hash_table *table,
 235 .                     const char *string)
 236 .{
 237 .  struct @var{entry_type} *ret = (@var{entry_type} *) entry;
 238 .
 239 . {* Allocate the structure if it has not already been allocated by a
 240 .    derived class.  *}
 241 .  if (ret == NULL)
 242 .    {
 243 .      ret = bfd_hash_allocate (table, sizeof (* ret));
 244 .      if (ret == NULL)
 245 .        return NULL;
 246 .    }
 247 .
 248 . {* Call the allocation method of the base class.  *}
 249 .  ret = ((@var{entry_type} *)
 250 .        @var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
 251 .
 252 . {* Initialize the local fields here.  *}
 253 .
 254 .  return (struct bfd_hash_entry *) ret;
 255 .}
 256
 257 DESCRIPTION
 258         The creation routine for the linker hash table, which is in
 259         <<linker.c>>, looks just like this example.
 260         @var{function_name} is <<_bfd_link_hash_newfunc>>.
 261         @var{entry_type} is <<struct bfd_link_hash_entry>>.
 262         @var{base_newfunc} is <<bfd_hash_newfunc>>, the creation
 263         routine for a basic hash table.
 264
 265         <<_bfd_link_hash_newfunc>> also initializes the local fields
 266         in a linker hash table entry: <<type>>, <<written>> and
 267         <<next>>.
 268
 269 INODE
 270 Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
 271 SUBSUBSECTION
 272         Write other derived routines
 273
 274         You will want to write other routines for your new hash table,
 275         as well.
 276
 277         You will want an initialization routine which calls the
 278         initialization routine of the hash table you are deriving from
 279         and initializes any other local fields.  For the linker hash
 280         table, this is <<_bfd_link_hash_table_init>> in <<linker.c>>.
 281
 282         You will want a lookup routine which calls the lookup routine
 283         of the hash table you are deriving from and casts the result.
 284         The linker hash table uses <<bfd_link_hash_lookup>> in
 285         <<linker.c>> (this actually takes an additional argument which
 286         it uses to decide how to return the looked up value).
 287
 288         You may want a traversal routine.  This should just call the
 289         traversal routine of the hash table you are deriving from with
 290         appropriate casts.  The linker hash table uses
 291         <<bfd_link_hash_traverse>> in <<linker.c>>.
 292
 293         These routines may simply be defined as macros.  For example,
 294         the a.out backend linker hash table, which is derived from the
 295         linker hash table, uses macros for the lookup and traversal
 296         routines.  These are <<aout_link_hash_lookup>> and
 297         <<aout_link_hash_traverse>> in aoutx.h.
 298 */
 299
 300 /* The default number of entries to use when creating a hash table.  */
 301 #define DEFAULT_SIZE 4051
 302
 303 /* The following function returns a nearest prime number which is
 304    greater than N, and near a power of two.  Copied from libiberty.
 305    Returns zero for ridiculously large N to signify an error.  */
 306
 307 static unsigned long
 308 higher_prime_number (unsigned long n)
 309 {
 310   /* These are primes that are near, but slightly smaller than, a
 311      power of two.  */
 312   static const unsigned long primes[] =
 313     {
 314       (unsigned long) 31,
 315       (unsigned long) 61,
 316       (unsigned long) 127,
 317       (unsigned long) 251,
 318       (unsigned long) 509,
 319       (unsigned long) 1021,
 320       (unsigned long) 2039,
 321       (unsigned long) 4093,
 322       (unsigned long) 8191,
 323       (unsigned long) 16381,
 324       (unsigned long) 32749,
 325       (unsigned long) 65521,
 326       (unsigned long) 131071,
 327       (unsigned long) 262139,
 328       (unsigned long) 524287,
 329       (unsigned long) 1048573,
 330       (unsigned long) 2097143,
 331       (unsigned long) 4194301,
 332       (unsigned long) 8388593,
 333       (unsigned long) 16777213,
 334       (unsigned long) 33554393,
 335       (unsigned long) 67108859,
 336       (unsigned long) 134217689,
 337       (unsigned long) 268435399,
 338       (unsigned long) 536870909,
 339       (unsigned long) 1073741789,
 340       (unsigned long) 2147483647,
 341                                         /* 4294967291L */
 342       ((unsigned long) 2147483647) + ((unsigned long) 2147483644),
 343   };
 344
 345   const unsigned long *low = &primes[0];
 346   const unsigned long *high = &primes[sizeof (primes) / sizeof (primes[0])];
 347
 348   while (low != high)
 349     {
 350       const unsigned long *mid = low + (high - low) / 2;
 351       if (n >= *mid)
 352         low = mid + 1;
 353       else
 354         high = mid;
 355     }
 356
 357   if (n >= *low)
 358     return 0;
 359
 360   return *low;
 361 }
 362
 363 static unsigned long bfd_default_hash_table_size = DEFAULT_SIZE;
 364
 365 /* Create a new hash table, given a number of entries.  */
 366
 367 bfd_boolean
 368 bfd_hash_table_init_n (struct bfd_hash_table *table,
 369                        struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
 370                                                           struct bfd_hash_table *,
 371                                                           const char *),
 372                        unsigned int entsize,
 373                        unsigned int size)
 374 {
 375   unsigned long alloc;
 376
 377   alloc = size;
 378   alloc *= sizeof (struct bfd_hash_entry *);
 379   if (alloc / sizeof (struct bfd_hash_entry *) != size)
 380     {
 381       bfd_set_error (bfd_error_no_memory);
 382       return FALSE;
 383     }
 384
 385   table->memory = (void *) objalloc_create ();
 386   if (table->memory == NULL)
 387     {
 388       bfd_set_error (bfd_error_no_memory);
 389       return FALSE;
 390     }
 391   table->table = (struct bfd_hash_entry **)
 392       objalloc_alloc ((struct objalloc *) table->memory, alloc);
 393   if (table->table == NULL)
 394     {
 395       bfd_hash_table_free (table);
 396       bfd_set_error (bfd_error_no_memory);
 397       return FALSE;
 398     }
 399   memset ((void *) table->table, 0, alloc);
 400   table->size = size;
 401   table->entsize = entsize;
 402   table->count = 0;
 403   table->frozen = 0;
 404   table->newfunc = newfunc;
 405   return TRUE;
 406 }
 407
 408 /* Create a new hash table with the default number of entries.  */
 409
 410 bfd_boolean
 411 bfd_hash_table_init (struct bfd_hash_table *table,
 412                      struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
 413                                                         struct bfd_hash_table *,
 414                                                         const char *),
 415                      unsigned int entsize)
 416 {
 417   return bfd_hash_table_init_n (table, newfunc, entsize,
 418                                 bfd_default_hash_table_size);
 419 }
 420
 421 /* Free a hash table.  */
 422
 423 void
 424 bfd_hash_table_free (struct bfd_hash_table *table)
 425 {
 426   objalloc_free ((struct objalloc *) table->memory);
 427   table->memory = NULL;
 428 }
 429
 430 static inline unsigned long
 431 bfd_hash_hash (const char *string, unsigned int *lenp)
 432 {
 433   const unsigned char *s;
 434   unsigned long hash;
 435   unsigned int len;
 436   unsigned int c;
 437
 438   hash = 0;
 439   len = 0;
 440   s = (const unsigned char *) string;
 441   while ((c = *s++) != '\0')
 442     {
 443       hash += c + (c << 17);
 444       hash ^= hash >> 2;
 445     }
 446   len = (s - (const unsigned char *) string) - 1;
 447   hash += len + (len << 17);
 448   hash ^= hash >> 2;
 449   if (lenp != NULL)
 450     *lenp = len;
 451   return hash;
 452 }
 453
 454 /* Look up a string in a hash table.  */
 455
 456 struct bfd_hash_entry *
 457 bfd_hash_lookup (struct bfd_hash_table *table,
 458                  const char *string,
 459                  bfd_boolean create,
 460                  bfd_boolean copy)
 461 {
 462   unsigned long hash;
 463   struct bfd_hash_entry *hashp;
 464   unsigned int len;
 465   unsigned int _index;
 466
 467   hash = bfd_hash_hash (string, &len);
 468   _index = hash % table->size;
 469   for (hashp = table->table[_index];
 470        hashp != NULL;
 471        hashp = hashp->next)
 472     {
 473       if (hashp->hash == hash
 474           && strcmp (hashp->string, string) == 0)
 475         return hashp;
 476     }
 477
 478   if (! create)
 479     return NULL;
 480
 481   if (copy)
 482     {
 483       char *new_string;
 484
 485       new_string = (char *) objalloc_alloc ((struct objalloc *) table->memory,
 486                                             len + 1);
 487       if (!new_string)
 488         {
 489           bfd_set_error (bfd_error_no_memory);
 490           return NULL;
 491         }
 492       memcpy (new_string, string, len + 1);
 493       string = new_string;
 494     }
 495
 496   return bfd_hash_insert (table, string, hash);
 497 }
 498
 499 /* Insert an entry in a hash table.  */
 500
 501 struct bfd_hash_entry *
 502 bfd_hash_insert (struct bfd_hash_table *table,
 503                  const char *string,
 504                  unsigned long hash)
 505 {
 506   struct bfd_hash_entry *hashp;
 507   unsigned int _index;
 508
 509   hashp = (*table->newfunc) (NULL, table, string);
 510   if (hashp == NULL)
 511     return NULL;
 512   hashp->string = string;
 513   hashp->hash = hash;
 514   _index = hash % table->size;
 515   hashp->next = table->table[_index];
 516   table->table[_index] = hashp;
 517   table->count++;
 518
 519   if (!table->frozen && table->count > table->size * 3 / 4)
 520     {
 521       unsigned long newsize = higher_prime_number (table->size);
 522       struct bfd_hash_entry **newtable;
 523       unsigned int hi;
 524       unsigned long alloc = newsize * sizeof (struct bfd_hash_entry *);
 525
 526       /* If we can't find a higher prime, or we can't possibly alloc
 527          that much memory, don't try to grow the table.  */
 528       if (newsize == 0 || alloc / sizeof (struct bfd_hash_entry *) != newsize)
 529         {
 530           table->frozen = 1;
 531           return hashp;
 532         }
 533
 534       newtable = ((struct bfd_hash_entry **)
 535                   objalloc_alloc ((struct objalloc *) table->memory, alloc));
 536       if (newtable == NULL)
 537         {
 538           table->frozen = 1;
 539           return hashp;
 540         }
 541       memset (newtable, 0, alloc);
 542
 543       for (hi = 0; hi < table->size; hi ++)
 544         while (table->table[hi])
 545           {
 546             struct bfd_hash_entry *chain = table->table[hi];
 547             struct bfd_hash_entry *chain_end = chain;
 548
 549             while (chain_end->next && chain_end->next->hash == chain->hash)
 550               chain_end = chain_end->next;
 551
 552             table->table[hi] = chain_end->next;
 553             _index = chain->hash % newsize;
 554             chain_end->next = newtable[_index];
 555             newtable[_index] = chain;
 556           }
 557       table->table = newtable;
 558       table->size = newsize;
 559     }
 560
 561   return hashp;
 562 }
 563
 564 /* Rename an entry in a hash table.  */
 565
 566 void
 567 bfd_hash_rename (struct bfd_hash_table *table,
 568                  const char *string,
 569                  struct bfd_hash_entry *ent)
 570 {
 571   unsigned int _index;
 572   struct bfd_hash_entry **pph;
 573
 574   _index = ent->hash % table->size;
 575   for (pph = &table->table[_index]; *pph != NULL; pph = &(*pph)->next)
 576     if (*pph == ent)
 577       break;
 578   if (*pph == NULL)
 579     abort ();
 580
 581   *pph = ent->next;
 582   ent->string = string;
 583   ent->hash = bfd_hash_hash (string, NULL);
 584   _index = ent->hash % table->size;
 585   ent->next = table->table[_index];
 586   table->table[_index] = ent;
 587 }
 588
 589 /* Replace an entry in a hash table.  */
 590
 591 void
 592 bfd_hash_replace (struct bfd_hash_table *table,
 593                   struct bfd_hash_entry *old,
 594                   struct bfd_hash_entry *nw)
 595 {
 596   unsigned int _index;
 597   struct bfd_hash_entry **pph;
 598
 599   _index = old->hash % table->size;
 600   for (pph = &table->table[_index];
 601        (*pph) != NULL;
 602        pph = &(*pph)->next)
 603     {
 604       if (*pph == old)
 605         {
 606           *pph = nw;
 607           return;
 608         }
 609     }
 610
 611   abort ();
 612 }
 613
 614 /* Allocate space in a hash table.  */
 615
 616 void *
 617 bfd_hash_allocate (struct bfd_hash_table *table,
 618                    unsigned int size)
 619 {
 620   void * ret;
 621
 622   ret = objalloc_alloc ((struct objalloc *) table->memory, size);
 623   if (ret == NULL && size != 0)
 624     bfd_set_error (bfd_error_no_memory);
 625   return ret;
 626 }
 627
 628 /* Base method for creating a new hash table entry.  */
 629
 630 struct bfd_hash_entry *
 631 bfd_hash_newfunc (struct bfd_hash_entry *entry,
 632                   struct bfd_hash_table *table,
 633                   const char *string ATTRIBUTE_UNUSED)
 634 {
 635   if (entry == NULL)
 636     entry = (struct bfd_hash_entry *) bfd_hash_allocate (table,
 637                                                          sizeof (* entry));
 638   return entry;
 639 }
 640
 641 /* Traverse a hash table.  */
 642
 643 void
 644 bfd_hash_traverse (struct bfd_hash_table *table,
 645                    bfd_boolean (*func) (struct bfd_hash_entry *, void *),
 646                    void * info)
 647 {
 648   unsigned int i;
 649
 650   table->frozen = 1;
 651   for (i = 0; i < table->size; i++)
 652     {
 653       struct bfd_hash_entry *p;
 654
 655       for (p = table->table[i]; p != NULL; p = p->next)
 656         if (! (*func) (p, info))
 657           goto out;
 658     }
 659  out:
 660   table->frozen = 0;
 661 }
 662 \f
 663 unsigned long
 664 bfd_hash_set_default_size (unsigned long hash_size)
 665 {
 666   /* Extend this prime list if you want more granularity of hash table size.  */
 667   static const unsigned long hash_size_primes[] =
 668     {
 669       31, 61, 127, 251, 509, 1021, 2039, 4091, 8191, 16381, 32749, 65537
 670     };
 671   unsigned int _index;
 672
 673   /* Work out best prime number near the hash_size.  */
 674   for (_index = 0; _index < ARRAY_SIZE (hash_size_primes) - 1; ++_index)
 675     if (hash_size <= hash_size_primes[_index])
 676       break;
 677
 678   bfd_default_hash_table_size = hash_size_primes[_index];
 679   return bfd_default_hash_table_size;
 680 }
 681 \f
 682 /* A few different object file formats (a.out, COFF, ELF) use a string
 683    table.  These functions support adding strings to a string table,
 684    returning the byte offset, and writing out the table.
 685
 686    Possible improvements:
 687    + look for strings matching trailing substrings of other strings
 688    + better data structures?  balanced trees?
 689    + look at reducing memory use elsewhere -- maybe if we didn't have
 690      to construct the entire symbol table at once, we could get by
 691      with smaller amounts of VM?  (What effect does that have on the
 692      string table reductions?)  */
 693
 694 /* An entry in the strtab hash table.  */
 695
 696 struct strtab_hash_entry
 697 {
 698   struct bfd_hash_entry root;
 699   /* Index in string table.  */
 700   bfd_size_type index;
 701   /* Next string in strtab.  */
 702   struct strtab_hash_entry *next;
 703 };
 704
 705 /* The strtab hash table.  */
 706
 707 struct bfd_strtab_hash
 708 {
 709   struct bfd_hash_table table;
 710   /* Size of strtab--also next available index.  */
 711   bfd_size_type size;
 712   /* First string in strtab.  */
 713   struct strtab_hash_entry *first;
 714   /* Last string in strtab.  */
 715   struct strtab_hash_entry *last;
 716   /* Whether to precede strings with a two byte length, as in the
 717      XCOFF .debug section.  */
 718   bfd_boolean xcoff;
 719 };
 720
 721 /* Routine to create an entry in a strtab.  */
 722
 723 static struct bfd_hash_entry *
 724 strtab_hash_newfunc (struct bfd_hash_entry *entry,
 725                      struct bfd_hash_table *table,
 726                      const char *string)
 727 {
 728   struct strtab_hash_entry *ret = (struct strtab_hash_entry *) entry;
 729
 730   /* Allocate the structure if it has not already been allocated by a
 731      subclass.  */
 732   if (ret == NULL)
 733     ret = (struct strtab_hash_entry *) bfd_hash_allocate (table,
 734                                                           sizeof (* ret));
 735   if (ret == NULL)
 736     return NULL;
 737
 738   /* Call the allocation method of the superclass.  */
 739   ret = (struct strtab_hash_entry *)
 740          bfd_hash_newfunc ((struct bfd_hash_entry *) ret, table, string);
 741
 742   if (ret)
 743     {
 744       /* Initialize the local fields.  */
 745       ret->index = (bfd_size_type) -1;
 746       ret->next = NULL;
 747     }
 748
 749   return (struct bfd_hash_entry *) ret;
 750 }
 751
 752 /* Look up an entry in an strtab.  */
 753
 754 #define strtab_hash_lookup(t, string, create, copy) \
 755   ((struct strtab_hash_entry *) \
 756    bfd_hash_lookup (&(t)->table, (string), (create), (copy)))
 757
 758 /* Create a new strtab.  */
 759
 760 struct bfd_strtab_hash *
 761 _bfd_stringtab_init (void)
 762 {
 763   struct bfd_strtab_hash *table;
 764   bfd_size_type amt = sizeof (* table);
 765
 766   table = (struct bfd_strtab_hash *) bfd_malloc (amt);
 767   if (table == NULL)
 768     return NULL;
 769
 770   if (!bfd_hash_table_init (&table->table, strtab_hash_newfunc,
 771                             sizeof (struct strtab_hash_entry)))
 772     {
 773       free (table);
 774       return NULL;
 775     }
 776
 777   table->size = 0;
 778   table->first = NULL;
 779   table->last = NULL;
 780   table->xcoff = FALSE;
 781
 782   return table;
 783 }
 784
 785 /* Create a new strtab in which the strings are output in the format
 786    used in the XCOFF .debug section: a two byte length precedes each
 787    string.  */
 788
 789 struct bfd_strtab_hash *
 790 _bfd_xcoff_stringtab_init (void)
 791 {
 792   struct bfd_strtab_hash *ret;
 793
 794   ret = _bfd_stringtab_init ();
 795   if (ret != NULL)
 796     ret->xcoff = TRUE;
 797   return ret;
 798 }
 799
 800 /* Free a strtab.  */
 801
 802 void
 803 _bfd_stringtab_free (struct bfd_strtab_hash *table)
 804 {
 805   bfd_hash_table_free (&table->table);
 806   free (table);
 807 }
 808
 809 /* Get the index of a string in a strtab, adding it if it is not
 810    already present.  If HASH is FALSE, we don't really use the hash
 811    table, and we don't eliminate duplicate strings.  If COPY is true
 812    then store a copy of STR if creating a new entry.  */
 813
 814 bfd_size_type
 815 _bfd_stringtab_add (struct bfd_strtab_hash *tab,
 816                     const char *str,
 817                     bfd_boolean hash,
 818                     bfd_boolean copy)
 819 {
 820   struct strtab_hash_entry *entry;
 821
 822   if (hash)
 823     {
 824       entry = strtab_hash_lookup (tab, str, TRUE, copy);
 825       if (entry == NULL)
 826         return (bfd_size_type) -1;
 827     }
 828   else
 829     {
 830       entry = (struct strtab_hash_entry *) bfd_hash_allocate (&tab->table,
 831                                                               sizeof (* entry));
 832       if (entry == NULL)
 833         return (bfd_size_type) -1;
 834       if (! copy)
 835         entry->root.string = str;
 836       else
 837         {
 838           size_t len = strlen (str) + 1;
 839           char *n;
 840
 841           n = (char *) bfd_hash_allocate (&tab->table, len);
 842           if (n == NULL)
 843             return (bfd_size_type) -1;
 844           memcpy (n, str, len);
 845           entry->root.string = n;
 846         }
 847       entry->index = (bfd_size_type) -1;
 848       entry->next = NULL;
 849     }
 850
 851   if (entry->index == (bfd_size_type) -1)
 852     {
 853       entry->index = tab->size;
 854       tab->size += strlen (str) + 1;
 855       if (tab->xcoff)
 856         {
 857           entry->index += 2;
 858           tab->size += 2;
 859         }
 860       if (tab->first == NULL)
 861         tab->first = entry;
 862       else
 863         tab->last->next = entry;
 864       tab->last = entry;
 865     }
 866
 867   return entry->index;
 868 }
 869
 870 /* Get the number of bytes in a strtab.  */
 871
 872 bfd_size_type
 873 _bfd_stringtab_size (struct bfd_strtab_hash *tab)
 874 {
 875   return tab->size;
 876 }
 877
 878 /* Write out a strtab.  ABFD must already be at the right location in
 879    the file.  */
 880
 881 bfd_boolean
 882 _bfd_stringtab_emit (bfd *abfd, struct bfd_strtab_hash *tab)
 883 {
 884   bfd_boolean xcoff;
 885   struct strtab_hash_entry *entry;
 886
 887   xcoff = tab->xcoff;
 888
 889   for (entry = tab->first; entry != NULL; entry = entry->next)
 890     {
 891       const char *str;
 892       size_t len;
 893
 894       str = entry->root.string;
 895       len = strlen (str) + 1;
 896
 897       if (xcoff)
 898         {
 899           bfd_byte buf[2];
 900
 901           /* The output length includes the null byte.  */
 902           bfd_put_16 (abfd, (bfd_vma) len, buf);
 903           if (bfd_bwrite ((void *) buf, (bfd_size_type) 2, abfd) != 2)
 904             return FALSE;
 905         }
 906
 907       if (bfd_bwrite ((void *) str, (bfd_size_type) len, abfd) != len)
 908         return FALSE;
 909     }
 910
 911   return TRUE;
 912 }