gold/stringpool.cc

   1 // stringpool.cc -- a string pool for gold
   2
   3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of gold.
   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 "gold.h"
  24
  25 #include <cstring>
  26 #include <algorithm>
  27 #include <vector>
  28
  29 #include "output.h"
  30 #include "parameters.h"
  31 #include "stringpool.h"
  32
  33 namespace gold
  34 {
  35
  36 template<typename Stringpool_char>
  37 Stringpool_template<Stringpool_char>::Stringpool_template()
  38   : string_set_(), key_to_offset_(), strings_(), strtab_size_(0),
  39     zero_null_(true), optimize_(false), offset_(sizeof(Stringpool_char))
  40 {
  41   if (parameters->options_valid() && parameters->options().optimize() >= 2)
  42     this->optimize_ = true;
  43 }
  44
  45 template<typename Stringpool_char>
  46 void
  47 Stringpool_template<Stringpool_char>::clear()
  48 {
  49   for (typename std::list<Stringdata*>::iterator p = this->strings_.begin();
  50        p != this->strings_.end();
  51        ++p)
  52     delete[] reinterpret_cast<char*>(*p);
  53   this->strings_.clear();
  54   this->key_to_offset_.clear();
  55   this->string_set_.clear();
  56 }
  57
  58 template<typename Stringpool_char>
  59 Stringpool_template<Stringpool_char>::~Stringpool_template()
  60 {
  61   this->clear();
  62 }
  63
  64 // Resize the internal hashtable with the expectation we'll get n new
  65 // elements.  Note that the hashtable constructor takes a "number of
  66 // buckets you'd like," rather than "number of elements you'd like,"
  67 // but that's the best we can do.
  68
  69 template<typename Stringpool_char>
  70 void
  71 Stringpool_template<Stringpool_char>::reserve(unsigned int n)
  72 {
  73   this->key_to_offset_.reserve(n);
  74
  75 #if defined(HAVE_TR1_UNORDERED_MAP)
  76   // rehash() implementation is broken in gcc 4.0.3's stl
  77   //this->string_set_.rehash(this->string_set_.size() + n);
  78   //return;
  79 #elif defined(HAVE_EXT_HASH_MAP)
  80   this->string_set_.resize(this->string_set_.size() + n);
  81   return;
  82 #endif
  83
  84   // This is the generic "reserve" code, if no #ifdef above triggers.
  85   String_set_type new_string_set(this->string_set_.size() + n);
  86   new_string_set.insert(this->string_set_.begin(), this->string_set_.end());
  87   this->string_set_.swap(new_string_set);
  88 }
  89
  90 // Compare two strings of arbitrary character type for equality.
  91
  92 template<typename Stringpool_char>
  93 bool
  94 Stringpool_template<Stringpool_char>::string_equal(const Stringpool_char* s1,
  95                                                    const Stringpool_char* s2)
  96 {
  97   while (*s1 != 0)
  98     if (*s1++ != *s2++)
  99       return false;
 100   return *s2 == 0;
 101 }
 102
 103 // Specialize string_equal for char.
 104
 105 template<>
 106 inline bool
 107 Stringpool_template<char>::string_equal(const char* s1, const char* s2)
 108 {
 109   return strcmp(s1, s2) == 0;
 110 }
 111
 112 // Equality comparison function for the hash table.
 113
 114 template<typename Stringpool_char>
 115 inline bool
 116 Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
 117     const Hashkey& h1,
 118     const Hashkey& h2) const
 119 {
 120   return (h1.hash_code == h2.hash_code
 121           && h1.length == h2.length
 122           && (h1.string == h2.string
 123               || memcmp(h1.string, h2.string,
 124                         h1.length * sizeof(Stringpool_char)) == 0));
 125 }
 126
 127 // Hash function.  The length is in characters, not bytes.
 128
 129 template<typename Stringpool_char>
 130 size_t
 131 Stringpool_template<Stringpool_char>::string_hash(const Stringpool_char* s,
 132                                                   size_t length)
 133 {
 134   return gold::string_hash<Stringpool_char>(s, length);
 135 }
 136
 137 // Add the string S to the list of canonical strings.  Return a
 138 // pointer to the canonical string.  If PKEY is not NULL, set *PKEY to
 139 // the key.  LENGTH is the length of S in characters.  Note that S may
 140 // not be NUL terminated.
 141
 142 template<typename Stringpool_char>
 143 const Stringpool_char*
 144 Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
 145                                                  size_t len)
 146 {
 147   // We are in trouble if we've already computed the string offsets.
 148   gold_assert(this->strtab_size_ == 0);
 149
 150   // The size we allocate for a new Stringdata.
 151   const size_t buffer_size = 1000;
 152   // The amount we multiply the Stringdata index when calculating the
 153   // key.
 154   const size_t key_mult = 1024;
 155   gold_assert(key_mult >= buffer_size);
 156
 157   // Convert len to the number of bytes we need to allocate, including
 158   // the null character.
 159   len = (len + 1) * sizeof(Stringpool_char);
 160
 161   size_t alc;
 162   bool front = true;
 163   if (len > buffer_size)
 164     {
 165       alc = sizeof(Stringdata) + len;
 166       front = false;
 167     }
 168   else if (this->strings_.empty())
 169     alc = sizeof(Stringdata) + buffer_size;
 170   else
 171     {
 172       Stringdata* psd = this->strings_.front();
 173       if (len > psd->alc - psd->len)
 174         alc = sizeof(Stringdata) + buffer_size;
 175       else
 176         {
 177           char* ret = psd->data + psd->len;
 178           memcpy(ret, s, len - sizeof(Stringpool_char));
 179           memset(ret + len - sizeof(Stringpool_char), 0,
 180                  sizeof(Stringpool_char));
 181
 182           psd->len += len;
 183
 184           return reinterpret_cast<const Stringpool_char*>(ret);
 185         }
 186     }
 187
 188   Stringdata* psd = reinterpret_cast<Stringdata*>(new char[alc]);
 189   psd->alc = alc - sizeof(Stringdata);
 190   memcpy(psd->data, s, len - sizeof(Stringpool_char));
 191   memset(psd->data + len - sizeof(Stringpool_char), 0,
 192          sizeof(Stringpool_char));
 193   psd->len = len;
 194
 195   if (front)
 196     this->strings_.push_front(psd);
 197   else
 198     this->strings_.push_back(psd);
 199
 200   return reinterpret_cast<const Stringpool_char*>(psd->data);
 201 }
 202
 203 // Add a string to a string pool.
 204
 205 template<typename Stringpool_char>
 206 const Stringpool_char*
 207 Stringpool_template<Stringpool_char>::add(const Stringpool_char* s, bool copy,
 208                                           Key* pkey)
 209 {
 210   return this->add_with_length(s, string_length(s), copy, pkey);
 211 }
 212
 213 // Add a new key offset entry.
 214
 215 template<typename Stringpool_char>
 216 void
 217 Stringpool_template<Stringpool_char>::new_key_offset(size_t length)
 218 {
 219   section_offset_type offset;
 220   if (this->zero_null_ && length == 0)
 221     offset = 0;
 222   else
 223     {
 224       offset = this->offset_;
 225       this->offset_ += (length + 1) * sizeof(Stringpool_char);
 226     }
 227   this->key_to_offset_.push_back(offset);
 228 }
 229
 230 template<typename Stringpool_char>
 231 const Stringpool_char*
 232 Stringpool_template<Stringpool_char>::add_with_length(const Stringpool_char* s,
 233                                                       size_t length,
 234                                                       bool copy,
 235                                                       Key* pkey)
 236 {
 237   typedef std::pair<typename String_set_type::iterator, bool> Insert_type;
 238
 239   // We add 1 so that 0 is always invalid.
 240   const Key k = this->key_to_offset_.size() + 1;
 241
 242   if (!copy)
 243     {
 244       // When we don't need to copy the string, we can call insert
 245       // directly.
 246
 247       std::pair<Hashkey, Hashval> element(Hashkey(s, length), k);
 248
 249       Insert_type ins = this->string_set_.insert(element);
 250
 251       typename String_set_type::const_iterator p = ins.first;
 252
 253       if (ins.second)
 254         {
 255           // We just added the string.  The key value has now been
 256           // used.
 257           this->new_key_offset(length);
 258         }
 259       else
 260         {
 261           gold_assert(k != p->second);
 262         }
 263
 264       if (pkey != NULL)
 265         *pkey = p->second;
 266       return p->first.string;
 267     }
 268
 269   // When we have to copy the string, we look it up twice in the hash
 270   // table.  The problem is that we can't insert S before we
 271   // canonicalize it by copying it into the canonical list. The hash
 272   // code will only be computed once.
 273
 274   Hashkey hk(s, length);
 275   typename String_set_type::const_iterator p = this->string_set_.find(hk);
 276   if (p != this->string_set_.end())
 277     {
 278       if (pkey != NULL)
 279         *pkey = p->second;
 280       return p->first.string;
 281     }
 282
 283   this->new_key_offset(length);
 284
 285   hk.string = this->add_string(s, length);
 286   // The contents of the string stay the same, so we don't need to
 287   // adjust hk.hash_code or hk.length.
 288
 289   std::pair<Hashkey, Hashval> element(hk, k);
 290
 291   Insert_type ins = this->string_set_.insert(element);
 292   gold_assert(ins.second);
 293
 294   if (pkey != NULL)
 295     *pkey = k;
 296   return hk.string;
 297 }
 298
 299 template<typename Stringpool_char>
 300 const Stringpool_char*
 301 Stringpool_template<Stringpool_char>::find(const Stringpool_char* s,
 302                                            Key* pkey) const
 303 {
 304   Hashkey hk(s);
 305   typename String_set_type::const_iterator p = this->string_set_.find(hk);
 306   if (p == this->string_set_.end())
 307     return NULL;
 308
 309   if (pkey != NULL)
 310     *pkey = p->second;
 311
 312   return p->first.string;
 313 }
 314
 315 // Comparison routine used when sorting into an ELF strtab.  We want
 316 // to sort this so that when one string is a suffix of another, we
 317 // always see the shorter string immediately after the longer string.
 318 // For example, we want to see these strings in this order:
 319 //   abcd
 320 //   cd
 321 //   d
 322 // When strings are not suffixes, we don't care what order they are
 323 // in, but we need to ensure that suffixes wind up next to each other.
 324 // So we do a reversed lexicographic sort on the reversed string.
 325
 326 template<typename Stringpool_char>
 327 bool
 328 Stringpool_template<Stringpool_char>::Stringpool_sort_comparison::operator()(
 329   const Stringpool_sort_info& sort_info1,
 330   const Stringpool_sort_info& sort_info2) const
 331 {
 332   const Hashkey& h1(sort_info1->first);
 333   const Hashkey& h2(sort_info2->first);
 334   const Stringpool_char* s1 = h1.string;
 335   const Stringpool_char* s2 = h2.string;
 336   const size_t len1 = h1.length;
 337   const size_t len2 = h2.length;
 338   const size_t minlen = len1 < len2 ? len1 : len2;
 339   const Stringpool_char* p1 = s1 + len1 - 1;
 340   const Stringpool_char* p2 = s2 + len2 - 1;
 341   for (size_t i = minlen; i > 0; --i, --p1, --p2)
 342     {
 343       if (*p1 != *p2)
 344         return *p1 > *p2;
 345     }
 346   return len1 > len2;
 347 }
 348
 349 // Return whether s1 is a suffix of s2.
 350
 351 template<typename Stringpool_char>
 352 bool
 353 Stringpool_template<Stringpool_char>::is_suffix(const Stringpool_char* s1,
 354                                                 size_t len1,
 355                                                 const Stringpool_char* s2,
 356                                                 size_t len2)
 357 {
 358   if (len1 > len2)
 359     return false;
 360   return memcmp(s1, s2 + len2 - len1, len1 * sizeof(Stringpool_char)) == 0;
 361 }
 362
 363 // Turn the stringpool into an ELF strtab: determine the offsets of
 364 // each string in the table.
 365
 366 template<typename Stringpool_char>
 367 void
 368 Stringpool_template<Stringpool_char>::set_string_offsets()
 369 {
 370   if (this->strtab_size_ != 0)
 371     {
 372       // We've already computed the offsets.
 373       return;
 374     }
 375
 376   const size_t charsize = sizeof(Stringpool_char);
 377
 378   // Offset 0 may be reserved for the empty string.
 379   section_offset_type offset = this->zero_null_ ? charsize : 0;
 380
 381   // Sorting to find suffixes can take over 25% of the total CPU time
 382   // used by the linker.  Since it's merely an optimization to reduce
 383   // the strtab size, and gives a relatively small benefit (it's
 384   // typically rare for a symbol to be a suffix of another), we only
 385   // take the time to sort when the user asks for heavy optimization.
 386   if (!this->optimize_)
 387     {
 388       // If we are not optimizing, the offsets are already assigned.
 389       offset = this->offset_;
 390     }
 391   else
 392     {
 393       size_t count = this->string_set_.size();
 394
 395       std::vector<Stringpool_sort_info> v;
 396       v.reserve(count);
 397
 398       for (typename String_set_type::iterator p = this->string_set_.begin();
 399            p != this->string_set_.end();
 400            ++p)
 401         v.push_back(Stringpool_sort_info(p));
 402
 403       std::sort(v.begin(), v.end(), Stringpool_sort_comparison());
 404
 405       section_offset_type last_offset = -1;
 406       for (typename std::vector<Stringpool_sort_info>::iterator last = v.end(),
 407              curr = v.begin();
 408            curr != v.end();
 409            last = curr++)
 410         {
 411           section_offset_type this_offset;
 412           if (this->zero_null_ && (*curr)->first.string[0] == 0)
 413             this_offset = 0;
 414           else if (last != v.end()
 415                    && is_suffix((*curr)->first.string,
 416                                 (*curr)->first.length,
 417                                 (*last)->first.string,
 418                                 (*last)->first.length))
 419             this_offset = (last_offset
 420                            + (((*last)->first.length - (*curr)->first.length)
 421                               * charsize));
 422           else
 423             {
 424               this_offset = offset;
 425               offset += ((*curr)->first.length + 1) * charsize;
 426             }
 427           this->key_to_offset_[(*curr)->second - 1] = this_offset;
 428           last_offset = this_offset;
 429         }
 430     }
 431
 432   this->strtab_size_ = offset;
 433 }
 434
 435 // Get the offset of a string in the ELF strtab.  The string must
 436 // exist.
 437
 438 template<typename Stringpool_char>
 439 section_offset_type
 440 Stringpool_template<Stringpool_char>::get_offset(const Stringpool_char* s)
 441   const
 442 {
 443   return this->get_offset_with_length(s, string_length(s));
 444 }
 445
 446 template<typename Stringpool_char>
 447 section_offset_type
 448 Stringpool_template<Stringpool_char>::get_offset_with_length(
 449     const Stringpool_char* s,
 450     size_t length) const
 451 {
 452   gold_assert(this->strtab_size_ != 0);
 453   Hashkey hk(s, length);
 454   typename String_set_type::const_iterator p = this->string_set_.find(hk);
 455   if (p != this->string_set_.end())
 456     return this->key_to_offset_[p->second - 1];
 457   gold_unreachable();
 458 }
 459
 460 // Write the ELF strtab into the buffer.
 461
 462 template<typename Stringpool_char>
 463 void
 464 Stringpool_template<Stringpool_char>::write_to_buffer(
 465     unsigned char* buffer,
 466     section_size_type bufsize)
 467 {
 468   gold_assert(this->strtab_size_ != 0);
 469   gold_assert(bufsize >= this->strtab_size_);
 470   if (this->zero_null_)
 471     buffer[0] = '\0';
 472   for (typename String_set_type::const_iterator p = this->string_set_.begin();
 473        p != this->string_set_.end();
 474        ++p)
 475     {
 476       const int len = (p->first.length + 1) * sizeof(Stringpool_char);
 477       const section_offset_type offset = this->key_to_offset_[p->second - 1];
 478       gold_assert(static_cast<section_size_type>(offset) + len
 479                   <= this->strtab_size_);
 480       memcpy(buffer + offset, p->first.string, len);
 481     }
 482 }
 483
 484 // Write the ELF strtab into the output file at the specified offset.
 485
 486 template<typename Stringpool_char>
 487 void
 488 Stringpool_template<Stringpool_char>::write(Output_file* of, off_t offset)
 489 {
 490   gold_assert(this->strtab_size_ != 0);
 491   unsigned char* view = of->get_output_view(offset, this->strtab_size_);
 492   this->write_to_buffer(view, this->strtab_size_);
 493   of->write_output_view(offset, this->strtab_size_, view);
 494 }
 495
 496 // Print statistical information to stderr.  This is used for --stats.
 497
 498 template<typename Stringpool_char>
 499 void
 500 Stringpool_template<Stringpool_char>::print_stats(const char* name) const
 501 {
 502 #if defined(HAVE_TR1_UNORDERED_MAP) || defined(HAVE_EXT_HASH_MAP)
 503   fprintf(stderr, _("%s: %s entries: %zu; buckets: %zu\n"),
 504           program_name, name, this->string_set_.size(),
 505           this->string_set_.bucket_count());
 506 #else
 507   fprintf(stderr, _("%s: %s entries: %zu\n"),
 508           program_name, name, this->table_.size());
 509 #endif
 510   fprintf(stderr, _("%s: %s Stringdata structures: %zu\n"),
 511           program_name, name, this->strings_.size());
 512 }
 513
 514 // Instantiate the templates we need.
 515
 516 template
 517 class Stringpool_template<char>;
 518
 519 template
 520 class Stringpool_template<uint16_t>;
 521
 522 template
 523 class Stringpool_template<uint32_t>;
 524
 525 } // End namespace gold.