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)
  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 // Return the length of a string of arbitrary character type.
  91
  92 template<typename Stringpool_char>
  93 size_t
  94 Stringpool_template<Stringpool_char>::string_length(const Stringpool_char* p)
  95 {
  96   size_t len = 0;
  97   for (; *p != 0; ++p)
  98     ++len;
  99   return len;
 100 }
 101
 102 // Specialize string_length for char.  Maybe we could just use
 103 // std::char_traits<>::length?
 104
 105 template<>
 106 inline size_t
 107 Stringpool_template<char>::string_length(const char* p)
 108 {
 109   return strlen(p);
 110 }
 111
 112 // Compare two strings of arbitrary character type for equality.
 113
 114 template<typename Stringpool_char>
 115 bool
 116 Stringpool_template<Stringpool_char>::string_equal(const Stringpool_char* s1,
 117                                                    const Stringpool_char* s2)
 118 {
 119   while (*s1 != 0)
 120     if (*s1++ != *s2++)
 121       return false;
 122   return *s2 == 0;
 123 }
 124
 125 // Specialize string_equal for char.
 126
 127 template<>
 128 inline bool
 129 Stringpool_template<char>::string_equal(const char* s1, const char* s2)
 130 {
 131   return strcmp(s1, s2) == 0;
 132 }
 133
 134 // Equality comparison function for the hash table.
 135
 136 template<typename Stringpool_char>
 137 inline bool
 138 Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
 139     const Hashkey& h1,
 140     const Hashkey& h2) const
 141 {
 142   return (h1.hash_code == h2.hash_code
 143           && h1.length == h2.length
 144           && (h1.string == h2.string
 145               || memcmp(h1.string, h2.string,
 146                         h1.length * sizeof(Stringpool_char)) == 0));
 147 }
 148
 149 // Hash function.  The length is in characters, not bytes.
 150
 151 template<typename Stringpool_char>
 152 size_t
 153 Stringpool_template<Stringpool_char>::string_hash(const Stringpool_char* s,
 154                                                   size_t length)
 155 {
 156   // This is the hash function used by the dynamic linker for
 157   // DT_GNU_HASH entries.  I compared this to a Fowler/Noll/Vo hash
 158   // for a C++ program with 385,775 global symbols.  This hash
 159   // function was very slightly worse.  However, it is much faster to
 160   // compute.  Overall wall clock time was a win.
 161   const unsigned char* p = reinterpret_cast<const unsigned char*>(s);
 162   size_t h = 5381;
 163   for (size_t i = 0; i < length * sizeof(Stringpool_char); ++i)
 164     h = h * 33 + *p++;
 165   return h;
 166 }
 167
 168 // Add the string S to the list of canonical strings.  Return a
 169 // pointer to the canonical string.  If PKEY is not NULL, set *PKEY to
 170 // the key.  LENGTH is the length of S in characters.  Note that S may
 171 // not be NUL terminated.
 172
 173 template<typename Stringpool_char>
 174 const Stringpool_char*
 175 Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
 176                                                  size_t len)
 177 {
 178   // We are in trouble if we've already computed the string offsets.
 179   gold_assert(this->strtab_size_ == 0);
 180
 181   // The size we allocate for a new Stringdata.
 182   const size_t buffer_size = 1000;
 183   // The amount we multiply the Stringdata index when calculating the
 184   // key.
 185   const size_t key_mult = 1024;
 186   gold_assert(key_mult >= buffer_size);
 187
 188   // Convert len to the number of bytes we need to allocate, including
 189   // the null character.
 190   len = (len + 1) * sizeof(Stringpool_char);
 191
 192   size_t alc;
 193   bool front = true;
 194   if (len > buffer_size)
 195     {
 196       alc = sizeof(Stringdata) + len;
 197       front = false;
 198     }
 199   else if (this->strings_.empty())
 200     alc = sizeof(Stringdata) + buffer_size;
 201   else
 202     {
 203       Stringdata *psd = this->strings_.front();
 204       if (len > psd->alc - psd->len)
 205         alc = sizeof(Stringdata) + buffer_size;
 206       else
 207         {
 208           char* ret = psd->data + psd->len;
 209           memcpy(ret, s, len - sizeof(Stringpool_char));
 210           memset(ret + len - sizeof(Stringpool_char), 0,
 211                  sizeof(Stringpool_char));
 212
 213           psd->len += len;
 214
 215           return reinterpret_cast<const Stringpool_char*>(ret);
 216         }
 217     }
 218
 219   Stringdata *psd = reinterpret_cast<Stringdata*>(new char[alc]);
 220   psd->alc = alc - sizeof(Stringdata);
 221   memcpy(psd->data, s, len - sizeof(Stringpool_char));
 222   memset(psd->data + len - sizeof(Stringpool_char), 0,
 223          sizeof(Stringpool_char));
 224   psd->len = len;
 225
 226   if (front)
 227     this->strings_.push_front(psd);
 228   else
 229     this->strings_.push_back(psd);
 230
 231   return reinterpret_cast<const Stringpool_char*>(psd->data);
 232 }
 233
 234 // Add a string to a string pool.
 235
 236 template<typename Stringpool_char>
 237 const Stringpool_char*
 238 Stringpool_template<Stringpool_char>::add(const Stringpool_char* s, bool copy,
 239                                           Key* pkey)
 240 {
 241   return this->add_with_length(s, string_length(s), copy, pkey);
 242 }
 243
 244 template<typename Stringpool_char>
 245 const Stringpool_char*
 246 Stringpool_template<Stringpool_char>::add_with_length(const Stringpool_char* s,
 247                                                       size_t length,
 248                                                       bool copy,
 249                                                       Key* pkey)
 250 {
 251   typedef std::pair<typename String_set_type::iterator, bool> Insert_type;
 252
 253   // We add 1 so that 0 is always invalid.
 254   const Key k = this->key_to_offset_.size() + 1;
 255
 256   if (!copy)
 257     {
 258       // When we don't need to copy the string, we can call insert
 259       // directly.
 260
 261       std::pair<Hashkey, Hashval> element(Hashkey(s, length), k);
 262
 263       Insert_type ins = this->string_set_.insert(element);
 264
 265       typename String_set_type::const_iterator p = ins.first;
 266
 267       if (ins.second)
 268         {
 269           // We just added the string.  The key value has now been
 270           // used.
 271           this->key_to_offset_.push_back(0);
 272         }
 273       else
 274         {
 275           gold_assert(k != p->second);
 276         }
 277
 278       if (pkey != NULL)
 279         *pkey = p->second;
 280       return p->first.string;
 281     }
 282
 283   // When we have to copy the string, we look it up twice in the hash
 284   // table.  The problem is that we can't insert S before we
 285   // canonicalize it by copying it into the canonical list. The hash
 286   // code will only be computed once.
 287
 288   Hashkey hk(s, length);
 289   typename String_set_type::const_iterator p = this->string_set_.find(hk);
 290   if (p != this->string_set_.end())
 291     {
 292       if (pkey != NULL)
 293         *pkey = p->second;
 294       return p->first.string;
 295     }
 296
 297   this->key_to_offset_.push_back(0);
 298
 299   hk.string = this->add_string(s, length);
 300   // The contents of the string stay the same, so we don't need to
 301   // adjust hk.hash_code or hk.length.
 302
 303   std::pair<Hashkey, Hashval> element(hk, k);
 304
 305   Insert_type ins = this->string_set_.insert(element);
 306   gold_assert(ins.second);
 307
 308   if (pkey != NULL)
 309     *pkey = k;
 310   return hk.string;
 311 }
 312
 313 template<typename Stringpool_char>
 314 const Stringpool_char*
 315 Stringpool_template<Stringpool_char>::find(const Stringpool_char* s,
 316                                            Key* pkey) const
 317 {
 318   Hashkey hk(s);
 319   typename String_set_type::const_iterator p = this->string_set_.find(hk);
 320   if (p == this->string_set_.end())
 321     return NULL;
 322
 323   if (pkey != NULL)
 324     *pkey = p->second;
 325
 326   return p->first.string;
 327 }
 328
 329 // Comparison routine used when sorting into an ELF strtab.  We want
 330 // to sort this so that when one string is a suffix of another, we
 331 // always see the shorter string immediately after the longer string.
 332 // For example, we want to see these strings in this order:
 333 //   abcd
 334 //   cd
 335 //   d
 336 // When strings are not suffixes, we don't care what order they are
 337 // in, but we need to ensure that suffixes wind up next to each other.
 338 // So we do a reversed lexicographic sort on the reversed string.
 339
 340 template<typename Stringpool_char>
 341 bool
 342 Stringpool_template<Stringpool_char>::Stringpool_sort_comparison::operator()(
 343   const Stringpool_sort_info& sort_info1,
 344   const Stringpool_sort_info& sort_info2) const
 345 {
 346   const Hashkey& h1(sort_info1->first);
 347   const Hashkey& h2(sort_info2->first);
 348   const Stringpool_char* s1 = h1.string;
 349   const Stringpool_char* s2 = h2.string;
 350   const size_t len1 = h1.length;
 351   const size_t len2 = h2.length;
 352   const size_t minlen = len1 < len2 ? len1 : len2;
 353   const Stringpool_char* p1 = s1 + len1 - 1;
 354   const Stringpool_char* p2 = s2 + len2 - 1;
 355   for (size_t i = minlen; i > 0; --i, --p1, --p2)
 356     {
 357       if (*p1 != *p2)
 358         return *p1 > *p2;
 359     }
 360   return len1 > len2;
 361 }
 362
 363 // Return whether s1 is a suffix of s2.
 364
 365 template<typename Stringpool_char>
 366 bool
 367 Stringpool_template<Stringpool_char>::is_suffix(const Stringpool_char* s1,
 368                                                 size_t len1,
 369                                                 const Stringpool_char* s2,
 370                                                 size_t len2)
 371 {
 372   if (len1 > len2)
 373     return false;
 374   return memcmp(s1, s2 + len2 - len1, len1 * sizeof(Stringpool_char)) == 0;
 375 }
 376
 377 // Turn the stringpool into an ELF strtab: determine the offsets of
 378 // each string in the table.
 379
 380 template<typename Stringpool_char>
 381 void
 382 Stringpool_template<Stringpool_char>::set_string_offsets()
 383 {
 384   if (this->strtab_size_ != 0)
 385     {
 386       // We've already computed the offsets.
 387       return;
 388     }
 389
 390   const size_t charsize = sizeof(Stringpool_char);
 391
 392   // Offset 0 may be reserved for the empty string.
 393   section_offset_type offset = this->zero_null_ ? charsize : 0;
 394
 395   // Sorting to find suffixes can take over 25% of the total CPU time
 396   // used by the linker.  Since it's merely an optimization to reduce
 397   // the strtab size, and gives a relatively small benefit (it's
 398   // typically rare for a symbol to be a suffix of another), we only
 399   // take the time to sort when the user asks for heavy optimization.
 400   if (!this->optimize_)
 401     {
 402       for (typename String_set_type::iterator curr = this->string_set_.begin();
 403            curr != this->string_set_.end();
 404            curr++)
 405         {
 406           section_offset_type* poff = &this->key_to_offset_[curr->second - 1];
 407           if (this->zero_null_ && curr->first.string[0] == 0)
 408             *poff = 0;
 409           else
 410             {
 411               *poff = offset;
 412               offset += (curr->first.length + 1) * charsize;
 413             }
 414         }
 415     }
 416   else
 417     {
 418       size_t count = this->string_set_.size();
 419
 420       std::vector<Stringpool_sort_info> v;
 421       v.reserve(count);
 422
 423       for (typename String_set_type::iterator p = this->string_set_.begin();
 424            p != this->string_set_.end();
 425            ++p)
 426         v.push_back(Stringpool_sort_info(p));
 427
 428       std::sort(v.begin(), v.end(), Stringpool_sort_comparison());
 429
 430       section_offset_type last_offset = -1;
 431       for (typename std::vector<Stringpool_sort_info>::iterator last = v.end(),
 432              curr = v.begin();
 433            curr != v.end();
 434            last = curr++)
 435         {
 436           section_offset_type this_offset;
 437           if (this->zero_null_ && (*curr)->first.string[0] == 0)
 438             this_offset = 0;
 439           else if (last != v.end()
 440                    && is_suffix((*curr)->first.string,
 441                                 (*curr)->first.length,
 442                                 (*last)->first.string,
 443                                 (*last)->first.length))
 444             this_offset = (last_offset
 445                            + (((*last)->first.length - (*curr)->first.length)
 446                               * charsize));
 447           else
 448             {
 449               this_offset = offset;
 450               offset += ((*curr)->first.length + 1) * charsize;
 451             }
 452           this->key_to_offset_[(*curr)->second - 1] = this_offset;
 453           last_offset = this_offset;
 454         }
 455     }
 456
 457   this->strtab_size_ = offset;
 458 }
 459
 460 // Get the offset of a string in the ELF strtab.  The string must
 461 // exist.
 462
 463 template<typename Stringpool_char>
 464 section_offset_type
 465 Stringpool_template<Stringpool_char>::get_offset(const Stringpool_char* s)
 466   const
 467 {
 468   return this->get_offset_with_length(s, string_length(s));
 469 }
 470
 471 template<typename Stringpool_char>
 472 section_offset_type
 473 Stringpool_template<Stringpool_char>::get_offset_with_length(
 474     const Stringpool_char* s,
 475     size_t length) const
 476 {
 477   gold_assert(this->strtab_size_ != 0);
 478   Hashkey hk(s, length);
 479   typename String_set_type::const_iterator p = this->string_set_.find(hk);
 480   if (p != this->string_set_.end())
 481     return this->key_to_offset_[p->second - 1];
 482   gold_unreachable();
 483 }
 484
 485 // Write the ELF strtab into the buffer.
 486
 487 template<typename Stringpool_char>
 488 void
 489 Stringpool_template<Stringpool_char>::write_to_buffer(
 490     unsigned char* buffer,
 491     section_size_type bufsize)
 492 {
 493   gold_assert(this->strtab_size_ != 0);
 494   gold_assert(bufsize >= this->strtab_size_);
 495   if (this->zero_null_)
 496     buffer[0] = '\0';
 497   for (typename String_set_type::const_iterator p = this->string_set_.begin();
 498        p != this->string_set_.end();
 499        ++p)
 500     {
 501       const int len = (p->first.length + 1) * sizeof(Stringpool_char);
 502       const section_offset_type offset = this->key_to_offset_[p->second - 1];
 503       gold_assert(static_cast<section_size_type>(offset) + len
 504                   <= this->strtab_size_);
 505       memcpy(buffer + offset, p->first.string, len);
 506     }
 507 }
 508
 509 // Write the ELF strtab into the output file at the specified offset.
 510
 511 template<typename Stringpool_char>
 512 void
 513 Stringpool_template<Stringpool_char>::write(Output_file* of, off_t offset)
 514 {
 515   gold_assert(this->strtab_size_ != 0);
 516   unsigned char* view = of->get_output_view(offset, this->strtab_size_);
 517   this->write_to_buffer(view, this->strtab_size_);
 518   of->write_output_view(offset, this->strtab_size_, view);
 519 }
 520
 521 // Print statistical information to stderr.  This is used for --stats.
 522
 523 template<typename Stringpool_char>
 524 void
 525 Stringpool_template<Stringpool_char>::print_stats(const char* name) const
 526 {
 527 #if defined(HAVE_TR1_UNORDERED_MAP) || defined(HAVE_EXT_HASH_MAP)
 528   fprintf(stderr, _("%s: %s entries: %zu; buckets: %zu\n"),
 529           program_name, name, this->string_set_.size(),
 530           this->string_set_.bucket_count());
 531 #else
 532   fprintf(stderr, _("%s: %s entries: %zu\n"),
 533           program_name, name, this->table_.size());
 534 #endif
 535   fprintf(stderr, _("%s: %s Stringdata structures: %zu\n"),
 536           program_name, name, this->strings_.size());
 537 }
 538
 539 // Instantiate the templates we need.
 540
 541 template
 542 class Stringpool_template<char>;
 543
 544 template
 545 class Stringpool_template<uint16_t>;
 546
 547 template
 548 class Stringpool_template<uint32_t>;
 549
 550 } // End namespace gold.