1 // stringpool.cc -- a string pool for gold
3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
4 // Written by Ian Lance Taylor <iant@google.com>.
6 // This file is part of gold.
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.
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.
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.
30 #include "parameters.h"
31 #include "stringpool.h"
36 template<typename Stringpool_char>
37 Stringpool_template<Stringpool_char>::Stringpool_template()
38 : string_set_(), key_to_offset_(), strings_(), strtab_size_(0),
43 template<typename Stringpool_char>
45 Stringpool_template<Stringpool_char>::clear()
47 for (typename std::list<Stringdata*>::iterator p = this->strings_.begin();
48 p != this->strings_.end();
50 delete[] reinterpret_cast<char*>(*p);
51 this->strings_.clear();
52 this->key_to_offset_.clear();
53 this->string_set_.clear();
56 template<typename Stringpool_char>
57 Stringpool_template<Stringpool_char>::~Stringpool_template()
62 // Resize the internal hashtable with the expectation we'll get n new
63 // elements. Note that the hashtable constructor takes a "number of
64 // buckets you'd like," rather than "number of elements you'd like,"
65 // but that's the best we can do.
67 template<typename Stringpool_char>
69 Stringpool_template<Stringpool_char>::reserve(unsigned int n)
71 this->key_to_offset_.reserve(n);
73 #if defined(HAVE_TR1_UNORDERED_MAP)
74 // rehash() implementation is broken in gcc 4.0.3's stl
75 //this->string_set_.rehash(this->string_set_.size() + n);
77 #elif defined(HAVE_EXT_HASH_MAP)
78 this->string_set_.resize(this->string_set_.size() + n);
82 // This is the generic "reserve" code, if no #ifdef above triggers.
83 String_set_type new_string_set(this->string_set_.size() + n);
84 new_string_set.insert(this->string_set_.begin(), this->string_set_.end());
85 this->string_set_.swap(new_string_set);
88 // Return the length of a string of arbitrary character type.
90 template<typename Stringpool_char>
92 Stringpool_template<Stringpool_char>::string_length(const Stringpool_char* p)
100 // Specialize string_length for char. Maybe we could just use
101 // std::char_traits<>::length?
105 Stringpool_template<char>::string_length(const char* p)
110 // Compare two strings of arbitrary character type for equality.
112 template<typename Stringpool_char>
114 Stringpool_template<Stringpool_char>::string_equal(const Stringpool_char* s1,
115 const Stringpool_char* s2)
123 // Specialize string_equal for char.
127 Stringpool_template<char>::string_equal(const char* s1, const char* s2)
129 return strcmp(s1, s2) == 0;
132 // Equality comparison function for the hash table.
134 template<typename Stringpool_char>
136 Stringpool_template<Stringpool_char>::Stringpool_eq::operator()(
138 const Hashkey& h2) const
140 return (h1.hash_code == h2.hash_code
141 && h1.length == h2.length
142 && (h1.string == h2.string
143 || memcmp(h1.string, h2.string,
144 h1.length * sizeof(Stringpool_char)) == 0));
147 // Hash function. The length is in characters, not bytes.
149 template<typename Stringpool_char>
151 Stringpool_template<Stringpool_char>::string_hash(const Stringpool_char* s,
154 // This is the hash function used by the dynamic linker for
155 // DT_GNU_HASH entries. I compared this to a Fowler/Noll/Vo hash
156 // for a C++ program with 385,775 global symbols. This hash
157 // function was very slightly worse. However, it is much faster to
158 // compute. Overall wall clock time was a win.
159 const unsigned char* p = reinterpret_cast<const unsigned char*>(s);
161 for (size_t i = 0; i < length * sizeof(Stringpool_char); ++i)
166 // Add the string S to the list of canonical strings. Return a
167 // pointer to the canonical string. If PKEY is not NULL, set *PKEY to
168 // the key. LENGTH is the length of S in characters. Note that S may
169 // not be NUL terminated.
171 template<typename Stringpool_char>
172 const Stringpool_char*
173 Stringpool_template<Stringpool_char>::add_string(const Stringpool_char* s,
176 // We are in trouble if we've already computed the string offsets.
177 gold_assert(this->strtab_size_ == 0);
179 // The size we allocate for a new Stringdata.
180 const size_t buffer_size = 1000;
181 // The amount we multiply the Stringdata index when calculating the
183 const size_t key_mult = 1024;
184 gold_assert(key_mult >= buffer_size);
186 // Convert len to the number of bytes we need to allocate, including
187 // the null character.
188 len = (len + 1) * sizeof(Stringpool_char);
192 if (len > buffer_size)
194 alc = sizeof(Stringdata) + len;
197 else if (this->strings_.empty())
198 alc = sizeof(Stringdata) + buffer_size;
201 Stringdata *psd = this->strings_.front();
202 if (len > psd->alc - psd->len)
203 alc = sizeof(Stringdata) + buffer_size;
206 char* ret = psd->data + psd->len;
207 memcpy(ret, s, len - sizeof(Stringpool_char));
208 memset(ret + len - sizeof(Stringpool_char), 0,
209 sizeof(Stringpool_char));
213 return reinterpret_cast<const Stringpool_char*>(ret);
217 Stringdata *psd = reinterpret_cast<Stringdata*>(new char[alc]);
218 psd->alc = alc - sizeof(Stringdata);
219 memcpy(psd->data, s, len - sizeof(Stringpool_char));
220 memset(psd->data + len - sizeof(Stringpool_char), 0,
221 sizeof(Stringpool_char));
225 this->strings_.push_front(psd);
227 this->strings_.push_back(psd);
229 return reinterpret_cast<const Stringpool_char*>(psd->data);
232 // Add a string to a string pool.
234 template<typename Stringpool_char>
235 const Stringpool_char*
236 Stringpool_template<Stringpool_char>::add(const Stringpool_char* s, bool copy,
239 return this->add_with_length(s, string_length(s), copy, pkey);
242 template<typename Stringpool_char>
243 const Stringpool_char*
244 Stringpool_template<Stringpool_char>::add_with_length(const Stringpool_char* s,
249 typedef std::pair<typename String_set_type::iterator, bool> Insert_type;
251 // We add 1 so that 0 is always invalid.
252 const Key k = this->key_to_offset_.size() + 1;
256 // When we don't need to copy the string, we can call insert
259 std::pair<Hashkey, Hashval> element(Hashkey(s, length), k);
261 Insert_type ins = this->string_set_.insert(element);
263 typename String_set_type::const_iterator p = ins.first;
267 // We just added the string. The key value has now been
269 this->key_to_offset_.push_back(0);
273 gold_assert(k != p->second);
278 return p->first.string;
281 // When we have to copy the string, we look it up twice in the hash
282 // table. The problem is that we can't insert S before we
283 // canonicalize it by copying it into the canonical list. The hash
284 // code will only be computed once.
286 Hashkey hk(s, length);
287 typename String_set_type::const_iterator p = this->string_set_.find(hk);
288 if (p != this->string_set_.end())
292 return p->first.string;
295 this->key_to_offset_.push_back(0);
297 hk.string = this->add_string(s, length);
298 // The contents of the string stay the same, so we don't need to
299 // adjust hk.hash_code or hk.length.
301 std::pair<Hashkey, Hashval> element(hk, k);
303 Insert_type ins = this->string_set_.insert(element);
304 gold_assert(ins.second);
311 template<typename Stringpool_char>
312 const Stringpool_char*
313 Stringpool_template<Stringpool_char>::find(const Stringpool_char* s,
317 typename String_set_type::const_iterator p = this->string_set_.find(hk);
318 if (p == this->string_set_.end())
324 return p->first.string;
327 // Comparison routine used when sorting into an ELF strtab. We want
328 // to sort this so that when one string is a suffix of another, we
329 // always see the shorter string immediately after the longer string.
330 // For example, we want to see these strings in this order:
334 // When strings are not suffixes, we don't care what order they are
335 // in, but we need to ensure that suffixes wind up next to each other.
336 // So we do a reversed lexicographic sort on the reversed string.
338 template<typename Stringpool_char>
340 Stringpool_template<Stringpool_char>::Stringpool_sort_comparison::operator()(
341 const Stringpool_sort_info& sort_info1,
342 const Stringpool_sort_info& sort_info2) const
344 const Hashkey& h1(sort_info1->first);
345 const Hashkey& h2(sort_info2->first);
346 const Stringpool_char* s1 = h1.string;
347 const Stringpool_char* s2 = h2.string;
348 const size_t len1 = h1.length;
349 const size_t len2 = h2.length;
350 const size_t minlen = len1 < len2 ? len1 : len2;
351 const Stringpool_char* p1 = s1 + len1 - 1;
352 const Stringpool_char* p2 = s2 + len2 - 1;
353 for (size_t i = minlen; i > 0; --i, --p1, --p2)
361 // Return whether s1 is a suffix of s2.
363 template<typename Stringpool_char>
365 Stringpool_template<Stringpool_char>::is_suffix(const Stringpool_char* s1,
367 const Stringpool_char* s2,
372 return memcmp(s1, s2 + len2 - len1, len1 * sizeof(Stringpool_char)) == 0;
375 // Turn the stringpool into an ELF strtab: determine the offsets of
376 // each string in the table.
378 template<typename Stringpool_char>
380 Stringpool_template<Stringpool_char>::set_string_offsets()
382 if (this->strtab_size_ != 0)
384 // We've already computed the offsets.
388 const size_t charsize = sizeof(Stringpool_char);
390 // Offset 0 may be reserved for the empty string.
391 section_offset_type offset = this->zero_null_ ? charsize : 0;
393 // Sorting to find suffixes can take over 25% of the total CPU time
394 // used by the linker. Since it's merely an optimization to reduce
395 // the strtab size, and gives a relatively small benefit (it's
396 // typically rare for a symbol to be a suffix of another), we only
397 // take the time to sort when the user asks for heavy optimization.
398 if (parameters->options().optimize() < 2)
400 for (typename String_set_type::iterator curr = this->string_set_.begin();
401 curr != this->string_set_.end();
404 section_offset_type* poff = &this->key_to_offset_[curr->second - 1];
405 if (this->zero_null_ && curr->first.string[0] == 0)
410 offset += (curr->first.length + 1) * charsize;
416 size_t count = this->string_set_.size();
418 std::vector<Stringpool_sort_info> v;
421 for (typename String_set_type::iterator p = this->string_set_.begin();
422 p != this->string_set_.end();
424 v.push_back(Stringpool_sort_info(p));
426 std::sort(v.begin(), v.end(), Stringpool_sort_comparison());
428 section_offset_type last_offset = -1;
429 for (typename std::vector<Stringpool_sort_info>::iterator last = v.end(),
434 section_offset_type this_offset;
435 if (this->zero_null_ && (*curr)->first.string[0] == 0)
437 else if (last != v.end()
438 && is_suffix((*curr)->first.string,
439 (*curr)->first.length,
440 (*last)->first.string,
441 (*last)->first.length))
442 this_offset = (last_offset
443 + (((*last)->first.length - (*curr)->first.length)
447 this_offset = offset;
448 offset += ((*curr)->first.length + 1) * charsize;
450 this->key_to_offset_[(*curr)->second - 1] = this_offset;
451 last_offset = this_offset;
455 this->strtab_size_ = offset;
458 // Get the offset of a string in the ELF strtab. The string must
461 template<typename Stringpool_char>
463 Stringpool_template<Stringpool_char>::get_offset(const Stringpool_char* s)
466 return this->get_offset_with_length(s, string_length(s));
469 template<typename Stringpool_char>
471 Stringpool_template<Stringpool_char>::get_offset_with_length(
472 const Stringpool_char* s,
475 gold_assert(this->strtab_size_ != 0);
476 Hashkey hk(s, length);
477 typename String_set_type::const_iterator p = this->string_set_.find(hk);
478 if (p != this->string_set_.end())
479 return this->key_to_offset_[p->second - 1];
483 // Write the ELF strtab into the buffer.
485 template<typename Stringpool_char>
487 Stringpool_template<Stringpool_char>::write_to_buffer(
488 unsigned char* buffer,
489 section_size_type bufsize)
491 gold_assert(this->strtab_size_ != 0);
492 gold_assert(bufsize >= this->strtab_size_);
493 if (this->zero_null_)
495 for (typename String_set_type::const_iterator p = this->string_set_.begin();
496 p != this->string_set_.end();
499 const int len = (p->first.length + 1) * sizeof(Stringpool_char);
500 const section_offset_type offset = this->key_to_offset_[p->second - 1];
501 gold_assert(static_cast<section_size_type>(offset) + len
502 <= this->strtab_size_);
503 memcpy(buffer + offset, p->first.string, len);
507 // Write the ELF strtab into the output file at the specified offset.
509 template<typename Stringpool_char>
511 Stringpool_template<Stringpool_char>::write(Output_file* of, off_t offset)
513 gold_assert(this->strtab_size_ != 0);
514 unsigned char* view = of->get_output_view(offset, this->strtab_size_);
515 this->write_to_buffer(view, this->strtab_size_);
516 of->write_output_view(offset, this->strtab_size_, view);
519 // Print statistical information to stderr. This is used for --stats.
521 template<typename Stringpool_char>
523 Stringpool_template<Stringpool_char>::print_stats(const char* name) const
525 #if defined(HAVE_TR1_UNORDERED_MAP) || defined(HAVE_EXT_HASH_MAP)
526 fprintf(stderr, _("%s: %s entries: %zu; buckets: %zu\n"),
527 program_name, name, this->string_set_.size(),
528 this->string_set_.bucket_count());
530 fprintf(stderr, _("%s: %s entries: %zu\n"),
531 program_name, name, this->table_.size());
533 fprintf(stderr, _("%s: %s Stringdata structures: %zu\n"),
534 program_name, name, this->strings_.size());
537 // Instantiate the templates we need.
540 class Stringpool_template<char>;
543 class Stringpool_template<uint16_t>;
546 class Stringpool_template<uint32_t>;
548 } // End namespace gold.