PR binutils/11742
[binutils.git] / gold / stringpool.h
blob2f9a3139358540ba517ba607b2698f321ad732a0
1 // stringpool.h -- a string pool for gold -*- C++ -*-
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.
23 #include <string>
24 #include <list>
25 #include <vector>
27 #ifndef GOLD_STRINGPOOL_H
28 #define GOLD_STRINGPOOL_H
30 namespace gold
33 class Output_file;
35 // Return the length of a string in units of Char_type.
37 template<typename Char_type>
38 inline size_t
39 string_length(const Char_type* p)
41 size_t len = 0;
42 for (; *p != 0; ++p)
43 ++len;
44 return len;
47 // Specialize string_length for char. Maybe we could just use
48 // std::char_traits<>::length?
50 template<>
51 inline size_t
52 string_length(const char* p)
54 return strlen(p);
57 // A Stringpool is a pool of unique strings. It provides the
58 // following features:
60 // Every string in the pool is unique. Thus, if you have two strings
61 // in the Stringpool, you can compare them for equality by using
62 // pointer comparison rather than string comparison.
64 // There is a key associated with every string in the pool. If you
65 // add strings to the Stringpool in the same order, then the key for
66 // each string will always be the same for any run of the linker.
67 // This is not true of the string pointers themselves, as they may
68 // change due to address space randomization. Some parts of the
69 // linker (e.g., the symbol table) use the key value instead of the
70 // string pointer so that repeated runs of the linker will generate
71 // precisely the same output.
73 // When you add a string to a Stringpool, Stringpool will optionally
74 // make a copy of it. Thus there is no requirement to keep a copy
75 // elsewhere.
77 // A Stringpool can be turned into a string table, a sequential series
78 // of null terminated strings. The first string may optionally be a
79 // single zero byte, as required for SHT_STRTAB sections. This
80 // conversion is only permitted after all strings have been added to
81 // the Stringpool. After doing this conversion, you can ask for the
82 // offset of any string (or any key) in the stringpool in the string
83 // table, and you can write the resulting string table to an output
84 // file.
86 // When a Stringpool is turned into a string table, then as an
87 // optimization it will reuse string suffixes to avoid duplicating
88 // strings. That is, given the strings "abc" and "bc", only the
89 // string "abc" will be stored, and "bc" will be represented by an
90 // offset into the middle of the string "abc".
93 // A simple chunked vector class--this is a subset of std::vector
94 // which stores memory in chunks. We don't provide iterators, because
95 // we don't need them.
97 template<typename Element>
98 class Chunked_vector
100 public:
101 Chunked_vector()
102 : chunks_(), size_(0)
105 // Clear the elements.
106 void
107 clear()
109 this->chunks_.clear();
110 this->size_ = 0;
113 // Reserve elements.
114 void
115 reserve(unsigned int n)
117 if (n > this->chunks_.size() * chunk_size)
119 this->chunks_.resize((n + chunk_size - 1) / chunk_size);
120 // We need to call reserve() of all chunks since changing
121 // this->chunks_ casues Element_vectors to be copied. The
122 // reserved capacity of an Element_vector may be lost in copying.
123 for (size_t i = 0; i < this->chunks_.size(); ++i)
124 this->chunks_[i].reserve(chunk_size);
128 // Get the number of elements.
129 size_t
130 size() const
131 { return this->size_; }
133 // Push a new element on the back of the vector.
134 void
135 push_back(const Element& element)
137 size_t chunk_index = this->size_ / chunk_size;
138 if (chunk_index >= this->chunks_.size())
140 this->chunks_.push_back(Element_vector());
141 this->chunks_.back().reserve(chunk_size);
142 gold_assert(chunk_index < this->chunks_.size());
144 this->chunks_[chunk_index].push_back(element);
145 this->size_++;
148 // Return a reference to an entry in the vector.
149 Element&
150 operator[](size_t i)
151 { return this->chunks_[i / chunk_size][i % chunk_size]; }
153 const Element&
154 operator[](size_t i) const
155 { return this->chunks_[i / chunk_size][i % chunk_size]; }
157 private:
158 static const unsigned int chunk_size = 8192;
160 typedef std::vector<Element> Element_vector;
161 typedef std::vector<Element_vector> Chunk_vector;
163 Chunk_vector chunks_;
164 size_t size_;
168 // Stringpools are implemented in terms of Stringpool_template, which
169 // is generalized on the type of character used for the strings. Most
170 // uses will want the Stringpool type which uses char. Other cases
171 // are used for merging wide string constants.
173 template<typename Stringpool_char>
174 class Stringpool_template
176 public:
177 // The type of a key into the stringpool. As described above, a key
178 // value will always be the same during any run of the linker. Zero
179 // is never a valid key value.
180 typedef size_t Key;
182 // Create a Stringpool.
183 Stringpool_template();
185 ~Stringpool_template();
187 // Clear all the data from the stringpool.
188 void
189 clear();
191 // Hint to the stringpool class that you intend to insert n additional
192 // elements. The stringpool class can use this info however it likes;
193 // in practice it will resize its internal hashtables to make room.
194 void
195 reserve(unsigned int n);
197 // Indicate that we should not reserve offset 0 to hold the empty
198 // string when converting the stringpool to a string table. This
199 // should not be called for a proper ELF SHT_STRTAB section.
200 void
201 set_no_zero_null()
203 gold_assert(this->string_set_.empty()
204 && this->offset_ == sizeof(Stringpool_char));
205 this->zero_null_ = false;
206 this->offset_ = 0;
209 // Indicate that this string pool should be optimized, even if not
210 // running with -O2.
211 void
212 set_optimize()
213 { this->optimize_ = true; }
215 // Add the string S to the pool. This returns a canonical permanent
216 // pointer to the string in the pool. If COPY is true, the string
217 // is copied into permanent storage. If PKEY is not NULL, this sets
218 // *PKEY to the key for the string.
219 const Stringpool_char*
220 add(const Stringpool_char* s, bool copy, Key* pkey);
222 // Add string S of length LEN characters to the pool. If COPY is
223 // true, S need not be null terminated.
224 const Stringpool_char*
225 add_with_length(const Stringpool_char* s, size_t len, bool copy, Key* pkey);
227 // If the string S is present in the pool, return the canonical
228 // string pointer. Otherwise, return NULL. If PKEY is not NULL,
229 // set *PKEY to the key.
230 const Stringpool_char*
231 find(const Stringpool_char* s, Key* pkey) const;
233 // Turn the stringpool into a string table: determine the offsets of
234 // all the strings. After this is called, no more strings may be
235 // added to the stringpool.
236 void
237 set_string_offsets();
239 // Get the offset of the string S in the string table. This returns
240 // the offset in bytes, not in units of Stringpool_char. This may
241 // only be called after set_string_offsets has been called.
242 section_offset_type
243 get_offset(const Stringpool_char* s) const;
245 // Get the offset of the string S in the string table.
246 section_offset_type
247 get_offset(const std::basic_string<Stringpool_char>& s) const
248 { return this->get_offset_with_length(s.c_str(), s.size()); }
250 // Get the offset of string S, with length LENGTH characters, in the
251 // string table.
252 section_offset_type
253 get_offset_with_length(const Stringpool_char* s, size_t length) const;
255 // Get the offset of the string with key K.
256 section_offset_type
257 get_offset_from_key(Key k) const
259 gold_assert(k <= this->key_to_offset_.size());
260 return this->key_to_offset_[k - 1];
263 // Get the size of the string table. This returns the number of
264 // bytes, not in units of Stringpool_char.
265 section_size_type
266 get_strtab_size() const
268 gold_assert(this->strtab_size_ != 0);
269 return this->strtab_size_;
272 // Write the string table into the output file at the specified
273 // offset.
274 void
275 write(Output_file*, off_t offset);
277 // Write the string table into the specified buffer, of the
278 // specified size. buffer_size should be at least
279 // get_strtab_size().
280 void
281 write_to_buffer(unsigned char* buffer, section_size_type buffer_size);
283 // Dump statistical information to stderr.
284 void
285 print_stats(const char*) const;
287 private:
288 Stringpool_template(const Stringpool_template&);
289 Stringpool_template& operator=(const Stringpool_template&);
291 // Return whether two strings are equal.
292 static bool
293 string_equal(const Stringpool_char*, const Stringpool_char*);
295 // Compute a hash code for a string. LENGTH is the length of the
296 // string in characters.
297 static size_t
298 string_hash(const Stringpool_char*, size_t length);
300 // We store the actual data in a list of these buffers.
301 struct Stringdata
303 // Length of data in buffer.
304 size_t len;
305 // Allocated size of buffer.
306 size_t alc;
307 // Buffer.
308 char data[1];
311 // Add a new key offset entry.
312 void
313 new_key_offset(size_t);
315 // Copy a string into the buffers, returning a canonical string.
316 const Stringpool_char*
317 add_string(const Stringpool_char*, size_t);
319 // Return whether s1 is a suffix of s2.
320 static bool
321 is_suffix(const Stringpool_char* s1, size_t len1,
322 const Stringpool_char* s2, size_t len2);
324 // The hash table key includes the string, the length of the string,
325 // and the hash code for the string. We put the hash code
326 // explicitly into the key so that we can do a find()/insert()
327 // sequence without having to recompute the hash. Computing the
328 // hash code is a significant user of CPU time in the linker.
329 struct Hashkey
331 const Stringpool_char* string;
332 // Length is in characters, not bytes.
333 size_t length;
334 size_t hash_code;
336 // This goes in an STL container, so we need a default
337 // constructor.
338 Hashkey()
339 : string(NULL), length(0), hash_code(0)
342 // Note that these constructors are relatively expensive, because
343 // they compute the hash code.
344 explicit Hashkey(const Stringpool_char* s)
345 : string(s), length(string_length(s)), hash_code(string_hash(s, length))
348 Hashkey(const Stringpool_char* s, size_t len)
349 : string(s), length(len), hash_code(string_hash(s, len))
353 // Hash function. This is trivial, since we have already computed
354 // the hash.
355 struct Stringpool_hash
357 size_t
358 operator()(const Hashkey& hk) const
359 { return hk.hash_code; }
362 // Equality comparison function for hash table.
363 struct Stringpool_eq
365 bool
366 operator()(const Hashkey&, const Hashkey&) const;
369 // The hash table is a map from strings to Keys.
371 typedef Key Hashval;
373 typedef Unordered_map<Hashkey, Hashval, Stringpool_hash,
374 Stringpool_eq> String_set_type;
376 // Comparison routine used when sorting into a string table.
378 typedef typename String_set_type::iterator Stringpool_sort_info;
380 struct Stringpool_sort_comparison
382 bool
383 operator()(const Stringpool_sort_info&, const Stringpool_sort_info&) const;
386 // Keys map to offsets via a Chunked_vector. We only use the
387 // offsets if we turn this into an string table section.
388 typedef Chunked_vector<section_offset_type> Key_to_offset;
390 // List of Stringdata structures.
391 typedef std::list<Stringdata*> Stringdata_list;
393 // Mapping from const char* to namepool entry.
394 String_set_type string_set_;
395 // Mapping from Key to string table offset.
396 Key_to_offset key_to_offset_;
397 // List of buffers.
398 Stringdata_list strings_;
399 // Size of string table.
400 section_size_type strtab_size_;
401 // Whether to reserve offset 0 to hold the null string.
402 bool zero_null_;
403 // Whether to optimize the string table.
404 bool optimize_;
405 // offset of the next string.
406 section_offset_type offset_;
409 // The most common type of Stringpool.
410 typedef Stringpool_template<char> Stringpool;
412 } // End namespace gold.
414 #endif // !defined(GOLD_STRINGPOOL_H)