| 1 | // stringpool.h -- a string pool for gold -*- C++ -*- |
| 2 | |
| 3 | // Copyright 2006, 2007 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 <string> |
| 24 | #include <list> |
| 25 | |
| 26 | #ifndef GOLD_STRINGPOOL_H |
| 27 | #define GOLD_STRINGPOOL_H |
| 28 | |
| 29 | namespace gold |
| 30 | { |
| 31 | |
| 32 | class Output_file; |
| 33 | |
| 34 | // A Stringpool is a pool of unique strings. It provides the |
| 35 | // following features: |
| 36 | |
| 37 | // Every string in the pool is unique. Thus, if you have two strings |
| 38 | // in the Stringpool, you can compare them for equality by using |
| 39 | // pointer comparison rather than string comparison. |
| 40 | |
| 41 | // There is a key associated with every string in the pool. If you |
| 42 | // add strings to the Stringpool in the same order, then the key for |
| 43 | // each string will always be the same for any run of the linker. |
| 44 | // This is not true of the string pointers themselves, as they may |
| 45 | // change due to address space randomization. Some parts of the |
| 46 | // linker (e.g., the symbol table) use the key value instead of the |
| 47 | // string pointer so that repeated runs of the linker will generate |
| 48 | // precisely the same output. |
| 49 | |
| 50 | // When you add a string to a Stringpool, Stringpool will optionally |
| 51 | // make a copy of it. Thus there is no requirement to keep a copy |
| 52 | // elsewhere. |
| 53 | |
| 54 | // A Stringpool can be turned into a string table, a sequential series |
| 55 | // of null terminated strings. The first string may optionally be a |
| 56 | // single zero byte, as required for SHT_STRTAB sections. This |
| 57 | // conversion is only permitted after all strings have been added to |
| 58 | // the Stringpool. After doing this conversion, you can ask for the |
| 59 | // offset of any string in the stringpool in the string table, and you |
| 60 | // can write the resulting string table to an output file. |
| 61 | |
| 62 | // When a Stringpool is turned into a string table, then as an |
| 63 | // optimization it will reuse string suffixes to avoid duplicating |
| 64 | // strings. That is, given the strings "abc" and "bc", only the |
| 65 | // string "abc" will be stored, and "bc" will be represented by an |
| 66 | // offset into the middle of the string "abc". |
| 67 | |
| 68 | // Stringpools are implemented in terms of Stringpool_template, which |
| 69 | // is generalized on the type of character used for the strings. Most |
| 70 | // uses will want the Stringpool type which uses char. Other cases |
| 71 | // are used for merging wide string constants. |
| 72 | |
| 73 | template<typename Stringpool_char> |
| 74 | class Stringpool_template |
| 75 | { |
| 76 | public: |
| 77 | // The type of a key into the stringpool. As described above, a key |
| 78 | // value will always be the same during any run of the linker. Zero |
| 79 | // is never a valid key value. |
| 80 | typedef size_t Key; |
| 81 | |
| 82 | // Create a Stringpool. |
| 83 | Stringpool_template(); |
| 84 | |
| 85 | ~Stringpool_template(); |
| 86 | |
| 87 | // Indicate that we should not reserve offset 0 to hold the empty |
| 88 | // string when converting the stringpool to a string table. This |
| 89 | // should not be called for a proper ELF SHT_STRTAB section. |
| 90 | void |
| 91 | set_no_zero_null() |
| 92 | { this->zero_null_ = false; } |
| 93 | |
| 94 | // Add the string S to the pool. This returns a canonical permanent |
| 95 | // pointer to the string in the pool. If COPY is true, the string |
| 96 | // is copied into permanent storage. If PKEY is not NULL, this sets |
| 97 | // *PKEY to the key for the string. |
| 98 | const Stringpool_char* |
| 99 | add(const Stringpool_char* s, bool copy, Key* pkey); |
| 100 | |
| 101 | // Add the prefix of length LEN of string S to the pool. |
| 102 | const Stringpool_char* |
| 103 | add_prefix(const Stringpool_char* s, size_t len, Key* pkey); |
| 104 | |
| 105 | // If the string S is present in the pool, return the canonical |
| 106 | // string pointer. Otherwise, return NULL. If PKEY is not NULL, |
| 107 | // set *PKEY to the key. |
| 108 | const Stringpool_char* |
| 109 | find(const Stringpool_char* s, Key* pkey) const; |
| 110 | |
| 111 | // Turn the stringpool into a string table: determine the offsets of |
| 112 | // all the strings. After this is called, no more strings may be |
| 113 | // added to the stringpool. |
| 114 | void |
| 115 | set_string_offsets(); |
| 116 | |
| 117 | // Get the offset of the string S in the string table. This returns |
| 118 | // the offset in bytes, not in units of Stringpool_char. This may |
| 119 | // only be called after set_string_offsets has been called. |
| 120 | off_t |
| 121 | get_offset(const Stringpool_char* s) const; |
| 122 | |
| 123 | // Get the offset of the string S in the string table. |
| 124 | off_t |
| 125 | get_offset(const std::basic_string<Stringpool_char>& s) const |
| 126 | { return this->get_offset(s.c_str()); } |
| 127 | |
| 128 | // Get the size of the string table. This returns the number of |
| 129 | // bytes, not in units of Stringpool_char. |
| 130 | off_t |
| 131 | get_strtab_size() const |
| 132 | { |
| 133 | gold_assert(this->strtab_size_ != 0); |
| 134 | return this->strtab_size_; |
| 135 | } |
| 136 | |
| 137 | // Write the string table into the output file at the specified |
| 138 | // offset. |
| 139 | void |
| 140 | write(Output_file*, off_t offset); |
| 141 | |
| 142 | private: |
| 143 | Stringpool_template(const Stringpool_template&); |
| 144 | Stringpool_template& operator=(const Stringpool_template&); |
| 145 | |
| 146 | // Return the length of a string in units of Stringpool_char. |
| 147 | static size_t |
| 148 | string_length(const Stringpool_char*); |
| 149 | |
| 150 | // We store the actual data in a list of these buffers. |
| 151 | struct Stringdata |
| 152 | { |
| 153 | // Length of data in buffer. |
| 154 | size_t len; |
| 155 | // Allocated size of buffer. |
| 156 | size_t alc; |
| 157 | // Buffer index. |
| 158 | unsigned int index; |
| 159 | // Buffer. |
| 160 | char data[1]; |
| 161 | }; |
| 162 | |
| 163 | // Copy a string into the buffers, returning a canonical string. |
| 164 | const Stringpool_char* |
| 165 | add_string(const Stringpool_char*, Key*); |
| 166 | |
| 167 | // Hash function. |
| 168 | struct Stringpool_hash |
| 169 | { |
| 170 | size_t |
| 171 | operator()(const Stringpool_char*) const; |
| 172 | }; |
| 173 | |
| 174 | // Equality comparison function for hash table. |
| 175 | struct Stringpool_eq |
| 176 | { |
| 177 | bool |
| 178 | operator()(const Stringpool_char* p1, const Stringpool_char* p2) const; |
| 179 | }; |
| 180 | |
| 181 | // Return whether s1 is a suffix of s2. |
| 182 | static bool |
| 183 | is_suffix(const Stringpool_char* s1, size_t len1, |
| 184 | const Stringpool_char* s2, size_t len2); |
| 185 | |
| 186 | // The hash table is a map from string names to a pair of Key and |
| 187 | // string table offsets. We only use the offsets if we turn this |
| 188 | // into an string table section. |
| 189 | |
| 190 | typedef std::pair<Key, off_t> Val; |
| 191 | |
| 192 | #ifdef HAVE_TR1_UNORDERED_SET |
| 193 | typedef Unordered_map<const Stringpool_char*, Val, Stringpool_hash, |
| 194 | Stringpool_eq, |
| 195 | std::allocator<std::pair<const Stringpool_char* const, |
| 196 | Val> >, |
| 197 | true> String_set_type; |
| 198 | #else |
| 199 | typedef Unordered_map<const Stringpool_char*, Val, Stringpool_hash, |
| 200 | Stringpool_eq> String_set_type; |
| 201 | #endif |
| 202 | |
| 203 | // Comparison routine used when sorting into a string table. We |
| 204 | // store string-sizes in the sort-vector so we don't have to |
| 205 | // recompute them log(n) times as we sort. |
| 206 | struct Stringpool_sort_info |
| 207 | { |
| 208 | typename String_set_type::iterator it; |
| 209 | size_t string_length; |
| 210 | Stringpool_sort_info(typename String_set_type::iterator i, size_t s) |
| 211 | : it(i), string_length(s) |
| 212 | { } |
| 213 | }; |
| 214 | |
| 215 | struct Stringpool_sort_comparison |
| 216 | { |
| 217 | bool |
| 218 | operator()(const Stringpool_sort_info&, const Stringpool_sort_info&) const; |
| 219 | }; |
| 220 | |
| 221 | // List of Stringdata structures. |
| 222 | typedef std::list<Stringdata*> Stringdata_list; |
| 223 | |
| 224 | // Mapping from const char* to namepool entry. |
| 225 | String_set_type string_set_; |
| 226 | // List of buffers. |
| 227 | Stringdata_list strings_; |
| 228 | // Size of string table. |
| 229 | off_t strtab_size_; |
| 230 | // Next Stringdata index. |
| 231 | unsigned int next_index_; |
| 232 | // Next key value for a string we don't copy. |
| 233 | int next_uncopied_key_; |
| 234 | // Whether to reserve offset 0 to hold the null string. |
| 235 | bool zero_null_; |
| 236 | }; |
| 237 | |
| 238 | // The most common type of Stringpool. |
| 239 | typedef Stringpool_template<char> Stringpool; |
| 240 | |
| 241 | } // End namespace gold. |
| 242 | |
| 243 | #endif // !defined(GOLD_STRINGPOOL_H) |