// stringpool.h -- a string pool for gold -*- C++ -*- // Copyright 2006, 2007, 2008 Free Software Foundation, Inc. // Written by Ian Lance Taylor <iant@google.com>. // This file is part of gold. // This program is free software; you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation; either version 3 of the License, or // (at your option) any later version. // This program is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // You should have received a copy of the GNU General Public License // along with this program; if not, write to the Free Software // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, // MA 02110-1301, USA. #include <string> #include <list> #include <vector> #ifndef GOLD_STRINGPOOL_H #define GOLD_STRINGPOOL_H namespace gold { class Output_file; // A Stringpool is a pool of unique strings. It provides the // following features: // Every string in the pool is unique. Thus, if you have two strings // in the Stringpool, you can compare them for equality by using // pointer comparison rather than string comparison. // There is a key associated with every string in the pool. If you // add strings to the Stringpool in the same order, then the key for // each string will always be the same for any run of the linker. // This is not true of the string pointers themselves, as they may // change due to address space randomization. Some parts of the // linker (e.g., the symbol table) use the key value instead of the // string pointer so that repeated runs of the linker will generate // precisely the same output. // When you add a string to a Stringpool, Stringpool will optionally // make a copy of it. Thus there is no requirement to keep a copy // elsewhere. // A Stringpool can be turned into a string table, a sequential series // of null terminated strings. The first string may optionally be a // single zero byte, as required for SHT_STRTAB sections. This // conversion is only permitted after all strings have been added to // the Stringpool. After doing this conversion, you can ask for the // offset of any string (or any key) in the stringpool in the string // table, and you can write the resulting string table to an output // file. // When a Stringpool is turned into a string table, then as an // optimization it will reuse string suffixes to avoid duplicating // strings. That is, given the strings "abc" and "bc", only the // string "abc" will be stored, and "bc" will be represented by an // offset into the middle of the string "abc". // A simple chunked vector class--this is a subset of std::vector // which stores memory in chunks. We don't provide iterators, because // we don't need them. template<typename Element> class Chunked_vector { public: Chunked_vector() : chunks_() { } // Clear the elements. void clear() { this->chunks_.clear(); } // Reserve elements. void reserve(unsigned int n) { n += chunk_size - 1; while (n >= chunk_size) { this->chunks_.push_back(Element_vector()); this->chunks_.back().reserve(chunk_size); n -= chunk_size; } } // Get the number of elements. size_t size() const { if (this->chunks_.empty()) return 0; else return ((this->chunks_.size() - 1) * chunk_size + this->chunks_.back().size()); } // Push a new element on the back of the vector. void push_back(const Element& element) { if (this->chunks_.empty() || this->chunks_.back().size() == chunk_size) { this->chunks_.push_back(Element_vector()); this->chunks_.back().reserve(chunk_size); } this->chunks_.back().push_back(element); } // Return a reference to an entry in the vector. Element& operator[](size_t i) { return this->chunks_[i / chunk_size][i % chunk_size]; } const Element& operator[](size_t i) const { return this->chunks_[i / chunk_size][i % chunk_size]; } private: static const unsigned int chunk_size = 8192; typedef std::vector<Element> Element_vector; typedef std::vector<Element_vector> Chunk_vector; Chunk_vector chunks_; }; // Stringpools are implemented in terms of Stringpool_template, which // is generalized on the type of character used for the strings. Most // uses will want the Stringpool type which uses char. Other cases // are used for merging wide string constants. template<typename Stringpool_char> class Stringpool_template { public: // The type of a key into the stringpool. As described above, a key // value will always be the same during any run of the linker. Zero // is never a valid key value. typedef size_t Key; // Create a Stringpool. Stringpool_template(); ~Stringpool_template(); // Clear all the data from the stringpool. void clear(); // Hint to the stringpool class that you intend to insert n additional // elements. The stringpool class can use this info however it likes; // in practice it will resize its internal hashtables to make room. void reserve(unsigned int n); // Indicate that we should not reserve offset 0 to hold the empty // string when converting the stringpool to a string table. This // should not be called for a proper ELF SHT_STRTAB section. void set_no_zero_null() { this->zero_null_ = false; } // Add the string S to the pool. This returns a canonical permanent // pointer to the string in the pool. If COPY is true, the string // is copied into permanent storage. If PKEY is not NULL, this sets // *PKEY to the key for the string. const Stringpool_char* add(const Stringpool_char* s, bool copy, Key* pkey); // Add string S of length LEN characters to the pool. If COPY is // true, S need not be null terminated. const Stringpool_char* add_with_length(const Stringpool_char* s, size_t len, bool copy, Key* pkey); // If the string S is present in the pool, return the canonical // string pointer. Otherwise, return NULL. If PKEY is not NULL, // set *PKEY to the key. const Stringpool_char* find(const Stringpool_char* s, Key* pkey) const; // Turn the stringpool into a string table: determine the offsets of // all the strings. After this is called, no more strings may be // added to the stringpool. void set_string_offsets(); // Get the offset of the string S in the string table. This returns // the offset in bytes, not in units of Stringpool_char. This may // only be called after set_string_offsets has been called. section_offset_type get_offset(const Stringpool_char* s) const; // Get the offset of the string S in the string table. section_offset_type get_offset(const std::basic_string<Stringpool_char>& s) const { return this->get_offset_with_length(s.c_str(), s.size()); } // Get the offset of string S, with length LENGTH characters, in the // string table. section_offset_type get_offset_with_length(const Stringpool_char* s, size_t length) const; // Get the offset of the string with key K. section_offset_type get_offset_from_key(Key k) const { gold_assert(k < this->key_to_offset_.size()); return this->key_to_offset_[k]; } // Get the size of the string table. This returns the number of // bytes, not in units of Stringpool_char. section_size_type get_strtab_size() const { gold_assert(this->strtab_size_ != 0); return this->strtab_size_; } // Write the string table into the output file at the specified // offset. void write(Output_file*, off_t offset); // Write the string table into the specified buffer, of the // specified size. buffer_size should be at least // get_strtab_size(). void write_to_buffer(unsigned char* buffer, section_size_type buffer_size); // Dump statistical information to stderr. void print_stats(const char*) const; private: Stringpool_template(const Stringpool_template&); Stringpool_template& operator=(const Stringpool_template&); // Return the length of a string in units of Stringpool_char. static size_t string_length(const Stringpool_char*); // Return whether two strings are equal. static bool string_equal(const Stringpool_char*, const Stringpool_char*); // Compute a hash code for a string. LENGTH is the length of the // string in characters. static size_t string_hash(const Stringpool_char*, size_t length); // We store the actual data in a list of these buffers. struct Stringdata { // Length of data in buffer. size_t len; // Allocated size of buffer. size_t alc; // Buffer. char data[1]; }; // Copy a string into the buffers, returning a canonical string. const Stringpool_char* add_string(const Stringpool_char*, size_t); // Return whether s1 is a suffix of s2. static bool is_suffix(const Stringpool_char* s1, size_t len1, const Stringpool_char* s2, size_t len2); // The hash table key includes the string, the length of the string, // and the hash code for the string. We put the hash code // explicitly into the key so that we can do a find()/insert() // sequence without having to recompute the hash. Computing the // hash code is a significant user of CPU time in the linker. struct Hashkey { const Stringpool_char* string; // Length is in characters, not bytes. size_t length; size_t hash_code; // This goes in an STL container, so we need a default // constructor. Hashkey() : string(NULL), length(0), hash_code(0) { } // Note that these constructors are relatively expensive, because // they compute the hash code. explicit Hashkey(const Stringpool_char* s) : string(s), length(string_length(s)), hash_code(string_hash(s, length)) { } Hashkey(const Stringpool_char* s, size_t len) : string(s), length(len), hash_code(string_hash(s, len)) { } }; // Hash function. This is trivial, since we have already computed // the hash. struct Stringpool_hash { size_t operator()(const Hashkey& hk) const { return hk.hash_code; } }; // Equality comparison function for hash table. struct Stringpool_eq { bool operator()(const Hashkey&, const Hashkey&) const; }; // The hash table is a map from strings to Keys. typedef Key Hashval; typedef Unordered_map<Hashkey, Hashval, Stringpool_hash, Stringpool_eq> String_set_type; // Comparison routine used when sorting into a string table. typedef typename String_set_type::iterator Stringpool_sort_info; struct Stringpool_sort_comparison { bool operator()(const Stringpool_sort_info&, const Stringpool_sort_info&) const; }; // Keys map to offsets via a Chunked_vector. We only use the // offsets if we turn this into an string table section. typedef Chunked_vector<section_offset_type> Key_to_offset; // List of Stringdata structures. typedef std::list<Stringdata*> Stringdata_list; // Mapping from const char* to namepool entry. String_set_type string_set_; // Mapping from Key to string table offset. Key_to_offset key_to_offset_; // List of buffers. Stringdata_list strings_; // Size of string table. section_size_type strtab_size_; // Whether to reserve offset 0 to hold the null string. bool zero_null_; }; // The most common type of Stringpool. typedef Stringpool_template<char> Stringpool; } // End namespace gold. #endif // !defined(GOLD_STRINGPOOL_H)