// stringpool.h -- a string pool for gold -*- C++ -*-// Copyright 2006, 2007, 2008, 2009, 2010, 2011 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_Hnamespace gold{class Output_file;// Return the length of a string in units of Char_type.template<typename Char_type>inline size_tstring_length(const Char_type* p){size_t len = 0;for (; *p != 0; ++p)++len;return len;}// Specialize string_length for char. Maybe we could just use// std::char_traits<>::length?template<>inline size_tstring_length(const char* p){return strlen(p);}// 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_(), size_(0){ }// Clear the elements.voidclear(){this->chunks_.clear();this->size_ = 0;}// Reserve elements.voidreserve(unsigned int n){if (n > this->chunks_.size() * chunk_size){this->chunks_.resize((n + chunk_size - 1) / chunk_size);// We need to call reserve() of all chunks since changing// this->chunks_ casues Element_vectors to be copied. The// reserved capacity of an Element_vector may be lost in copying.for (size_t i = 0; i < this->chunks_.size(); ++i)this->chunks_[i].reserve(chunk_size);}}// Get the number of elements.size_tsize() const{ return this->size_; }// Push a new element on the back of the vector.voidpush_back(const Element& element){size_t chunk_index = this->size_ / chunk_size;if (chunk_index >= this->chunks_.size()){this->chunks_.push_back(Element_vector());this->chunks_.back().reserve(chunk_size);gold_assert(chunk_index < this->chunks_.size());}this->chunks_[chunk_index].push_back(element);this->size_++;}// 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_;size_t size_;};// 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.voidclear();// 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.voidreserve(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.voidset_no_zero_null(){gold_assert(this->string_set_.empty()&& this->offset_ == sizeof(Stringpool_char));this->zero_null_ = false;this->offset_ = 0;}// Indicate that this string pool should be optimized, even if not// running with -O2.voidset_optimize(){ this->optimize_ = true; }// 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 the string S to the pool.const Stringpool_char*add(const std::basic_string<Stringpool_char>& s, bool copy, Key* pkey){ return this->add_with_length(s.data(), s.size(), copy, 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.voidset_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_typeget_offset(const Stringpool_char* s) const;// Get the offset of the string S in the string table.section_offset_typeget_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_typeget_offset_with_length(const Stringpool_char* s, size_t length) const;// Get the offset of the string with key K.section_offset_typeget_offset_from_key(Key k) const{gold_assert(k <= this->key_to_offset_.size());return this->key_to_offset_[k - 1];}// Get the size of the string table. This returns the number of// bytes, not in units of Stringpool_char.section_size_typeget_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.voidwrite(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().voidwrite_to_buffer(unsigned char* buffer, section_size_type buffer_size);// Dump statistical information to stderr.voidprint_stats(const char*) const;private:Stringpool_template(const Stringpool_template&);Stringpool_template& operator=(const Stringpool_template&);// Return whether two strings are equal.static boolstring_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_tstring_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];};// Add a new key offset entry.voidnew_key_offset(size_t);// 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 boolis_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_toperator()(const Hashkey& hk) const{ return hk.hash_code; }};// Equality comparison function for hash table.struct Stringpool_eq{booloperator()(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{booloperator()(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_;// Whether to optimize the string table.bool optimize_;// offset of the next string.section_offset_type offset_;};// The most common type of Stringpool.typedef Stringpool_template<char> Stringpool;} // End namespace gold.#endif // !defined(GOLD_STRINGPOOL_H)