| // stringpool.h -- a string pool for gold -*- C++ -*- |
| |
| // Copyright (C) 2006-2021 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; |
| |
| // Return the length of a string in units of Char_type. |
| |
| template<typename Char_type> |
| inline size_t |
| string_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_t |
| string_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. |
| void |
| clear() |
| { |
| this->chunks_.clear(); |
| this->size_ = 0; |
| } |
| |
| // Reserve elements. |
| void |
| reserve(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_ causes 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_t |
| size() const |
| { return this->size_; } |
| |
| // Push a new element on the back of the vector. |
| void |
| push_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(uint64_t addralign = 1); |
| |
| ~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() |
| { |
| 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. |
| void |
| set_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. |
| 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 - 1]; |
| } |
| |
| // 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 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]; |
| }; |
| |
| // Add a new key offset entry. |
| void |
| new_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 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_; |
| // Whether to optimize the string table. |
| bool optimize_; |
| // offset of the next string. |
| section_offset_type offset_; |
| // The alignment of strings in the stringpool. |
| uint64_t addralign_; |
| }; |
| |
| // The most common type of Stringpool. |
| typedef Stringpool_template<char> Stringpool; |
| |
| } // End namespace gold. |
| |
| #endif // !defined(GOLD_STRINGPOOL_H) |