--- /dev/null
+// 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; }
+
+ // 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 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 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_;
+ // Whether to optimize the string table.
+ bool optimize_;
+};
+
+// The most common type of Stringpool.
+typedef Stringpool_template<char> Stringpool;
+
+} // End namespace gold.
+
+#endif // !defined(GOLD_STRINGPOOL_H)
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