binutils-gdb/gold/stringpool.h

288 lines
9.3 KiB
C++

// stringpool.h -- a string pool for gold -*- C++ -*-
// Copyright 2006, 2007 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>
#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 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".
// 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 the prefix of length LEN of string S to the pool.
const Stringpool_char*
add_prefix(const Stringpool_char* s, size_t len, 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.
off_t
get_offset(const Stringpool_char* s) const;
// Get the offset of the string S in the string table.
off_t
get_offset(const std::basic_string<Stringpool_char>& s) const
{ return this->get_offset(s.c_str()); }
// Get the size of the string table. This returns the number of
// bytes, not in units of Stringpool_char.
off_t
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, size_t 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 index.
unsigned int index;
// Buffer.
char data[1];
};
// Copy a string into the buffers, returning a canonical string.
const Stringpool_char*
add_string(const Stringpool_char*, size_t, Key*);
// 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.
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 a pair of Key and string
// table offsets. We only use the offsets if we turn this into an
// string table section.
typedef std::pair<Key, off_t> 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;
};
// List of Stringdata structures.
typedef std::list<Stringdata*> Stringdata_list;
// Mapping from const char* to namepool entry.
String_set_type string_set_;
// List of buffers.
Stringdata_list strings_;
// Size of string table.
off_t strtab_size_;
// Next Stringdata index.
unsigned int next_index_;
// Next key value for a string we don't copy.
int next_uncopied_key_;
// 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)