#include <string>
#include <list>
-// Stringpool
-// Manage a pool of unique strings.
-
#ifndef GOLD_STRINGPOOL_H
#define GOLD_STRINGPOOL_H
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.
+
+// 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. A key value will always
- // be the same during any run of the linker. The string pointers
- // may change when using address space randomization. We use key
- // values in order to get repeatable runs when the value is inserted
- // into an unordered hash table. Zero is never a valid key.
+ // 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. ZERO_NULL is true if we should reserve
- // offset 0 to hold the empty string.
+ // offset 0 to hold the empty string when converting the stringpool
+ // to a string table. ZERO_NULL should be true if you want a proper
+ // ELF SHT_STRTAB section.
Stringpool_template(bool zero_null = true);
~Stringpool_template();
- // Add a string to the pool. This returns a canonical permanent
- // pointer to the string. If PKEY is not NULL, this sets *PKEY to
- // the key for the string.
+ // Add the string S to the pool. This returns a canonical permanent
+ // pointer to the string in the pool. If PKEY is not NULL, this
+ // sets *PKEY to the key for the string.
const Stringpool_char*
- add(const Stringpool_char*, Key* pkey);
+ add(const Stringpool_char* s, Key* pkey);
+ // Add the string S to the pool.
const Stringpool_char*
add(const std::basic_string<Stringpool_char>& s, Key* pkey)
{ return this->add(s.c_str(), pkey); }
- // Add the prefix of a string to the pool.
+ // Add the prefix of length LEN of string S to the pool.
const Stringpool_char*
- add(const Stringpool_char*, size_t, Key* pkey);
+ add(const Stringpool_char* s, size_t len, Key* pkey);
- // If a string is present, return the canonical string. Otherwise,
- // return NULL. If PKEY is not NULL, set *PKEY to the key.
+ // 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*, Key* pkey) const;
+ find(const Stringpool_char* s, Key* pkey) const;
- // Turn the stringpool into an ELF strtab: determine the offsets of
- // all the strings.
+ // 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 a string in an ELF strtab. This returns the
- // offset in bytes, not characters.
+ // 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*) const;
+ 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 ELF strtab. This returns the number of
- // bytes, not characters.
+ // 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
{
return this->strtab_size_;
}
- // Write the strtab into the output file at the specified offset.
+ // Write the string table into the output file at the specified
+ // offset.
void
write(Output_file*, off_t offset);
Stringpool_template(const Stringpool_template&);
Stringpool_template& operator=(const Stringpool_template&);
- // Return the length of a string.
+ // Return the length of a string in units of Stringpool_char.
static size_t
string_length(const Stringpool_char*);
const Stringpool_char*
add_string(const Stringpool_char*, Key*);
+ // Hash function.
struct Stringpool_hash
{
size_t
operator()(const Stringpool_char*) const;
};
+ // Equality comparison function for hash table.
struct Stringpool_eq
{
bool
const Stringpool_char* s2, size_t len2);
// The hash table is a map from string names to a pair of Key and
- // ELF strtab offsets. We only use the offsets if we turn this into
- // an ELF strtab section.
+ // string table offsets. We only use the offsets if we turn this
+ // into an string table section.
typedef std::pair<Key, off_t> Val;
Stringpool_eq> String_set_type;
#endif
- // Comparison routine used when sorting into an ELF strtab. We
+ // Comparison routine used when sorting into a string table. We
// store string-sizes in the sort-vector so we don't have to
// recompute them log(n) times as we sort.
struct Stringpool_sort_info
String_set_type string_set_;
// List of buffers.
Stringdata_list strings_;
- // Size of ELF strtab.
+ // Size of string table.
off_t strtab_size_;
// Next Stringdata index.
unsigned int next_index_;
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