Add support for SHF_MERGE sections.

1 files changed, 226 insertions, 0 deletions

diff --git a/gold/merge.h b/gold/merge.h
new file mode 100644
index 00000000000..dd97bf2d39e
--- /dev/null
+++ b/gold/merge.h
@@ -0,0 +1,226 @@
+// merge.h -- handle section merging for gold  -*- C++ -*-
+
+#ifndef GOLD_MERGE_H
+#define GOLD_MERGE_H
+
+#include <climits>
+
+#include "stringpool.h"
+#include "output.h"
+
+namespace gold
+{
+
+// A general class for SHF_MERGE data, to hold functions shared by
+// fixed-size constant data and string data.
+
+class Output_merge_base : public Output_section_data
+{
+ public:
+  Output_merge_base(uint64_t entsize)
+    : Output_section_data(1), merge_map_(), entsize_(entsize)
+  { }
+
+  // Return the output address for an input address.
+  bool
+  do_output_address(const Relobj* object, unsigned int shndx, off_t offset,
+		    uint64_t output_section_address, uint64_t* poutput) const;
+
+ protected:
+  // Return the entry size.
+  uint64_t
+  entsize() const
+  { return this->entsize_; }
+
+  // Add a mapping from an OFFSET in input section SHNDX in object
+  // OBJECT to an OUTPUT_OFFSET in the output section.
+  void
+  add_mapping(Relobj* object, unsigned int shndx, off_t offset,
+	      off_t output_offset);
+
+ private:
+  // We build a mapping from OBJECT/SHNDX/OFFSET to an offset in the
+  // output section.
+  struct Merge_key
+  {
+    const Relobj* object;
+    unsigned int shndx;
+    off_t offset;
+  };
+
+  struct Merge_key_less
+  {
+    bool
+    operator()(const Merge_key&, const Merge_key&) const;
+  };
+
+  typedef std::map<Merge_key, off_t, Merge_key_less> Merge_map;
+
+  // A mapping from input object/section/offset to offset in output
+  // section.
+  Merge_map merge_map_;
+
+  // The entry size.  For fixed-size constants, this is the size of
+  // the constants.  For strings, this is the size of a character.
+  uint64_t entsize_;
+};
+
+// Handle SHF_MERGE sections with fixed-size constant data.
+
+class Output_merge_data : public Output_merge_base
+{
+ public:
+  Output_merge_data(uint64_t entsize)
+    : Output_merge_base(entsize), p_(NULL), len_(0), alc_(0),
+      hashtable_(128, Merge_data_hash(this), Merge_data_eq(this))
+  { }
+
+  // Add an input section.
+  bool
+  do_add_input_section(Relobj* object, unsigned int shndx);
+
+  // Set the final data size.
+  void
+  do_set_address(uint64_t, off_t);
+
+  // Write the data to the file.
+  void
+  do_write(Output_file*);
+
+ private:
+  // We build a hash table of the fixed-size constants.  Each constant
+  // is stored as a pointer into the section data we are accumulating.
+
+  // A key in the hash table.  This is an offset in the section
+  // contents we are building.
+  typedef off_t Merge_data_key;
+
+  // Compute the hash code.  To do this we need a pointer back to the
+  // object holding the data.
+  class Merge_data_hash
+  {
+   public:
+    Merge_data_hash(const Output_merge_data* pomd)
+      : pomd_(pomd)
+    { }
+
+    size_t
+    operator()(Merge_data_key) const;
+
+   private:
+    const Output_merge_data* pomd_;
+  };
+
+  friend class Merge_data_hash;
+
+  // Compare two entries in the hash table for equality.  To do this
+  // we need a pointer back to the object holding the data.  Note that
+  // we now have a pointer to the object stored in two places in the
+  // hash table.  Fixing this would require specializing the hash
+  // table, which would be hard to do portably.
+  class Merge_data_eq
+  {
+   public:
+    Merge_data_eq(const Output_merge_data* pomd)
+      : pomd_(pomd)
+    { }
+
+    bool
+    operator()(Merge_data_key k1, Merge_data_key k2) const;
+
+   private:
+    const Output_merge_data* pomd_;
+  };
+
+  friend class Merge_data_eq;
+
+  // The type of the hash table.
+  typedef Unordered_set<Merge_data_key, Merge_data_hash, Merge_data_eq>
+    Merge_data_hashtable;
+
+  // Given a hash table key, which is just an offset into the section
+  // data, return a pointer to the corresponding constant.
+  const unsigned char*
+  constant(Merge_data_key k) const
+  {
+    gold_assert(k >= 0 && k < this->len_);
+    return this->p_ + k;
+  }
+
+  // Add a constant to the output.
+  void
+  add_constant(const unsigned char*);
+
+  // The accumulated data.
+  unsigned char* p_;
+  // The length of the accumulated data.
+  off_t len_;
+  // The size of the allocated buffer.
+  size_t alc_;
+  // The hash table.
+  Merge_data_hashtable hashtable_;
+};
+
+// Handle SHF_MERGE sections with string data.  This is a template
+// based on the type of the characters in the string.
+
+template<typename Char_type>
+class Output_merge_string : public Output_merge_base
+{
+ public:
+  Output_merge_string()
+    : Output_merge_base(sizeof(Char_type)), stringpool_(false), hashtable_()
+  { }
+
+  // Add an input section.
+  bool
+  do_add_input_section(Relobj* object, unsigned int shndx);
+
+  // Set the final data size.
+  void
+  do_set_address(uint64_t, off_t);
+
+  // Write the data to the file.
+  void
+  do_write(Output_file*);
+
+ private:
+  // As we see input sections, we build a mapping from object, section
+  // index and offset to strings.
+  struct Merge_string_key
+  {
+    Relobj* object;
+    unsigned int shndx;
+    off_t offset;
+
+    Merge_string_key(Relobj *objecta, unsigned int shndxa, off_t offseta)
+      : object(objecta), shndx(shndxa), offset(offseta)
+    { }
+  };
+
+  struct Merge_string_key_hash
+  {
+    size_t
+    operator()(const Merge_string_key&) const;
+  };
+
+  struct Merge_string_key_eq
+  {
+    bool
+    operator()(const Merge_string_key&, const Merge_string_key&) const;
+  };
+
+  typedef Unordered_map<Merge_string_key, const Char_type*,
+			Merge_string_key_hash, Merge_string_key_eq>
+    Merge_string_hashtable;
+
+  // As we see the strings, we add them to a Stringpool.
+  Stringpool_template<Char_type> stringpool_;
+  // Map from a location in an input object to an entry in the
+  // Stringpool.
+  Merge_string_hashtable hashtable_;
+};
+
+} // End namespace gold.
+
+#endif // !defined(GOLD_MERGE_H)