gold/merge.h

   1 // merge.h -- handle section merging for gold  -*- C++ -*-
   2
   3 // Copyright 2006, 2007 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of gold.
   7
   8 // This program is free software; you can redistribute it and/or modify
   9 // it under the terms of the GNU General Public License as published by
  10 // the Free Software Foundation; either version 3 of the License, or
  11 // (at your option) any later version.
  12
  13 // This program is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17
  18 // You should have received a copy of the GNU General Public License
  19 // along with this program; if not, write to the Free Software
  20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21 // MA 02110-1301, USA.
  22
  23 #ifndef GOLD_MERGE_H
  24 #define GOLD_MERGE_H
  25
  26 #include <climits>
  27
  28 #include "stringpool.h"
  29 #include "output.h"
  30
  31 namespace gold
  32 {
  33
  34 // This class manages mappings from input sections to offsets in an
  35 // output section.  This is used where input sections are merged.  The
  36 // actual data is stored in fields in Object.
  37
  38 class Merge_map
  39 {
  40  public:
  41   Merge_map()
  42   { }
  43
  44   // Add a mapping for the bytes from OFFSET to OFFSET + LENGTH in the
  45   // input section SHNDX in object OBJECT to OUTPUT_OFFSET in the
  46   // output section.  An OUTPUT_OFFSET of -1 means that the bytes are
  47   // discarded.
  48   void
  49   add_mapping(Relobj* object, unsigned int shndx,
  50               section_offset_type offset, section_size_type length,
  51               section_offset_type output_offset);
  52
  53   // Return the output offset for an input address.  The input address
  54   // is at offset OFFSET in section SHNDX in OBJECT.  This sets
  55   // *OUTPUT_OFFSET to the offset in the output section; this will be
  56   // -1 if the bytes are not being copied to the output.  This returns
  57   // true if the mapping is known, false otherwise.
  58   bool
  59   get_output_offset(const Relobj* object, unsigned int shndx,
  60                     section_offset_type offset,
  61                     section_offset_type *output_offset) const;
  62 };
  63
  64 // A general class for SHF_MERGE data, to hold functions shared by
  65 // fixed-size constant data and string data.
  66
  67 class Output_merge_base : public Output_section_data
  68 {
  69  public:
  70   Output_merge_base(uint64_t entsize, uint64_t addralign)
  71     : Output_section_data(addralign), merge_map_(), entsize_(entsize)
  72   { }
  73
  74   // Return the output offset for an input offset.
  75   bool
  76   do_output_offset(const Relobj* object, unsigned int shndx,
  77                    section_offset_type offset,
  78                    section_offset_type* poutput) const;
  79
  80  protected:
  81   // Return the entry size.
  82   uint64_t
  83   entsize() const
  84   { return this->entsize_; }
  85
  86   // Add a mapping from an OFFSET in input section SHNDX in object
  87   // OBJECT to an OUTPUT_OFFSET in the output section.
  88   void
  89   add_mapping(Relobj* object, unsigned int shndx, section_offset_type offset,
  90               section_size_type length, section_offset_type output_offset)
  91   {
  92     this->merge_map_.add_mapping(object, shndx, offset, length, output_offset);
  93   }
  94
  95  private:
  96   // A mapping from input object/section/offset to offset in output
  97   // section.
  98   Merge_map merge_map_;
  99   // The entry size.  For fixed-size constants, this is the size of
 100   // the constants.  For strings, this is the size of a character.
 101   uint64_t entsize_;
 102 };
 103
 104 // Handle SHF_MERGE sections with fixed-size constant data.
 105
 106 class Output_merge_data : public Output_merge_base
 107 {
 108  public:
 109   Output_merge_data(uint64_t entsize, uint64_t addralign)
 110     : Output_merge_base(entsize, addralign), p_(NULL), len_(0), alc_(0),
 111       input_count_(0),
 112       hashtable_(128, Merge_data_hash(this), Merge_data_eq(this))
 113   { }
 114
 115  protected:
 116   // Add an input section.
 117   bool
 118   do_add_input_section(Relobj* object, unsigned int shndx);
 119
 120   // Set the final data size.
 121   void
 122   set_final_data_size();
 123
 124   // Write the data to the file.
 125   void
 126   do_write(Output_file*);
 127
 128   // Write the data to a buffer.
 129   void
 130   do_write_to_buffer(unsigned char*);
 131
 132   // Print merge stats to stderr.
 133   void
 134   do_print_merge_stats(const char* section_name);
 135
 136  private:
 137   // We build a hash table of the fixed-size constants.  Each constant
 138   // is stored as a pointer into the section data we are accumulating.
 139
 140   // A key in the hash table.  This is an offset in the section
 141   // contents we are building.
 142   typedef section_offset_type Merge_data_key;
 143
 144   // Compute the hash code.  To do this we need a pointer back to the
 145   // object holding the data.
 146   class Merge_data_hash
 147   {
 148    public:
 149     Merge_data_hash(const Output_merge_data* pomd)
 150       : pomd_(pomd)
 151     { }
 152
 153     size_t
 154     operator()(Merge_data_key) const;
 155
 156    private:
 157     const Output_merge_data* pomd_;
 158   };
 159
 160   friend class Merge_data_hash;
 161
 162   // Compare two entries in the hash table for equality.  To do this
 163   // we need a pointer back to the object holding the data.  Note that
 164   // we now have a pointer to the object stored in two places in the
 165   // hash table.  Fixing this would require specializing the hash
 166   // table, which would be hard to do portably.
 167   class Merge_data_eq
 168   {
 169    public:
 170     Merge_data_eq(const Output_merge_data* pomd)
 171       : pomd_(pomd)
 172     { }
 173
 174     bool
 175     operator()(Merge_data_key k1, Merge_data_key k2) const;
 176
 177    private:
 178     const Output_merge_data* pomd_;
 179   };
 180
 181   friend class Merge_data_eq;
 182
 183   // The type of the hash table.
 184   typedef Unordered_set<Merge_data_key, Merge_data_hash, Merge_data_eq>
 185     Merge_data_hashtable;
 186
 187   // Given a hash table key, which is just an offset into the section
 188   // data, return a pointer to the corresponding constant.
 189   const unsigned char*
 190   constant(Merge_data_key k) const
 191   {
 192     gold_assert(k >= 0 && k < static_cast<section_offset_type>(this->len_));
 193     return this->p_ + k;
 194   }
 195
 196   // Add a constant to the output.
 197   void
 198   add_constant(const unsigned char*);
 199
 200   // The accumulated data.
 201   unsigned char* p_;
 202   // The length of the accumulated data.
 203   section_size_type len_;
 204   // The size of the allocated buffer.
 205   section_size_type alc_;
 206   // The number of entries seen in input files.
 207   size_t input_count_;
 208   // The hash table.
 209   Merge_data_hashtable hashtable_;
 210 };
 211
 212 // Handle SHF_MERGE sections with string data.  This is a template
 213 // based on the type of the characters in the string.
 214
 215 template<typename Char_type>
 216 class Output_merge_string : public Output_merge_base
 217 {
 218  public:
 219   Output_merge_string(uint64_t addralign)
 220     : Output_merge_base(sizeof(Char_type), addralign), stringpool_(),
 221       merged_strings_(), input_count_(0)
 222   {
 223     gold_assert(addralign <= sizeof(Char_type));
 224     this->stringpool_.set_no_zero_null();
 225   }
 226
 227  protected:
 228   // Add an input section.
 229   bool
 230   do_add_input_section(Relobj* object, unsigned int shndx);
 231
 232   // Do all the final processing after the input sections are read in.
 233   // Returns the final data size.
 234   section_size_type
 235   finalize_merged_data();
 236
 237   // Set the final data size.
 238   void
 239   set_final_data_size();
 240
 241   // Write the data to the file.
 242   void
 243   do_write(Output_file*);
 244
 245   // Write the data to a buffer.
 246   void
 247   do_write_to_buffer(unsigned char*);
 248
 249   // Print merge stats to stderr.
 250   void
 251   do_print_merge_stats(const char* section_name);
 252
 253   // Writes the stringpool to a buffer.
 254   void
 255   stringpool_to_buffer(unsigned char* buffer, section_size_type buffer_size)
 256   { this->stringpool_.write_to_buffer(buffer, buffer_size); }
 257
 258   // Clears all the data in the stringpool, to save on memory.
 259   void
 260   clear_stringpool()
 261   { this->stringpool_.clear(); }
 262
 263  private:
 264   // The name of the string type, for stats.
 265   const char*
 266   string_name();
 267
 268   // As we see input sections, we build a mapping from object, section
 269   // index and offset to strings.
 270   struct Merged_string
 271   {
 272     // The input object where the string was found.
 273     Relobj* object;
 274     // The input section in the input object.
 275     unsigned int shndx;
 276     // The offset in the input section.
 277     section_offset_type offset;
 278     // The string itself, a pointer into a Stringpool.
 279     const Char_type* string;
 280     // The length of the string in bytes, including the null terminator.
 281     size_t length;
 282
 283     Merged_string(Relobj *objecta, unsigned int shndxa,
 284                   section_offset_type offseta, const Char_type* stringa,
 285                   size_t lengtha)
 286       : object(objecta), shndx(shndxa), offset(offseta), string(stringa),
 287         length(lengtha)
 288     { }
 289   };
 290
 291   typedef std::vector<Merged_string> Merged_strings;
 292
 293   // As we see the strings, we add them to a Stringpool.
 294   Stringpool_template<Char_type> stringpool_;
 295   // Map from a location in an input object to an entry in the
 296   // Stringpool.
 297   Merged_strings merged_strings_;
 298   // The number of entries seen in input files.
 299   size_t input_count_;
 300 };
 301
 302 } // End namespace gold.
 303
 304 #endif // !defined(GOLD_MERGE_H)