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.  OUTPUT_OFFSET is not the offset from the start of the
  48   // output section, it is the offset from the start of the merged
  49   // data within the output section.
  50   void
  51   add_mapping(Relobj* object, unsigned int shndx,
  52               section_offset_type offset, section_size_type length,
  53               section_offset_type output_offset);
  54
  55   // Return the output offset for an input address.  The input address
  56   // is at offset OFFSET in section SHNDX in OBJECT.  This sets
  57   // *OUTPUT_OFFSET to the offset in the output section; this will be
  58   // -1 if the bytes are not being copied to the output.  This returns
  59   // true if the mapping is known, false otherwise.  This returns the
  60   // value stored by add_mapping, namely the offset from the start of
  61   // the merged data within the output section.
  62   bool
  63   get_output_offset(const Relobj* object, unsigned int shndx,
  64                     section_offset_type offset,
  65                     section_offset_type *output_offset) const;
  66 };
  67
  68 // A general class for SHF_MERGE data, to hold functions shared by
  69 // fixed-size constant data and string data.
  70
  71 class Output_merge_base : public Output_section_data
  72 {
  73  public:
  74   Output_merge_base(uint64_t entsize, uint64_t addralign)
  75     : Output_section_data(addralign), merge_map_(), entsize_(entsize)
  76   { }
  77
  78   // Return the output offset for an input offset.
  79   bool
  80   do_output_offset(const Relobj* object, unsigned int shndx,
  81                    section_offset_type offset,
  82                    section_offset_type* poutput) const;
  83
  84  protected:
  85   // Return the entry size.
  86   uint64_t
  87   entsize() const
  88   { return this->entsize_; }
  89
  90   // Add a mapping from an OFFSET in input section SHNDX in object
  91   // OBJECT to an OUTPUT_OFFSET in the output section.  OUTPUT_OFFSET
  92   // is the offset from the start of the merged data in the output
  93   // section.
  94   void
  95   add_mapping(Relobj* object, unsigned int shndx, section_offset_type offset,
  96               section_size_type length, section_offset_type output_offset)
  97   {
  98     this->merge_map_.add_mapping(object, shndx, offset, length, output_offset);
  99   }
 100
 101  private:
 102   // A mapping from input object/section/offset to offset in output
 103   // section.
 104   Merge_map merge_map_;
 105   // The entry size.  For fixed-size constants, this is the size of
 106   // the constants.  For strings, this is the size of a character.
 107   uint64_t entsize_;
 108 };
 109
 110 // Handle SHF_MERGE sections with fixed-size constant data.
 111
 112 class Output_merge_data : public Output_merge_base
 113 {
 114  public:
 115   Output_merge_data(uint64_t entsize, uint64_t addralign)
 116     : Output_merge_base(entsize, addralign), p_(NULL), len_(0), alc_(0),
 117       input_count_(0),
 118       hashtable_(128, Merge_data_hash(this), Merge_data_eq(this))
 119   { }
 120
 121  protected:
 122   // Add an input section.
 123   bool
 124   do_add_input_section(Relobj* object, unsigned int shndx);
 125
 126   // Set the final data size.
 127   void
 128   set_final_data_size();
 129
 130   // Write the data to the file.
 131   void
 132   do_write(Output_file*);
 133
 134   // Write the data to a buffer.
 135   void
 136   do_write_to_buffer(unsigned char*);
 137
 138   // Print merge stats to stderr.
 139   void
 140   do_print_merge_stats(const char* section_name);
 141
 142  private:
 143   // We build a hash table of the fixed-size constants.  Each constant
 144   // is stored as a pointer into the section data we are accumulating.
 145
 146   // A key in the hash table.  This is an offset in the section
 147   // contents we are building.
 148   typedef section_offset_type Merge_data_key;
 149
 150   // Compute the hash code.  To do this we need a pointer back to the
 151   // object holding the data.
 152   class Merge_data_hash
 153   {
 154    public:
 155     Merge_data_hash(const Output_merge_data* pomd)
 156       : pomd_(pomd)
 157     { }
 158
 159     size_t
 160     operator()(Merge_data_key) const;
 161
 162    private:
 163     const Output_merge_data* pomd_;
 164   };
 165
 166   friend class Merge_data_hash;
 167
 168   // Compare two entries in the hash table for equality.  To do this
 169   // we need a pointer back to the object holding the data.  Note that
 170   // we now have a pointer to the object stored in two places in the
 171   // hash table.  Fixing this would require specializing the hash
 172   // table, which would be hard to do portably.
 173   class Merge_data_eq
 174   {
 175    public:
 176     Merge_data_eq(const Output_merge_data* pomd)
 177       : pomd_(pomd)
 178     { }
 179
 180     bool
 181     operator()(Merge_data_key k1, Merge_data_key k2) const;
 182
 183    private:
 184     const Output_merge_data* pomd_;
 185   };
 186
 187   friend class Merge_data_eq;
 188
 189   // The type of the hash table.
 190   typedef Unordered_set<Merge_data_key, Merge_data_hash, Merge_data_eq>
 191     Merge_data_hashtable;
 192
 193   // Given a hash table key, which is just an offset into the section
 194   // data, return a pointer to the corresponding constant.
 195   const unsigned char*
 196   constant(Merge_data_key k) const
 197   {
 198     gold_assert(k >= 0 && k < static_cast<section_offset_type>(this->len_));
 199     return this->p_ + k;
 200   }
 201
 202   // Add a constant to the output.
 203   void
 204   add_constant(const unsigned char*);
 205
 206   // The accumulated data.
 207   unsigned char* p_;
 208   // The length of the accumulated data.
 209   section_size_type len_;
 210   // The size of the allocated buffer.
 211   section_size_type alc_;
 212   // The number of entries seen in input files.
 213   size_t input_count_;
 214   // The hash table.
 215   Merge_data_hashtable hashtable_;
 216 };
 217
 218 // Handle SHF_MERGE sections with string data.  This is a template
 219 // based on the type of the characters in the string.
 220
 221 template<typename Char_type>
 222 class Output_merge_string : public Output_merge_base
 223 {
 224  public:
 225   Output_merge_string(uint64_t addralign)
 226     : Output_merge_base(sizeof(Char_type), addralign), stringpool_(),
 227       merged_strings_(), input_count_(0)
 228   {
 229     gold_assert(addralign <= sizeof(Char_type));
 230     this->stringpool_.set_no_zero_null();
 231   }
 232
 233  protected:
 234   // Add an input section.
 235   bool
 236   do_add_input_section(Relobj* object, unsigned int shndx);
 237
 238   // Do all the final processing after the input sections are read in.
 239   // Returns the final data size.
 240   section_size_type
 241   finalize_merged_data();
 242
 243   // Set the final data size.
 244   void
 245   set_final_data_size();
 246
 247   // Write the data to the file.
 248   void
 249   do_write(Output_file*);
 250
 251   // Write the data to a buffer.
 252   void
 253   do_write_to_buffer(unsigned char*);
 254
 255   // Print merge stats to stderr.
 256   void
 257   do_print_merge_stats(const char* section_name);
 258
 259   // Writes the stringpool to a buffer.
 260   void
 261   stringpool_to_buffer(unsigned char* buffer, section_size_type buffer_size)
 262   { this->stringpool_.write_to_buffer(buffer, buffer_size); }
 263
 264   // Clears all the data in the stringpool, to save on memory.
 265   void
 266   clear_stringpool()
 267   { this->stringpool_.clear(); }
 268
 269  private:
 270   // The name of the string type, for stats.
 271   const char*
 272   string_name();
 273
 274   // As we see input sections, we build a mapping from object, section
 275   // index and offset to strings.
 276   struct Merged_string
 277   {
 278     // The input object where the string was found.
 279     Relobj* object;
 280     // The input section in the input object.
 281     unsigned int shndx;
 282     // The offset in the input section.
 283     section_offset_type offset;
 284     // The string itself, a pointer into a Stringpool.
 285     const Char_type* string;
 286     // The length of the string in bytes, including the null terminator.
 287     size_t length;
 288     // The key in the Stringpool.
 289     Stringpool::Key stringpool_key;
 290
 291     Merged_string(Relobj *objecta, unsigned int shndxa,
 292                   section_offset_type offseta, const Char_type* stringa,
 293                   size_t lengtha, Stringpool::Key stringpool_keya)
 294       : object(objecta), shndx(shndxa), offset(offseta), string(stringa),
 295         length(lengtha), stringpool_key(stringpool_keya)
 296     { }
 297   };
 298
 299   typedef std::vector<Merged_string> Merged_strings;
 300
 301   // As we see the strings, we add them to a Stringpool.
 302   Stringpool_template<Char_type> stringpool_;
 303   // Map from a location in an input object to an entry in the
 304   // Stringpool.
 305   Merged_strings merged_strings_;
 306   // The number of entries seen in input files.
 307   size_t input_count_;
 308 };
 309
 310 } // End namespace gold.
 311
 312 #endif // !defined(GOLD_MERGE_H)