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.
  36
  37 class Merge_map
  38 {
  39  public:
  40   Merge_map()
  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, off_t offset, off_t length,
  50               off_t output_offset);
  51
  52   // Return the output offset for an input address.  The input address
  53   // is at offset OFFSET in section SHNDX in OBJECT.  This sets
  54   // *OUTPUT_OFFSET to the offset in the output section; this will be
  55   // -1 if the bytes are not being copied to the output.  This returns
  56   // true if the mapping is known, false otherwise.
  57   bool
  58   get_output_offset(const Relobj* object, unsigned int shndx, off_t offset,
  59                     off_t *output_offset) const;
  60
  61  private:
  62   // We build a mapping from OBJECT/SHNDX/OFFSET to an offset and
  63   // length in the output section.
  64   struct Merge_key
  65   {
  66     const Relobj* object;
  67     unsigned int shndx;
  68     off_t offset;
  69   };
  70
  71   struct Merge_key_less
  72   {
  73     inline bool
  74     operator()(const Merge_key&, const Merge_key&) const;
  75   };
  76
  77   struct Merge_value
  78   {
  79     off_t length;
  80     off_t output_offset;
  81   };
  82
  83   typedef std::map<Merge_key, Merge_value, Merge_key_less> Merge_mapping;
  84
  85   // A mapping from input object/section/offset to offset in output
  86   // section.
  87   Merge_mapping merge_map_;
  88 };
  89
  90 // A general class for SHF_MERGE data, to hold functions shared by
  91 // fixed-size constant data and string data.
  92
  93 class Output_merge_base : public Output_section_data
  94 {
  95  public:
  96   Output_merge_base(uint64_t entsize, uint64_t addralign)
  97     : Output_section_data(addralign), merge_map_(), entsize_(entsize)
  98   { }
  99
 100   // Return the output offset for an input offset.
 101   bool
 102   do_output_offset(const Relobj* object, unsigned int shndx, off_t offset,
 103                    off_t* poutput) const;
 104
 105  protected:
 106   // Return the entry size.
 107   uint64_t
 108   entsize() const
 109   { return this->entsize_; }
 110
 111   // Add a mapping from an OFFSET in input section SHNDX in object
 112   // OBJECT to an OUTPUT_OFFSET in the output section.
 113   void
 114   add_mapping(Relobj* object, unsigned int shndx, off_t offset,
 115               off_t length, off_t output_offset)
 116   {
 117     this->merge_map_.add_mapping(object, shndx, offset, length, output_offset);
 118   }
 119
 120  private:
 121   // A mapping from input object/section/offset to offset in output
 122   // section.
 123   Merge_map merge_map_;
 124   // The entry size.  For fixed-size constants, this is the size of
 125   // the constants.  For strings, this is the size of a character.
 126   uint64_t entsize_;
 127 };
 128
 129 // Handle SHF_MERGE sections with fixed-size constant data.
 130
 131 class Output_merge_data : public Output_merge_base
 132 {
 133  public:
 134   Output_merge_data(uint64_t entsize, uint64_t addralign)
 135     : Output_merge_base(entsize, addralign), p_(NULL), len_(0), alc_(0),
 136       hashtable_(128, Merge_data_hash(this), Merge_data_eq(this))
 137   { }
 138
 139   // Add an input section.
 140   bool
 141   do_add_input_section(Relobj* object, unsigned int shndx);
 142
 143   // Set the final data size.
 144   void
 145   do_set_address(uint64_t, off_t);
 146
 147   // Write the data to the file.
 148   void
 149   do_write(Output_file*);
 150
 151  private:
 152   // We build a hash table of the fixed-size constants.  Each constant
 153   // is stored as a pointer into the section data we are accumulating.
 154
 155   // A key in the hash table.  This is an offset in the section
 156   // contents we are building.
 157   typedef off_t Merge_data_key;
 158
 159   // Compute the hash code.  To do this we need a pointer back to the
 160   // object holding the data.
 161   class Merge_data_hash
 162   {
 163    public:
 164     Merge_data_hash(const Output_merge_data* pomd)
 165       : pomd_(pomd)
 166     { }
 167
 168     size_t
 169     operator()(Merge_data_key) const;
 170
 171    private:
 172     const Output_merge_data* pomd_;
 173   };
 174
 175   friend class Merge_data_hash;
 176
 177   // Compare two entries in the hash table for equality.  To do this
 178   // we need a pointer back to the object holding the data.  Note that
 179   // we now have a pointer to the object stored in two places in the
 180   // hash table.  Fixing this would require specializing the hash
 181   // table, which would be hard to do portably.
 182   class Merge_data_eq
 183   {
 184    public:
 185     Merge_data_eq(const Output_merge_data* pomd)
 186       : pomd_(pomd)
 187     { }
 188
 189     bool
 190     operator()(Merge_data_key k1, Merge_data_key k2) const;
 191
 192    private:
 193     const Output_merge_data* pomd_;
 194   };
 195
 196   friend class Merge_data_eq;
 197
 198   // The type of the hash table.
 199   typedef Unordered_set<Merge_data_key, Merge_data_hash, Merge_data_eq>
 200     Merge_data_hashtable;
 201
 202   // Given a hash table key, which is just an offset into the section
 203   // data, return a pointer to the corresponding constant.
 204   const unsigned char*
 205   constant(Merge_data_key k) const
 206   {
 207     gold_assert(k >= 0 && k < this->len_);
 208     return this->p_ + k;
 209   }
 210
 211   // Add a constant to the output.
 212   void
 213   add_constant(const unsigned char*);
 214
 215   // The accumulated data.
 216   unsigned char* p_;
 217   // The length of the accumulated data.
 218   off_t len_;
 219   // The size of the allocated buffer.
 220   size_t alc_;
 221   // The hash table.
 222   Merge_data_hashtable hashtable_;
 223 };
 224
 225 // Handle SHF_MERGE sections with string data.  This is a template
 226 // based on the type of the characters in the string.
 227
 228 template<typename Char_type>
 229 class Output_merge_string : public Output_merge_base
 230 {
 231  public:
 232   Output_merge_string(uint64_t addralign)
 233     : Output_merge_base(sizeof(Char_type), addralign), stringpool_(),
 234       merged_strings_()
 235   {
 236     gold_assert(addralign <= sizeof(Char_type));
 237     this->stringpool_.set_no_zero_null();
 238   }
 239
 240   // Add an input section.
 241   bool
 242   do_add_input_section(Relobj* object, unsigned int shndx);
 243
 244   // Set the final data size.
 245   void
 246   do_set_address(uint64_t, off_t);
 247
 248   // Write the data to the file.
 249   void
 250   do_write(Output_file*);
 251
 252  private:
 253   // As we see input sections, we build a mapping from object, section
 254   // index and offset to strings.
 255   struct Merged_string
 256   {
 257     // The input object where the string was found.
 258     Relobj* object;
 259     // The input section in the input object.
 260     unsigned int shndx;
 261     // The offset in the input section.
 262     off_t offset;
 263     // The string itself, a pointer into a Stringpool.
 264     const Char_type* string;
 265     // The length of the string in bytes, including the null terminator.
 266     size_t length;
 267
 268     Merged_string(Relobj *objecta, unsigned int shndxa, off_t offseta,
 269                   const Char_type* stringa, size_t lengtha)
 270       : object(objecta), shndx(shndxa), offset(offseta), string(stringa),
 271         length(lengtha)
 272     { }
 273   };
 274
 275   typedef std::vector<Merged_string> Merged_strings;
 276
 277   // As we see the strings, we add them to a Stringpool.
 278   Stringpool_template<Char_type> stringpool_;
 279   // Map from a location in an input object to an entry in the
 280   // Stringpool.
 281   Merged_strings merged_strings_;
 282 };
 283
 284 } // End namespace gold.
 285
 286 #endif // !defined(GOLD_MERGE_H)