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, 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
  62 // A general class for SHF_MERGE data, to hold functions shared by
  63 // fixed-size constant data and string data.
  64
  65 class Output_merge_base : public Output_section_data
  66 {
  67  public:
  68   Output_merge_base(uint64_t entsize, uint64_t addralign)
  69     : Output_section_data(addralign), merge_map_(), entsize_(entsize)
  70   { }
  71
  72   // Return the output offset for an input offset.
  73   bool
  74   do_output_offset(const Relobj* object, unsigned int shndx, off_t offset,
  75                    off_t* poutput) const;
  76
  77  protected:
  78   // Return the entry size.
  79   uint64_t
  80   entsize() const
  81   { return this->entsize_; }
  82
  83   // Add a mapping from an OFFSET in input section SHNDX in object
  84   // OBJECT to an OUTPUT_OFFSET in the output section.
  85   void
  86   add_mapping(Relobj* object, unsigned int shndx, off_t offset,
  87               off_t length, off_t output_offset)
  88   {
  89     this->merge_map_.add_mapping(object, shndx, offset, length, output_offset);
  90   }
  91
  92  private:
  93   // A mapping from input object/section/offset to offset in output
  94   // section.
  95   Merge_map merge_map_;
  96   // The entry size.  For fixed-size constants, this is the size of
  97   // the constants.  For strings, this is the size of a character.
  98   uint64_t entsize_;
  99 };
 100
 101 // Handle SHF_MERGE sections with fixed-size constant data.
 102
 103 class Output_merge_data : public Output_merge_base
 104 {
 105  public:
 106   Output_merge_data(uint64_t entsize, uint64_t addralign)
 107     : Output_merge_base(entsize, addralign), p_(NULL), len_(0), alc_(0),
 108       hashtable_(128, Merge_data_hash(this), Merge_data_eq(this))
 109   { }
 110
 111   // Add an input section.
 112   bool
 113   do_add_input_section(Relobj* object, unsigned int shndx);
 114
 115   // Set the final data size.
 116   void
 117   do_set_address(uint64_t, off_t);
 118
 119   // Write the data to the file.
 120   void
 121   do_write(Output_file*);
 122
 123  private:
 124   // We build a hash table of the fixed-size constants.  Each constant
 125   // is stored as a pointer into the section data we are accumulating.
 126
 127   // A key in the hash table.  This is an offset in the section
 128   // contents we are building.
 129   typedef off_t Merge_data_key;
 130
 131   // Compute the hash code.  To do this we need a pointer back to the
 132   // object holding the data.
 133   class Merge_data_hash
 134   {
 135    public:
 136     Merge_data_hash(const Output_merge_data* pomd)
 137       : pomd_(pomd)
 138     { }
 139
 140     size_t
 141     operator()(Merge_data_key) const;
 142
 143    private:
 144     const Output_merge_data* pomd_;
 145   };
 146
 147   friend class Merge_data_hash;
 148
 149   // Compare two entries in the hash table for equality.  To do this
 150   // we need a pointer back to the object holding the data.  Note that
 151   // we now have a pointer to the object stored in two places in the
 152   // hash table.  Fixing this would require specializing the hash
 153   // table, which would be hard to do portably.
 154   class Merge_data_eq
 155   {
 156    public:
 157     Merge_data_eq(const Output_merge_data* pomd)
 158       : pomd_(pomd)
 159     { }
 160
 161     bool
 162     operator()(Merge_data_key k1, Merge_data_key k2) const;
 163
 164    private:
 165     const Output_merge_data* pomd_;
 166   };
 167
 168   friend class Merge_data_eq;
 169
 170   // The type of the hash table.
 171   typedef Unordered_set<Merge_data_key, Merge_data_hash, Merge_data_eq>
 172     Merge_data_hashtable;
 173
 174   // Given a hash table key, which is just an offset into the section
 175   // data, return a pointer to the corresponding constant.
 176   const unsigned char*
 177   constant(Merge_data_key k) const
 178   {
 179     gold_assert(k >= 0 && k < this->len_);
 180     return this->p_ + k;
 181   }
 182
 183   // Add a constant to the output.
 184   void
 185   add_constant(const unsigned char*);
 186
 187   // The accumulated data.
 188   unsigned char* p_;
 189   // The length of the accumulated data.
 190   off_t len_;
 191   // The size of the allocated buffer.
 192   size_t alc_;
 193   // The hash table.
 194   Merge_data_hashtable hashtable_;
 195 };
 196
 197 // Handle SHF_MERGE sections with string data.  This is a template
 198 // based on the type of the characters in the string.
 199
 200 template<typename Char_type>
 201 class Output_merge_string : public Output_merge_base
 202 {
 203  public:
 204   Output_merge_string(uint64_t addralign)
 205     : Output_merge_base(sizeof(Char_type), addralign), stringpool_(),
 206       merged_strings_()
 207   {
 208     gold_assert(addralign <= sizeof(Char_type));
 209     this->stringpool_.set_no_zero_null();
 210   }
 211
 212   // Add an input section.
 213   bool
 214   do_add_input_section(Relobj* object, unsigned int shndx);
 215
 216   // Set the final data size.
 217   void
 218   do_set_address(uint64_t, off_t);
 219
 220   // Write the data to the file.
 221   void
 222   do_write(Output_file*);
 223
 224  private:
 225   // As we see input sections, we build a mapping from object, section
 226   // index and offset to strings.
 227   struct Merged_string
 228   {
 229     // The input object where the string was found.
 230     Relobj* object;
 231     // The input section in the input object.
 232     unsigned int shndx;
 233     // The offset in the input section.
 234     off_t offset;
 235     // The string itself, a pointer into a Stringpool.
 236     const Char_type* string;
 237     // The length of the string in bytes, including the null terminator.
 238     size_t length;
 239
 240     Merged_string(Relobj *objecta, unsigned int shndxa, off_t offseta,
 241                   const Char_type* stringa, size_t lengtha)
 242       : object(objecta), shndx(shndxa), offset(offseta), string(stringa),
 243         length(lengtha)
 244     { }
 245   };
 246
 247   typedef std::vector<Merged_string> Merged_strings;
 248
 249   // As we see the strings, we add them to a Stringpool.
 250   Stringpool_template<Char_type> stringpool_;
 251   // Map from a location in an input object to an entry in the
 252   // Stringpool.
 253   Merged_strings merged_strings_;
 254 };
 255
 256 } // End namespace gold.
 257
 258 #endif // !defined(GOLD_MERGE_H)