gold/reduced_debug_output.cc

   1 // reduced_debug_output.cc -- output reduced debugging information to save space
   2
   3 // Copyright (C) 2008-2024 Free Software Foundation, Inc.
   4 // Written by Caleb Howe <cshowe@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 #include "gold.h"
  24
  25 #include "parameters.h"
  26 #include "options.h"
  27 #include "dwarf.h"
  28 #include "dwarf_reader.h"
  29 #include "reduced_debug_output.h"
  30 #include "int_encoding.h"
  31
  32 #include <vector>
  33
  34 namespace gold
  35 {
  36
  37 // Given a pointer to the beginning of a die and the beginning of the associated
  38 // abbreviation fills in die_end with the end of the information entry.  If
  39 // successful returns true.  Get_die_end also takes a pointer to the end of the
  40 // buffer containing the die.  If die_end would be beyond the end of the
  41 // buffer, or if an unsupported dwarf form is encountered returns false.
  42 bool
  43 Output_reduced_debug_info_section::get_die_end(
  44     unsigned char* die, unsigned char* abbrev, unsigned char** die_end,
  45     unsigned char* buffer_end, int address_size, bool is64)
  46 {
  47   size_t LEB_size;
  48   uint64_t LEB_decoded;
  49   for(;;)
  50     {
  51       uint64_t attribute = read_unsigned_LEB_128(abbrev, &LEB_size);
  52       abbrev += LEB_size;
  53       elfcpp::DW_FORM form =
  54           static_cast<elfcpp::DW_FORM>(read_unsigned_LEB_128(abbrev,
  55                                                              &LEB_size));
  56       abbrev += LEB_size;
  57       if (!(attribute || form))
  58         break;
  59       if (die >= buffer_end)
  60         return false;
  61       switch(form)
  62         {
  63           case elfcpp::DW_FORM_flag_present:
  64             break;
  65           case elfcpp::DW_FORM_strp:
  66           case elfcpp::DW_FORM_sec_offset:
  67             die += is64 ? 8 : 4;
  68             break;
  69           case elfcpp::DW_FORM_addr:
  70           case elfcpp::DW_FORM_ref_addr:
  71             die += address_size;
  72             break;
  73           case elfcpp::DW_FORM_block1:
  74             die += *die;
  75             die += 1;
  76             break;
  77           case elfcpp::DW_FORM_block2:
  78             {
  79               uint16_t block_size;
  80               block_size = read_from_pointer<16>(&die);
  81               die += block_size;
  82               break;
  83             }
  84           case elfcpp::DW_FORM_block4:
  85             {
  86               uint32_t block_size;
  87               block_size = read_from_pointer<32>(&die);
  88               die += block_size;
  89               break;
  90             }
  91           case elfcpp::DW_FORM_block:
  92           case elfcpp::DW_FORM_exprloc:
  93             LEB_decoded = read_unsigned_LEB_128(die, &LEB_size);
  94             die += (LEB_decoded + LEB_size);
  95             break;
  96           case elfcpp::DW_FORM_data1:
  97           case elfcpp::DW_FORM_ref1:
  98           case elfcpp::DW_FORM_flag:
  99             die += 1;
 100             break;
 101           case elfcpp::DW_FORM_data2:
 102           case elfcpp::DW_FORM_ref2:
 103             die += 2;
 104             break;
 105           case elfcpp::DW_FORM_data4:
 106           case elfcpp::DW_FORM_ref4:
 107             die += 4;
 108             break;
 109           case elfcpp::DW_FORM_data8:
 110           case elfcpp::DW_FORM_ref8:
 111           case elfcpp::DW_FORM_ref_sig8:
 112             die += 8;
 113             break;
 114           case elfcpp::DW_FORM_ref_udata:
 115           case elfcpp::DW_FORM_udata:
 116             read_unsigned_LEB_128(die, &LEB_size);
 117             die += LEB_size;
 118             break;
 119           case elfcpp::DW_FORM_sdata:
 120             read_signed_LEB_128(die, &LEB_size);
 121             die += LEB_size;
 122             break;
 123           case elfcpp::DW_FORM_string:
 124             {
 125               size_t length = strlen(reinterpret_cast<char*>(die));
 126               die += length + 1;
 127               break;
 128             }
 129           case elfcpp::DW_FORM_indirect:
 130           case elfcpp::DW_FORM_GNU_addr_index:
 131           case elfcpp::DW_FORM_GNU_str_index:
 132           default:
 133             return false;
 134       }
 135     }
 136   *die_end = die;
 137   return true;
 138 }
 139
 140 void
 141 Output_reduced_debug_abbrev_section::set_final_data_size()
 142 {
 143   if (this->sized_ || this->failed_)
 144     return;
 145
 146   uint64_t abbrev_number;
 147   size_t LEB_size;
 148   unsigned char* abbrev_data = this->postprocessing_buffer();
 149   unsigned char* abbrev_end = this->postprocessing_buffer() +
 150                               this->postprocessing_buffer_size();
 151   this->write_to_postprocessing_buffer();
 152   while(abbrev_data < abbrev_end)
 153     {
 154       uint64_t abbrev_offset = abbrev_data - this->postprocessing_buffer();
 155       while((abbrev_number = read_unsigned_LEB_128(abbrev_data, &LEB_size)))
 156         {
 157           if (abbrev_data >= abbrev_end)
 158             {
 159               failed("Debug abbreviations extend beyond .debug_abbrev "
 160                      "section; failed to reduce debug abbreviations");
 161               return;
 162             }
 163           abbrev_data += LEB_size;
 164
 165           // Together with the abbreviation number these fields make up
 166           // the header for each abbreviation.
 167           uint64_t abbrev_type = read_unsigned_LEB_128(abbrev_data, &LEB_size);
 168           abbrev_data += LEB_size;
 169
 170           // This would ordinarily be the has_children field of the
 171           // abbreviation.  But it's going to be false after reducing the
 172           // information, so there's no point in storing it.
 173           abbrev_data++;
 174
 175           // Read to the end of the current abbreviation.
 176           // This is indicated by two zero unsigned LEBs in a row.  We don't
 177           // need to parse the data yet, so we just scan through the data
 178           // looking for two consecutive 0 bytes indicating the end of the
 179           // abbreviation.
 180           unsigned char* current_abbrev;
 181           for (current_abbrev = abbrev_data;
 182                current_abbrev[0] || current_abbrev[1];
 183                current_abbrev++)
 184             {
 185               if (current_abbrev >= abbrev_end)
 186                 {
 187                   this->failed(_("Debug abbreviations extend beyond "
 188                                  ".debug_abbrev section; failed to reduce "
 189                                  "debug abbreviations"));
 190                   return;
 191                 }
 192             }
 193           // Account for the two nulls and advance to the start of the
 194           // next abbreviation.
 195           current_abbrev += 2;
 196
 197           // We're eliminating every entry except for compile units, so we
 198           // only need to store abbreviations that describe them
 199           if (abbrev_type == elfcpp::DW_TAG_compile_unit)
 200             {
 201               write_unsigned_LEB_128(&this->data_, ++this->abbrev_count_);
 202               write_unsigned_LEB_128(&this->data_, abbrev_type);
 203               // has_children is false for all entries
 204               this->data_.push_back(0);
 205               this->abbrev_mapping_[std::make_pair(abbrev_offset,
 206                                                    abbrev_number)] =
 207                   std::make_pair(abbrev_count_, this->data_.size());
 208               this->data_.insert(this->data_.end(), abbrev_data,
 209                                  current_abbrev);
 210             }
 211           abbrev_data = current_abbrev;
 212         }
 213       gold_assert(LEB_size == 1);
 214       abbrev_data += LEB_size;
 215     }
 216   // Null terminate the list of abbreviations
 217   this->data_.push_back(0);
 218   this->set_data_size(data_.size());
 219   this->sized_ = true;
 220 }
 221
 222 void
 223 Output_reduced_debug_abbrev_section::do_write(Output_file* of)
 224 {
 225   off_t offset = this->offset();
 226   off_t data_size = this->data_size();
 227   unsigned char* view = of->get_output_view(offset, data_size);
 228   if (this->failed_)
 229     memcpy(view, this->postprocessing_buffer(),
 230            this->postprocessing_buffer_size());
 231   else
 232     memcpy(view, &this->data_.front(), data_size);
 233   of->write_output_view(offset, data_size, view);
 234 }
 235
 236 // Locates the abbreviation with abbreviation_number abbrev_number in the
 237 // abbreviation table at offset abbrev_offset.  abbrev_number is updated with
 238 // its new abbreviation number and a pointer to the beginning of the
 239 // abbreviation is returned.
 240 unsigned char*
 241 Output_reduced_debug_abbrev_section::get_new_abbrev(
 242   uint64_t* abbrev_number, uint64_t abbrev_offset)
 243 {
 244   set_final_data_size();
 245   std::pair<uint64_t, uint64_t> abbrev_info =
 246       this->abbrev_mapping_[std::make_pair(abbrev_offset, *abbrev_number)];
 247   *abbrev_number = abbrev_info.first;
 248   return &this->data_[abbrev_info.second];
 249 }
 250
 251 void Output_reduced_debug_info_section::set_final_data_size()
 252 {
 253   if (this->failed_)
 254     return;
 255   unsigned char* debug_info = this->postprocessing_buffer();
 256   unsigned char* debug_info_end = (this->postprocessing_buffer()
 257                                    + this->postprocessing_buffer_size());
 258   unsigned char* next_compile_unit;
 259   this->write_to_postprocessing_buffer();
 260
 261   while (debug_info < debug_info_end)
 262     {
 263       uint32_t compile_unit_start = read_from_pointer<32>(&debug_info);
 264       // The first 4 bytes of each compile unit determine whether or
 265       // not we're using dwarf32 or dwarf64.  This is not necessarily
 266       // related to whether the binary is 32 or 64 bits.
 267       if (compile_unit_start == 0xFFFFFFFF)
 268         {
 269           // Technically the size can be up to 96 bits.  Rather than handle
 270           // 96/128 bit integers we just truncate the size at 64 bits.
 271           if (0 != read_from_pointer<32>(&debug_info))
 272             {
 273               this->failed(_("Extremely large compile unit in debug info; "
 274                              "failed to reduce debug info"));
 275               return;
 276             }
 277           const int dwarf64_header_size = sizeof(uint64_t) + sizeof(uint16_t) +
 278                                           sizeof(uint64_t) + sizeof(uint8_t);
 279           if (debug_info + dwarf64_header_size >= debug_info_end)
 280             {
 281               this->failed(_("Debug info extends beyond .debug_info section;"
 282                              "failed to reduce debug info"));
 283               return;
 284             }
 285
 286           uint64_t compile_unit_size = read_from_pointer<64>(&debug_info);
 287           next_compile_unit = debug_info + compile_unit_size;
 288           uint16_t version = read_from_pointer<16>(&debug_info);
 289           uint64_t abbrev_offset = read_from_pointer<64>(&debug_info);
 290           uint8_t address_size = read_from_pointer<8>(&debug_info);
 291           size_t LEB_size;
 292           uint64_t abbreviation_number = read_unsigned_LEB_128(debug_info,
 293                                                                &LEB_size);
 294           debug_info += LEB_size;
 295           unsigned char* die_abbrev = this->associated_abbrev_->get_new_abbrev(
 296               &abbreviation_number, abbrev_offset);
 297           unsigned char* die_end;
 298           if (!this->get_die_end(debug_info, die_abbrev, &die_end,
 299                                  debug_info_end, address_size, true))
 300             {
 301               this->failed(_("Invalid DIE in debug info; "
 302                              "failed to reduce debug info"));
 303               return;
 304             }
 305
 306           insert_into_vector<32>(&this->data_, 0xFFFFFFFF);
 307           insert_into_vector<32>(&this->data_, 0);
 308           insert_into_vector<64>(
 309               &this->data_,
 310               (11 + get_length_as_unsigned_LEB_128(abbreviation_number)
 311                + die_end - debug_info));
 312           insert_into_vector<16>(&this->data_, version);
 313           insert_into_vector<64>(&this->data_, 0);
 314           insert_into_vector<8>(&this->data_, address_size);
 315           write_unsigned_LEB_128(&this->data_, abbreviation_number);
 316           this->data_.insert(this->data_.end(), debug_info, die_end);
 317         }
 318       else
 319         {
 320           const int dwarf32_header_size =
 321               sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint8_t);
 322           if (debug_info + dwarf32_header_size >= debug_info_end)
 323             {
 324               this->failed(_("Debug info extends beyond .debug_info section; "
 325                              "failed to reduce debug info"));
 326               return;
 327             }
 328           uint32_t compile_unit_size = compile_unit_start;
 329           next_compile_unit = debug_info + compile_unit_size;
 330           uint16_t version = read_from_pointer<16>(&debug_info);
 331           uint32_t abbrev_offset = read_from_pointer<32>(&debug_info);
 332           uint8_t address_size = read_from_pointer<8>(&debug_info);
 333           size_t LEB_size;
 334           uint64_t abbreviation_number = read_unsigned_LEB_128(debug_info,
 335                                                                &LEB_size);
 336           debug_info += LEB_size;
 337           unsigned char* die_abbrev = this->associated_abbrev_->get_new_abbrev(
 338               &abbreviation_number, abbrev_offset);
 339           unsigned char* die_end;
 340           if (!this->get_die_end(debug_info, die_abbrev, &die_end,
 341                                  debug_info_end, address_size, false))
 342             {
 343               this->failed(_("Invalid DIE in debug info; "
 344                              "failed to reduce debug info"));
 345               return;
 346             }
 347
 348           insert_into_vector<32>(
 349               &this->data_,
 350               (7 + get_length_as_unsigned_LEB_128(abbreviation_number)
 351                + die_end - debug_info));
 352           insert_into_vector<16>(&this->data_, version);
 353           insert_into_vector<32>(&this->data_, 0);
 354           insert_into_vector<8>(&this->data_, address_size);
 355           write_unsigned_LEB_128(&this->data_, abbreviation_number);
 356           this->data_.insert(this->data_.end(), debug_info, die_end);
 357         }
 358       debug_info = next_compile_unit;
 359     }
 360   this->set_data_size(data_.size());
 361 }
 362
 363 void Output_reduced_debug_info_section::do_write(Output_file* of)
 364 {
 365   off_t offset = this->offset();
 366   off_t data_size = this->data_size();
 367   unsigned char* view = of->get_output_view(offset, data_size);
 368   if (this->failed_)
 369     memcpy(view, this->postprocessing_buffer(),
 370            this->postprocessing_buffer_size());
 371   else
 372     memcpy(view, &this->data_.front(), data_size);
 373   of->write_output_view(offset, data_size, view);
 374 }
 375
 376 } // End namespace gold.