1 // dwarf_reader.cc -- parse dwarf2/3 debug information
3 // Copyright 2007 Free Software Foundation, Inc.
4 // Written by Ian Lance Taylor <iant@google.com>.
6 // This file is part of gold.
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.
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.
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.
25 #include "elfcpp_swap.h"
29 #include "dwarf_reader.h"
33 // Read an unsigned LEB128 number. Each byte contains 7 bits of
34 // information, plus one bit saying whether the number continues or
38 read_unsigned_LEB_128(const unsigned char* buffer, size_t* len)
42 unsigned int shift = 0;
49 result |= (static_cast<uint64_t>(byte & 0x7f)) << shift;
59 // Read a signed LEB128 number. These are like regular LEB128
60 // numbers, except the last byte may have a sign bit set.
63 read_signed_LEB_128(const unsigned char* buffer, size_t* len)
74 result |= (static_cast<uint64_t>(byte & 0x7f) << shift);
79 if ((shift < 8 * static_cast<int>(sizeof(result))) && (byte & 0x40))
80 result |= -((static_cast<int64_t>(1)) << shift);
85 } // End anonymous namespace.
90 // This is the format of a DWARF2/3 line state machine that we process
91 // opcodes using. There is no need for anything outside the lineinfo
92 // processor to know how this works.
94 struct LineStateMachine
100 unsigned int shndx; // the section address refers to
101 bool is_stmt; // stmt means statement.
107 ResetLineStateMachine(struct LineStateMachine* lsm, bool default_is_stmt)
114 lsm->is_stmt = default_is_stmt;
115 lsm->basic_block = false;
116 lsm->end_sequence = false;
119 template<int size, bool big_endian>
120 Dwarf_line_info<size, big_endian>::Dwarf_line_info(Object* object)
121 : data_valid_(false), buffer_(NULL), symtab_buffer_(NULL),
122 directories_(1), files_(1)
124 unsigned int debug_shndx;
125 for (debug_shndx = 0; debug_shndx < object->shnum(); ++debug_shndx)
126 if (object->section_name(debug_shndx) == ".debug_line")
129 this->buffer_ = object->section_contents(
130 debug_shndx, &buffer_size, false);
131 this->buffer_end_ = this->buffer_ + buffer_size;
134 if (this->buffer_ == NULL)
137 // Find the relocation section for ".debug_line".
138 bool got_relocs = false;
139 for (unsigned int reloc_shndx = 0;
140 reloc_shndx < object->shnum();
143 unsigned int reloc_sh_type = object->section_type(reloc_shndx);
144 if ((reloc_sh_type == elfcpp::SHT_REL
145 || reloc_sh_type == elfcpp::SHT_RELA)
146 && object->section_info(reloc_shndx) == debug_shndx)
148 got_relocs = this->track_relocs_.initialize(object, reloc_shndx,
156 // Finally, we need the symtab section to interpret the relocs.
157 unsigned int symtab_shndx;
158 for (symtab_shndx = 0; symtab_shndx < object->shnum(); ++symtab_shndx)
159 if (object->section_type(symtab_shndx) == elfcpp::SHT_SYMTAB)
162 this->symtab_buffer_ = object->section_contents(
163 symtab_shndx, &symtab_size, false);
164 this->symtab_buffer_end_ = this->symtab_buffer_ + symtab_size;
167 if (this->symtab_buffer_ == NULL)
170 // Now that we have successfully read all the data, parse the debug
172 this->data_valid_ = true;
173 this->read_line_mappings();
176 // Read the DWARF header.
178 template<int size, bool big_endian>
180 Dwarf_line_info<size, big_endian>::read_header_prolog(
181 const unsigned char* lineptr)
183 uint32_t initial_length = elfcpp::Swap<32, big_endian>::readval(lineptr);
186 // In DWARF2/3, if the initial length is all 1 bits, then the offset
187 // size is 8 and we need to read the next 8 bytes for the real length.
188 if (initial_length == 0xffffffff)
190 header_.offset_size = 8;
191 initial_length = elfcpp::Swap<64, big_endian>::readval(lineptr);
195 header_.offset_size = 4;
197 header_.total_length = initial_length;
199 gold_assert(lineptr + header_.total_length <= buffer_end_);
201 header_.version = elfcpp::Swap<16, big_endian>::readval(lineptr);
204 if (header_.offset_size == 4)
205 header_.prologue_length = elfcpp::Swap<32, big_endian>::readval(lineptr);
207 header_.prologue_length = elfcpp::Swap<64, big_endian>::readval(lineptr);
208 lineptr += header_.offset_size;
210 header_.min_insn_length = *lineptr;
213 header_.default_is_stmt = *lineptr;
216 header_.line_base = *reinterpret_cast<const signed char*>(lineptr);
219 header_.line_range = *lineptr;
222 header_.opcode_base = *lineptr;
225 header_.std_opcode_lengths.reserve(header_.opcode_base + 1);
226 header_.std_opcode_lengths[0] = 0;
227 for (int i = 1; i < header_.opcode_base; i++)
229 header_.std_opcode_lengths[i] = *lineptr;
236 // The header for a debug_line section is mildly complicated, because
237 // the line info is very tightly encoded.
239 template<int size, bool big_endian>
241 Dwarf_line_info<size, big_endian>::read_header_tables(
242 const unsigned char* lineptr)
244 // It is legal for the directory entry table to be empty.
250 const unsigned char* dirname = lineptr;
251 gold_assert(dirindex == static_cast<int>(directories_.size()));
252 directories_.push_back(reinterpret_cast<const char*>(dirname));
253 lineptr += directories_.back().size() + 1;
259 // It is also legal for the file entry table to be empty.
266 const char* filename = reinterpret_cast<const char*>(lineptr);
267 lineptr += strlen(filename) + 1;
269 uint64_t dirindex = read_unsigned_LEB_128(lineptr, &len);
270 if (dirindex >= directories_.size())
274 read_unsigned_LEB_128(lineptr, &len); // mod_time
277 read_unsigned_LEB_128(lineptr, &len); // filelength
280 gold_assert(fileindex == static_cast<int>(files_.size()));
281 files_.push_back(std::pair<int, std::string>(dirindex, filename));
290 // Process a single opcode in the .debug.line structure.
292 // Templating on size and big_endian would yield more efficient (and
293 // simpler) code, but would bloat the binary. Speed isn't important
296 template<int size, bool big_endian>
298 Dwarf_line_info<size, big_endian>::process_one_opcode(
299 const unsigned char* start, struct LineStateMachine* lsm, size_t* len)
303 unsigned char opcode = *start;
307 // If the opcode is great than the opcode_base, it is a special
308 // opcode. Most line programs consist mainly of special opcodes.
309 if (opcode >= header_.opcode_base)
311 opcode -= header_.opcode_base;
312 const int advance_address = ((opcode / header_.line_range)
313 * header_.min_insn_length);
314 lsm->address += advance_address;
316 const int advance_line = ((opcode % header_.line_range)
317 + header_.line_base);
318 lsm->line_num += advance_line;
319 lsm->basic_block = true;
324 // Otherwise, we have the regular opcodes
327 case elfcpp::DW_LNS_copy:
328 lsm->basic_block = false;
332 case elfcpp::DW_LNS_advance_pc:
334 const uint64_t advance_address
335 = read_unsigned_LEB_128(start, &templen);
337 lsm->address += header_.min_insn_length * advance_address;
341 case elfcpp::DW_LNS_advance_line:
343 const uint64_t advance_line = read_signed_LEB_128(start, &templen);
345 lsm->line_num += advance_line;
349 case elfcpp::DW_LNS_set_file:
351 const uint64_t fileno = read_unsigned_LEB_128(start, &templen);
353 lsm->file_num = fileno;
357 case elfcpp::DW_LNS_set_column:
359 const uint64_t colno = read_unsigned_LEB_128(start, &templen);
361 lsm->column_num = colno;
365 case elfcpp::DW_LNS_negate_stmt:
366 lsm->is_stmt = !lsm->is_stmt;
369 case elfcpp::DW_LNS_set_basic_block:
370 lsm->basic_block = true;
373 case elfcpp::DW_LNS_fixed_advance_pc:
376 advance_address = elfcpp::Swap<16, big_endian>::readval(start);
378 lsm->address += advance_address;
382 case elfcpp::DW_LNS_const_add_pc:
384 const int advance_address = (header_.min_insn_length
385 * ((255 - header_.opcode_base)
386 / header_.line_range));
387 lsm->address += advance_address;
391 case elfcpp::DW_LNS_extended_op:
393 const uint64_t extended_op_len
394 = read_unsigned_LEB_128(start, &templen);
396 oplen += templen + extended_op_len;
398 const unsigned char extended_op = *start;
403 case elfcpp::DW_LNE_end_sequence:
404 lsm->end_sequence = true;
408 case elfcpp::DW_LNE_set_address:
410 typename Reloc_map::const_iterator it
411 = reloc_map_.find(start - this->buffer_);
412 if (it != reloc_map_.end())
416 (elfcpp::Swap<size, big_endian>::readval(start)
417 + it->second.second);
418 lsm->shndx = it->second.first;
422 // Every set_address should have an associated
424 this->data_valid_ = false;
428 case elfcpp::DW_LNE_define_file:
430 const char* filename = reinterpret_cast<const char*>(start);
431 templen = strlen(filename) + 1;
434 uint64_t dirindex = read_unsigned_LEB_128(start, &templen);
435 if (dirindex >= directories_.size())
439 read_unsigned_LEB_128(start, &templen); // mod_time
442 read_unsigned_LEB_128(start, &templen); // filelength
445 files_.push_back(std::pair<int, std::string>(dirindex,
455 // Ignore unknown opcode silently
456 for (int i = 0; i < header_.std_opcode_lengths[opcode]; i++)
459 read_unsigned_LEB_128(start, &templen);
470 // Read the debug information at LINEPTR and store it in the line
473 template<int size, bool big_endian>
475 Dwarf_line_info<size, big_endian>::read_lines(unsigned const char* lineptr)
477 struct LineStateMachine lsm;
479 // LENGTHSTART is the place the length field is based on. It is the
480 // point in the header after the initial length field.
481 const unsigned char* lengthstart = buffer_;
483 // In 64 bit dwarf, the initial length is 12 bytes, because of the
484 // 0xffffffff at the start.
485 if (header_.offset_size == 8)
490 while (lineptr < lengthstart + header_.total_length)
492 ResetLineStateMachine(&lsm, header_.default_is_stmt);
493 while (!lsm.end_sequence)
496 bool add_line = this->process_one_opcode(lineptr, &lsm, &oplength);
499 Offset_to_lineno_entry entry
500 = { lsm.address, lsm.file_num, lsm.line_num };
501 line_number_map_[lsm.shndx].push_back(entry);
507 return lengthstart + header_.total_length;
510 // Looks in the symtab to see what section a symbol is in.
512 template<int size, bool big_endian>
514 Dwarf_line_info<size, big_endian>::symbol_section(
516 typename elfcpp::Elf_types<size>::Elf_Addr* value)
518 const int symsize = elfcpp::Elf_sizes<size>::sym_size;
519 gold_assert(this->symtab_buffer_ + sym * symsize < this->symtab_buffer_end_);
520 elfcpp::Sym<size, big_endian> elfsym(this->symtab_buffer_ + sym * symsize);
521 *value = elfsym.get_st_value();
522 return elfsym.get_st_shndx();
525 // Read the relocations into a Reloc_map.
527 template<int size, bool big_endian>
529 Dwarf_line_info<size, big_endian>::read_relocs()
531 if (this->symtab_buffer_ == NULL)
534 typename elfcpp::Elf_types<size>::Elf_Addr value;
536 while ((reloc_offset = this->track_relocs_.next_offset()) != -1)
538 const unsigned int sym = this->track_relocs_.next_symndx();
539 const unsigned int shndx = this->symbol_section(sym, &value);
540 this->reloc_map_[reloc_offset] = std::make_pair(shndx, value);
541 this->track_relocs_.advance(reloc_offset + 1);
545 // Read the line number info.
547 template<int size, bool big_endian>
549 Dwarf_line_info<size, big_endian>::read_line_mappings()
551 gold_assert(this->data_valid_ == true);
554 while (this->buffer_ < this->buffer_end_)
556 const unsigned char* lineptr = this->buffer_;
557 lineptr = this->read_header_prolog(lineptr);
558 lineptr = this->read_header_tables(lineptr);
559 lineptr = this->read_lines(lineptr);
560 this->buffer_ = lineptr;
563 // Sort the lines numbers, so addr2line can use binary search.
564 for (typename Lineno_map::iterator it = line_number_map_.begin();
565 it != line_number_map_.end();
567 // Each vector needs to be sorted by offset.
568 std::sort(it->second.begin(), it->second.end());
571 // Return a string for a file name and line number.
573 template<int size, bool big_endian>
575 Dwarf_line_info<size, big_endian>::addr2line(unsigned int shndx, off_t offset)
577 if (this->data_valid_ == false)
580 const Offset_to_lineno_entry lookup_key = { offset, 0, 0 };
581 std::vector<Offset_to_lineno_entry>& offsets = this->line_number_map_[shndx];
585 typename std::vector<Offset_to_lineno_entry>::const_iterator it
586 = std::lower_bound(offsets.begin(), offsets.end(), lookup_key);
588 // If we found an exact match, great, otherwise find the last entry
589 // before the passed-in offset.
590 if (it->offset > offset)
592 if (it == offsets.begin())
595 gold_assert(it->offset < offset);
598 // Convert the file_num + line_num into a string.
600 gold_assert(it->file_num < static_cast<int>(files_.size()));
601 const std::pair<int, std::string>& filename_pair = files_[it->file_num];
602 gold_assert(filename_pair.first < static_cast<int>(directories_.size()));
603 const std::string& dirname = directories_[filename_pair.first];
604 const std::string& filename = filename_pair.second;
605 if (!dirname.empty())
614 char buffer[64]; // enough to hold a line number
615 snprintf(buffer, sizeof(buffer), "%d", it->line_num);
622 #ifdef HAVE_TARGET_32_LITTLE
624 class Dwarf_line_info<32, false>;
627 #ifdef HAVE_TARGET_32_BIG
629 class Dwarf_line_info<32, true>;
632 #ifdef HAVE_TARGET_64_LITTLE
634 class Dwarf_line_info<64, false>;
637 #ifdef HAVE_TARGET_64_BIG
639 class Dwarf_line_info<64, true>;
642 } // End namespace gold.