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(
121 Sized_relobj<size, big_endian>* object)
122 : data_valid_(true), buffer_(NULL), symtab_buffer_(NULL),
123 directories_(1), files_(1)
125 unsigned int debug_shndx;
126 for (debug_shndx = 0; debug_shndx < object->shnum(); ++debug_shndx)
127 if (object->section_name(debug_shndx) == ".debug_line")
130 this->buffer_ = object->section_contents(
131 debug_shndx, &buffer_size, false);
132 this->buffer_end_ = this->buffer_ + buffer_size;
135 if (this->buffer_ == NULL)
137 this->data_valid_ = false;
141 // Find the relocation section for ".debug_line".
142 bool got_relocs = false;
143 for (unsigned int reloc_shndx = 0;
144 reloc_shndx < object->shnum();
147 unsigned int reloc_sh_type = object->section_type(reloc_shndx);
148 if ((reloc_sh_type == elfcpp::SHT_REL
149 || reloc_sh_type == elfcpp::SHT_RELA)
150 && object->section_info(reloc_shndx) == debug_shndx)
152 got_relocs = this->track_relocs_.initialize(object, reloc_shndx,
159 this->data_valid_ = false;
163 // Finally, we need the symtab section to interpret the relocs.
164 unsigned int symtab_shndx;
165 for (symtab_shndx = 0; symtab_shndx < object->shnum(); ++symtab_shndx)
166 if (object->section_type(symtab_shndx) == elfcpp::SHT_SYMTAB)
169 this->symtab_buffer_ = object->section_contents(
170 symtab_shndx, &symtab_size, false);
171 this->symtab_buffer_end_ = this->symtab_buffer_ + symtab_size;
174 if (this->symtab_buffer_ == NULL)
176 this->data_valid_ = false;
180 // Now that we have successfully read all the data, parse the debug
182 this->read_line_mappings();
185 // Read the DWARF header.
187 template<int size, bool big_endian>
189 Dwarf_line_info<size, big_endian>::read_header_prolog(
190 const unsigned char* lineptr)
192 uint32_t initial_length = elfcpp::Swap<32, big_endian>::readval(lineptr);
195 // In DWARF2/3, if the initial length is all 1 bits, then the offset
196 // size is 8 and we need to read the next 8 bytes for the real length.
197 if (initial_length == 0xffffffff)
199 header_.offset_size = 8;
200 initial_length = elfcpp::Swap<64, big_endian>::readval(lineptr);
204 header_.offset_size = 4;
206 header_.total_length = initial_length;
208 gold_assert(lineptr + header_.total_length <= buffer_end_);
210 header_.version = elfcpp::Swap<16, big_endian>::readval(lineptr);
213 if (header_.offset_size == 4)
214 header_.prologue_length = elfcpp::Swap<32, big_endian>::readval(lineptr);
216 header_.prologue_length = elfcpp::Swap<64, big_endian>::readval(lineptr);
217 lineptr += header_.offset_size;
219 header_.min_insn_length = *lineptr;
222 header_.default_is_stmt = *lineptr;
225 header_.line_base = *reinterpret_cast<const signed char*>(lineptr);
228 header_.line_range = *lineptr;
231 header_.opcode_base = *lineptr;
234 header_.std_opcode_lengths.reserve(header_.opcode_base + 1);
235 header_.std_opcode_lengths[0] = 0;
236 for (int i = 1; i < header_.opcode_base; i++)
238 header_.std_opcode_lengths[i] = *lineptr;
245 // The header for a debug_line section is mildly complicated, because
246 // the line info is very tightly encoded.
248 template<int size, bool big_endian>
250 Dwarf_line_info<size, big_endian>::read_header_tables(
251 const unsigned char* lineptr)
253 // It is legal for the directory entry table to be empty.
259 const unsigned char* dirname = lineptr;
260 gold_assert(dirindex == static_cast<int>(directories_.size()));
261 directories_.push_back(reinterpret_cast<const char*>(dirname));
262 lineptr += directories_.back().size() + 1;
268 // It is also legal for the file entry table to be empty.
275 const char* filename = reinterpret_cast<const char*>(lineptr);
276 lineptr += strlen(filename) + 1;
278 uint64_t dirindex = read_unsigned_LEB_128(lineptr, &len);
279 if (dirindex >= directories_.size())
283 read_unsigned_LEB_128(lineptr, &len); // mod_time
286 read_unsigned_LEB_128(lineptr, &len); // filelength
289 gold_assert(fileindex == static_cast<int>(files_.size()));
290 files_.push_back(std::pair<int, std::string>(dirindex, filename));
299 // Process a single opcode in the .debug.line structure.
301 // Templating on size and big_endian would yield more efficient (and
302 // simpler) code, but would bloat the binary. Speed isn't important
305 template<int size, bool big_endian>
307 Dwarf_line_info<size, big_endian>::process_one_opcode(
308 const unsigned char* start, struct LineStateMachine* lsm, size_t* len)
312 unsigned char opcode = *start;
316 // If the opcode is great than the opcode_base, it is a special
317 // opcode. Most line programs consist mainly of special opcodes.
318 if (opcode >= header_.opcode_base)
320 opcode -= header_.opcode_base;
321 const int advance_address = ((opcode / header_.line_range)
322 * header_.min_insn_length);
323 lsm->address += advance_address;
325 const int advance_line = ((opcode % header_.line_range)
326 + header_.line_base);
327 lsm->line_num += advance_line;
328 lsm->basic_block = true;
333 // Otherwise, we have the regular opcodes
336 case elfcpp::DW_LNS_copy:
337 lsm->basic_block = false;
341 case elfcpp::DW_LNS_advance_pc:
343 const uint64_t advance_address
344 = read_unsigned_LEB_128(start, &templen);
346 lsm->address += header_.min_insn_length * advance_address;
350 case elfcpp::DW_LNS_advance_line:
352 const uint64_t advance_line = read_signed_LEB_128(start, &templen);
354 lsm->line_num += advance_line;
358 case elfcpp::DW_LNS_set_file:
360 const uint64_t fileno = read_unsigned_LEB_128(start, &templen);
362 lsm->file_num = fileno;
366 case elfcpp::DW_LNS_set_column:
368 const uint64_t colno = read_unsigned_LEB_128(start, &templen);
370 lsm->column_num = colno;
374 case elfcpp::DW_LNS_negate_stmt:
375 lsm->is_stmt = !lsm->is_stmt;
378 case elfcpp::DW_LNS_set_basic_block:
379 lsm->basic_block = true;
382 case elfcpp::DW_LNS_fixed_advance_pc:
385 advance_address = elfcpp::Swap<16, big_endian>::readval(start);
387 lsm->address += advance_address;
391 case elfcpp::DW_LNS_const_add_pc:
393 const int advance_address = (header_.min_insn_length
394 * ((255 - header_.opcode_base)
395 / header_.line_range));
396 lsm->address += advance_address;
400 case elfcpp::DW_LNS_extended_op:
402 const uint64_t extended_op_len
403 = read_unsigned_LEB_128(start, &templen);
405 oplen += templen + extended_op_len;
407 const unsigned char extended_op = *start;
412 case elfcpp::DW_LNE_end_sequence:
413 lsm->end_sequence = true;
417 case elfcpp::DW_LNE_set_address:
419 typename Reloc_map::const_iterator it
420 = reloc_map_.find(start - this->buffer_);
421 if (it != reloc_map_.end())
425 (elfcpp::Swap<size, big_endian>::readval(start)
426 + it->second.second);
427 lsm->shndx = it->second.first;
431 // Every set_address should have an associated
433 this->data_valid_ = false;
437 case elfcpp::DW_LNE_define_file:
439 const char* filename = reinterpret_cast<const char*>(start);
440 templen = strlen(filename) + 1;
443 uint64_t dirindex = read_unsigned_LEB_128(start, &templen);
444 if (dirindex >= directories_.size())
448 read_unsigned_LEB_128(start, &templen); // mod_time
451 read_unsigned_LEB_128(start, &templen); // filelength
454 files_.push_back(std::pair<int, std::string>(dirindex,
464 // Ignore unknown opcode silently
465 for (int i = 0; i < header_.std_opcode_lengths[opcode]; i++)
468 read_unsigned_LEB_128(start, &templen);
479 // Read the debug information at LINEPTR and store it in the line
482 template<int size, bool big_endian>
484 Dwarf_line_info<size, big_endian>::read_lines(unsigned const char* lineptr)
486 struct LineStateMachine lsm;
488 // LENGTHSTART is the place the length field is based on. It is the
489 // point in the header after the initial length field.
490 const unsigned char* lengthstart = buffer_;
492 // In 64 bit dwarf, the initial length is 12 bytes, because of the
493 // 0xffffffff at the start.
494 if (header_.offset_size == 8)
499 while (lineptr < lengthstart + header_.total_length)
501 ResetLineStateMachine(&lsm, header_.default_is_stmt);
502 while (!lsm.end_sequence)
505 bool add_line = this->process_one_opcode(lineptr, &lsm, &oplength);
508 Offset_to_lineno_entry entry
509 = { lsm.address, lsm.file_num, lsm.line_num };
510 line_number_map_[lsm.shndx].push_back(entry);
516 return lengthstart + header_.total_length;
519 // Looks in the symtab to see what section a symbol is in.
521 template<int size, bool big_endian>
523 Dwarf_line_info<size, big_endian>::symbol_section(
525 typename elfcpp::Elf_types<size>::Elf_Addr* value)
527 const int symsize = elfcpp::Elf_sizes<size>::sym_size;
528 gold_assert(this->symtab_buffer_ + sym * symsize < this->symtab_buffer_end_);
529 elfcpp::Sym<size, big_endian> elfsym(this->symtab_buffer_ + sym * symsize);
530 *value = elfsym.get_st_value();
531 return elfsym.get_st_shndx();
534 // Read the relocations into a Reloc_map.
536 template<int size, bool big_endian>
538 Dwarf_line_info<size, big_endian>::read_relocs()
540 if (this->symtab_buffer_ == NULL)
543 typename elfcpp::Elf_types<size>::Elf_Addr value;
545 while ((reloc_offset = this->track_relocs_.next_offset()) != -1)
547 const unsigned int sym = this->track_relocs_.next_symndx();
548 const unsigned int shndx = this->symbol_section(sym, &value);
549 this->reloc_map_[reloc_offset] = std::make_pair(shndx, value);
550 this->track_relocs_.advance(reloc_offset + 1);
554 // Read the line number info.
556 template<int size, bool big_endian>
558 Dwarf_line_info<size, big_endian>::read_line_mappings()
560 if (this->data_valid_ == false)
564 while (this->buffer_ < this->buffer_end_)
566 const unsigned char* lineptr = this->buffer_;
567 lineptr = this->read_header_prolog(lineptr);
568 lineptr = this->read_header_tables(lineptr);
569 lineptr = this->read_lines(lineptr);
570 this->buffer_ = lineptr;
573 // Sort the lines numbers, so addr2line can use binary search.
574 for (typename Lineno_map::iterator it = line_number_map_.begin();
575 it != line_number_map_.end();
577 // Each vector needs to be sorted by offset.
578 std::sort(it->second.begin(), it->second.end());
581 // Return a string for a file name and line number.
583 template<int size, bool big_endian>
585 Dwarf_line_info<size, big_endian>::addr2line(unsigned int shndx, off_t offset)
587 if (this->data_valid_ == false)
590 const Offset_to_lineno_entry lookup_key = { offset, 0, 0 };
591 std::vector<Offset_to_lineno_entry>& offsets = this->line_number_map_[shndx];
595 typename std::vector<Offset_to_lineno_entry>::const_iterator it
596 = std::lower_bound(offsets.begin(), offsets.end(), lookup_key);
598 // If we found an exact match, great, otherwise find the last entry
599 // before the passed-in offset.
600 if (it->offset > offset)
602 if (it == offsets.begin())
605 gold_assert(it->offset < offset);
608 // Convert the file_num + line_num into a string.
610 gold_assert(it->file_num < static_cast<int>(files_.size()));
611 const std::pair<int, std::string>& filename_pair = files_[it->file_num];
612 gold_assert(filename_pair.first < static_cast<int>(directories_.size()));
613 const std::string& dirname = directories_[filename_pair.first];
614 const std::string& filename = filename_pair.second;
615 if (!dirname.empty())
624 char buffer[64]; // enough to hold a line number
625 snprintf(buffer, sizeof(buffer), "%d", it->line_num);
632 #ifdef HAVE_TARGET_32_LITTLE
634 class Dwarf_line_info<32, false>;
637 #ifdef HAVE_TARGET_32_BIG
639 class Dwarf_line_info<32, true>;
642 #ifdef HAVE_TARGET_64_LITTLE
644 class Dwarf_line_info<64, false>;
647 #ifdef HAVE_TARGET_64_BIG
649 class Dwarf_line_info<64, true>;
652 } // End namespace gold.