LibDebug: Parse line number information from DWARF format

DWARF line number information, if generated, is stored  in the
.debug_line section of an object file.

The information is encoded as instructions for a VM that is defined in
the DWARF specification.
By executing these instructions, we can extract the encoded line number
information.

1 files changed, 247 insertions, 0 deletions

diff --git a/Libraries/LibDebug/Dwarf/LineProgram.cpp b/Libraries/LibDebug/Dwarf/LineProgram.cpp
new file mode 100644
index 0000000000..2bc629daff
--- /dev/null
+++ b/Libraries/LibDebug/Dwarf/LineProgram.cpp
@@ -0,0 +1,247 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "LineProgram.h"
+
+LineProgram::LineProgram(BufferStream& stream)
+    : m_stream(stream)
+{
+    m_unit_offset = m_stream.offset();
+    parse_unit_header();
+    parse_source_directories();
+    parse_source_files();
+    run_program();
+}
+
+void LineProgram::parse_unit_header()
+{
+    m_stream.read_raw((u8*)&m_unit_header, sizeof(m_unit_header));
+
+    ASSERT(m_unit_header.version == DWARF_VERSION);
+    ASSERT(m_unit_header.opcode_base == SPECIAL_OPCODES_BASE);
+
+#ifdef DWARF_DEBUG
+    dbg() << "unit length: " << unit_header.length;
+#endif
+}
+
+void LineProgram::parse_source_directories()
+{
+    m_source_directories.append(".");
+    while (m_stream.peek()) {
+        String directory;
+        m_stream >> directory;
+#ifdef DWARF_DEBUG
+        dbg() << "directory: " << directory;
+#endif
+        m_source_directories.append(move(directory));
+    }
+    m_stream.advance(1);
+}
+
+void LineProgram::parse_source_files()
+{
+    m_source_files.append({ ".", 0 });
+    while (m_stream.peek()) {
+        String file_name;
+        m_stream >> file_name;
+        size_t directory_index = 0;
+        m_stream.read_LEB128_unsigned(directory_index);
+        size_t _unused = 0;
+        m_stream.read_LEB128_unsigned(_unused); // skip modification time
+        m_stream.read_LEB128_unsigned(_unused); // skip file size
+#ifdef DWARF_DEBUG
+        dbg() << "file: " << file_name << ", directory index: " << directory_index;
+#endif
+        m_source_files.append({ file_name, directory_index });
+    }
+    m_stream.advance(1);
+    ASSERT(!m_stream.handle_read_failure());
+}
+
+void LineProgram::append_to_line_info()
+{
+#ifdef DWARF_DEBUG
+    dbg() << "appending line info: " << (void*)address << ", " << files[file_index].name << ":" << line;
+#endif
+    if (!m_is_statement)
+        return;
+
+    String directory = m_source_directories[m_source_files[m_file_index].directory_index];
+    String full_path = String::format("%s/%s", directory.characters(), m_source_files[m_file_index].name.characters());
+    m_lines.append({ m_address, full_path, m_line });
+}
+
+void LineProgram::reset_registers()
+{
+    m_address = 0;
+    m_line = 1;
+    m_file_index = 1;
+    m_is_statement = m_unit_header.default_is_stmt == 1;
+}
+
+void LineProgram::handle_extended_opcode()
+{
+    size_t length = 0;
+    m_stream.read_LEB128_unsigned(length);
+
+    u8 sub_opcode = 0;
+    m_stream >> sub_opcode;
+
+    switch (sub_opcode) {
+    case ExtendedOpcodes::EndSequence: {
+        append_to_line_info();
+        reset_registers();
+        break;
+    }
+    case ExtendedOpcodes::SetAddress: {
+        ASSERT(length == sizeof(size_t) + 1);
+        m_stream >> m_address;
+#ifdef DWARF_DEBUG
+        dbg() << "SetAddress: " << (void*)address;
+#endif
+        break;
+    }
+    case ExtendedOpcodes::SetDiscriminator: {
+#ifdef DWARF_DEBUG
+        dbg() << "SetDiscriminator";
+#endif
+        m_stream.advance(1);
+        break;
+    }
+    default:
+#ifdef DWARF_DEBUG
+        dbg() << "offset: " << (void*)m_stream.offset();
+#endif
+        ASSERT_NOT_REACHED();
+    }
+}
+void LineProgram::handle_standard_opcode(u8 opcode)
+{
+    switch (opcode) {
+    case StandardOpcodes::Copy: {
+        append_to_line_info();
+        break;
+    }
+    case StandardOpcodes::AdvancePc: {
+        size_t operand = 0;
+        m_stream.read_LEB128_unsigned(operand);
+        size_t delta = operand * m_unit_header.min_instruction_length;
+#ifdef DWARF_DEBUG
+        dbg() << "AdvnacePC by: " << delta << " to: " << (void*)(address + delta);
+#endif
+        m_address += delta;
+        break;
+    }
+    case StandardOpcodes::SetFile: {
+        size_t new_file_index = 0;
+        m_stream.read_LEB128_unsigned(new_file_index);
+#ifdef DWARF_DEBUG
+        dbg() << "SetFile: new file index: " << new_file_index;
+#endif
+        m_file_index = new_file_index;
+        break;
+    }
+    case StandardOpcodes::SetColumn: {
+        // not implemented
+#ifdef DWARF_DEBUG
+        dbg() << "SetColumn";
+#endif
+        size_t new_column;
+        m_stream.read_LEB128_unsigned(new_column);
+
+        break;
+    }
+    case StandardOpcodes::AdvanceLine: {
+        ssize_t line_delta;
+        m_stream.read_LEB128_signed(line_delta);
+        // dbg() << "line_delta: " << line_delta;
+        ASSERT(line_delta >= 0 || m_line >= (size_t)(-line_delta));
+        m_line += line_delta;
+#ifdef DWARF_DEBUG
+        dbg() << "AdvanceLine: " << line;
+#endif
+        break;
+    }
+    case StandardOpcodes::NegateStatement: {
+#ifdef DWARF_DEBUG
+        dbg() << "NegateStatement";
+#endif
+        m_is_statement = !m_is_statement;
+        break;
+    }
+    case StandardOpcodes::ConstAddPc: {
+        u8 adjusted_opcode = 255 - SPECIAL_OPCODES_BASE;
+        ssize_t address_increment = (adjusted_opcode / m_unit_header.line_range) * m_unit_header.min_instruction_length;
+        address_increment *= m_unit_header.min_instruction_length;
+#ifdef DWARF_DEBUG
+        dbg() << "ConstAddPc: advance pc by: " << address_increment << " to: " << (address + address_increment);
+#endif
+        m_address += address_increment;
+        break;
+    }
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+void LineProgram::handle_sepcial_opcode(u8 opcode)
+{
+    u8 adjusted_opcode = opcode - SPECIAL_OPCODES_BASE;
+    ssize_t address_increment = (adjusted_opcode / m_unit_header.line_range) * m_unit_header.min_instruction_length;
+    ssize_t line_increment = m_unit_header.line_base + (adjusted_opcode % m_unit_header.line_range);
+
+    m_address += address_increment;
+    m_line += line_increment;
+
+#ifdef DWARF_DEBUG
+    dbg() << "Special adjusted_opcode: " << adjusted_opcode << ", delta_address: " << address_increment << ", delta_line: " << line_increment;
+    dbg() << "Address is now:" << (void*)m_address << ", and line is: " << source_files[m_file_index].name << ":" << line;
+#endif
+
+    append_to_line_info();
+}
+
+void LineProgram::run_program()
+{
+    reset_registers();
+
+    while ((size_t)m_stream.offset() < m_unit_offset + sizeof(u32) + m_unit_header.length) {
+        u8 opcode = 0;
+        m_stream >> opcode;
+
+#ifdef DWARF_DEBUG
+        dbg() << (void*)(m_stream.offset() - 1) << ": opcode: " << opcode;
+#endif
+
+        if (opcode == 0) {
+            handle_extended_opcode();
+        } else if (opcode >= 1 && opcode <= 12) {
+            handle_standard_opcode(opcode);
+        } else {
+            handle_sepcial_opcode(opcode);
+        }
+    }
+}