DWARF调试信息格式详解与应用

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"DWARF4调试信息格式是用于编译器和调试器支持源代码级别调试的一种标准格式。它适用于C、C++、Fortran等过程性语言，并且设计为可扩展以适应其他语言。DWARF独立于架构，可以在任何处理器或操作系统上使用，常见于Unix、Linux和其他操作系统以及独立环境。" DWARF（Debugging With Attributed Record Formats）是一种广泛采用的调试信息格式，它的第4版（DWARF4）是调试信息标准的最新版本之一，由DWARF调试信息格式委员会维护和更新。该格式的主要目的是提供一种方式，让编译器生成关于源代码的元数据，以便调试器能够理解程序的结构，包括变量、函数、类型和源代码行号等信息。 DWARF4包含了一些关键特性： 1. **源代码映射**：DWARF4提供了从机器代码到源代码的精确映射，允许调试器在运行时追踪程序执行的源代码路径。 2. **类型信息**：它记录了程序中的数据类型，包括结构体、联合体、枚举和指针等，使得调试器可以解析和显示变量的值。 3. **变量与局部作用域**：DWARF4可以表示函数内的局部变量，包括它们的作用域、初始值和生命周期。 4. **异常处理**：它支持对异常处理信息的编码，帮助调试器理解如何处理运行时错误。 5. **线程和进程上下文**：DWARF4可以记录多线程和多进程程序的状态，使得调试器能跟踪不同线程的执行。 6. **扩展性**：由于设计上的灵活性，DWARF4可以扩展以支持新的编程语言特性和调试需求。 7. **模块和编译单元**：DWARF4将源代码划分为多个编译单元，每个单元对应源文件的一部分，这有助于管理和处理大型项目。 8. **调试信息效率**：尽管DWARF提供了丰富的调试信息，但它通常被优化以减少对程序执行的影响。 DWARF4文档还包括对之前版本的改进和增强，比如错误修复、性能优化和新功能的添加。例如，可能增加了对新编程语言的支持，或者改善了对复杂数据类型的处理。文档本身遵循GNU Free Documentation License，允许自由复制、分发和修改，以促进技术交流和知识共享。 DWARF4是软件开发中不可或缺的一部分，特别是在复杂系统和跨平台环境中，它确保了调试工具的强大功能和兼容性。开发者和调试器实现者都依赖DWARF4来构建高效且用户友好的调试体验。

DWARF Debugging Information Format, Version 4

Page 2 June 10, 2010

The informational content is described in Sections 2 through 6. Section 2 describes the overall

structure of the information and attributes that is common to many or all of the different

debugging information entries. Sections 3, 4 and 5 describe the specific debugging information

entries and how they communicate the necessary information about the source program to a

debugger. Section 6 describes debugging information contained outside of the debugging

information entries. The encoding of the DWARF information is presented in Section 7.

This organization closely follows that used in the DWARF Version 3 document. Except where

needed to incorporate new material or to correct errors, the DWARF Version 3 text is generally

reused in this document with little or no modification.

In the following sections, text in normal font describes required aspects of the DWARF format.

Text in italics is explanatory or supplementary material, and not part of the format definition

itself. The several appendices consist only of explanatory or supplementary material, and are not

part of the formal definition.

1.3 Vendor Extensibility

This document does not attempt to cover all interesting languages or even to cover all of the

interesting debugging information needs for its primary target languages. Therefore, the

document provides vendors a way to define their own debugging information tags, attributes,

base type encodings, location operations, language names, calling conventions and call frame

instructions by reserving a subset of the valid values for these constructs for vendor specific

additions and defining related naming conventions. Vendors may also use debugging information

entries and attributes defined here in new situations. Future versions of this document will not

use names or values reserved for vendor specific additions. All names and values not reserved

for vendor additions, however, are reserved for future versions of this document.

DWARF Version 4 is intended to be permissive rather than prescriptive. Where this specification

provides a means for describing the source language, implementors are expected to adhere to that

specification. For language features that are not supported, implementors may use existing

attributes in novel ways or add vendor-defined attributes. Implementors who make extensions

are strongly encouraged to design them to be compatible with this specification in the absence of

those extensions.

The DWARF format is organized so that a consumer can skip over data which it does not

recognize. This may allow a consumer to read and process files generated according to a later

version of this standard or which contain vendor extensions, albeit possibly in a degraded

manner.

SECTION 1-- INTRODUCTION

June 10, 2010 Page 3

1.4 Changes from Version 3 to Version 4

The following is a list of the major changes made to the DWARF Debugging Information

Format since Version 3 was published. The list is not meant to be exhaustive.

• Reformulate Section 2.6 to better distinguish DWARF location descriptions, which

compute the location where a value is found (such as an address in memory or a register

name) from DWARF expressions, which compute a final value (such as an array bound).

• Add support for bundled instructions on machine architectures where instructions do not

occupy a whole number of bytes.

• Add a new attribute form for section offsets, DW_FORM_sec_offset, to replace the use

of DW_FORM_data4 and DW_FORM_data8 for section offsets.

• Add an attribute, DW_AT_main_subprogram, to identify the main subprogram of a

program.

• Define default array lower bound values for each supported language.

• Add a new technique using separate type units, type signatures and COMDAT sections to

improve compression and duplicate elimination of DWARF information.

• Add support for new C++ language constructs, including rvalue references, generalized

constant expressions, Unicode character types and template aliases.

• Clarify and generalize support for packed arrays and structures.

• Add new line number table support to facilitate profile based compiler optimization.

•

Add additional support for template parameters in instantiations.

•

Add support for strongly typed enumerations in languages (such as C++) that have two

kinds of enumeration declarations.

DWARF Version 4 is compatible with DWARF Version 3 except as follows:

•

DWARF attributes that use any of the new forms of attribute value representation (for

section offsets, flag compression, type signature references, and so on) cannot be read by

DWARF Version 3 consumers because the consumer will not know how to skip over the

unexpected form of data.

•

DWARF frame and line table sections include a additional fields that affect the location

and interpretation of other data in the section.

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