优化代码的调试信息验证

Yuanbo Li, Shuo Ding, Qirun Zhang, Davide Italiano
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引用次数: 16

摘要

几乎所有的现代生产软件都是经过优化编译的。调试优化的代码是一个理想的功能。例如,开发人员通常对软件崩溃产生的核心转储执行事后调试。为优化的代码设计可靠的调试技术在过去已经得到了很好的研究。然而,在调试优化代码时,对优化编译器生成的调试信息的正确性知之甚少。优化编译器发出调试信息(例如,DWARF信息)以支持源代码调试器。错误的调试信息会导致调试器崩溃或显示错误的变量值。现有的调试器验证技术只关注于测试动态语言调试器的交互方面(即,使用未优化的代码)。验证优化代码的调试信息会带来一些独特的挑战:(1)由于代码优化,调试器无法到达许多断点;(2)检查一些任意变量(如未初始化的变量)会引入未定义行为。本文提出了第一个用优化代码系统测试调试信息的通用框架。我们引入了一个新概念,叫做可操作程序。一个可操作的程序P⟨s, v⟩包含一个程序位置s和一个要检查的变量v。我们的关键见解是,在未优化的程序P⟨s,v⟩和优化的程序P⟨s,v⟩中,调试器应该能够在程序位置s处停止并检查变量v的值而没有任何未定义的行为。我们的框架生成可操作的程序,并通过比较P⟨s, v⟩'的调试器输出和P⟨s, v⟩中第s行上v的实际值来进行系统测试。我们已经将我们的框架应用于两种主流的优化C编译器(即GCC和LLVM)。我们的框架产生了47个已确认的bug报告,其中11个已经修复。此外,在三天内,我们的技术在Rust编译器中发现了2个已确认的bug。结果证明了该框架的有效性和通用性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Debug information validation for optimized code
Almost all modern production software is compiled with optimization. Debugging optimized code is a desirable functionality. For example, developers usually perform post-mortem debugging on the coredumps produced by software crashes. Designing reliable debugging techniques for optimized code has been well-studied in the past. However, little is known about the correctness of the debug information generated by optimizing compilers when debugging optimized code. Optimizing compilers emit debug information (e.g., DWARF information) to support source code debuggers. Wrong debug information causes debuggers to either crash or to display wrong variable values. Existing debugger validation techniques only focus on testing the interactive aspect of debuggers for dynamic languages (i.e., with unoptimized code). Validating debug information for optimized code raises some unique challenges: (1) many breakpoints cannot be reached by debuggers due to code optimization; and (2) inspecting some arbitrary variables such as uninitialized variables introduces undefined behaviors. This paper presents the first generic framework for systematically testing debug information with optimized code. We introduce a novel concept called actionable program. An actionable program P⟨ s, v⟩ contains a program location s and a variable v to inspect. Our key insight is that in both the unoptimized program P⟨ s,v⟩ and the optimized program P⟨ s,v⟩′, debuggers should be able to stop at the program location s and inspect the value of the variable v without any undefined behaviors. Our framework generates actionable programs and does systematic testing by comparing the debugger output of P⟨ s, v⟩′ and the actual value of v at line s in P⟨ s, v⟩. We have applied our framework to two mainstream optimizing C compilers (i.e., GCC and LLVM). Our framework has led to 47 confirmed bug reports, 11 of which have already been fixed. Moreover, in three days, our technique has found 2 confirmed bugs in the Rust compiler. The results have demonstrated the effectiveness and generality of our framework.
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