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36th IEEE/ACM International Conference on Automated Software Engineering (ASE)

作者： Tomassi, David A. Rubio-Gonzalez, Cindy Univ Calif Davis Davis CA 95616 USA

ISBN: (纸本)9781665403375

Static bug detectors aim at helping developers to automatically find and prevent bugs. In this experience paper, we study the effectiveness of static bug detectors at identifying null pointer Dereferences or null pointer exceptions (NPEs). NPEs pervade all programming domains from systems to web development. Specifically, our study measures the effectiveness of five Java static bug detectors: CheckerFramework, ERADICATE, INFER, nullAWAY, and SPOTBUGS. We conduct our study on 102 real-world and reproducible NPEs from 42 open-source projects found in the BUGSWARM and DEFECTs4J datasets. We apply two known methods to determine whether a bug is found by a given tool, and introduce two new methods that leverage stack trace and code coverage information. Additionally, we provide a categorization of the tool's capabilities and the bug characteristics to better understand the strengths and weaknesses of the tools. Overall, the tools under study only find 30 out of 102 bugs (29.4%), with the majority found by ERADICATE. Based on our observations, we identify and discuss opportunities to make the tools more effective and useful.

关键词： static bug detectors null pointer exceptions null pointer dereferences bug finding BugSwarm Defects4J Java

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Tracking bad apples: Reporting the origin of null and undefined value errors 07

Tracking bad apples: Reporting the origin of null and undefi...

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22nd International Conference on Object-Oriented Programming, Systems, Languages and Applications

作者： Bond, Michael D. Nethercote, Nicholas Kent, Stephen W. Guyer, Samuel Z. McKinley, Kathryn S. Univ Texas Austin Dept Comp Sci Austin TX 78712 USA

ISBN: (纸本)9781595937865

Programs sometimes crash due to unusable values, for example, when Java and C# programs dereference null pointers and when C and C++ programs use undefined values to affect program behavior. A stack trace produced on such a crash identifies the effect of the unusable value, not its cause, and is often not much help to the programmer. This paper presents efficient origin tracking of unusable values;it shows how to record where these values come into existence, correctly propagate them, and report them if they cause an error. The key idea is value piggybacking: when the original program stores an unusable value, value piggybacking instead stores origin information in the spare bits of the unusable value. Modest compiler support alters the program to propagate these modified values through operations such as assignments and comparisons. We evaluate two implementations: the first tracks null pointer origins in a JVM, and the second tracks undefined value origins in a memory-checking tool built with Valgrind. These implementations show that origin tracking via value piggybacking is fast and often useful, and in the Java case, has low enough overhead for use in a production environment.

关键词： reliability performance experimentation debugging low-overhead run-time support null pointer exceptions undefined values managed languages Java Valgrind

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Harvesting the Wisdom of the Crowd to Infer Method nullness in Java 17

Harvesting the Wisdom of the Crowd to Infer Method Nullness ...

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IEEE 17th International Working Conference on Source Code Analysis and Manipulation (SCAM)

作者： Leuenberger, Manuel Osman, Haidar Ghafari, Mohammad Nierstrasz, Oscar Univ Bern Software Composit Grp Bern Switzerland

ISBN: (纸本)9781538632383

null pointer exceptions are common bugs in Java projects. Previous research has shown that dereferencing the results of method calls is the main source of these bugs, as developers do not anticipate that some methods return null. To make matters worse, we find that whether a method returns null or not (nullness), is rarely documented. We argue that method nullness is a vital piece of information that can help developers avoid this category of bugs. This is especially important for external APIs where developers may not even have access to the code. In this paper, we study the method nullness of Apache Lucene, the de facto standard library for text processing in Java. Particularly, we investigate how often the result of each Lucene method is checked against null in Lucene clients. We call this measure method nullability, which can serve as a proxy for method nullness. Analyzing Lucene internal and external usage, we find that most methods are never checked for null. External clients check more methods than Lucene checks internally. Manually inspecting our dataset reveals that some null checks are unnecessary. We present an IDE plugin that complements existing documentation and makes up for missing documentation regarding method nullness and generates nullness annotations, so that static analysis can pinpoint potentially missing or unnecessary null checks.

关键词： static analysis API usage analysis dependency management systems null pointer exceptions

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Masked Types for Sound Object Initialization 09

Masked Types for Sound Object Initialization

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36th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages

作者： Qi, Xin Myers, Andrew C. Cornell Univ Dept Comp Sci Ithaca NY 14853 USA

ISBN: (纸本)9781605583792

This paper presents a type-based solution to the long-standing problem of object initialization. Constructors, the conventional mechanism for object initialization, have semantics that are surprising to programmers and that lead to bugs. They also contribute to the problem of null-pointer exceptions, which make software less reliable. Masked types are a new type-state mechanism that explicitly tracks the initialization state of objects and prevents reading from uninitialized fields. In the resulting language, constructors are ordinary methods that operate on uninitialized objects, and no special default value (null) is needed in the language. Initialization of cyclic data structures is achieved with the use of conditionally masked types. Masked types are modular and compatible with data abstraction. The type system is presented in a simplified object calculus and is proved to soundly prevent reading from uninitialized fields. Masked types have been implemented as an extension to Java, in which compilation simply erases extra type information. Experience using the extended language suggests that masked types work well on real code.

关键词： Languages Reliability invariants null pointer exceptions conditional masks cyclic data structures data abstraction

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Tracking bad apples: Reporting the origin of null and undefined value errors

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ACM SIGPLAN NOTICES 2007年第10期42卷 405-422页

作者： Bond, Michael D. Nethercote, Nicholas Kent, Stephen W. Guyer, Samuel Z. McKinley, Kathryn S. Univ Texas Austin Dept Comp Sci Austin TX 78712 USA

关键词： reliability performance experimentation debugging low-overhead run-time support null pointer exceptions undefined values managed languages Java Valgrind

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