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1. Modeling code manipulation in JIT compilers

   https://doi.org/10.1145/3520313.3534656  

   Lim, HeuiChan ; Kang, Xiyu ; Debray, Saumya ( June 2022 , Proceedings of the 11th ACM SIGPLAN International Workshop on the State Of the Art in Program Analysis)

   Gonnord, Laure ; Titolo, Laura (Ed.)

   Just-in-Time (JIT) compilers are widely used to improve the performance of interpreter-based language implementations by creating optimized code at runtime. However, bugs in the JIT compiler’s code manipulation and optimization can result in the generation of incorrect code. Such bugs can be difficult to diagnose and fix, and can result in exploitable vulnerabilities. Unfortunately, existing approaches to automatic bug localization do not carry over well to such bugs. This paper discusses a different approach to analyzing JIT compiler optimization behaviors, based on using dynamic analysis to construct abstract models of the JIT compiler’s optimizer and back end. By comparing the models obtained for buggy and non-buggy executions of the JIT compiler, we can pinpoint the components of the JIT compiler’s internal representation that have been affected by the bug; this can then be mapped back to identify the buggy code. Our ex- periments with two real bugs for Google V8 JIT compiler, TurboFan, show the utility and practicality of our approach. 

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2. Automatically Localizing Dynamic Code Generation Bugs in JIT Compiler Back-End

   https://doi.org/10.1145/3578360.3580260  

   Lim, HeuiChan ; Debray, Saumya ( February 2023 , ACM)

   Just-in-Time (JIT) compilers are ubiquitous in modern computing systems and are used in a wide variety of software. Dynamic code generation bugs, where the JIT compiler silently emits incorrect code, can result in exploitable vulnerabilities. They, therefore, pose serious security concerns and make quick mitigation essential. However, due to the size and complexity of JIT compilers, quickly locating and fixing bugs is often challenging. In addition, the unique characteristics of JIT compilers make existing bug localization approaches inapplicable. Therefore, this paper proposes a new approach to automatic bug localization, explicitly targeting the JIT compiler back-end. The approach is based on explicitly modeling architecture-independent back-end representation and architecture-specific code-generation. Experiments using a prototype implementation on a widely used JIT compiler (Turbofan) indicate that it can successfully localize dynamic code generation bugs in the back-end with high accuracy. 

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3. Visualizing JIT Compiler Graphs

   Lim, HeuiChan ; Kobourov, Stephen ( September 2021 , 29th International Symposium on Graph Drawing and Network Visualization (GD 2021))

   null (Ed.)

   Just-in-time (JIT) compilers are used by many modern programming systems in order to improve performance. Bugs in JIT compilers provide exploitable security vulnerabilities and debugging them is difficult as they are large, complex, and dynamic. Current debugging and visualization tools deal with static code and are not suitable in this domain. We describe a new approach for simplifying the large and complex intermediate representation, generated by a JIT compiler and visualize it with a metro map metaphor to aid developers in debugging. 

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4. Compiler bug isolation via effective witness test program generation

   https://doi.org/10.1145/3338906.3338957  

   Chen, Junjie ; Han, Jiaqi ; Sun, Peiyi ; Zhang, Lingming ; Hao, Dan ; Zhang, Lu ( January 2019 , ACM Joint Meeting on European Software Engineering Conference and Symposium on the Foundations of Software Engineering)

   Compiler bugs are extremely harmful, but are notoriously difficult to debug because compiler bugs usually produce few debugging information. Given a bug-triggering test program for a compiler, hundreds of compiler files are usually involved during compilation, and thus are suspect buggy files. Although there are lots of automated bug isolation techniques, they are not applicable to compilers due to the scalability or effectiveness problem. To solve this problem, in this paper, we transform the compiler bug isolation problem into a search problem, i.e., searching for a set of effective witness test programs that are able to eliminate innocent compiler files from suspects. Based on this intuition, we propose an automated compiler bug isolation technique, DiWi, which (1) proposes a heuristic-based search strategy to generate such a set of effective witness test programs via applying our designed witnessing mutation rules to the given failing test program, and (2) compares their coverage to isolate bugs following the practice of spectrum-based bug isolation. The experimental results on 90 real bugs from popular GCC and LLVM compilers show that DiWi effectively isolates 66.67%/78.89% bugs within Top-10/Top-20 compiler files, significantly outperforming state-of-the-art bug isolation techniques. 

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5. CirC: Compiler infrastructure for proof systems, software verification, and more

   https://doi.org/10.1109/SP46214.2022.9833782  

   Ozdemir, Alex ; Brown, Fraser ; Wahby, Riad S. ( May 2022 , 2022 IEEE Symposium on Security and Privacy)

   Cryptographic tools like proof systems, multi-party computation, and fully homomorphic encryption are usually applied to computations expressed as systems of arithmetic constraints. In practice, this means that these applications rely on compilers from high-level programming languages (like C) to such constraints. This compilation task is challenging, but not entirely new: the software verification community has a rich literature on compiling programs to logical constraints (like SAT or SMT). In this work, we show that building shared compiler infrastructure for compiling to constraint representations is possible, because these representations share a common abstraction: stateless, non-uniform, non-deterministic computations that we call existentially quantified circuits, or EQCs. Moreover, we show that this shared infrastructure is useful, because it allows compilers for proof systems to benefit from decades of work on constraint compilation techniques for software verification. To make our approach concrete we create CirC, an infrastructure for building compilers to EQCs. CirC makes it easy to compile to new EQCs: we build support for three, R1CS (used for proof systems), SMT (used for verification and bug-finding), and ILP (used for optimization), in ≈2000 LOC. It’s also easy to extend CirC to support new source languages: we build a feature-complete compiler for a cryptographic language in one week and ≈900 LOC, whereas the reference compiler for the same language took years to write, comprises ≈24000 LOC, and produces worse-performing output than our compiler. Finally, CirC enables novel applications that combine multiple EQCs. For example, we build the first pipeline that (1) automatically identifies bugs in programs, then (2) automatically constructs cryptographic proofs of the bugs’ existence. 

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