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Documents authored by Scholliers, Christophe

Document
Short Paper
DOI: 10.4230/OASIcs.SLATE.2026.20
Out of the Loop No More: Online Abstract Debugging with Loop Stepping (Short Paper)

Authors: João Alvim, Maarten Steevens, and Christophe Scholliers

Published in: OASIcs, Volume 144, 15th Symposium on Languages, Applications and Technologies (SLATE 2026)

Abstract
Traditional debugging makes it practically impossible to manually explore all execution paths, often leaving hypotheses insufficiently explored. Abstract debugging addresses this problem by safely over-approximating all program behaviours through a familiar stepping interface. However, existing approaches operate offline, pre-computing fixed loop summaries that developers cannot interactively refine or inspect at the individual iteration level. In this paper, we propose online abstract debugging, which performs abstract interpretation on demand as the developer steps through the program. This novel architecture enables loop stepping: developers can step into a loop body for precise, iteration-specific states, or step-over to obtain a coarser summary. By interleaving analysis with execution, developers gain direct control over the cost-precision trade-off, computing high precision only where needed to settle a hypothesis. We instantiate this model for WebAssembly and present a prototype implementation, demonstrating that developers can effectively draw sound conclusions about complex, potentially non-terminating looping programs.
Cite as

João Alvim, Maarten Steevens, and Christophe Scholliers. Out of the Loop No More: Online Abstract Debugging with Loop Stepping (Short Paper). In 15th Symposium on Languages, Applications and Technologies (SLATE 2026). Open Access Series in Informatics (OASIcs), Volume 144, pp. 20:1-20:10, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{alvim_et_al:OASIcs.SLATE.2026.20,
  author =	{Alvim, Jo\~{a}o and Steevens, Maarten and Scholliers, Christophe},
  title =	{{Out of the Loop No More: Online Abstract Debugging with Loop Stepping}},
  booktitle =	{15th Symposium on Languages, Applications and Technologies (SLATE 2026)},
  pages =	{20:1--20:10},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-440-6},
  ISSN =	{2190-6807},
  year =	{2026},
  volume =	{144},
  editor =	{Batista, Fernando and Ribeiro, Eug\'{e}nio and Ribeiro, Ricardo and Santos, Andr\'{e} L.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.SLATE.2026.20},
  URN =		{urn:nbn:de:0030-drops-267180},
  doi =		{10.4230/OASIcs.SLATE.2026.20},
  annote =	{Keywords: Debugging, Abstract Interpretation}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2026.27
Remote Concolic Multiverse Debugging

Authors: Maarten Steevens, Tom Lauwaerts, and Christophe Scholliers

Published in: LIPIcs, Volume 372, 40th European Conference on Object-Oriented Programming (ECOOP 2026)

Abstract
Debugging nondeterministic programs is inherently difficult, particularly in microcontroller environments where execution paths can diverge unpredictably due to external sensor inputs. Traditional debugging techniques often fail to capture or reproduce this nondeterministic behavior effectively. Multiverse debugging has emerged as a compelling technique to debug nondeterministic programs, allowing developers to systematically explore all possible execution paths. Unfortunately, current multiverse debuggers are snapshot-based and most operate over a model of the program, which limits their use for debugging resource-constrained microcontrollers. Additionally, current multiverse debuggers, even ones specifically designed for microcontrollers suffer from state explosion making the state space overwhelming during debugging. To address these challenges, we introduce a trace-based multiverse debugger with a novel state-space reduction technique based on concolic execution. Our approach interleaves concolic analysis with live debugging to identify input values that define unique program paths. This hybrid technique efficiently prunes redundant paths from the state space while ensuring full code coverage. Unlike MIO, a recently published multiverse debugger for microcontrollers that focuses on IO consistency, our approach directly targets state explosion by leveraging concolic execution and uses a trace-based approach, significantly reducing the memory and communication overhead. We implemented a prototype using the WARDuino WebAssembly virtual machine on an STM32 microcontroller, demonstrating the feasibility and efficiency of our approach in real-world scenarios. Our results highlight substantial reductions in the state space compared to traditional multiverse debugging. This makes multiverse debugging more accessible and efficient for developers working with complex, nondeterministic programs running on microcontrollers.
Cite as

Maarten Steevens, Tom Lauwaerts, and Christophe Scholliers. Remote Concolic Multiverse Debugging. In 40th European Conference on Object-Oriented Programming (ECOOP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 372, pp. 27:1-27:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{steevens_et_al:LIPIcs.ECOOP.2026.27,
  author =	{Steevens, Maarten and Lauwaerts, Tom and Scholliers, Christophe},
  title =	{{Remote Concolic Multiverse Debugging}},
  booktitle =	{40th European Conference on Object-Oriented Programming (ECOOP 2026)},
  pages =	{27:1--27:29},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-423-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{372},
  editor =	{Krebbers, Robbert and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2026.27},
  URN =		{urn:nbn:de:0030-drops-261238},
  doi =		{10.4230/LIPIcs.ECOOP.2026.27},
  annote =	{Keywords: Multiverse Debugging, Embedded devices, WebAssembly}
}
Document
Artifact
DOI: 10.4230/DARTS.12.1.11
Remote Concolic Multiverse Debugging (Artifact)

Authors: Maarten Steevens, Tom Lauwaerts, and Christophe Scholliers

Published in: DARTS, Volume 12, Issue 1, Special Issue of the 40th European Conference on Object-Oriented Programming (ECOOP 2026)

Abstract
This artifact accompanies our work "Remote Concolic Multiverse Debugging". In this work we present a novel multiverse debugger capable of effectively pruning redundant paths from the state space to reduce the effect of state explosion. This is accomplished by leveraging the power of concolic execution which is able to reduce the number of paths while ensuring full code coverage. Additionally, this work uses a trace-based approach which significantly reduces the overhead of multiverse debugging. This approach differs from previous works such as MIO, which uses a snapshot-based approach and focuses on IO consistency instead of the state explosion problem. The artifact consists of three components which are bundled in the form of a VM image. This image consists of our prototype Remote Concolic Multiverse Debugger, an evaluation of our state-space reduction system and a performance comparison between trace and snapshot-based approaches.
Cite as

Maarten Steevens, Tom Lauwaerts, and Christophe Scholliers. Remote Concolic Multiverse Debugging (Artifact). In Special Issue of the 40th European Conference on Object-Oriented Programming (ECOOP 2026). Dagstuhl Artifacts Series (DARTS), Volume 12, Issue 1, pp. 11:1-11:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@Article{steevens_et_al:DARTS.12.1.11,
  author =	{Steevens, Maarten and Lauwaerts, Tom and Scholliers, Christophe},
  title =	{{Remote Concolic Multiverse Debugging (Artifact)}},
  pages =	{11:1--11:8},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2026},
  volume =	{12},
  number =	{1},
  editor =	{Steevens, Maarten and Lauwaerts, Tom and Scholliers, Christophe},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.12.1.11},
  URN =		{urn:nbn:de:0030-drops-261486},
  doi =		{10.4230/DARTS.12.1.11},
  annote =	{Keywords: Multiverse Debugging, Embedded devices, WebAssembly}
}
Document
Artifact
DOI: 10.4230/DARTS.5.2.4
Multiverse Debugging: Non-Deterministic Debugging for Non-Deterministic Programs (Artifact)

Authors: Robbert Gurdeep Singh, Carmen Torres Lopez, Stefan Marr, Elisa Gonzalez Boix, and Christophe Scholliers

Published in: DARTS, Volume 5, Issue 2, Special Issue of the 33rd European Conference on Object-Oriented Programming (ECOOP 2019)

Abstract
Many of today’s software systems are parallel or concurrent. With the rise of Node.js and more generally event-loop architectures, many systems need to handle concurrency. However, their non-deterministic behavior makes it hard to debug. Today’s interactive debuggers unfortunately do not support developers in debugging non-deterministic issues. They only allow exploring a single execution path. Therefore, some bugs may never be reproduced in the debugging session, because the conditions to trigger are not reached. As a solution, we propose multiverse debugging, a new approach for debugging non-deterministic programs that allow developers to observe all possible execution paths of a parallel program and debug it interactively. We introduce the concepts of multiverse breakpoints and stepping, which can halt a program in different execution paths, i.e. universes. We apply multiverse debugging to AmbientTalk, an actor-based language, resulting in Voyager, a proof of concept multiverse debugger that takes as input Featherweight AmbientTalk programs written in PLT-Redex, and allows programmers to interactively browse all possible execution states by means of multiverse breakpoints and stepping commands. We provide a proof of non-interference, i.e we prove that observing the behavior of a program by the debugger does not affect the behavior of that program and vice versa. Multiverse debugging establishes the foundation for debugging non-deterministic programs interactively, which we believe can aid the development of parallel and concurrent systems.
Cite as

Robbert Gurdeep Singh, Carmen Torres Lopez, Stefan Marr, Elisa Gonzalez Boix, and Christophe Scholliers. Multiverse Debugging: Non-Deterministic Debugging for Non-Deterministic Programs (Artifact). In Special Issue of the 33rd European Conference on Object-Oriented Programming (ECOOP 2019). Dagstuhl Artifacts Series (DARTS), Volume 5, Issue 2, pp. 4:1-4:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@Article{singh_et_al:DARTS.5.2.4,
  author =	{Singh, Robbert Gurdeep and Lopez, Carmen Torres and Marr, Stefan and Boix, Elisa Gonzalez and Scholliers, Christophe},
  title =	{{Multiverse Debugging: Non-Deterministic Debugging for Non-Deterministic Programs}},
  pages =	{4:1--4:3},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2019},
  volume =	{5},
  number =	{2},
  editor =	{Singh, Robbert Gurdeep and Lopez, Carmen Torres and Marr, Stefan and Boix, Elisa Gonzalez and Scholliers, Christophe},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.5.2.4},
  URN =		{urn:nbn:de:0030-drops-107815},
  doi =		{10.4230/DARTS.5.2.4},
  annote =	{Keywords: Debugging, Concurrency, Actors, Formal Semantics}
}
Document
Brave New Idea Paper
DOI: 10.4230/LIPIcs.ECOOP.2019.27
Multiverse Debugging: Non-Deterministic Debugging for Non-Deterministic Programs (Brave New Idea Paper)

Authors: Carmen Torres Lopez, Robbert Gurdeep Singh, Stefan Marr, Elisa Gonzalez Boix, and Christophe Scholliers

Published in: LIPIcs, Volume 134, 33rd European Conference on Object-Oriented Programming (ECOOP 2019)

Abstract
Many of today’s software systems are parallel or concurrent. With the rise of Node.js and more generally event-loop architectures, many systems need to handle concurrency. However, its non-deterministic behavior makes it hard to reproduce bugs. Today’s interactive debuggers unfortunately do not support developers in debugging non-deterministic issues. They only allow us to explore a single execution path. Therefore, some bugs may never be reproduced in the debugging session, because the right conditions are not triggered. As a solution, we propose multiverse debugging, a new approach for debugging non-deterministic programs that allows developers to observe all possible execution paths of a parallel program and debug it interactively. We introduce the concepts of multiverse breakpoints and stepping, which can halt a program in different execution paths, i.e. universes. We apply multiverse debugging to AmbientTalk, an actor-based language, resulting in Voyager, a multiverse debugger implemented on top of the AmbientTalk operational semantics. We provide a proof of non-interference, i.e., we prove that observing the behavior of a program by the debugger does not affect the behavior of that program and vice versa. Multiverse debugging establishes the foundation for debugging non-deterministic programs interactively, which we believe can aid the development of parallel and concurrent systems.
Cite as

Carmen Torres Lopez, Robbert Gurdeep Singh, Stefan Marr, Elisa Gonzalez Boix, and Christophe Scholliers. Multiverse Debugging: Non-Deterministic Debugging for Non-Deterministic Programs (Brave New Idea Paper). In 33rd European Conference on Object-Oriented Programming (ECOOP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 134, pp. 27:1-27:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{torreslopez_et_al:LIPIcs.ECOOP.2019.27,
  author =	{Torres Lopez, Carmen and Gurdeep Singh, Robbert and Marr, Stefan and Gonzalez Boix, Elisa and Scholliers, Christophe},
  title =	{{Multiverse Debugging: Non-Deterministic Debugging for Non-Deterministic Programs}},
  booktitle =	{33rd European Conference on Object-Oriented Programming (ECOOP 2019)},
  pages =	{27:1--27:30},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-111-5},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{134},
  editor =	{Donaldson, Alastair F.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2019.27},
  URN =		{urn:nbn:de:0030-drops-108192},
  doi =		{10.4230/LIPIcs.ECOOP.2019.27},
  annote =	{Keywords: Debugging, Parallelism, Concurrency, Actors, Formal Semantics}
}
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