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Documents authored by Sutherland, Julian

Document
DOI: 10.4230/LIPIcs.ECOOP.2023.19
Exact Separation Logic: Towards Bridging the Gap Between Verification and Bug-Finding

Authors: Petar Maksimović, Caroline Cronjäger, Andreas Lööw, Julian Sutherland, and Philippa Gardner

Published in: LIPIcs, Volume 263, 37th European Conference on Object-Oriented Programming (ECOOP 2023)

Abstract
Over-approximating (OX) program logics, such as separation logic (SL), are used for verifying properties of heap-manipulating programs: all terminating behaviour is characterised, but established results and errors need not be reachable. OX function specifications are thus incompatible with true bug-finding supported by symbolic execution tools such as Pulse and Pulse-X. In contrast, under-approximating (UX) program logics, such as incorrectness separation logic, are used to find true results and bugs: established results and errors are reachable, but there is no mechanism for understanding if all terminating behaviour has been characterised. We introduce exact separation logic (ESL), which provides fully-verified function specifications compatible with both OX verification and UX true bug-funding: all terminating behaviour is characterised and all established results and errors are reachable. We prove soundness for ESL with mutually recursive functions, demonstrating, for the first time, function compositionality for a UX logic. We show that UX program logics require subtle definitions of internal and external function specifications compared with the familiar definitions of OX logics. We investigate the expressivity of ESL and, for the first time, explore the role of abstraction in UX reasoning by verifying abstract ESL specifications of various data-structure algorithms. In doing so, we highlight the difference between abstraction (hiding information) and over-approximation (losing information). Our findings demonstrate that abstraction cannot be used as freely in UX logics as in OX logics, but also that it should be feasible to use ESL to provide tractable function specifications for self-contained, critical code, which would then be used for both verification and true bug-finding.
Cite as

Petar Maksimović, Caroline Cronjäger, Andreas Lööw, Julian Sutherland, and Philippa Gardner. Exact Separation Logic: Towards Bridging the Gap Between Verification and Bug-Finding. In 37th European Conference on Object-Oriented Programming (ECOOP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 263, pp. 19:1-19:27, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{maksimovic_et_al:LIPIcs.ECOOP.2023.19,
  author =	{Maksimovi\'{c}, Petar and Cronj\"{a}ger, Caroline and L\"{o}\"{o}w, Andreas and Sutherland, Julian and Gardner, Philippa},
  title =	{{Exact Separation Logic: Towards Bridging the Gap Between Verification and Bug-Finding}},
  booktitle =	{37th European Conference on Object-Oriented Programming (ECOOP 2023)},
  pages =	{19:1--19:27},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-281-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{263},
  editor =	{Ali, Karim and Salvaneschi, Guido},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2023.19},
  URN =		{urn:nbn:de:0030-drops-182123},
  doi =		{10.4230/LIPIcs.ECOOP.2023.19},
  annote =	{Keywords: Separation logic, program correctness, program incorrectness, abstraction}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2018.4
A Concurrent Specification of POSIX File Systems

Authors: Gian Ntzik, Pedro da Rocha Pinto, Julian Sutherland, and Philippa Gardner

Published in: LIPIcs, Volume 109, 32nd European Conference on Object-Oriented Programming (ECOOP 2018)

Abstract
POSIX is a standard for operating systems, with a substantial part devoted to specifying file-system operations. File-system operations exhibit complex concurrent behaviour, comprising multiple actions affecting different parts of the state: typically, multiple atomic reads followed by an atomic update. However, the standard's description of concurrent behaviour is unsatisfactory: it is fragmented; contains ambiguities; and is generally under-specified. We provide a formal concurrent specification of POSIX file systems and demonstrate scalable reasoning for clients. Our specification is based on a concurrent specification language, which uses a modern concurrent separation logic for reasoning about abstract atomic operations, and an associated refinement calculus. Our reasoning about clients highlights an important difference between reasoning about modules built over a heap, where the interference on the shared state is restricted to the operations of the module, and modules built over a file system, where the interference cannot be restricted as the file system is a public namespace. We introduce specifications conditional on context invariants used to restrict the interference, and apply our reasoning to the example of lock files.
Cite as

Gian Ntzik, Pedro da Rocha Pinto, Julian Sutherland, and Philippa Gardner. A Concurrent Specification of POSIX File Systems. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 4:1-4:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{ntzik_et_al:LIPIcs.ECOOP.2018.4,
  author =	{Ntzik, Gian and da Rocha Pinto, Pedro and Sutherland, Julian and Gardner, Philippa},
  title =	{{A Concurrent Specification of POSIX File Systems}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{4:1--4:28},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-079-8},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{109},
  editor =	{Millstein, Todd},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2018.4},
  URN =		{urn:nbn:de:0030-drops-92092},
  doi =		{10.4230/LIPIcs.ECOOP.2018.4},
  annote =	{Keywords: POSIX, concurrency, file systems, refinement, separation logic, atomicity}
}
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