# rems-all.bib

@inproceedings{Mulligan:2014:LRE:2628136.2628143,
author = {Mulligan, Dominic P. and Owens, Scott and Gray, Kathryn E. and Ridge, Tom and Sewell, Peter},
title = {Lem: Reusable Engineering of Real-world Semantics},
booktitle = {\textbf{ICFP 2014}: Proceedings of the 19th ACM SIGPLAN International Conference on Functional Programming},
conf = {ICFP 2014},
year = {2014},
month = sep,
isbn = {978-1-4503-2873-9},
location = {Gothenburg, Sweden},
pages = {175--188},
numpages = {14},
url = {http://doi.acm.org/10.1145/2628136.2628143},
pdf = {http://www.cl.cam.ac.uk/~pes20/lem/built-doc/lem-icfp-2014.pdf},
doi = {10.1145/2628136.2628143},
acmid = {2628143},
publisher = {ACM},
address = {New York, NY, USA},
optkeywords = {lem, proof assistants, real-world semantics, specification languages},
abstract = {
Recent years have seen remarkable successes in rigorous engineering: using mathematically rigorous semantic models (not just idealised calculi) of real-world processors, programming languages, protocols, and security mechanisms, for testing, proof, analysis, and design. Building these models is challenging, requiring experimentation, dialogue with vendors or standards bodies, and validation; their scale adds engineering issues akin to those of programming to the task of writing clear and usable mathematics. But language and tool support for specification is lacking. Proof assistants can be used but bring their own difficulties, and a model produced in one, perhaps requiring many person-years effort and maintained over an extended period, cannot be used by those familiar with another.

We introduce Lem, a language for engineering reusable large-scale semantic models. The Lem design takes inspiration both from functional programming languages and from proof assistants, and Lem definitions are translatable into OCaml for testing, Coq, HOL4, and Isabelle/HOL for proof, and LaTeX and HTML for presentation. This requires a delicate balance of expressiveness, careful library design, and implementation of transformations - akin to compilation, but subject to the constraint of producing usable and human-readable code for each target. Lem's effectiveness is demonstrated by its use in practice.
}
}

@inproceedings{ITP-sub,
author = {Anthony C. J. Fox},
title = {Improved Tool Support for Machine-Code Decompilation in {HOL4}},
abstract = {The HOL4 interactive theorem prover provides a sound logical environment for reasoning about machine-code programs.  The rigour of HOL's LCF-style kernel naturally guarantees very high levels of assurance, but it does present challenges when it comes implementing efficient proof tools. This paper presents improvements that have been made to our methodology for soundly \emph{decompiling} machine-code programs to functions expressed in HOL logic. These advancements have been facilitated by the development of a domain specific language, called L3, for the specification of Instruction Set Architectures (ISAs). As a result of these improvements, decompilation is faster (on average by one to two orders of magnitude), the instruction set specifications are easier to write, and the proof tools are easier to maintain.
},
booktitle = {{\textbf{ITP 2015}}:Interactive Theorem Proving - 6th International Conference, Nanjing, China},
conf = {ITP 2015},
pages = {187--202},
year = {2015},
month = aug,
optcrossref = {DBLP:conf/itp/2015},
url = {http://dx.doi.org/10.1007/978-3-319-22102-1_12},
pdf = {http://www.cl.cam.ac.uk/~acjf3/papers/itp15.pdf},
doi = {10.1007/978-3-319-22102-1_12},
timestamp = {Mon, 24 Aug 2015 16:29:06 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/itp/Fox15},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@misc{BasileMPRI,
optkey = {},
author = {Basile Clement},
title = {Running programming language specifications},
opthowpublished = {},
month = aug,
year = 2014,
note = {MPRI report},
conf = {MPRI report},
optannote = {}
}

@inproceedings{PittsAM:deptta,
author = {A. M. Pitts and J. Matthiesen and J. Derikx},
title = {A Dependent Type Theory with Abstractable Names},
booktitle = {\textbf{LSFA 2014}: Proceedings of the 9th Workshop on Logical and
Semantic Frameworks, with Applications},
conf = {LSFA 2014},
year = 2015,
month = apr,
editor = {I. Mackie and M. Ayala-Rincon},
volume = 312,
series = {Electronic Notes in Theoretical Computer Science},
pages = {19--50},
doi = {http://dx.doi.org/10.1016/j.entcs.2015.04.003},
pdf = {https://www.repository.cam.ac.uk/bitstream/handle/1810/247863/Pitts_et_al-2015-Electronic_Notes_in_Theoretical_Computer_Science.pdf?sequence=1},
abstract = {This paper describes a version of Martin-Löf's dependent type theory extended with names and constructs for freshness and name-abstraction derived from the theory of nominal sets. We aim for a type theory for computing and proving (via a Curry-Howard correspondence) with syntactic structures which captures familiar, but informal, "nameful" practices when dealing with binders.},
publisher = {Elsevier}
}

@inproceedings{rems-fmics14,
title = {Randomised Testing of a Microprocessor Model Using {SMT}-Solver State Generation},
author = {Brian Campbell and Ian Stark},
booktitle = {\textbf{FMICS 2014}: Formal Methods for Industrial Critical Systems},
conf = {FMICS 2014},
year = 2014,
month = sep,
editor = {Fr{\'{e}}d{\'{e}}ric Lang and Francesco Flammini},
volume = 8718,
series = {Lecture Notes in Computer Science},
pages = {185--199},
publisher = {Springer},
doi = {10.1007/978-3-319-10702-8_13},
slides = {rems/fmics-m0-talk.pdf},
preprint = {rems/fmics2014.pdf},
url = {http://homepages.inf.ed.ac.uk/bcampbe2/rems/fmics2014.pdf},
preprintnote = {The final publication is available at link.springer.com},
abstract = {We validate a HOL4 model of the ARM Cortex-M0 microcontroller core by testing the model's behaviour on randomly chosen
instructions against a real chip.
The model and our intended application involve precise timing information about instruction execution, but the implementations are pipelined,
so checking the behaviour of single instructions would not give us sufficient confidence in the model. Thus we test the model using sequences
of randomly chosen instructions.
The main challenge is to meet the constraints on the initial and intermediate execution states: we must ensure that memory accesses are in
range and that we respect restrictions on the instructions. By careful
transformation of these constraints an off-the-shelf SMT solver can be
used to find suitable states for executing test sequences.
}
}

@article{rems-scico15,
author = {Brian Campbell and Ian Stark},
title = {Randomised Testing of a Microprocessor Model Using {SMT}-Solver State Generation},
journal = {\textbf{Sci. Comput. Program.}},
volume = 118,
pages = {60--76},
year = 2016,
month = mar,
issn = {0167-6423},
doi = {10.1016/j.scico.2015.10.012},
pdf = {http://homepages.inf.ed.ac.uk/bcampbe2/rems/scico2015.pdf},
abstract = {We validate a HOL4 model of the ARM Cortex-M0 microcontroller core by testing the model’s behaviour on randomly chosen instructions against real chips from several manufacturers.
The model and our intended application involve precise timing information about instruction execution, but the implementations are pipelined, so checking the behaviour of single instructions would not give us sufficient confidence in the model. Thus we test the model using sequences of randomly chosen instructions.
The main challenge is to meet the constraints on the initial and intermediate execution states: we must ensure that memory accesses are in range and that we respect restrictions on the instructions. By careful transformation of these constraints an off-the-shelf SMT solver can be used to find suitable states for executing test sequences. We also use additional constraints to test our hypotheses about the timing anomalies encountered.}
}

@misc{HCSS2015-Flur,
optkey = {},
author = {S. Flur and K. Gray and G. Kerneis and D. Mulligan and C. Pulte and S. Sarkar and P. Sewell},
title = {Rigorous Architectural Modelling for Production Multiprocessors},
opthowpublished = {},
month = may,
year = 2015,
note = {Presentation at HCSS 2015: the Fifteenth Annual
High Confidence Software and Systems Conference},
optannote = {},
abstract = {
Processor architectures are critical interfaces in computing, but they
are typically defined only by prose and pseudocode documentation.
This is especially problematic for the subtle concurrency behaviour of
weakly consistent multiprocessors such as ARM and IBM POWER: the
traditional documentation does not define precisely what
programmer-observable behaviour is (and is not) allowed for concurrent
code; it is not executable as a test oracle for pre-Silicon or
post-Silicon hardware testing; it is not executable as an emulator for
software testing; and it is not mathematically rigorous enough to
serve as a foundation for software verification.

We present a rigorous architectural envelope model for IBM POWER
multiprocessors, and similar work in progress for ARM, that aims to
support all of these for small-but-intricate test cases, integrating
an operational concurrency model with an ISA model for the sequential
behaviour of a substantial fragment of the user-mode instruction set
(largely automatically derived from the vendor pseudocode, and
expressed in a new ISA description language).  The key question is the
interface between these two: we have to allow all the required
relaxed-memory behaviour, without overcommitting to some particular
microarchitectural model.  Our models can be automatically translated
into executable code, which, combined with front-ends for concurrency
litmus tests and ELF executables, can interactively or exhaustively
explore all the allowed behaviours of small test cases.
}
}

@inproceedings{DBLP:conf/asplos/AlglaveBDGKPSW15,
Mark Batty and
Alastair F. Donaldson and
Ganesh Gopalakrishnan and
Jeroen Ketema and
Daniel Poetzl and
Tyler Sorensen and
John Wickerson},
title = {{GPU} Concurrency: Weak Behaviours and Programming Assumptions},
booktitle = {\textbf{ASPLOS 2015}: Proceedings of the Twentieth International Conference on Architectural
Support for Programming Languages and Operating Systems, Istanbul, Turkey},
conf = {ASPLOS 2015},
pages = {577--591},
year = {2015},
month = mar,
optcrossref = {DBLP:conf/asplos/2015},
url = {http://doi.acm.org/10.1145/2694344.2694391},
doi = {10.1145/2694344.2694391},
timestamp = {Thu, 26 Feb 2015 17:21:18 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/asplos/AlglaveBDGKPSW15},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {
Concurrency is pervasive and perplexing, particularly on graphics processing units (GPUs). Current specifications of languages and hardware are inconclusive; thus programmers often rely on folklore assumptions when writing software.

To remedy this state of affairs, we conducted a large empirical study of the concurrent behaviour of deployed GPUs. Armed with litmus tests (i.e. short concurrent programs), we questioned the assumptions in programming guides and vendor documentation about the guarantees provided by hardware. We developed a tool to generate thousands of litmus tests and run them under stressful workloads. We observed a litany of previously elusive weak behaviours, and exposed folklore beliefs about GPU programming---often supported by official tutorials---as false.

As a way forward, we propose a model of Nvidia GPU hardware, which correctly models every behaviour witnessed in our experiments. The model is a variant of SPARC Relaxed Memory Order (RMO), structured following the GPU concurrency hierarchy.
}
}

@inproceedings{CHERI-Oakland,
author = {Robert N. M. Watson and Jonathan Woodruff and Peter G. Neumann and Simon W. Moore and Jonathan Anderson and David Chisnall and Nirav Dave and Brooks Davis and Khilan Gudka and Ben Laurie and Steven J. Murdoch and Robert Norton and Michael Roe and Stacey Son and Munraj Vadera},
title = {{CHERI}: A Hybrid Capability-System Architecture for Scalable Software Compartmentalization},
optcrossref = {},
optkey = {},
booktitle = {\textbf{Security and Privacy 2015}: {Proceedings of the 36th IEEE Symposium on Security and Privacy (Oakland'')}},
conf = {Security and Privacy 2015},
optpages = {},
year = {2015},
opteditor = {},
optvolume = {},
optnumber = {},
optseries = {},
month = may,
optorganization = {},
optpublisher = {},
optnote = {},
optannote = {},
doi = {http://dx.doi.org/10.1109/SP.2015.9},
url = {http://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/201505-oakland2015-cheri-compartmentalization.pdf},
abstract = {CHERI extends a conventional RISC Instruction-Set Architecture, compiler, and operating system to support
fine-grained, capability-based memory protection to mitigate
memory-related vulnerabilities in C-language TCBs. We describe
how CHERI capabilities can also underpin a hardware-software
object-capability model for application compartmentalization
that can mitigate broader classes of attack. Prototyped as an
extension to the open-source 64-bit BERI RISC FPGA softcore processor, FreeBSD operating system, and LLVM compiler,
we demonstrate multiple orders-of-magnitude improvement in
scalability, simplified programmability, and resulting tangible
security benefits as compared to compartmentalization based on
pure Memory-Management Unit (MMU) designs. We evaluate
incrementally deployable CHERI-based compartmentalization
using several real-world UNIX libraries and applications.
}
}

@inproceedings{DBLP:conf/micro/GrayKMPSS15,
author = {Kathryn E. Gray and
Gabriel Kerneis and
Dominic P. Mulligan and
Christopher Pulte and
Susmit Sarkar and
Peter Sewell},
title = {An integrated concurrency and core-{ISA} architectural envelope definition,
and test oracle, for {IBM} {POWER} multiprocessors},
abstract = {Weakly consistent multiprocessors such as ARM and IBM POWER have been with us for decades, but their subtle programmer-visible concurrency behaviour remains challenging, both to implement and to use; the traditional architecture documentation, with its mix of prose and pseudocode, leaves much unclear.

In this paper we show how a precise architectural envelope model for such architectures can be defined, taking IBM POWER as our example.  Our model specifies, for an arbitrary test program, the set of all its allowable executions, not just those of some particular implementation.  The model integrates an operational concurrency model with an ISA model for the fixed-point non-vector user-mode instruction set (largely automatically derived from the vendor pseudocode, and expressed in a new ISA description language).  The key question is the interface between these two: allowing all the required concurrency behaviour, without overcommitting to some particular microarchitectural implementation, requires a novel abstract structure.

Our model is expressed in a mathematically rigorous language that can be automatically translated to an executable test-oracle tool; this lets one either interactively explore or exhaustively compute the set of all allowed behaviours of intricate test cases, to provide a reference for hardware and software development.
},
booktitle = {\textbf{MICRO 2015}: Proceedings of the 48th International Symposium on Microarchitecture,
, Waikiki, HI, USA},
conf = {MICRO 2015},
pages = {635--646},
year = {2015},
month = dec,
optcrossref = {DBLP:conf/micro/2015},
url = {http://doi.acm.org/10.1145/2830772.2830775},
pdf = {http://www.cl.cam.ac.uk/~pes20/micro-48-2015.pdf},
doi = {10.1145/2830772.2830775},
timestamp = {Sun, 10 Jan 2016 12:42:56 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/micro/GrayKMPSS15},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@inproceedings{DBLP:conf/popl/FlurGPSSMDS16,
author = {Shaked Flur and
Kathryn E. Gray and
Christopher Pulte and
Susmit Sarkar and
Ali Sezgin and
Luc Maranget and
Will Deacon and
Peter Sewell},
title = {Modelling the {ARMv8} architecture, operationally: concurrency and {ISA}},
abstract = {In this paper we develop semantics for key aspects of the ARMv8 multiprocessor architecture: the concurrency model and much of the 64-bit application-level instruction set (ISA).  Our goal is to clarify what the range of architecturally allowable behaviour is, and thereby to support future work on formal verification, analysis, and testing of concurrent ARM software and hardware.

Establishing such models with high confidence is intrinsically difficult: it involves capturing the vendor's architectural intent, aspects of which (especially for concurrency) have not previously been precisely defined.  We therefore first develop a concurrency model with a microarchitectural flavour, abstracting from many hardware implementation concerns but still close to hardware-designer intuition.  This means it can be discussed in detail with ARM architects.  We then develop a more abstract model, better suited for use as an architectural specification, which we prove sound w.r.t.~the first.

The instruction semantics involves further difficulties, handling the mass of detail and the subtle intensional information required to interface to the concurrency model.  We have a novel ISA description language, with a lightweight dependent type system, letting us do both with a rather direct representation of the ARM reference manual instruction descriptions.

We build a tool from the combined semantics that lets one explore, either interactively or exhaustively, the full range of architecturally allowed behaviour, for litmus tests and (small) ELF executables.  We prove correctness of some optimisations needed for tool performance.

We validate the models by discussion with ARM staff, and by comparison against ARM hardware behaviour, for ISA single- instruction tests and concurrent litmus tests.},
booktitle = {\textbf{POPL 2016}: Proceedings of the 43rd Annual {ACM} {SIGPLAN-SIGACT} Symposium on
Principles of Programming Languages, St. Petersburg,
FL, USA },
conf = {POPL 2016},
pages = {608--621},
year = {2016},
month = jan,
optcrossref = {DBLP:conf/popl/2016},
url = {http://doi.acm.org/10.1145/2837614.2837615},
pdf = {http://www.cl.cam.ac.uk/~pes20/popl16-armv8/top.pdf},
doi = {10.1145/2837614.2837615},
timestamp = {Fri, 08 Jan 2016 18:18:25 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/popl/FlurGPSSMDS16},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@inproceedings{DBLP:conf/memocode/NaylorM15,
author = {Matthew Naylor and
Simon W. Moore},
title = {A generic synthesisable test bench},
booktitle = {\textbf{MEMOCODE 2015}: {ACM/IEEE} International Conference on Formal
Methods and Models
for Codesign,  Austin, TX, USA},
conf = {MEMOCODE 2015},
pages = {128--137},
year = {2015},
month = sep,
url = {http://dx.doi.org/10.1109/MEMCOD.2015.7340479},
doi = {10.1109/MEMCOD.2015.7340479},
timestamp = {Tue, 08 Dec 2015 17:08:30 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/memocode/NaylorM15},
bibsource = {dblp computer science bibliography, http://dblp.org},
pdf = {http://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/201509-memocode2015-bluecheck.pdf},
abstract = {
Writing test benches is one of the most frequently-performed tasks in
the hardware development process.  The ability to reuse common
test bench features is therefore key to productivity.  In this paper,
we present a generic test bench, parameterised by a
specification of correctness, which can be used to test any
design.  Our test bench provides several important features, including
automatic test-sequence generation and shrinking of counter-examples,
and is fully synthesisable, allowing rigorous testing on FPGA as well
as in simulation.  The approach is easy to use, cheap to implement,
and encourages the formal specification of hardware components through
the reward of automatic testing and simple failure cases.
}
}

@techreport{UCAM-CL-TR-876,
author = {Watson, Robert N. M. and Neumann, Peter G. and Woodruff,
Jonathan and Roe, Michael and Anderson, Jonathan and
Chisnall, David and Davis, Brooks and Joannou, Alexandre
and Laurie, Ben and Moore, Simon W. and Murdoch, Steven J.
and Norton, Robert and Son, Stacey},
title = {{Capability Hardware Enhanced RISC Instructions: CHERI
Instruction-Set Architecture}},
year = 2015,
month = sep,
url = {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-876.pdf},
institution = {University of Cambridge, Computer Laboratory},
number = {UCAM-CL-TR-876},
abstract = {This technical report describes CHERI ISAv4, the fourth version of the Capability Hardware Enhanced RISC Instructions (CHERI) Instruction-Set Architecture (ISA). CHERI is being developed by SRI International and the University of Cambridge. This design captures four years of research, development, refinement, formal analysis, and testing, and is a substantial enhancement to the ISA version described in UCAM-CL-TR-850. Key improvements lie in tighter C-language integration, and more mature support for software object-capability models; these changes result from experience gained in adapting substantial software stacks to run on prototype hardware.

The CHERI instruction set is based on a hybrid capability-system architecture that adds new capability-system primitives to a commodity 64-bit RISC ISA enabling software to efficiently implement fine-grained memory protection and a hardware-software object-capability security model. These extensions support incrementally adoptable, high-performance, formally based, programmer-friendly underpinnings for fine-grained software decomposition and compartmentalization, motivated by and capable of enforcing the principle of least privilege.

The CHERI system architecture purposefully addresses known performance and robustness gaps in commodity ISAs that hinder the adoption of more secure programming models centered around the principle of least privilege. To this end, CHERI blends traditional paged virtual memory with a per-address-space capability model that includes capability registers, capability instructions, and tagged memory that have been added to the 64-bit MIPS ISA via a new capability coprocessor. CHERI also learns from the C-language fat-pointer literature: CHERI capabilities can describe not only regions of memory, but can also capture C pointer semantics allowing capabilities to be substituted for pointers in generated code.

CHERI’s hybrid system approach, inspired by the Capsicum security model, allows incremental adoption of capability-oriented software design: software implementations that are more robust and resilient can be deployed where they are most needed, while leaving less critical software largely unmodified, but nevertheless suitably constrained to be incapable of having adverse effects. For example, we are focusing conversion efforts on low-level TCB components of the system: separation kernels, hypervisors, operating system kernels, language runtimes, and userspace TCBs such as web browsers. Likewise, we see early-use scenarios (such as data compression, protocol parsing, image processing, and video processing) that relate to particularly high-risk software libraries, which are concentrations of both complex and historically vulnerability-prone code combined with untrustworthy data sources, while leaving containing applications unchanged.

This report describes the CHERI Instruction-Set Architecture (ISA) and design, and provides reference documentation and potential memory models, along with their requirements. It also briefly addresses the CHERI system hardware-software architecture, documenting our current thinking on integrating programming languages and operating systems with the CHERI hardware.}
}

@techreport{UCAM-CL-TR-877,
author = {Watson, Robert N. M. and Chisnall, David and Davis, Brooks
and Koszek, Wojciech and Moore, Simon W. and Murdoch,
Steven J. and Neumann, Peter G. and Woodruff, Jonathan},
title = {{Capability Hardware Enhanced RISC Instructions: CHERI
Programmer's Guide}},
year = 2015,
month = sep,
url = {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-877.pdf},
institution = {University of Cambridge, Computer Laboratory},
number = {UCAM-CL-TR-877},
abstract = {The CHERI Programmer's Guide documents the software environment for the Capability Hardware Enhanced RISC Instructions (CHERI) prototype developed by SRI International and the
University of Cambridge. The Guide is targeted at hardware and software developers working
with capability-enhanced software. It describes how to use the CHERI Clang/LLVM compiler
suite and CheriBSD operating system -- versions of the off-the-shelf LLVM suite and FreeBSD
operating system adapted to use CHERI’s protection features -- as well as implementation details of both.}
}

@inproceedings{NaylorFMCAD2016,
author = {M. Naylor and S. W. Moore and A. Mujumdar},
booktitle = {\textbf{FMCAD 2016}: Formal Methods in Computer-Aided Design},
title = {A Consistency Checker for Memory Subsystem Traces},
year = {2016},
month = sep,
abstract = {Verifying the memory subsystem in a modern
shared-memory multiprocessor is a big challenge. Optimized
implementations are highly sophisticated, yet must provide subtle
consistency and liveness guarantees for the correct execution of
concurrent programs. We present a tool that supports efficient
specification-based testing of the memory subsystem against a
range of formally specified consistency models. Our tool operates
directly on the memory subsystem interface, promoting a compositional
approach to system-on-chip verification, and can be
used to search for simple failure cases – assisting rapid debug. It
has recently been incorporated into the development flows of two
open-source implementations -- Berkeley’s Rocket Chip (RISCV)
and Cambridge’s BERI (MIPS) -- where it has uncovered a
number of serious bugs.},
doi = {http://dx.doi.org/10.17863/CAM.4451}
}

@inproceedings{mixed17,
author = {Shaked Flur and Susmit Sarkar and Christopher Pulte and Kyndylan Nienhuis and Luc Maranget and Kathryn E. Gray and Ali Sezgin and Mark Batty and Peter Sewell},
title = {Mixed-size Concurrency: {ARM}, {POWER}, {C/C++11}, and {SC}},
booktitle = {\textbf{POPL 2017}: The 44st Annual {ACM} {SIGPLAN-SIGACT} Symposium on Principles of
Programming Languages,  Paris, France},
conf = {POPL 2017},
year = {2017},
month = jan,
pages = {429--442},
numpages = {14},
url = {http://doi.acm.org/10.1145/3009837.3009839},
doi = {10.1145/3009837.3009839},
abstract = {Previous work on the semantics of relaxed shared-memory concurrency has only considered the case in which each load reads the data of exactly one store.  In practice, however, multiprocessors support mixed-size accesses, and these are used by systems software and (to some degree) exposed at the C/C++ language level.  A semantic foundation for software, therefore, has to address them.

We investigate the mixed-size behaviour of ARMv8 and IBM POWER architectures and implementations: by experiment, by developing semantic models, by testing the correspondence between these, and by discussion with ARM and IBM staff.  This turns out to be surprisingly subtle, and on the way we have to revisit the fundamental concepts of coherence and sequential consistency, which change in this setting.  In particular, we show that adding a memory barrier between each instruction does not restore sequential consistency.  We go on to extend the C/C++11 model to support non-atomic mixed-size memory accesses.

This is a necessary step towards semantics for real-world shared-memory concurrent code, beyond litmus tests.
},
pdf = {http://www.cl.cam.ac.uk/~pes20/popl17/mixed-size.pdf}
}

@article{Watson2015,
author = {Robert N.M. Watson and Robert M. Norton and Jonathan Woodruff
and Simon W. Moore and Peter G. Neumann and Jonathan Anderson and
David Chisnall and Brooks Davis and Ben Laurie and Michael Roe and
Nirav H. Dave and Khilan Gudka and Alexandre Joannou and
A. Theodore Markettos and Ed Maste and Steven J. Murdoch and Colin Rothwell
and Stacey D. Son and Munraj Vadera},
title = {Fast Protection-Domain Crossing in the {CHERI} Capability-System
Architecture},
journal = {IEEE Micro},
volume = {36},
number = {5},
pages = {38--49},
month = sep,
year = 2016,
doi = {10.1109/MM.2016.84},
pdf = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7723791},
abstract = {Capability Hardware Enhanced RISC Instructions (CHERI) supplement
the conventional memory management unit (MMU) with instruction-set architecture
(ISA) extensions that implement a capability system model in the address space.
CHERI can also underpin a hardware-software object-capability model for
scalable application compartmentalization that can mitigate broader classes of
protection-domain switching, not only in terms of low cycle count, but also
efficient memory sharing with mutual distrust. The authors propose ISA support
for sealed capabilities, hardware-assisted checking during protection-domain
switching, a lightweight capability flow-control model, and fast register
clearing, while retaining the flexibility of a software-defined
protection-domain transition model. They validate this approach through a
full-system experimental design, including ISA extensions, a field-programmable
gate array prototype (implemented in Bluespec SystemVerilog), and a software
stack including an OS (based on FreeBSD), compiler (based on LLVM), software
compartmentalization model, and open-source applications.}
}

@inproceedings{rems-fmcad16,
title = {Extracting Behaviour from an Executable Instruction Set Model},
author = {Brian Campbell and Ian Stark},
booktitle = {\textbf{FMCAD 2016}: Formal Methods in Computer-Aided Design},
year = 2016,
month = oct,
editor = {Ruzica Piskac and Muralidhar Talupur},
pages = {33--40},
isbn = {978-0-9835678-6-8},
abstract = {Presenting large formal instruction set models as executable functions makes them accessible to engineers and useful for less formal purposes such as simulation.  However, it is more difficult to extract information about the behaviour of individual instructions for reasoning.  We present a method which combines symbolic evaluation and symbolic execution techniques to provide a rule-based view of instruction behaviour, with particular application to automatic test generation for large MIPS-like models.}
}

@techreport{UCAM-CL-TR-907,
author = {Watson, Robert N. M. and Neumann, Peter G. and Woodruff,
Jonathan and Roe, Michael and Anderson, Jonathan and
Baldwin, John and Chisnall, David and Davis, Brooks and
Joannou, Alexandre and Laurie, Ben and Moore, Simon W. and
Murdoch, Steven J. and Norton, Robert and Son, Stacey and
Xia, Hongyan},
title = {{Capability Hardware Enhanced RISC Instructions: CHERI
Instruction-Set Architecture (Version 6)}},
year = 2017,
month = apr,
url = {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-907.pdf},
institution = {University of Cambridge, Computer Laboratory},
number = {UCAM-CL-TR-907}
}

@inproceedings{Joannou2017Tags,
author = {Alexandre Joannou and Jonathan Woodruff and Robert Kovacsics and Simon W. Moore and Alex Bradbury and Hongyan Xia and Robert N. M. Watson and David Chisnall and Michael Roe and Brooks Davis and Edward Napierala and John Baldwin and Khilan Gudka and Peter G. Neumann and Alfredo Mazzinghi and Alex Richardson and Stacey Son and A. Theodore Markettos},
title = {Efficient Tagged Memory},
booktitle = {\textbf{ICCD 2017}: IEEE 35th International Conference on Computer Design},
conf = {ICCD 2017},
year = {2017},
month = nov,
url = {},
doi = {},
pdf = {http://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/201711-iccd2017-efficient-tags.pdf},
abstract = {We characterize the cache behavior of an in-memory tag table and demonstrate that an optimized implementation can typically achieve a near-zero memory traffic overhead. Both industry and academia have repeatedly demonstrated tagged memory as a key mechanism to enable enforcement of power- ful security invariants, including capabilities, pointer integrity, watchpoints, and information-flow tracking. A single-bit tag shadowspace is the most commonly proposed requirement, as one bit is the minimum metadata needed to distinguish between an untyped data word and any number of new hardware- enforced types. We survey various tag shadowspace approaches and identify their common requirements and positive features of their implementations. To avoid non-standard memory widths, we identify the most practical implementation for tag storage to be an in-memory table managed next to the DRAM controller. We characterize the caching performance of such a tag table and demonstrate a DRAM traffic overhead below 5\% for the vast majority of applications. We identify spatial locality on a page scale as the primary factor that enables surprisingly high table cache-ability. We then demonstrate tag-table compression for a set of common applications. A hierarchical structure with elegantly simple optimizations reduces DRAM traffic overhead to below 1% for most applications. These insights and optimizations pave the way for commercial applications making use of single-bit tags stored in commodity memory.}
}

@inproceedings{armv8-mca,
author = {Christopher Pulte and Shaked Flur and Will Deacon and Jon French and Susmit Sarkar and Peter Sewell},
title = {{Simplifying ARM Concurrency: Multicopy-atomic Axiomatic and Operational Models for ARMv8}},
booktitle = {\textbf{POPL 2018}},
conf = {POPL 2018},
optcrossref = {},
optkey = {},
optbooktitle = {},
optpages = {},
year = {2018},
opteditor = {},
optvolume = {},
optnumber = {},
optseries = {},
month = jan,
optorganization = {},
optpublisher = {},
optnote = {Draft},
optannote = {},
pdf = {http://www.cl.cam.ac.uk/~pes20/armv8-mca/armv8-mca-draft.pdf},
project = {http://www.cl.cam.ac.uk/~pes20/armv8-mca/},
abstract = {ARM has a relaxed memory model, previously specified in informal prose for ARMv7 and ARMv8.  Over time, and partly due to work building formal semantics for ARM concurrency, it has become clear that some of the complexity of the model is not justified by the potential benefits.  In particular, the model was originally \emph{non-multicopy-atomic}: writes could become visible to some other threads before becoming visible to all --- but this has not been exploited in production implementations, the corresponding potential hardware optimisations are thought to have insufficient benefits in the ARM context, and it gives rise to subtle complications when combined with other ARMv8 features.  The ARMv8 architecture has therefore been revised: it now has a multicopy-atomic model.  It has also been simplified in other respects, including more straightforward notions of dependency, and the architecture now includes a formal concurrency model.

In this paper we detail these changes and discuss their motivation. We define two formal concurrency models: an operational one, simplifying the Flowing model of Flur et al., and the axiomatic model of the revised ARMv8 specification. The models were developed by an academic group and by ARM staff, respectively, and this extended collaboration partly motivated the above changes. We prove the equivalence of the two models. The operational model is integrated into an executable exploration tool with new web interface, demonstrated by exhaustively checking the possible behaviours of a loop-unrolled version of a Linux kernel lock implementation, a previously known bug due to unprevented speculation, and a fixed version.
},
topic = {Power_and_ARM},
recent = {true}
}

@inproceedings{ChisnallCPDP11,
author = {Chisnall, David and Rothwell, Colin and Davis, Brooks and Watson, Robert N.M. and Woodruff, Jonathan and Vadera, Munraj and Moore, Simon W. and Neumann, Peter G. and Roe, Michael},
title = {Beyond the {PDP-11}: Processor support for a memory-safe {C} abstract machine},
booktitle = {\textbf{ASPLOS 2015}: Proceedings of the Fifteenth Edition of ASPLOS on Architectural Support for Programming Languages and Operating Systems},
conf = {ASPLOS 2015},
series = {ASPLOS XX},
year = {2015},
month = mar,
location = {Istanbul, Turkey},
numpages = {15},
publisher = {ACM},
address = {New York, NY, USA},
optkeywords = {C, memory safety, memory models, code generation},
doi = {10.1145/2694344.2694367},
pdf = {papers/asplos15-memory-safe-c.pdf},
abstract = {We propose a new memory-safe interpretation of the C abstract machine that provides stronger protection to benefit
security and debugging. Despite ambiguities in the specification intended to provide implementation flexibility, contemporary implementations of C have converged on a memory model similar to the PDP-11, the original target for C.
This model lacks support for \emph{memory safety} despite well-documented impacts on security and reliability.

Attempts to change this model are often hampered by assumptions embedded in a large body of existing C code, dating back to the memory model exposed by the original C
compiler for the PDP-11. Our experience with attempting to
implement a memory-safe variant of C on the CHERI experimental microprocessor led us to identify a number of
problematic idioms. We describe these as well as their interaction with existing memory safety schemes and the assumptions that they make beyond the requirements of the C
specification. Finally, we refine the CHERI ISA and abstract
model for C, by combining elements of the CHERI capability model and fat pointers, and present a softcore CPU that
implements a C abstract machine that can run legacy C code
with strong memory protection guarantees.
}
}

@inproceedings{BMNPS2015,
author = {Mark Batty and
Kayvan Memarian and
Kyndylan Nienhuis and
Jean Pichon{-}Pharabod and
Peter Sewell},
title = {The Problem of Programming Language Concurrency Semantics},
abstract = {Despite decades of research, we do not have a satisfactory concurrency semantics for any general-purpose programming language that aims to support concurrent systems code. The Java Memory Model has been shown to be unsound with respect to standard compiler optimisations, while the C/C++11 model is too weak, admitting undesirable thin-air executions. Our goal in this paper is to articulate this major open problem as clearly as is currently possible, showing how it arises from the combination of multiprocessor relaxed-memory behaviour and the desire to accommodate current compiler optimisations. We make several novel contributions that each shed some light on the problem, constraining the possible solutions and identifying new difficulties.},
booktitle = {\textbf{ESOP 2015}: Programming Languages and Systems - 24th European Symposium on Programming,
Held as Part of the European Joint Conferences on Theory
and Practice of Software, {ETAPS} 2015, London, UK, April 11-18, 2015.
},
conf = {ESOP 2015},
pages = {283--307},
year = {2015},
month = apr,
optcrossref = {DBLP:conf/esop/2015},
url = {http://dx.doi.org/10.1007/978-3-662-46669-8_12},
pdf = {http://www.cl.cam.ac.uk/~pes20/cpp/c_concurrency_challenges.pdf},
doi = {10.1007/978-3-662-46669-8_12},
timestamp = {Tue, 07 Apr 2015 15:19:02 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/esop/BattyMNPS15},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@misc{EBC2014,
optkey = {},
author = {Reinoud Elhorst and Mark Batty and David Chisnall},
title = {Efficient code generation for weakly ordered architectures},
howpublished = {Presentation at the 4th European LLVM conference  (EuroLLVM)},
month = apr,
year = 2014,
note = {Slides and report available at \url{http://llvm.org/devmtg/2014-04/}},
optannote = {},
abstract = {This report explores the way LLVM generates the
memory barriers needed to support the C11/C++11 atomics
for ARM. I measure the influence of memory barriers on
performance, and I show that in some cases LLVM generates
too many barriers. By leaving these barriers out, performance
increases significantly. I introduce two LLVM passes, which will
remove these extra barriers, improving performance in my test
by 40\%. I believe one of these passes is ready to be upstreamed
to LLVM, while the other will need more testing.
}
}

@misc{Elhorst2014,
optkey = {},
author = {Reinoud Elhorst},
title = {Lowering {C11} Atomics for {ARM} in {LLVM}},
opthowpublished = {},
optmonth = {},
year = {2014},
month = mar,
optnote = {},
optannote = {},
url = {http://llvm.org/devmtg/2014-04/PDFs/Talks/Reinoud-report.pdf},
abstract = {This report explores the way LLVM generates the
memory barriers needed to support the C11/C++11 atomics
for ARM. I measure the influence of memory barriers on
performance, and I show that in some cases LLVM generates
too many barriers. By leaving these barriers out, performance
increases significantly. I introduce two LLVM passes, which will
remove these extra barriers, improving performance in my test
by 40\%. I believe one of these passes is ready to be upstreamed
to LLVM, while the other will need more testing.
}
}

@misc{HCSS2015-Memarian,
optkey = {},
author = {Kayvan Memarian and Kyndylan Nienhuis and Justus Matthiesen and James Lingard and Peter Sewell},
title = {Cerberus: towards an Executable Semantics for Sequential and Concurrent {C11}},
opthowpublished = {},
month = may,
year = 2015,
note = {Presentation at HCSS 2015: the Fifteenth Annual
High Confidence Software and Systems Conference},
optmonth = {},
optyear = {},
optannote = {},
abstract = {C remains central to our computing infrastructure but still lacks a
clear and complete semantics. Programmers lack tools to explore the
range of behaviours they should expect; compiler development lacks
test oracles; and formal verification and analysis must make
(explicitly or implicitly) many choices about the specific C they
target.

We describe Cerberus, a semantics for a substantial fragment of C11.
Its thread-local semantics is factored via an elaboration into a
simpler Core language, to make it conceptually and mathematically
tractable.  This is integrated with an operational model for C11
concurrency, with a mechanised proof of equivalence to the axiomatic
C11 model of Batty et al.  The front-end includes a parser that
closely follows the C11 standard grammar and a typechecker.  Cerberus
is executable, to explore all behaviours or single paths of test
programs, and it supports proof, as shown by a preliminary experiment
in translation validation for the front-end of Clang, for very simple
programs.  This is a step towards a clear, consistent, and unambiguous
semantics for C.
}
}

@inproceedings{Kell:2014:ST:2661136.2661154,
author = {Kell, Stephen},
title = {In Search of Types},
booktitle = {\textbf{Onward! 2014}: Proceedings of the 2014 ACM International Symposium on New
Ideas, New Paradigms, and Reflections on Programming \& Software},
conf = {Onward! 2014},
series = {Onward! 2014},
year = {2014},
month = oct,
isbn = {978-1-4503-3210-1},
location = {Portland, Oregon, USA},
pages = {227--241},
numpages = {15},
url = {http://doi.acm.org/10.1145/2661136.2661154},
doi = {10.1145/2661136.2661154},
acmid = {2661154},
publisher = {ACM},
address = {New York, NY, USA},
optkeywords = {abstraction, data types, information hiding, type
discipline, type system},
abstract = {The concept of "type" has been used without a consistent,
precise definition in discussions about programming languages for 60 years.
In this essay I explore various concepts lurking behind distinct uses of this word,
highlighting two traditions in which the word came into use largely independently:
engineering traditions on the one hand, and those of symbolic logic on the other.
These traditions are founded on differing attitudes to the nature and purpose of abstraction,
but their distinct uses of "type" have never been explicitly unified.
One result is that discourse across these traditions often finds itself at cross purposes,
such as overapplying one sense of "type" where another is appropriate, and occasionally
proceeding to draw wrong conclusions. I illustrate this with examples from well-known
and justly well-regarded literature, and argue that ongoing developments in both the
theory and practice of programming make now a good time to resolve these problems. }
}

@inproceedings{DBLP:conf/pepm/KerneisSH14,
author = {Gabriel Kerneis and
Charlie Shepherd and
Stefan Hajnoczi},
title = {{QEMU/CPC:} static analysis and {CPS} conversion for safe, portable,
and efficient coroutines},
booktitle = {\textbf{PEPM 2014}: Proceedings of the {ACM} {SIGPLAN} 2014 workshop on Partial evaluation
and program manipulation, San Diego,
California, {USA}},
conf = {PEPM 2014},
pages = {83--94},
year = {2014},
month = jan,
optcrossref = {DBLP:conf/pepm/2014},
url = {http://doi.acm.org/10.1145/2543728.2543733},
doi = {10.1145/2543728.2543733},
timestamp = {Thu, 09 Jan 2014 10:44:12 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/pepm/KerneisSH14},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {

Coroutines and events are two common abstractions for writing concurrent programs. Because coroutines are often more convenient, but events more portable and efficient, it is natural to want to translate the former into the latter. CPC is such a source-to-source translator for C programs, based on a partial conversion into continuation-passing style (CPS conversion) of functions annotated as cooperative.

In this article, we study the application of the CPC translator to QEMU, an open-source machine emulator which also uses annotated coroutine functions for concurrency. We first propose a new type of annotations to identify functions which never cooperate, and we introduce CoroCheck, a tool for the static analysis and inference of cooperation annotations. Then, we improve the CPC translator, defining CPS conversion as a calling convention for the C language, with support for indirect calls to CPS-converted function through function pointers. Finally, we apply CoroCheck and CPC to QEMU (750 000 lines of C code), fixing hundreds of missing annotations and comparing performance of the translated code with existing implementations of coroutines in QEMU.

Our work shows the importance of static annotation checking to prevent actual concurrency bugs, and demonstrates that CPS conversion is a flexible, portable, and efficient compilation technique, even for very large programs written in an imperative language.
}
}

@inproceedings{DBLP:conf/popl/Pichon-Pharabod16,
author = {Jean Pichon{-}Pharabod and
Peter Sewell},
title = {A concurrency semantics for relaxed atomics that permits optimisation
and avoids thin-air executions},
abstract = {Despite much research on concurrent programming languages, especially for Java and C/C++, we still do not have a satisfactory definition of their semantics, one that admits all common optimisations without also admitting undesired behaviour. Especially problematic are the thin-air'' examples involving high-performance concurrent accesses, such as C/C++11 relaxed atomics.  The C/C++11 model is in a per-candidate-execution style, and previous work has identified a tension between that and the fact that compiler optimisations do not operate over single candidate executions in isolation; rather, they operate over syntactic representations that represent all executions.

In this paper we propose a novel approach that circumvents this difficulty.  We define a concurrency semantics for a core calculus, including relaxed-atomic and non-atomic accesses, and locks, that admits a wide range of optimisation while still forbidding the classic thin-air examples.  It also addresses other problems relating to undefined behaviour.

The basic idea is to use an event-structure representation of the current state of each thread, capturing all of its potential executions, and to permit interleaving of execution and transformation steps over that to reflect optimisation (possibly dynamic) of the code. These are combined with a non-multi-copy-atomic storage subsystem, to reflect common hardware behaviour.

The semantics is defined in a mechanised and executable form, and designed to be implementable above current relaxed hardware and strong enough to support the programming idioms that C/C++11 does for this fragment.  It offers a potential way forward for concurrent programming language semantics, beyond the current C/C++11 and Java models.
},
booktitle = {\textbf{POPL 2016}: Proceedings of the 43rd Annual {ACM} {SIGPLAN-SIGACT} Symposium on
Principles of Programming Languages,  St. Petersburg,
FL, USA, January 20 - 22, 2016},
conf = {POPL 2016},
pages = {622--633},
year = {2016},
month = jan,
optcrossref = {DBLP:conf/popl/2016},
url = {http://doi.acm.org/10.1145/2837614.2837616},
pdf = {http://www.cl.cam.ac.uk/~jp622/popl16-thinair/a_concurrency_semantics.pdf},
doi = {10.1145/2837614.2837616},
timestamp = {Fri, 08 Jan 2016 18:18:25 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/popl/Pichon-Pharabod16},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@inproceedings{Cerberus-PLDI16,
author = {
Kayvan Memarian and
Justus Matthiesen and
James Lingard and
Kyndylan Nienhuis and
David Chisnall and
Robert N.M. Watson and
Peter Sewell
},
title = {Into the depths of {C}: elaborating the de facto standards},
abstract = {
C remains central to our computing infrastructure.  It is notionally defined by ISO standards, but in reality the properties of C assumed by systems code and those implemented by compilers have diverged, both from the ISO standards and from each other, and none of these are clearly understood.

We make two contributions to help improve this error-prone situation.  First, we describe an in-depth analysis of the design space for the semantics of pointers and memory in C as it is used in practice.  We articulate many specific questions, build a suite of semantic test cases, gather experimental data from multiple implementations, and survey what C experts believe about the de facto standards.  We identify questions where there is a consensus (either following ISO or differing) and where there are conflicts. We apply all this to an experimental C implemented above capability hardware.  Second, we describe a formal model, Cerberus, for large parts of C.  Cerberus is parameterised on its memory model; it is linkable either with a candidate de facto memory object model, under construction, or with an operational C11 concurrency model; it is defined by elaboration to a much simpler Core language for accessibility, and it is executable as a test oracle on small examples.

This should provide a solid basis for discussion of what mainstream C is now: what programmers and analysis tools can assume and what compilers aim to implement. Ultimately we hope it will be a step towards clear, consistent, and accepted semantics for the various use-cases of C.
},
optcrossref = {},
optkey = {},
booktitle = {\textbf{PLDI 2016}},
conf = {PLDI 2016},
optpages = {},
year = {2016},
opteditor = {},
optvolume = {},
optnumber = {},
optseries = {},
month = jun,
optorganization = {},
optpublisher = {},
note = {PLDI 2016 Distinguished Paper award},
pdf = {http://www.cl.cam.ac.uk/users/pes20/cerberus/pldi16.pdf},
optannote = {}
}

@inproceedings{gudka15:soaap,
author = {Khilan Gudka and Robert N. M. Watson and Jonathan Anderson and David Chisnall and Brooks Davis and Ben Laurie and Ilias Marinos and Peter G. Neumann and Alex Richardson},
title = {{Clean Application Compartmentalization with SOAAP}},
booktitle = {\textbf{CCS 2015}: {Proceedings of the 22nd ACM Conference on Computer and Communications Security}},
conf = {CCS 2015},
month = oct,
year = {2015},
pdf = {https://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/2015ccs-soaap.pdf},
abstract = {Application compartmentalization, a vulnerability mitigation technique
employed in programs such as OpenSSH and the Chromium web browser,
decomposes software into isolated components to limit privileges leaked
or otherwise available to attackers.
However, compartmentalizing applications -- and maintaining that
compartmentalization -- is hindered by ad hoc
methodologies and significantly increased programming effort.
In practice, programmers stumble through (rather than overtly reason
about) compartmentalization spaces of possible decompositions,
unknowingly trading off correctness, security, complexity, and
performance.
We present a new conceptual framework embodied in an LLVM-based tool: the
Security-Oriented Analysis of Application Programs (SOAAP) that allows
programmers to reason about co mpartmentalization using source-code
annotations (compartmentalization hypotheses).
We demonstrate considerable benefit when creating new compartmentalizations
for complex applications, and analyze existing compartmentalized
applications to discover design faults and maintenance issues arising
from application evolution.}
}

@misc{N2012,
optkey = {},
author = {Kayvan Memarian and Peter Sewell},
title = {Clarifying the {C} memory object model},
howpublished = {ISO SC22 WG14 N2012, \url{http://www.cl.cam.ac.uk/~pes20/cerberus/notes64-wg14.html}},
month = mar,
year = 2016,
optnote = {},
optannote = {}
}

@misc{N2013,
optkey = {},
author = {David Chisnall and Justus Matthiesen and Kayvan Memarian and Kyndylan Nienhuis and Peter Sewell and Robert N. M. Watson},
title = {C memory object and value semantics: the space of de facto and {ISO} standards},
howpublished = {ISO SC22 WG14 N2013, \url{http://www.cl.cam.ac.uk/~pes20/cerberus/notes30.pdf}},
month = mar,
year = 2016,
optnote = {},
optannote = {}
}

@misc{N2014,
optkey = {},
author = {Kayvan Memarian and Peter Sewell},
title = {What is {C} in practice? ({Cerberus} survey v2): Analysis of Responses},
howpublished = {ISO SC22 WG14 N2014, \url{http://www.cl.cam.ac.uk/~pes20/cerberus/notes50-survey-discussion.html}},
month = mar,
year = 2016,
optnote = {},
optannote = {}
}

@misc{N2015,
optkey = {},
author = {Kayvan Memarian and Peter Sewell},
title = {What is {C} in practice? ({Cerberus} survey v2): Analysis of Responses -- with Comments},
howpublished = {ISO SC22 WG14 N2015, \url{http://www.cl.cam.ac.uk/~pes20/cerberus/analysis-2016-02-05-anon.txt}},
month = mar,
year = 2016,
optnote = {},
optannote = {}
}

@phdthesis{battyPhD,
author = {Mark John Batty},
title = {The C11 and C++11 Concurrency Model},
school = {University of Cambridge Computer Laboratory},
year = {2014},
month = nov,
optkey = {},
opttype = {},
optmonth = {},
note = {Winner of 2015 ACM SIGPLAN John C. Reynolds
Doctoral Dissertation Award and 2015 CPHC/BCS Distinguished
Dissertation competition},
optannote = {}
}

@inproceedings{kell_dynamically_2016,
author = {Kell, Stephen},
title = {Dynamically diagnosing type errors in unsafe code},
booktitle = {\textbf{OOPSLA 2016}: Proceedings of the ACM SIGPLAN International Conference on Object-Oriented Programming, Systems, Languages, and Applications},
conf = {OOPSLA 2016},
series = {OOPSLA 2016},
year = {2016},
month = nov,
location = {Amsterdam, The Netherlands},
numpages = {20},
publisher = {ACM},
address = {New York, NY, USA},
keywords = {C, unsafe code, pointers, type information},
abstract = {Existing approaches for detecting type errors in unsafe languages are limited.
Static analysis methods are imprecise,
and often require source-level changes, while
most dynamic methods check only memory properties
(bounds, liveness, etc.), owing to a lack of run-time type information.
This paper describes \textsf{libcrunch},
a system for binary-compatible \emph{run-time} type checking of unmodified
unsafe code, currently focusing on C.
Practical experience shows that our prototype implementation
is easily applicable to many real codebases without source-level modification,
correctly flags programmer errors with a very low rate of false positives,
offers a very low run-time overhead,
and covers classes of error caught by no previously existing tool.},
pdf = {http://www.cl.cam.ac.uk/~pes20/rems/papers/typebugs.pdf}
}

@inproceedings{kell_missing_2016,
author = {Stephen Kell and Dominic P. Mulligan and Peter Sewell},
booktitle = {\textbf{OOPSLA 2016}: Proceedings of the ACM SIGPLAN International Conference on Object-Oriented Programming, Systems, Languages, and Applications},
conf = {OOPSLA 2016},
series = {OOPSLA 2016},
year = {2016},
month = nov,
location = {Amsterdam, The Netherlands},
numpages = {17},
publisher = {ACM},
address = {New York, NY, USA},
abstract = {Beneath the surface, software usually depends on complex \emph{linker
behaviour} to work as intended.  Even linking
\texttt{hello\_world.c} is surprisingly involved, and systems software
such as \texttt{libc} and operating system kernels rely on a host of
programmers and has largely been neglected by language researchers.

In this paper we survey the many use-cases that linkers support and
the poorly specified \emph{linker speak} by which they are controlled:
language.  We provide the first validated formalisation of a realistic
executable and linkable format (ELF), and capture aspects of the
Application Binary Interfaces for four mainstream platforms (AArch64,
AMD64, Power64, and IA32).  Using these, we develop an executable
small C programs (we use the example of \textsf{bzip2}) into a correctly
running executable.  We
provide our specification in Lem and Isabelle/HOL forms.  This is the
first formal specification of mainstream linking.  We have used the
Isabelle/HOL version to prove a sample
correctness property for one case of AMD64 ABI relocation,
demonstrating that the specification supports formal proof, and as a
first step towards the much more ambitious goal of verified linking.
Our work should enable several novel strands of research, including
linker-aware verified compilation and program analysis, and better
},
}

@inproceedings{operational-semantics-c11-2016,
author = {Kyndylan Nienhuis and Kayvan Memarian and Peter Sewell},
title = {An operational semantics for {C/C++11} concurrency},
booktitle = {\textbf{OOPSLA 2016}: Proceedings of the ACM SIGPLAN International Conference on Object-Oriented Programming, Systems, Languages, and Applications},
conf = {OOPSLA 2016},
location = {Amsterdam, The Netherlands},
numpages = {18},
publisher = {ACM},
address = {New York, NY, USA},
month = nov,
year = {2016},
abstract = {The C/C++11 concurrency model balances two goals: it is relaxed enough to be efficiently implementable and (leaving aside the thin-air'' problem) it is strong enough to give useful guarantees to programmers. It is mathematically precise and has been used in verification research and compiler testing. However, the model is expressed in an axiomatic style, as predicates on complete candidate executions. This suffices for computing the set of allowed executions of a small litmus test, but it does not directly support the incremental construction of executions of larger programs. It is also at odds with conventional operational semantics, as used implicitly in the rest of the C/C++ standards.

Our main contribution is the development of an operational model for C/C++11 concurrency. This covers all the features of the previous formalised axiomatic model, and we have a mechanised proof that the two are equivalent, in Isabelle/HOL. We also integrate this semantics with an operational semantics for sequential C (described elsewhere); the combined semantics can incrementally execute programs in a small fragment of C.

Doing this uncovered several new aspects of the C/C++11 model: we show that one cannot build an equivalent operational model that simply follows program order, sequential consistent order, or the synchronises-with order. The first negative result is forced by hardware-observable behaviour, but the latter two are not, and so might be ameliorated by changing C/C++11. More generally, we hope that this work, with its focus on incremental construction of executions, will inform the future design of new concurrency models.},
pdf = {http://www.cl.cam.ac.uk/~pes20/rems/papers/nienhuis-oopsla-2016.pdf}
}

@misc{N2089,
optkey = {},
author = {Kayvan Memarian and Peter Sewell},
title = {Clarifying Unspecified Values (Draft Defect Report or Proposal for C2x)},
howpublished = {ISO SC22 WG14 N2089, \url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2089.htm}},
month = sep,
year = 2016,
optnote = {},
optannote = {}
}

@misc{N2090,
optkey = {},
author = {Kayvan Memarian and Peter Sewell},
title = {Clarifying Pointer Provenance (Draft Defect Report or Proposal for C2x)},
howpublished = {ISO SC22 WG14 N2090, \url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2090.htm}},
month = sep,
year = 2016,
optnote = {},
optannote = {}
}

@misc{N2091,
optkey = {},
author = {Kayvan Memarian and Peter Sewell},
title = {Clarifying Trap Representations (Draft Defect Report or Proposal for C2x)},
howpublished = {ISO SC22 WG14 N2091, \url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2091.htm}},
month = sep,
year = 2016,
optnote = {},
optannote = {}
}

@inproceedings{Chisnall2017,
author = {David Chisnall and Brooks Davis and Khilan Gudka and
Alexandre Joannou and Robert N. M. Watson and David Brazdil and
Jonathan Woodruff and A. Theodore Markettos and J. Edward Maste and
Robert Norton and Stacey Son and Michael Roe and Simon W. Moore and
Peter G. Neumann and Ben Laurie},
title = {Sinking the {Java} security model into the {C}},
booktitle = {Proceedings of \textbf{ASPLOS 2017}: the 22nd ACM International Conference on
Architectural Support for Programming Languages and Operating Systems},
conf = {ASPLOS 2017},
year = 2017,
month = apr,
abstract = {Java provides security and robustness by building a high-level
security model atop the foundation of memory protection.
Unfortunately, any native code linked into a Java program --
including the million lines used to implement the standard library --
is able to bypass both the memory protection and the higher-level policies.
We present a hardware-assisted implementation of the Java native code
interface, which extends the guarantees required for Java's security model to
native code.
Our design supports safe direct access to buffers owned by the JVM,
including hardware-enforced read-only access where appropriate.
We also present Java language syntax to declaratively describe isolated
compartments for native code.
We show that it is possible to preserve the memory safety and isolation
requirements of the Java security model in C code, allowing native code to run
in the same process as Java code with the same impact on security as running
equivalent Java code.
Our approach has a negligible impact on performance, compared with the
existing unsafe native code interface.
We demonstrate a prototype implementation running on the CHERI
microprocessor synthesized in FPGA.}
}

@inproceedings{DBLP:conf/popl/KumarMNO14,
author = {Ramana Kumar and
Magnus O. Myreen and
Michael Norrish and
Scott Owens},
title = {{CakeML}: a verified implementation of {ML}},
booktitle = {\textbf{POPL 2014}: The 41st Annual {ACM} {SIGPLAN-SIGACT} Symposium on Principles of
Programming Languages,  San Diego, CA, USA},
conf = {POPL 2014},
pages = {179--192},
year = {2014},
month = jan,
optcrossref = {DBLP:conf/popl/2014},
url = {http://doi.acm.org/10.1145/2535838.2535841},
doi = {10.1145/2535838.2535841},
timestamp = {Thu, 09 Jan 2014 08:32:32 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/popl/KumarMNO14},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {
We have developed and mechanically verified an ML system called CakeML, which supports a substantial subset of Standard ML. CakeML is implemented as an interactive read-eval-print loop (REPL) in x86-64 machine code. Our correctness theorem ensures that this REPL implementation prints only those results permitted by the semantics of CakeML. Our verification effort touches on a breadth of topics including lexing, parsing, type checking, incremental and dynamic compilation, garbage collection, arbitrary-precision arithmetic, and compiler bootstrapping.

Our contributions are twofold. The first is simply in building a system that is end-to-end verified, demonstrating that each piece of such a verification effort can in practice be composed with the others, and ensuring that none of the pieces rely on any over-simplifying assumptions. The second is developing novel approaches to some of the more challenging aspects of the verification. In particular, our formally verified compiler can bootstrap itself: we apply the verified compiler to itself to produce a verified machine-code implementation of the compiler. Additionally, our compiler proof handles diverging input programs with a lightweight approach based on logical timeout exceptions. The entire development was carried out in the HOL4 theorem prover.}
}

@article{DBLP:journals/jfp/MyreenO14,
author = {Magnus O. Myreen and
Scott Owens},
title = {Proof-producing translation of higher-order logic into pure and stateful
{ML}},
journal = {\textbf{J. Funct. Program.}},
volume = {24},
number = {2-3},
pages = {284--315},
year = {2014},
month = jan,
url = {http://dx.doi.org/10.1017/S0956796813000282},
doi = {10.1017/S0956796813000282},
timestamp = {Mon, 26 May 2014 10:31:52 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/journals/jfp/MyreenO14},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {
The higher-order logic found in proof assistants such as Coq and various HOL systems provides a convenient setting for the development and verification of functional programs. However, to efficiently run these programs, they must be converted (or extracted') to functional programs in a programming language such as ML or Haskell. With current techniques, this step, which must be trusted, relates similar looking objects that have very different semantic definitions, such as the set-theoretic model of a logic and the operational semantics of a programming language. In this paper, we show how to increase the trustworthiness of this step with an automated technique. Given a functional program expressed in higher-order logic, our technique provides the corresponding program for a functional language defined with an operational semantics, and it provides a mechanically checked theorem relating the two. This theorem can then be used to transfer verified properties of the logical function to the program. We have implemented our technique in the HOL4 theorem prover, translating functions to a subset of Standard ML, and have applied the implementation to examples including functional data structures, a parser generator, cryptographic algorithms, a garbage collector and the 500-line kernel of the HOL light theorem prover. This paper extends our previous conference publication with new material that shows how functions defined in terms of a state-and-exception monad can be translated, with proofs, into stateful ML code. The HOL light example is also new.}
}

@inproceedings{YongKiamMKFON16,
author = {Tan, Yong Kiam and Magnus O. Myreen and Ramana Kumar and
Anthony Fox and Scott Owens and Michael Norrish},
title = {A New Verified Compiler Backend for {CakeML}},
booktitle = {Proc. \textbf{ICFP 2016}: International Conference on Functional Programming},
conf = {ICFP 2016},
year = 2016,
month = sep,
doi = {10.1145/2951913.2951924},
pdf = {https://cakeml.org/icfp16.pdf},
publisher = {ACM Press},
abstract = {
We have developed and mechanically verified a new compiler backend
for CakeML.  Our new compiler features a sequence of intermediate
languages that allows it to incrementally compile away high-level
features and enables verification at the right levels of semantic
detail.  In this way, it resembles mainstream (unverified)
compilers for strict functional languages.  The compiler supports
efficient curried multi-argument functions, configurable data
representations, exceptions that unwind the call stack, register
allocation, and more.  The compiler targets several architectures:
x86-64, ARMv6, ARMv8, MIPS-64, and RISC-V.

In this paper, we present the overall structure of the compiler,
including its 12 intermediate languages, and explain how
everything fits together.  We focus particularly on the
interaction between the verification of the register allocator and
the garbage collector, and memory representations.  The entire
development has been carried out within the HOL4 theorem prover.
}
}

@inproceedings{FoxMTK17,
author = {Anthony C. J. Fox and
Magnus O. Myreen and
Yong Kiam Tan and
Ramana Kumar},
title = {Verified compilation of {CakeML} to multiple
machine-code targets},
booktitle = {Proc. \textbf{CPP 2017}: Certified Programs and Proofs},
conf = {CPP 2017},
year = {2017},
month = jan,
doi = {10.1145/3018610.3018621},
editor = {Yves Bertot and Viktor Vafeiadis},
pdf = {https://cakeml.org/cpp17.pdf},
publisher = {{ACM}},
abstract = {
This paper describes how the latest CakeML compiler supports
verified compilation down to multiple realistically modelled
target architectures.  In particular, we describe how the compiler
definition, the various language semantics, and the correctness
proofs were organised to minimize target-specific overhead.  With
our setup we have incorporated compilation to four 64-bit
architectures, ARMv8, x86-64, MIPS-62, RISC-V, and one 32-bit
architecture, ARMv6.  Our correctness theorem allows interference
from the environment: the top-level correctness statement takes
into account execution of foreign code and per-instruction
interference from external processes, such as interrupt handlers
in operating systems.  The entire CakeML development is formalised
in the HOL4 theorem prover.

}
}

@inproceedings{kell_towards_20XX,
author = {Stephen Kell},
title = {Towards a dynamic object model within {Unix} processes},
booktitle = {\textbf{Onward! 2015}: 2015 {ACM} International Symposium on New Ideas, New Paradigms, and
Reflections on Programming and Software,  Pittsburgh,
PA, USA},
conf = {Onward! 2015},
pages = {224--239},
year = {2015},
month = oct,
xcrossref = {DBLP:conf/oopsla/2015onward},
url = {http://doi.acm.org/10.1145/2814228.2814238},
doi = {10.1145/2814228.2814238},
timestamp = {Wed, 28 Oct 2015 16:51:55 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/oopsla/Kell15},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {Programmers face much complexity from the co-existence of
native'' (Unix-like) and virtual machine (VM) managed'' run-time environments.
Rather than having VMs replace Unix processes, we investigate whether it makes
sense for the latter to become VMs'', by evolving Unix's
user-level services to subsume those of VMs.
We survey the (little-understood) VM-like features in modern Unix, noting
common shortcomings: a lack of semantic metadata (type information'')
and the inability to bind from objects back'' to their metadata.
We describe the design and implementation of
a system, \textsf{liballocs}, which adds these capabilities in a highly compatible way,
and explore its consequences.},
pdf = {http://www.cl.cam.ac.uk/~srk31/research/papers/kell15towards-preprint.pdf}
}

@inproceedings{kell_some_2017,
author = {Kell, Stephen},
title = {Some were meant for {C}: the endurance of an unmanageable language},
booktitle = {\textbf{Onward! 2017}: Proceedings of the 2017 ACM International Symposium on New Ideas, New Paradigms, and Reflections on Programming \& Software},
conf = {Onward! 2017},
series = {Onward! 2017},
year = {2017},
month = oct,
location = {Vancouver, British Columbia, Canada},
numpages = {18},
url = {http://www.cl.cam.ac.uk/~srk31/research/papers/kell17some-preprint.pdf},
doi = {10.1145/3133850.3133867},
publisher = {ACM},
address = {New York, NY, USA},
keywords = {systems programming, virtual machine, managed languages, safety, undefined behavior},
abstract = {The C language leads a double life: as an application
programming language of yesteryear, perpetuated by
circumstance, and as a systems programming language
which remains a weapon of choice decades after its cre-
ation. This essay is a C programmer's reaction to the call
to abandon ship. It questions several properties com-
monly held to define the experience of using C; these
include unsafety, undefined behaviour, and the moti-
vation of performance. It argues all these are in fact
inessential; rather, it traces C's ultimate strength to a
communicative design which does not fit easily within
the usual conception of a programming language'', but
can be seen as a counterpoint to so-called managed
languages''. This communicativity is what facilitates the
essential aspect of system-building: creating parts which
interact with other, remote parts---being alongside'' not
within''. }
}

@article{YALLOP2017,
title = {A modular foreign function interface},
journal = {Science of Computer Programming},
year = {2017},
month = apr,
issn = {0167-6423},
doi = {https://doi.org/10.1016/j.scico.2017.04.002},
url = {http://www.sciencedirect.com/science/article/pii/S0167642317300709},
pdf = {https://www.cl.cam.ac.uk/~jdy22/papers/a-modular-foreign-function-interface.pdf},
author = {Jeremy Yallop and David Sheets and Anil Madhavapeddy},
keywords = {Foreign functions},
keywords = {Functional programming},
keywords = {Modularity},
abstract = {Abstract foreign function interfaces are typically organised monolithically, tying together the specification of each foreign function with the mechanism used to make the function available in the host language. This leads to inflexible systems, where switching from one binding mechanism to another (say from dynamic binding to static code generation) often requires changing tools and rewriting large portions of code. We show that ML-style module systems support exactly the kind of abstraction needed to separate these two aspects of a foreign function binding, leading to declarative foreign function bindings that support switching between a wide variety of binding mechanisms — static and dynamic, synchronous and asynchronous, etc. — with no changes to the function specifications. Note. This is a revised and expanded version of an earlier paper, Declarative Foreign Function Binding Through Generic Programming. This paper brings a greater focus on modularity, and adds new sections on error handling, and on the practicality of the approach we describe.}
}

@inproceedings{TaDa2014,
year = {2014},
month = jul,
isbn = {978-3-662-44201-2},
booktitle = {\textbf{ECOOP 2014}},
conf = {ECOOP 2014},
volume = {8586},
series = {Lecture Notes in Computer Science},
editor = {Jones, Richard},
doi = {10.1007/978-3-662-44202-9_9},
title = {{TaDA}: A Logic for Time and Data Abstraction},
url = {http://dx.doi.org/10.1007/978-3-662-44202-9_9},
publisher = {Springer Berlin Heidelberg},
author = {da Rocha Pinto, Pedro and Dinsdale-Young, Thomas and Gardner, Philippa},
pages = {207-231},
language = {English},
abstract = {To avoid data races, concurrent operations should either be at distinct times or on distinct data. Atomicity is the abstraction that an operation takes effect at a single, discrete instant in time, with linearisability being a well-known correctness condition which asserts that concurrent operations appear to behave atomically. Disjointness is the abstraction that operations act on distinct data resource, with concurrent separation logics enabling reasoning about threads that appear to operate independently on disjoint resources.

We present TaDA, a program logic that combines the benefits of abstract atomicity and abstract disjointness. Our key contribution is the introduction of atomic triples, which offer an expressive approach to specifying program modules. By building up examples, we show that TaDA supports elegant modular reasoning in a way that was not previously possible.
}
}

@inproceedings{DBLP:conf/esop/GardnerNW14,
author = {Philippa Gardner and
Gian Ntzik and
title = {Local Reasoning for the {POSIX} File System},
booktitle = {\textbf{ESOP 2014}: Programming Languages and Systems - 23rd European Symposium on Programming,
Held as Part of the European Joint Conferences on Theory
and Practice of Software, {ETAPS} 2014, Grenoble, France},
conf = {ESOP 2014},
pages = {169--188},
year = {2014},
month = apr,
optcrossref = {DBLP:conf/esop/2014},
url = {http://dx.doi.org/10.1007/978-3-642-54833-8_10},
doi = {10.1007/978-3-642-54833-8_10},
timestamp = {Sun, 23 Mar 2014 10:48:25 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/esop/GardnerNW14},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {We provide a program logic for specifying a core subset of the sequential POSIX file system, and for reasoning abstractly about client programs working with the file system.}
}

@article{DBLP:journals/entcs/GardnerRWW14,
author = {Philippa Gardner and
Mark J. Wheelhouse and
title = {Abstract Local Reasoning for Concurrent Libraries: Mind the Gap},
journal = {\textbf{MFPS 2014}: Electr. Notes Theor. Comput. Sci.},
conf = {MFPS 2014},
volume = {308},
pages = {147--166},
year = {2014},
month = jun,
url = {http://dx.doi.org/10.1016/j.entcs.2014.10.009},
doi = {10.1016/j.entcs.2014.10.009},
timestamp = {Tue, 04 Nov 2014 10:58:51 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/journals/entcs/GardnerRWW14},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {We study abstract local reasoning for concurrent libraries. There are two main approaches: provide a specification of a library by abstracting from concrete reasoning about an implementation; or provide a direct abstract library specification, justified by refining to an implementation. Both approaches have a significant gap in their reasoning, due to a mismatch between the abstract connectivity of the abstract data structures and the concrete connectivity of the concrete heap representations. We demonstrate this gap using structural separation logic (SSL) for specifying a concurrent tree library and concurrent abstract predicates (CAP) for reasoning about a concrete tree implementation. The gap between the abstract and concrete connectivity emerges as a mismatch between the SSL tree predicates and CAP heap predicates. This gap is closed by an interface function I which links the abstract and concrete connectivity. In the accompanying technical report, we generalise our SSL reasoning and results to arbitrary concurrent data libraries.}
}

@inproceedings{daRochaPinto2016Modular,
title = {Modular Termination Verification for Non-blocking Concurrency},
author = {{da Rocha Pinto}, Pedro and Dinsdale-Young, Thomas and Gardner, Philippa and Sutherland, Julian},
booktitle = {\textbf{ESOP 2016}: Proceedings of the 25th European Symposium on Programming},
conf = {ESOP 2016},
year = {2016},
month = apr,
pages = {176--201},
url = {http://dx.doi.org/10.1007/978-3-662-49498-1_8},
doi = {10.1007/978-3-662-49498-1_8},
pdf = {http://www.doc.ic.ac.uk/~pmd09/research/publications/2016/esop/modular-termination-verification-for-non-blocking-concurrency.pdf},
abstract = {We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread's concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for non-blocking algorithms, e.g. a counter and a stack. Our specifications can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other.},
project = { concurrency, tada }
}

@inproceedings{Ntzik2015Fault,
title = {{Fault-tolerant Resource Reasoning}},
author = {Ntzik, Gian and {da Rocha Pinto}, Pedro and Gardner, Philippa},
booktitle = {\textbf{APLAS 2015}: Proceedings of the 13th Asian Symposium on Programming Languages and Systems},
conf = {APLAS 2015},
year = {2015},
month = dec,
pages = {169--188},
url = {http://dx.doi.org/10.1007/978-3-319-26529-2_10},
doi = {10.1007/978-3-319-26529-2_10},
pdf = {http://www.doc.ic.ac.uk/~pmd09/research/publications/2015/aplas/fault-tolerant-resource-reasoning.pdf},
abstract = {Separation logic has been successful at verifying that programs do not crash due to illegal use of resources. The underlying assumption, however, is that machines do not fail. In practice, machines can fail unpredictably for various reasons, e.g. power loss, corrupting resources. Critical software, e.g. file systems, employ recovery methods to mitigate these effects. We introduce an extension of the Views framework to reason about such methods. We use concurrent separation logic as an instance of the framework to illustrate our reasoning, and explore programs using write-ahead logging, e.g. an ARIES recovery algorithm.}
}

@inproceedings{daRochaPinto2015Steps,
title = {{Steps in Modular Specifications for Concurrent Modules (Invited Tutorial Paper)}},
author = {{da Rocha Pinto}, Pedro and Dinsdale-Young, Thomas and Gardner, Philippa},
booktitle = {\textbf{MFPS 2015}: Proceedings of the 31st Conference on the Mathematical Foundations of Programming Semantics},
conf = {MFPS 2015},
year = {2015},
month = jun,
pages = {3--18},
url = {http://www.sciencedirect.com/science/article/pii/S1571066115000699},
doi = {10.1016/j.entcs.2015.12.002},
pdf = {http://www.doc.ic.ac.uk/~pmd09/research/publications/2015/mfps/steps-in-modular-specifications-for-concurrent-modules.pdf},
abstract = {The specification of a concurrent program module is a difficult problem. The specifications must be strong enough to enable reasoning about the intended clients without reference to the underlying module implementation. We survey a range of verification techniques for specifying concurrent modules, in particular highlighting four key concepts: auxiliary state, interference abstraction, resource ownership and atomicity. We show how these concepts combine to provide powerful approaches to specifying concurrent modules.}
}

@inproceedings{icaptso-esop,
author = {Filip Sieczkowski and Kasper Svendsen and Lars Birkedal and Jean Pichon-Pharabod},
title = {A Separation Logic for Fictional Sequential Consistency},
optcrossref = {},
optkey = {},
booktitle = {\textbf{ESOP 2015}},
conf = {ESOP 2015},
optpages = {},
year = 2015,
opteditor = {},
optvolume = {},
optnumber = {},
optseries = {},
month = apr,
optorganization = {},
optpublisher = {},
optnote = {},
optannote = {},
doi = {10.1007/978-3-662-46669-8_30},
abstract = {To improve performance, modern multiprocessors and programming languages typically implement \emph{relaxed} memory models that
do not require all processors/threads to observe memory operations in
the same order. To relieve programmers from having to reason directly
about these relaxed behaviors, languages often provide efficient synchronization primitives and concurrent data structures with stronger high-level guarantees about memory reorderings. For instance, locks usually
ensure that when a thread acquires a lock, it can observe all memory
operations of the releasing thread, prior to the release. When used correctly, these synchronization primitives and data structures allow clients
to recover a fiction of a \emph{sequentially consistent} memory model.

In this paper we propose a new proof system, iCAP-TSO, that captures
this fiction formally, for a language with a TSO memory model. The
logic supports reasoning about libraries that directly exploit the relaxed
memory model to achieve maximum efficiency. When these libraries provide sufficient guarantees, the logic hides the underlying complexity and
high-level clients.
}
}

@inproceedings{CoLoSL2015,
author = {Azalea Raad and Jules Villard and Philippa Gardner},
title = {{CoLoSL}: Concurrent Local Subjective Logic},
optcrossref = {},
optkey = {},
booktitle = {\textbf{ESOP 2015}},
conf = {ESOP 2015},
optpages = {},
year = {2015},
opteditor = {},
optvolume = {},
optnumber = {},
optseries = {},
month = apr,
optorganization = {},
optpublisher = {},
optnote = {},
optannote = {},
doi = {10.1007/978-3-662-46669-8_29},
url = {http://www.doc.ic.ac.uk/~azalea/papers/CoLoSL.pdf},
abstract = {A key difficulty in verifying shared-memory concurrent programs is reasoning compositionally about each thread in isolation. Existing
verification techniques for fine-grained concurrency typically require reasoning about either the entire shared state or disjoint parts of the shared
state, impeding compositionality. This paper introduces the program logic
CoLoSL, where each thread is verified with respect to its subjective view
of the global shared state. This subjective view describes only that part of
the state accessed by the thread. Subjective views may arbitrarily overlap
with each other, and expand and contract depending on the resource
required by the thread. This flexibility gives rise to small specifications
and, hence, more compositional reasoning for concurrent programs. We
demonstrate our reasoning on a range of examples, including a concurrent
computation of a spanning tree of a graph.
}
}

@article{DBLP:journals/corr/ChakrabortyHSV15,
author = {Soham Chakraborty and
Thomas A. Henzinger and
Ali Sezgin and
title = {Aspect-oriented linearizability proofs},
journal = {\textbf{Logical Methods in Computer Science}},
volume = {11},
number = {1},
pages = {1--33},
year = {2015},
month = apr,
url = {http://arxiv.org/abs/1502.07639},
doi = {10.2168/LMCS-11(1:20)2015},
biburl = {http://dblp.uni-trier.de/rec/bib/journals/corr/ChakrabortyHSV15},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {Linearizability of concurrent data structures is usually proved by monolithic simulation arguments relying on the identification of the so-called linearization points. Regrettably, such proofs, whether manual or automatic, are often complicated and scale poorly to advanced non-blocking concurrency patterns, such as helping and optimistic updates. In response, we propose a more modular way of checking linearizability of concurrent queue algorithms that does not involve identifying linearization points. We reduce the task of proving linearizability with respect to the queue specification to establishing four basic properties, each of which can be proved independently by simpler arguments. As a demonstration of our approach, we verify the Herlihy and Wing queue, an algorithm that is challenging to verify by a simulation proof. }
}

@inproceedings{ocaml14tls,
author = {Hannes Mehnert and David Kaloper Mersinjak},
title = {Transport {L}ayer {S}ecurity purely in {O}{C}aml},
booktitle = {Proceedings of the ACM OCaml 2014 Workshop},
conf = {OCaml 2014},
year = 2014,
month = sep,
url = {https://ocaml.org/meetings/ocaml/2014/ocaml2014_4.pdf},
abstract = {Transport Layer Security (TLS) is probably the most
widely deployed security protocol on the Internet.  It is used to
setup virtual private networks, secure various services such as web
and email, etc.  In this paper we describe our clean slate TLS
implementation developed in OCaml.  Our motivating goals are
reliability, robustness, and API conciseness.  While our
implementation is still a work in progress and lacks some of the
protocol features (such as client authentication and session
resumption), it already interoperates with other existing TLS
implementations.  Preliminary performance evaluation shows that our
library is roughly five times slower compared to OpenSSL, but we
expect to improve our performance.}
}

@inproceedings{DBLP:conf/RelMiCS/HoareSMSVZO14,
author = {Tony Hoare and
Bernhard M{\"{o}}ller and
Georg Struth and
Jules Villard and
Huibiao Zhu and
Peter W. O'Hearn},
title = {Developments in Concurrent {Kleene} Algebra},
booktitle = {\textbf{RAMiCS 2014}: Relational and Algebraic Methods in Computer Science - 14th International
Conference, Marienstatt, Germany},
conf = {RAMiCS 2014},
pages = {1--18},
year = {2014},
month = apr,
optcrossref = {DBLP:conf/RelMiCS/2014},
url = {http://dx.doi.org/10.1007/978-3-319-06251-8_1},
doi = {10.1007/978-3-319-06251-8_1},
timestamp = {Tue, 08 Apr 2014 19:30:22 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/RelMiCS/HoareSMSVZO14},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {This report summarises recent progress in the research of its co-authors towards the construction of links between algebraic presentations of the principles of programming and the exploitation of concurrency in modern programming practice. The research concentrates on the construction of a realistic family of partial order models for Concurrent Kleene Algebra (aka, the Laws of Programming). The main elements of the model are objects and the events in which they engage. Further primitive concepts are traces, errors and failures, and transferrable ownership. In terms of these we can define other concepts which have proved useful in reasoning about concurrent programs, for example causal dependency and independence, sequentiality and concurrency, allocation and disposal, synchrony and asynchrony, sharing and locality, input and output.}
}

@misc{31c3tls,
optkey = {},
author = {David Kaloper Mer{\v{s}}injak and Hannes Mehnert},
title = {Trustworthy secure modular operating system engineering},
howpublished = {Invited talk at 31st Chaos Communication
Congress (31C3)},
month = jan,
year = 2015,
optnote = {},
optannote = {},
abstract = {We present Mirage OS, a modular library operating system developed from scratch in the functional programming language OCaml. Each service, called unikernel, is an OCaml application using libraries such as a TCP/IP stack, DNS. It is either compiled to a Xen virtual machine image or to a Unix binary (for development). State in 2014 is that it runs on x86 and arm, we implemented a clean-slate TLS (1.0, 1.1, 1.2), X.509, ASN.1 stack, crypto primitives, Off-the-record. We also have TCP/IP, HTTP, a persistent branchable store (similar to git) - all implemented in OCaml. A virtual machine serving data via https is roughly 2MB in size - no libc inside :)}
}

@misc{HCSS-Kaloper,
optkey = {},
author = {David Kaloper Mer{\v{s}}injak and Hannes Mehnert and Anil Madhavapeddy and Peter Sewell},
title = {Not-quite-so-broken {TLS}: lessons in re-engineering a security protocol
specification and implementation},
opthowpublished = {},
month = may,
year = 2015,
note = {Presentation at HCSS 2015: the Fifteenth Annual
High Confidence Software and Systems Conference},
optmonth = {},
optyear = {},
optnote = {},
optannote = {},
abstract = {Transport Layer Security (TLS) implementations have a history of
security flaws.  The immediate causes of these range from simple
programming errors, such as memory management, to subtle violations of
the protocol logic.  Deeper causes can be seen in the challenges of
interpreting the ambiguous prose specification, the complexities
inherent in large APIs and code bases, unsafe performance-oriented
programming choices, and the impossibility of directly testing
conformance between implementations and the specification.

We present nqsb-TLS, the result of our re-engineering approach
to improve the quality of security protocol implementations.  The same
code serves dual roles: it is both a specification of TLS, executable
as a test oracle to check conformance of traces from arbitrary
implementations, and a secure and usable executable implementation of
TLS.  nqsb-TLS employs a modular and declarative programming
style that also allows it to be compiled into a Xen unikernel (a
specialised virtual machine image) with a TCB that is 2.5\% of a
standalone system running a standard Linux/OpenSSL stack, with all
network traffic being handled in a memory-safe language.

nqsb-TLS focuses on protocol-level interoperability, and makes
no effort to be compatible with existing (and often poorly designed)
library APIs such as OpenSSL.  The higher-level API in nqsb-TLS
makes it harder to misuse the library, and is demonstrated via several
unikernel applications ranging over HTTPS, IMAP, Git, Websocket clients
and servers.
}
}

@inproceedings{nqsbTLS-sub,
author = {David Kaloper{-}Mersinjak and
Hannes Mehnert and
Peter Sewell},
title = {Not-Quite-So-Broken {TLS:} Lessons in Re-Engineering a Security Protocol
Specification and Implementation},
abstract = {Transport Layer Security (TLS) implementations have a history of security flaws.  The immediate causes of these are often programming errors, e.g.~in memory management, but the root causes are more fundamental: the challenges of interpreting the ambiguous prose specification, the complexities inherent in large APIs and code bases, inherently unsafe programming choices, and the impossibility of directly testing conformance between implementations and the specification.

We present \emph{nqsb-TLS}, the result of our re-engineered approach to security protocol specification and implementation that addresses these root causes.  The same code serves dual roles: it is both a specification of TLS, executable as a test oracle to check conformance of traces from arbitrary implementations, and a usable implementation of TLS; a modular and declarative programming style provides clean separation between its components.  Many security flaws are thus excluded by construction.

nqsb-TLS can be used in standalone applications, which we demonstrate with a messaging client, and can also be compiled into a Xen unikernel (a specialised virtual machine image) with a TCB that is 4\% of a standalone system running a standard Linux/OpenSSL stack, with all network traffic being handled in a memory-safe language; this supports applications including HTTPS, IMAP, Git, and Websocket clients and servers.
},
booktitle = {\textbf{USENIX Security 2015}: 24th {USENIX} Security Symposium,  Washington,
D.C., USA},
conf = {USENIX Security 2015},
pages = {223--238},
year = {2015},
month = aug,
optcrossref = {DBLP:conf/uss/2015},
url = {https://www.usenix.org/conference/usenixsecurity15/technical-sessions/presentation/kaloper-mersinjak},
pdf = {http://www.cl.cam.ac.uk/~pes20/nqsbtls-usenix-security15.pdf},
timestamp = {Thu, 20 Aug 2015 14:07:40 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/uss/Kaloper-Mersinjak15},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@inproceedings{SibylFS-sub,
author = {Tom Ridge and
David Sheets and
Thomas Tuerk and
Andrea Giugliano and
Peter Sewell},
title = {{SibylFS}: formal specification and oracle-based testing for {POSIX}
and real-world file systems},
abstract = {Systems depend critically on the behaviour of file systems, but that behaviour differs in many details, both between implementations and between each implementation and the POSIX (and other) prose specifications.  Building robust and portable software requires understanding these details and differences, but there is currently no good way to systematically describe, investigate, or test file system behaviour across this complex multi-platform interface.

In this paper we show how to characterise the envelope of allowed
behaviour of file systems in a form that enables practical and highly
discriminating testing.  We give a mathematically rigorous model of
file system behaviour, SibylFS, that specifies the range of allowed
behaviours of a file system for any sequence of the system calls
within our scope, and that can be used as a \emph{test oracle} to
decide whether an observed trace is allowed by the model, both for
validating the model and for testing file systems against it.  SibylFS
is modular enough to not only describe POSIX, but also specific
Linux, OSX and FreeBSD behaviours.  We complement the model
with an extensive test suite of over 21000 tests; this can be run on
a target file system and checked in less than 5 minutes, making it
usable in practice.  Finally, we report experimental results for
around 40 configurations of many file systems, identifying many
differences and some serious flaws.
},
booktitle = {\textbf{SOSP 2015}: Proceedings of the 25th Symposium on Operating Systems Principles,
Monterey, CA, USA},
conf = {SOSP 2015},
pages = {38--53},
year = {2015},
month = oct,
optcrossref = {DBLP:conf/sosp/2015},
url = {http://doi.acm.org/10.1145/2815400.2815411},
pdf = {http://www.cl.cam.ac.uk/~pes20/SOSP15-paper102-submitted.pdf},
doi = {10.1145/2815400.2815411},
timestamp = {Fri, 02 Oct 2015 08:59:57 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/sosp/RidgeSTGMS15},
bibsource = {dblp computer science bibliography, http://dblp.org}
}

@inproceedings{nqsb-testing,
author = {David Kaloper-Mer{\v s}injak and Hannes Mehnert},
title = {Not-quite-so-broken {TLS} 1.3 mechanised conformance checking},
booktitle = {{TLSv1.3} -- Ready or Not?  ({TRON}) workshop},
conf = {TRON workshop 2016},
year = {2016},
month = feb,
pdf = {https://www.cl.cam.ac.uk/~hm519/tron.pdf},
abstract = {We present a set of tools to aid TLS 1.3 implementors, all derived from a single TLS implementation/model.  These include an automated offline TLS protocol conformance checker, a test oracle validating recorded sessions, a tool replicating recorded sessions with other implementations, and an interactive online handshake visualisation.

The conformance checker repeatedly runs a user-provided TLS implementation, attempting to establish TLS sessions with it; the checker explores the TLS parameter space to determine feature coverage of the provided implementation. The test oracle takes a recorded session between two endpoints and decides whether the session was conformant with the specification.  The replication utility re-runs one side of a recorded session against another TLS implementation, and observes its behaviour.  The online visualisation accepts connections from clients and presents the TLS session as an interactive sequence diagram.

All of these tools are based on our clean-slate nqsb-TLS implementation/model.  It already supports TLS 1.0-1.2, and interoperates with a broad range of other TLS implementations.  We are currently extending nqsb-TLS with TLS 1.3 support, and tracking the progress of the TLS 1.3 draft, adapting our implementation/model accordingly.

We invite the community to use our tools while implementing the TLS 1.3 RFC, and provide feedback on deviations in the interpretation thereof.  This process enables the community to converge to a single, mechanically checkable TLS 1.3 model, as implemented by nqsb-TLS.}
}

@inproceedings{biglater,
author = {Kasper Svendsen and Filip Sieczkowski and Lars Birkedal},
title = {Transfinite Step-indexing: Decoupling Concrete and Logical Steps},
booktitle = {\textbf{ESOP 2016}},
conf = {ESOP 2016},
year = 2016,
month = apr,
pages = {727--751},
url = {http://dx.doi.org/10.1007/978-3-662-49498-1_28},
doi = {10.1007/978-3-662-49498-1_28},
pdf = {http://www.cs.au.dk/~birke/papers/biglater-conf.pdf},
abstract = { Step-indexing has proven to be a powerful technique for defining logical relations for languages with advanced type systems and models of expressive program logics. In both cases, the model is stratified using natural numbers to solve a recursive equation that has no naive solutions. As a result of this stratification, current models require that each unfolding of the recursive equation -- each logical step -- must coincide with a concrete reduction step. This tight coupling is problematic for applications where the number of logical steps cannot be statically bounded.

In this paper we demonstrate that this tight coupling between logical and concrete steps is artificial and show how to loosen it using transfinite step-indexing. We present a logical relation that supports an arbitrary but finite number of logical steps for each concrete step. }
}

@inproceedings{Ntzik2015Reasoning,
title = {{Reasoning about the {POSIX} File System: Local Update and Global Pathnames}},
author = {Ntzik, Gian and Gardner, Philippa},
booktitle = {\textbf{OOPSLA 2015}: Proceedings of the 30th Annual {ACM} {SIGPLAN} Conference on Object-Oriented Programming, Systems, Languages, and Applications},
conf = {OOPSLA 2015},
year = {2015},
month = oct,
abstract = {We introduce a program logic for specifying a core sequential subset of the POSIX file system and for reasoning abstractly about client programs working with the file system. The challenge is to reason about the combination of local directory update and global pathname traversal (including '..' and symbolic links) which may overlap the directories being updated. Existing reasoning techniques are either based on first-order logic and do not scale, or on separation logic and can only handle linear pathnames (no '..' or symbolic links). We introduce fusion logic for reasoning about local update and global pathname traversal, introducing a novel effect frame rule to propagate the effect of a local update on overlapping pathnames. We apply our reasoning to the standard recursive remove utility (rm -r), discovering bugs in well-known implementations.}
}

@inproceedings{DBLP:conf/vstte/SezginT15,
author = {Ali Sezgin and
Serdar Tasiran},
title = {Moving Around: Lipton's Reduction for {TSO} - (Regular Submission)},
booktitle = {\textbf{VSTTE 2015}: Verified Software: Theories, Tools, and Experiments - 7th International
Conference, San Francisco, CA, USA.
Revised Selected Papers},
conf = {VSTTE 2015},
pages = {165--182},
year = {2015},
month = jul,
optcrossref = {DBLP:conf/vstte/2015},
url = {http://dx.doi.org/10.1007/978-3-319-29613-5_10},
doi = {10.1007/978-3-319-29613-5_10},
timestamp = {Fri, 12 Feb 2016 10:43:40 +0100},
biburl = {http://dblp.uni-trier.de/rec/bib/conf/vstte/SezginT15},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {We generalize Lipton’s reduction theory, hitherto limited to SC, for TSO programs. We demonstrate the use of our theory by specifying the conditions under which a particular write is SC-like (i.e. placing a fence immediately after the write does not constrain the behavior of the overall program) and a library implementation can be safely used (i.e. compositionality). Our theory is complete: a program has only SC behaviors iff there is a proof that establishes that every write in the program is SC-like. We adapt the notion of program abstraction to TSO analysis via our theory. We define precisely what is meant by abstraction, and propose a methodology by which one can obtain via abstraction SC summaries of a program which may have non-SC behaviors. Finally, we show how checking whether a write instruction is SC-like can be mechanized. We describe a transformation in which the execution of each thread of the original program (under TSO) is simulated by the execution of two tightly coupled threads in the new program (under SC).}
}

@inproceedings{GomesStruth16,
author = {Victor B. F. Gomes and
Georg Struth},
title = {Modal {K}leene algebra applied to program correctness},
booktitle = {\textbf{FM 2016}: Formal Methods -- 21st International Symposium,
Limassol},
conf = {FM 2016},
year = {2016},
month = nov,
editor = {John S. Fitzgerald and
Stefania Gnesi and
Constance L. Heitmeyer},
series = {Lecture Notes in Computer Science},
publisher = {Springer},
pages = {310--325},
url = {http://dx.doi.org/10.1007/978-3-319-48989-6_19},
doi = {10.1007/978-3-319-48989-6_19},
abstract = {
Modal Kleene algebras are relatives of dynamic logics that support
program construction and verification by equational reasoning.  We
describe their application in implementing versatile program
correctness components in interactive theorem provers such as
Isabelle/HOL. Starting from a weakest precondition based component
with a simple relational store model, we show how variants for Hoare
logic, strongest postconditions and program refinement can be built
in  a principled way. Modularity of the approach is demonstrated
by variants that capture program termination and recursion,
memory models for programs with pointers, and program trace
semantics.
},
url = {https://www.repository.cam.ac.uk/handle/1810/260625},
pdf = {http://www.cl.cam.ac.uk/~pes20/rems/papers/GomesStruthMKA.pdf}
}

@inproceedings{KSB17,
author = {Morten Krogh-Jespersen and
Kasper Svendsen and
Lars Birkedal},
title = {A Relational Model of Types-and-Effects in Higher-Order
Concurrent Separation Logic},
booktitle = {\textbf{POPL 2017}: The 44st Annual {ACM} {SIGPLAN-SIGACT} Symposium on Principles of
Programming Languages,  Paris, France},
optpages = {179--192},
year = {2017},
conf = {POPL 2017},
month = jan,
isbn = {978-1-4503-4660-3},
location = {Paris, France},
pages = {218--231},
numpages = {14},
url = {http://doi.acm.org/10.1145/3009837.3009877},
doi = {10.1145/3009837.3009877},
acmid = {3009877},
publisher = {ACM},
address = {New York, NY, USA},
abstract = {
Recently we have seen a renewed interest in programming languages that tame the complexity of state and concurrency through refined type systems with more fine-grained control over effects. In addition to simplifying reasoning and eliminating whole classes of bugs, statically tracking effects opens the door to advanced compiler optimizations.

In this paper we present a relational model of a type-and-effect system for a higher-order, concurrent programming language. The model precisely captures the semantic invariants expressed by the effect annotations. We demonstrate that these invariants are strong enough to prove advanced program transformations, including automatic parallelization of expressions with suitably disjoint effects. The model also supports refinement proofs between abstract data types implementations with different internal data representations, including proofs that fine-grained concurrent algorithms refine their coarse-grained counterparts. This is the first model for such an expressive language that supports both effect-based optimizations and data abstraction.

The logical relation is defined in Iris, a state-of-the-art higher-order concurrent separation logic. This greatly simplifies proving well-definedness of the logical relation and also provides us with a powerful logic for reasoning in the model.}
}

@inproceedings{Caper,
author = {Thomas Dinsdale{-}Young and
Pedro da Rocha Pinto and
Kristoffer Just Andersen and
Lars Birkedal},
title = {{Caper: Automatic Verification for Fine-grained Concurrency}},
booktitle = {Proc. \textbf{ESOP 2017}: 26th European Symposium on Programming},
conf = {ESOP 2017},
series = {Lecture Notes in Computer Science},
publisher = {Springer},
year = {2017},
pdf = {https://www.doc.ic.ac.uk/~pmd09/research/publications/2017/esop/caper-automatic-verification-for-fine-grained-concurrency.pdf},
month = apr,
abstract = {Recent program logics based on separation logic emphasise a modular approach to proving functional correctness for fine-grained concurrent programs. However, these logics have no automation support. In this paper, we present Caper, a prototype tool for automated reasoning in such a logic. Caper is based on symbolic execution, integrating reasoning about interference on shared data and about ghost resources that are used to mediate this interference. This enables Caper to verify the functional correctness of fine-grained concurrent algorithms.}
}

@inproceedings{Maps,
author = {Shale Xiong and
Pedro da Rocha Pinto and
Gian Ntzik and
Philippa Gardner},
title = {{Abstract Specifications for Concurrent Maps}},
booktitle = {Proc. \textbf{ESOP 2017}: 26th European Symposium on Programming},
conf = {ESOP 2017},
series = {Lecture Notes in Computer Science},
publisher = {Springer},
year = {2017},
month = apr,
pdf = {https://www.doc.ic.ac.uk/~pmd09/research/publications/2017/esop/abstract-specifications-for-concurrent-maps.pdf},
abstract = {Despite recent advances in reasoning about concurrent data structure libraries, the largest implementations in java.util.concurrent have yet to be verified.  The key issue lies in the development of  modular specifications, which provide clear logical boundaries  between clients and implementations.  A solution is to use recent advances in fine-grained concurrency reasoning, in particular the introduction of abstract atomicity to concurrent separation logic reasoning. We present two specifications of concurrent maps, both providing the clear boundaries we seek. We show that these specifications are equivalent, in that they can be built from each other. We show how we can verify client programs, such as a concurrent set and a producer-consumer client. We also give a substantial first proof that the main operations of ConcurrentSkipListMap in java.util.concurrent satisfy the map specification. This work demonstrates that we now have the technology to verify the largest implementations in java.util.concurrent.}
}

@inproceedings{ocaml16conex,
author = {Hannes Mehnert and Louis Gesbert},
title = {Conex --- establishing trust into data repositories},
booktitle = {Proceedings of the ACM \textbf{OCaml 2016} Workshop},
conf = {OCaml 2016},
year = 2016,
month = sep,
url = {https://github.com/hannesm/conex-paper/raw/master/paper.pdf},
abstract = {Opam is a software update system, responsible for
community repositories.  The data and metadata at each step should be
authenticated to originate from a (transitively) trusted author.  Opam
does not include any mechanism to authenticate any step at the moment.
We propose conex, which establishes digital signatures from the package
author to the user.  Using conex, neither the distribution server nor
the transport layer need to be trusted.  Clients will install
authenticated packages, and notice conex only if signatures cannot be
verified.  Authors need to adapt their workflow slightly, an updated
opam publish will be developed.  Janitors (repository maintainers) need
to adapt their workflow to emit cryptographic signatures to the
repository (in addition to pressing merge PR buttons).}
}

@inproceedings{ocaml16libtls,
author = {Enguerrand Decorne and Jeremy Yallop and David Mer{\v{s}}injak},
title = {OCaml inside: a drop-in replacement for libtls (extended abstract)},
booktitle = {Proceedings of the ACM \textbf{OCaml 2016} Workshop},
conf = {OCaml 2016},
year = 2016,
month = sep,
url = {https://www.cl.cam.ac.uk/users/jdy22/papers/ocaml-inside-a-drop-in-replacement-for-libtls.pdf},
abstract = {The C programming language pervades systems software. An operating
system in the Unix tradition consists of a kernel, written
in C, and a collection of libraries and executables, also written in
C, which communicate in large part via APIs defined as C types
and functions. Systems built in C typically suffer from a number of
problems, ranging from buffer overflows and other violations that
APIs that result from an inexpressive type system and a lack of
automatic memory management.
The openssl library, which implements the cryptographic protocols
TLS and SSL, suffers from both these problems. The lack
of bounds checking in C led to the notorious Heartbleed bug in
2014; a study two years earlier found that almost no clients of
openssl use the library correctly, apparently due to its unhelpful
interface (Georgiev et al. 2012).
In response to the Heartbleed bug, the OpenBSD team created
libressl, a fork of openssl with the aim of correcting the deficiencies.
One early fruit of the libressl project is libtls, a
much simpler, more disciplined interface to the TLS protocol implementation
in libressl.
However, libtls is still built in C, and so is still vulnerable
to potential buffer overflows, type errors, and similar defects. In
this talk we describe one approach to avoiding these problems,
namely replacing libtls with a fully compatible library written in
OCaml. Our library, libnqsb-tls1, matches the libtls function-for-function, but the implementation contains no C; instead, it it
wraps the pure OCaml TLS implementation ocaml-tls (Kaloper-Mer{\v{s}}injak et al. 2015)}
}

@inproceedings{haas_et_al:LIPIcs:2016:6180,
author = {Andreas Haas and Thomas A. Henzinger and Andreas Holzer and Christoph M. Kirsch and Michael Lippautz and Hannes Payer and Ali Sezgin and Ana Sokolova and Helmut Veith},
abstract = {The semantics of concurrent data structures is usually given by a sequential specification and a consistency condition. Linearizability is the most popular consistency condition due to its simplicity and general applicability. Nevertheless, for applications that do not require all guarantees offered by linearizability, recent research has focused on improving performance and scalability of concurrent data structures by relaxing their semantics.
In this paper, we present local linearizability, a relaxed consistency
condition that is applicable to container-type concurrent data
structures like pools, queues, and stacks. While linearizability requires that the effect of each operation is observed by all threads at the same time, local linearizability only requires that for each thread T, the effects of its local insertion operations and the effects of those removal operations that remove values inserted by T are observed by all threads at the same time. We investigate theoretical and practical properties of local linearizability and its relationship to many existing consistency conditions. We present a generic implementation method for locally linearizable data structures that uses existing linearizable data structures as building blocks. Our implementations show performance and scalability improvements over the original building blocks and outperform the fastest existing container-type implementations.},
title = {{Local Linearizability for Concurrent Container-Type Data Structures}},
booktitle = {27th International Conference on Concurrency Theory (\textbf{CONCUR 2016})},
conf = {CONCUR 2016},
pages = {6:1--6:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
isbn = {978-3-95977-017-0},
issn = {1868-8969},
year = {2016},
month = aug,
volume = {59},
publisher = {Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
doi = {10.4230/LIPIcs.CONCUR.2016.6},
pdf = {http://drops.dagstuhl.de/opus/volltexte/2016/6180/pdf/LIPIcs-CONCUR-2016-6.pdf}
}

@article{GomesGHSW16,
author = {Victor B. F. Gomes and
Walter Guttmann and
Peter H{\"{o}}fner and
Georg Struth and
Tjark Weber},
title = {Kleene Algebras with Domain},
journal = {Archive of Formal Proofs},
volume = {2016},
year = {2016},
month = apr,
abstract = {Kleene algebras with domain are Kleene algebras endowed with an operation that maps each element of the algebra to its domain of definition (or its complement) in abstract fashion. They form a simple algebraic basis for Hoare logics, dynamic logics or predicate transformer semantics. We formalise a modular hierarchy of algebras with domain and antidomain (domain complement) operations in Isabelle/HOL that ranges from domain and antidomain semigroups to modal Kleene algebras and divergence Kleene algebras. We link these algebras with models of binary relations and program traces. We include some examples from modal logics, termination and program analysis.}
}

@article{GomesS16,
author = {Victor B. F. Gomes and
Georg Struth},
title = {Program Construction and Verification Components Based on {K}leene Algebra},
journal = {Archive of Formal Proofs},
volume = {2016},
year = {2016},
month = jun,
url = {https://www.isa-afp.org/entries/Algebraic_VCs.shtml},
abstract = {Variants of Kleene algebra support program construction and verification by algebraic reasoning. This entry provides a verification component for Hoare logic based on Kleene algebra with tests, verification components for weakest preconditions and strongest postconditions based on Kleene algebra with domain and a component for step-wise refinement based on refinement Kleene algebra with tests. In addition to these components for the partial correctness of while programs, a verification component for total correctness based on divergence Kleene algebras and one for (partial correctness) of recursive programs based on domain quantales are provided. Finally we have integrated memory models for programs with pointers and a program trace semantics into the weakest precondition component.}
}

@inproceedings{Raad2016Verifying,
title = {Verifying Concurrent Graph Algorithms},
author = {Raad, Azalea and Hobor, Aquinas and Villard, Jules and Gardner, Philippa},
booktitle = {Proc. \textbf{APLAS 2016}: 14th Asian Symposium on Programming Languages and Systems},
conf = {APLAS 2016},
year = {2016},
month = nov,
pages = {314--334},
url = {http://dx.doi.org/10.1007/978-3-319-47958-3_17},
doi = {10.1007/978-3-319-47958-3_17},
abstract = {We show how to verify four challenging concurrent finegrained graph-manipulating algorithms, including graph copy, a speculatively parallel Dijkstra, graph marking and spanning tree. We develop a reasoning method for such algorithms that dynamically tracks the contributions and responsibilities of each thread operating on a graph, even in cases of arbitrary recursive thread creation. We demonstrate how to use a logic without abstraction (CoLoSL) to carry out abstract reasoning in the style of iCAP, by building the abstraction into the proof structure rather than incorporating it into the semantic model of the logic.}
}

@inproceedings{Raad2016DOM,
title = {{DOM:} Specification and Client Reasoning},
author = {Raad, Azalea and {Fragoso Santos}, Jos{\'{e}} and Gardner, Philippa},
booktitle = {Proc. \textbf{APLAS 2016}: 14th Asian Symposium on Programming Languages and Systems},
conf = {APLAS 2016},
year = {2016},
month = nov,
pages = {401--422},
url = {http://dx.doi.org/10.1007/978-3-319-47958-3_21},
doi = {10.1007/978-3-319-47958-3_21},
abstract = {We present an axiomatic specification of a key fragment of DOM using structural separation logic. This specfication allows us to develop modular reasoning about client programs that call the DOM.}
}

@inproceedings{Kaloper-Mersinjak:2016:GPD:2976022.2976028,
author = {Kaloper-Mer\v{s}injak, David and Yallop, Jeremy},
title = {Generic Partially-static Data (Extended Abstract)},
booktitle = {Proceedings of the 1st International Workshop on Type-Driven Development},
conf = {TyDe 2016},
series = {TyDe 2016},
year = {2016},
month = sep,
isbn = {978-1-4503-4435-7},
location = {Nara, Japan},
pages = {39--40},
numpages = {2},
url = {http://doi.acm.org/10.1145/2976022.2976028},
doi = {10.1145/2976022.2976028},
acmid = {2976028},
publisher = {ACM},
address = {New York, NY, USA},
keywords = {generic programming, partial evaluation, staging},
pdf = {http://dl.acm.org/ft_gateway.cfm?id=2976028&ftid=1783813&dwn=1&CFID=738558588&CFTOKEN=28095393},
abstract = {We describe a generic approach to defining partially-static data
and corresponding operations.}
}

@phdthesis{Ntzik2017Reasoning,
author = {Ntzik, Gian},
title = {Reasoning About {POSIX} File Systems},
school = {Imperial College London},
month = sep,
year = {2016},
opttype = {phdthesis},
url = {https://psvg.doc.ic.ac.uk/publications/Ntzik2017Reasoning.pdf},
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
speciation 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 lock files and
named pipes. Program reasoning based on separation logic has been successful
at verifying that programs do not crash due to illegal use of resources,
such invalid memory accesses. The underlying assumption of separation
logics, however, is that machines do not fail. In practice, machines can
fail unpredictably for various reasons, such as power loss, corrupting
resources or resulting in permanent data loss. Critical software, such as
file systems and databases, employ recovery methods to mitigate these
effects. We introduce an extension of the Views framework to reason about
programs in the presence of such events and their associated recovery
methods. We use concurrent separation logic as an instance of the framework
to illustrate our reasoning, and explore programs using write-ahead logging,
such a stylised ARIES recovery algorithm.}
}

@phdthesis{daRochaPinto2017Reasoning,
author = {{da Rocha Pinto}, Pedro},
title = {Reasoning with Time and Data Abstractions},
school = {Imperial College London},
year = {2016},
month = sep,
url = {https://psvg.doc.ic.ac.uk/publications/daRochaPinto2017Reasoning.pdf},
abstract = {In this thesis, we address the problem of verifying the
functional correctness of concurrent programs, with emphasis on fine-grained
concurrent data structures. Reasoning about such programs is challenging
since data can be concurrently accessed by multiple threads: the reasoning
must account for the interference between threads, which is often subtle. To
reason about interference, concurrent operations should either be at
distinct times or on distinct data. We present TaDA, a sound program logic
for verifying clients and implementations that use abstract specifications
that incorporate both abstract atomicity---the abstraction that operations
take effect at a single, discrete instant in time---and abstract
disjointness---the abstraction that operations act on distinct data resources.
Our key contribution is the introduction of atomic triples, which offer an
expressive approach for specifying program modules. We also present
Total-TaDA, a sound extension of TaDA with which we can verify total
correctness of concurrent programs, i.e. that such programs both produce the
correct result and terminate. With Total-TaDA, we can specify constraints on
a thread=92s concurrent environment that are necessary to guarantee
termination. This allows us to verify total correctness for nonblocking
algorithms and express lock- and wait-freedom. More generally, the abstract
specifications can express that one operation cannot impede the progress of
another, a new non-blocking property that we call non-impedance. Finally, we
describe how to extend TaDA for proving abstract atomicity for data
structures that make use of helping---where one thread is performing an
abstract operation on behalf of another---and speculation---where an abstract
operation is determined by future behaviour.}
}

@phdthesis{Raad2017Abstraction,
title = {Abstraction, Refinement and Concurrent Reasoning},
school = {Imperial College London},
year = {2016},
month = sep,
opttype = {phdthesis},
abstract = {This thesis explores the challenges in abstract library
specification, library refinement and reasoning about fine-grained
concurrent programs.For abstract library specification, this thesis applies
structural separation logic (SSL) to formally specify the behaviour of
several libraries in an abstract, local and compositional manner. This
thesis further generalises the theory of SSL to allow for library
specifications that are language independent. Most notably, we specify a
fragment of the Document Object Model (DOM) library. This result is
compelling as it significantly improves upon existing DOM formalisms in that
the specifications produced are local, compositional and
language-independent. Concerning library refinement, this thesis explores
two existing approaches to library refinement for separation logic,
identifying their advantages and limitations in different settings. This
thesis then introduces a hybrid approach to refinement, combining the
strengths of both techniques for simple scalable library refinement. These
ideas are then adapted to refinement for SSL by presenting a JavaScript
implementation of the DOM fragment studied and establishing its correctness
with respect to its specification using the hybrid refinement approach.As to
concurrent reasoning, this thesis introduces concurrent local subjective
logic (CoLoSL) for compositional reasoning about fine-grained concurrent
programs. CoLoSL introduces subjective views, where each thread is verified
with respect to a customised local view of the state, as well as the general
composition and framing of interference relations, allowing for better proof
reuse.}
}

@inproceedings{Cerone2017Algebraic,
author = {Cerone, Andrea and Gotsman, Alexey and Yang, Hongseok},
title = {Algebraic Laws for Weak Consistency},
booktitle = {\textbf{CONCUR 2017}: Proceedings of 28th International Conference on Concurrency Theory},
conf = {CONCUR 2017},
year = {2017},
month = sep,
url = {https://psvg.doc.ic.ac.uk/publications/Cerone2017Algebraic.html},
doi = {10.4230/LIPIcs.CONCUR.2017.26},
abstract = {Modern distributed systems often rely on so called
weakly-consistent databases, which achieve scalability by sacrificing the
consistency guarantee of distributed transaction processing. Such databases
have been formalised in two different styles, one based on abstract
executions and the other based on dependency graphs. The choice between
these styles has been made according to intended applications. The former
has been used for specifying and verifying the implementation of these
databases, while the latter for proving properties of client programs of the
databases. In this paper, we present a set of novel algebraic laws (i.e.
inequations) that connect these two styles of specifications. The laws
relate binary relations used in a specification based on abstract
executions, to those used in a specification based on dependency graphs. We
then show that this algebraic connection gives rise to so called robustness
criteria, conditions which ensure that a client program of a
weakly-consistent database does not exhibit anomalous behaviours due to weak
consistency. These criteria make it easy to reason about these client
programs, and may become a basis for dynamic or static program analyses. For
a certain class of consistency models specifications, we prove a full
abstraction result that connects the two styles of specifications.}
}

@inproceedings{DBLP:conf/cade/SantosGMN17,
author = {Jos{\'{e}} Fragoso Santos and
Philippa Gardner and
Petar Maksimovic and
Daiva Naudziuniene},
editor = {Leonardo de Moura},
title = {Towards Logic-Based Verification of JavaScript Programs},
booktitle = {\textbf{CADE 2017}: 26th International
Conference on Automated Deduction},
series = {Lecture Notes in Computer Science},
volume = {10395},
pages = {8--25},
publisher = {Springer},
month = aug,
year = {2017},
opturl = {https://doi.org/10.1007/978-3-319-63046-5_2},
url = {https://psvg.doc.ic.ac.uk/publications/FragosoSantos2017Towards.html},
doi = {10.1007/978-3-319-63046-5_2},
timestamp = {Wed, 12 Jul 2017 10:22:36 +0200},
bibsource = {dblp computer science bibliography}
}

@inproceedings{gomes-oopsla2017,
author = {Victor B. F. Gomes and Martin Kleppmann and Dominic P. Mulligan and Alastair R. Beresford},
title = {Verifying Strong Eventual Consistency in Distributed Systems},
booktitle = {\textbf{OOPSLA 2017}: Proceedings of the {ACM} {SIGPLAN} International
Conference on Object-Oriented Programming, Systems, Languages, and
Applications ({OOPSLA})},
conf = {OOPSLA 2017},
year = {2017},
month = oct,
note = {Distinguished Paper award}
}

@inproceedings{matache-aplas2017,
author = {Cristina Matache and Victor B. F. Gomes and Dominic P. Mulligan},
title = {Programming and proving with classical types},
booktitle = {\textbf{APLAS 2017}: Proceedings of the 15th {Asian} Symposium on Programming Languages and Systems},
conf = {APLAS 2017},
year = {2017},
month = nov,
optnote = {To appear}
}

@article{DBLP:journals/corr/BirkedalDJST17,
author = {Lars Birkedal and
Thomas Dinsdale{-}Young and
Guilhem Jaber and
Kasper Svendsen and
Nikos Tzevelekos},
title = {Trace Properties from Separation Logic Specifications},
journal = {CoRR},
volume = {abs/1702.02972},
year = {2017},
month = feb,
url = {http://arxiv.org/abs/1702.02972},
pdf = {https://arxiv.org/pdf/1702.02972},
timestamp = {Wed, 07 Jun 2017 14:40:31 +0200},
biburl = {http://dblp.uni-trier.de/rec/bib/journals/corr/BirkedalDJST17},
bibsource = {dblp computer science bibliography, http://dblp.org},
abstract = {We propose a formal approach for relating abstract separation logic library specifications with the trace properties they enforce on interactions between a client and a library. Separation logic with abstract predicates enforces a resource discipline that constrains when and how calls may be made between a client and a library. Intuitively, this can enforce a protocol on the interaction trace. This intuition is broadly used in the separation logic community but has not previously been formalised. We provide just such a formalisation. Our approach is based on using wrappers which instrument library code to induce execution traces for the properties under examination. By considering a separation logic extended with trace resources, we prove that when a library satisfies its separation logic specification then its wrapped version satisfies the same specification and, moreover, maintains the trace properties as an invariant. Consequently, any client and library implementation that are correct with respect to the separation logic specification will satisfy the trace properties.}
}
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