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.
Wed 15 JunDisplayed time zone: Tijuana, Baja California change
10:30 - 12:00
|Into the depths of C: elaborating the de facto standards|
Kayvan Memarian University of Cambridge, Justus Matthiesen University of Cambridge, James Lingard University of Cambridge (when this work was done), Kyndylan Nienhuis University of Cambridge, David Chisnall University of Cambridge, Robert N. M. Watson University of Cambridge, Peter Sewell University of CambridgeLink to publication Media Attached
|Living on the edge: Rapid-toggling probes with cross modification on x86|
Buddhika Chamith , Bo Joel Svensson Indiana University, Luke Dalessandro Indiana University, Ryan R. Newton Indiana UniversityPre-print Media Attached
|Polymorphic Type Inference for Machine Code|
Research PapersPre-print Media Attached