Xoc, an extension-oriented compiler for systems programming

Abstract

Today's system programmers go to great lengths to extend the languages in which they program. For instance, system-specific compilers find errors in Linux and other systems, and add support for specialized control flow to Qt and event-based programs. These compilers are difficult to build and cannot always understand each other's language changes. However, they can greatly improve code understandability and correctness, advantages that should be accessible to all programmers.We describe an extension-oriented compiler for C called xoc. An extension-oriented compiler, unlike a conventional extensible compiler, implements new features via many small extensions that are loaded together as needed. Xoc gives extension writers full control over program syntax and semantics while hiding many compiler internals. Xoc programmers concisely define powerful compiler extensions that, by construction, can be combined; even some parts of the base compiler, such as GNU C compatibility, are structured as extensions.Xoc is based on two key interfaces. Syntax patterns allow extension writers to manipulate language fragments using concrete syntax. Lazy computation of attributes allows extension writers to use the results of analyses by other extensions or the core without needing to worry about pass scheduling.Extensions built using xoc include xsparse, a 345-line extension that mimics Sparse, Linux's C front end, and xlambda, a 170-line extension that adds function expressions to C. An evaluation of xoc using these and 13 other extensions shows that xoc extensions are typically more concise than equivalent extensions written for conventional extensible compilers and that it is possible to compose extensions.

Using C language extensions for developing embedded software: a case study

“…The interrupt-triggered tasks include reading the raw measurements (triggered by the ADC interrupt 7 ) as well handling recalibration requests (triggered by UART-Receive). Interrupt-triggered tasks preempt the foreground tasks and always run to completion, which makes them time-sensitive.…”

“…mbeddr is different because it provides an open framework and tool for defining modular extensions of C, as well as the IDE. Xoc [7] supports parser-based modular extensibility, but it is limited to textual notations and also does not address IDE extension. Our SMT study shows that developers actually use this extension possibility.…”

Reliably composable language extensions

“…C has had several other extensible compilers implemented for it already, including xtc [94], Xoc [95], and mbeddr [96]. As such, we believe it is a good starting point.…”

“…Most notable are XTC [94] and Xoc [95]. XTC supports modular specification of syntactic extensions to C using parsing expression grammars (PEGs).…”

“…AbleC shares the same goals of programmer-directed composition of language extensions as Xoc [95], another extensible C compiler. Xoc uses an attribute grammarlike mechanism for semantic analysis and uses GLR-based parser, so extension specifications have a form similar to those in AbleC.…”