A CIL Tutorial - Department of Computer Science - ETH Zürich

Introduction
The C Intermediate Language(CIL) [8] is a source-to-source compiler for C. Since CIL is written in
OCaml [6], and since it performs a number of simplifying transformations to the C AST, it is very
well suited for use in rapid-prototyping new static and dynamic analyses, and for designing and
trying out new language extensions. The purpose of this tutorial is to show how CIL can be used
to construct a compiler front-end that performs additional analysis, or implements new language
extensions. Through a series of examples, we will cover the basics of CIL's AST, its dataow
analysis framework, its facilities for instrumenting programs, the ease of extending C's type system,
and how to employ a theorem prover in the compilation process. In the later chapters, the tutorial
will scratch the surface of some more advanced techniques. These examples will hopefully point in
the direction of full-edged implementations of these advanced techniques, and serve as a template
and starting point for your future projects.
Alternatives
Similar results could certainly be achieved by working directly with gcc or Clang/LLVM [1, 5],
however the learning curve for these tools is much steeper, and the coding burden much higher.
Furthermore, with Clang/LLVM in particular, there is no easy way to add custom statements to C,
to make deep changes to its type-system, or to make changes at the level of the AST. Indeed, using
Clang/LLVM, language extensions are typically written by interpreting new #pragma directives, e.g.
in [9]; and new types are added by extending a complicated class hierarchy designed for speed rather
than for ease of understanding or rapid prototyping. As we will see in this tutorial, with CIL, making
these sorts of changes is straightforward. However, there is at least one downside with CIL: unlike
working directly with gcc, or with Clang/LLVM, there is no support for C++. Language researchers
and analysis designers must consider this trade-o when deciding on a compiler framework.
How to read this tutorial
This tutorial is written in the style of Literate Programming [4]. The source les in the src, ciltutlib,
and test directories may be compiled with the OCaml or C compilers as appropriate, and may
be processed by ocamlweb [3] (in the case of OCaml code) and pygmentize [2] (in the case of C
code) to produce the LATEX code that denes this document. In the template version of this source
tree, the comments that generate this document are omitted.
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