Datalog for Program Analysis

Table of Contents

• 1 Introduction
  • 1.1 What is Datalog?
    • 1.1.1 Syntax
    • 1.1.2 Setting Up Datalog
• 2 Your First Datalog Program
  • 2.1 Facts
  • 2.2 Rules
  • 2.3 Query
• 3 Applying Datalog to Program Analysis

1 Introduction

Welcome to the first installment of our tutorial series on leveraging Datalog for program analysis. In this series, we will explore the fundamentals of Datalog, its syntax, and how it can be applied to solve various program analysis problems. Datalog is a powerful declarative logic programming language that is particularly well-suited for querying relational data, making it an excellent tool for program analysis.

1.1 What is Datalog?

Datalog is a declarative logic programming language that is a subset of Prolog. It is used primarily for deductive databases and declarative queries. Unlike imperative languages, Datalog focuses on what the program should accomplish rather than how to achieve it.

1.1.1 Syntax

The syntax of Datalog is based on facts, rules, and queries.

Facts: Represent basic assertions about the world. For example:

parent("enzo", "mia").

Rules: Define relationships between facts using logical implications. For example:

ancestor(X, Y) :- parent(X, Y).
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).

Queries: Questions posed to the Datalog system to infer information based on the facts and rules. For example:

?- ancestor("enzo", "mia").

1.1.2 Setting Up Datalog

To get started with Datalog, you’ll need an environment that supports Datalog queries. One popular choice is Soufflé, a Datalog engine that is efficient and easy to use.

Installation:

For Linux:

sudo apt install souffle

For macOS:

brew install souffle-lang/souffle/souffle

2 Your First Datalog Program

Let’s write a simple Datalog program to understand its structure. Consider a program that defines family relationships.

2.1 Facts

parent("enzo", "mia").
parent("mia", "piper").
parent("piper", "owen").

2.2 Rules

ancestor(X, Y) :- parent(X, Y).
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).

2.3 Query

.output ancestor

Now, save the above content into a file called family.dl and run it using Soufflé:

souffle -D . family.dl

Wait, that didn’t seem to work correctly, what’s missing?

.decl parent (n: symbol, m: symbol)
...
.decl ancestor (n: symbol, m: symbol)

So now the full family.dl should look like:

.decl parent (n: symbol, m: symbol)
parent("enzo", "mia").
parent("mia", "piper").
parent("piper", "owen").

.decl ancestor (n: symbol, m: symbol)
ancestor(X, Y) :- parent(X, Y).
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).

.output ancestor

Which will output a CSV file, ancestor.csv, showing all the relationships in the input program (the facts):

enzo	mia
enzo	piper
enzo	owen
mia	piper
mia	owen
piper	owen

3 Applying Datalog to Program Analysis

Datalog can be a powerful tool for program analysis due to its ability to express complex relationships in a concise manner. Let’s consider a simple example of points-to analysis, which is used to determine what pointers can point to at various points in a program.

TODO.