[Colloq] Master's Thesis Defense - Louis Bloom - April 14, 11am, 366 - Structured Intermediate Representation Modification in the LLVM Compiler Infrastructure

[Jessica Biron]

Louis Bloom 


Type : Masters 

Title : Structured Intermediate Representation Modification in the LLVM Compiler Infrastructure 

Date : 14 April 

Time : 11:00 a.m. 

Location : 366 WVH 



Abstract : In this thesis we propose a new approach for modifying programs expressed 

in an intermediate representation (IR) that leverages the many-to-one relationship 

between source languages and IR and also supports modifying code 

emitted from binary-to-IR decompilers. The open source LLVM Compiler 

Infrastructure offers a semantically well-defined IR and supports a variety 

of popular source languages and target instruction set architectures (ISAs). 

LLVM currently supports program modification by translating source 

code into LLVM IR and performing a fixed set of transformations on the 

IR. This functionality is part of the LLVM optimizer and exists in order 

to improve a program’s execution performance while preserving its visible 

behavior. 

We improve LLVM’s techniques for systematic program modification 

by introducing structured methods for behavior alteration. The targets for 

modification are programs written in LLVM IR. First, this work presents a 

call graph transformation algebra which allows for call graph manipulation 

while preserving structural validity of a target graph. Second, this thesis 

explores the implementation of a structured IR editor based on this transformation 

algebra that allows users to modify a target program in terms of its 

call graph. Finally, we demonstrate the usefulness of our IR editor through 

an example in which we retrofit security features into the OpenSSH codebase.