Decompilation, or reverse compilation, takes a computer program and produces high-level code that works like the original source code. This makes it easier to understand a computer program when source code is not available. However, there are very few tools for decompilation available today. This report describes the design and implementation of Desquirr, a decompilation plug-in for Interactive Disassembler Pro. Desquirr has an object-oriented design and performs basic decompilation of programs running on Intel x86 processors. The low-level analysis uses knowledge about specialized compiler constructs, called idioms, to perform a more accurate decompilation. Desquirr implements data flow analysis, meaning the conversion from primitive machine code instructions into code in a high-level language. The major part of the data flow analysis is the Register Copy Propagation which builds high-level expressions from primitive instructions. Control flow analysis, meaning to restore high-level language constructs such as if/else and for loops, is not implemented. A high level representation of a piece of machine code contains the same information as an assembly language representation of the same machine code, but in a format that is easier to comprehend. Symbols such as ?*? and ?+? are used in high-level language expressions, compared to instructions such as ?mul? and ?add? in assembly language. Two small test cases which compares decompiled code with assembly language shows promising results in reducing the amount of information needed to comprehend a program.

Dekompilering, eller omvänd kompilering, tar ett datorprogram och omvandlar det till högnivåspråk som fungerar som den ursprungliga källkoden. Detta gör det lättare att förstå ett datorprogram när källkod inte finns tillgänglig. Det finns väldigt få verktyg för dekompilering tillgängliga idag. Den här rapporten beskriver design och implementation av Desquirr, en dekomplator-plugin för Interactive Disassembler Pro. Desquirr har en objekt-orienterad design och utför grundläggande dekompilering av program som kör på Intel x86-processorer.