A decompiler is a computer program that translates an executable file back into high-level source code. Unlike a compiler, which converts high-level code into machine code, a decompiler performs the reverse process. While disassemblers translate executables into assembly language, decompilers go a step further by reconstructing the disassembly into higher-level languages like C. Due to the one-way nature of the compilation process, decompilers usually cannot perfectly recreate the original source code. They often produce obfuscated and less readable code.

Decompilation is the process of transforming executable code into a high-level, human-readable format using a decompiler. This process is commonly used for tasks that involve reverse-engineering the logic behind executable code, such as recovering lost or unavailable source code. Decompilers face inherent challenges due to the loss of critical information during the compilation process, such as variable names, comments, and code structure.

Certain factors can impact the success of decompilation. Executables containing detailed metadata, such as those used by Java and .NET, are easier to reverse-engineer because they often retain class structures, method signatures, and debugging information. Executable files stripped of such context are far more challenging to translate into meaningful source code.

Some software developers may obfuscate, pack, or encrypt parts of their executable programs, making the decompiled code much harder to interpret. These techniques are often done to deter reverse-engineering, making the process more difficult and time-intensive.

Decompilers can be thought of as composed of a series of phases each of which contributes specific aspects of the overall decompilation process.

The first decompilation phase loads and parses the input machine code or intermediate language program's binary file format. It should be able to discover basic facts about the input program, such as the architecture (Pentium, PowerPC, etc.) and the entry point. In many cases, it should be able to find the equivalent of the main function of a C program, which is the start of the user written code. This excludes the runtime initialization code, which should not be decompiled if possible. If available the symbol tables and debug data are also loaded. The front end may be able to identify the libraries used even if they are linked with the code, this will provide library interfaces. If it can determine the compiler or compilers used it may provide useful information in identifying code idioms.

The next logical phase is the disassembly of machine code instructions into a machine independent intermediate representation (IR). For example, the Pentium machine instruction

might be translated to the IR