Reverse Engineering

RetDec – A Retargetable Machine-Code Decompiler

January 7, 2018
7 Min Read

RetDec is a retargetable machine-code decompiler based on LLVM.
The decompiler is not limited to any particular target architecture, operating system, or executable file format:

  • Supported file formats: ELF, PE, Mach-O, COFF, AR (archive), Intel HEX, and raw machine code.
  • Supported architectures (32b only): Intel x86, ARM, MIPS, PIC32, and PowerPC.

Features:

  • Static analysis of executable files with detailed information.
  • Compiler and packer detection.
  • Loading and instruction decoding.
  • Signature-based removal of statically linked library code.
  • Extraction and utilization of debugging information (DWARF, PDB).
  • Reconstruction of instruction idioms.
  • Detection and reconstruction of C++ class hierarchies (RTTI, vtables).
  • Demangling of symbols from C++ binaries (GCC, MSVC, Borland).
  • Reconstruction of functions, types, and high-level constructs.
  • Integrated disassembler.
  • Output in two high-level languages: C and a Python-like language.
  • Generation of call graphs, control-flow graphs, and various statistics.

For more information, check out our

Installation and Use
Currently, we support only Windows (7 or later), Linux, and unofficially macOS.
Warning: Decompilations of larger binaries (1 MB or more) may require a lot of RAM. When running decompilations, we advise you to limit the maximal virtual memory for processes before decompiling to prevent potential swapping and unresponsiveness. On Linux, you can run e.g. ulimit -Sv 9863168 in your shell to limit the maximal virtual memory to 8 GB.

Windows

  1. Either download and unpack a pre-built package from the following list, or build and install the decompiler by yourself (the process is described below):
  2. Install Microsoft Visual C++ Redistributable for Visual Studio 2015.
  3. Install MSYS2 and other needed applications by following RetDec’s Windows environment setup guide.
  4. Now, you are all set to run the decompiler. To decompile a binary file named test.exe, go into $RETDEC_INSTALL_DIR/bin and run: 
    bash decompile.sh test.exe

    For more information, run bash decompile.sh --help.

Linux

  1. There are currently no pre-built packages for Linux. You will have to build and install the decompiler by yourself. The process is described below.
  2. After you have built the decompiler, you will need to install the following packages via your distribution’s package manager:
  3. Now, you are all set to run the decompiler. To decompile a binary file named test.exe, go into $RETDEC_INSTALL_DIR/bin and run: 
    ./decompile.sh test.exe

    For more information, run ./decompile.sh --help.

macOS
Warning: macOS build was added based on community feedback and is not directly supported by the RetDec team. We do not guarantee you that these instructions will work for you. If you encounter any problem with your build, submit an issue so the macOS community can help you out.

  1. There are currently no pre-built packages for macOS. You will have to build and install the decompiler by yourself. The process is described below.
  2. After you have built the decompiler, you will need to install the following packages:
  3. Now, you are all set to run the decompiler. To decompile a binary file named test.exe, go into $RETDEC_INSTALLED_DIR/bin and run: 
    # /usr/local/bin/bash if installed via Homebrew
/path/to/gnu/bash ./decompile.sh test.exe

    For more information, run ./decompile.sh --help.

Build and Installation
This section describes a manual build and installation of RetDec.

Requirements

Linux

On Debian-based distributions (e.g. Ubuntu), the required packages can be installed with apt-get:

sudo apt-get install build-essential cmake git perl python3 bash coreutils wget bc doxygen graphviz upx flex bison zlib1g-dev libtinfo-dev autoconf automake pkg-config m4 libtool

On RPM-based distributions (e.g. Fedora), the required packages can be installed with dnf:

sudo dnf install git cmake make gcc gcc-c++ perl python3 bash zlib-devel flex bison m4 coreutils autoconf automake libtool ncurses-devel wget bc doxygen graphviz upx pkg-config

On Arch Linux, the required packages can be installed with pacman:

sudo pacman -S base-devel cmake git perl python3 bash coreutils wget bc doxygen graphviz upx flex bison zlib ncurses autoconf automake pkg-config m4 libtool

Windows

  • Microsoft Visual C++ (version >= Visual Studio 2015 Update 2)
  • Git
  • MSYS2 and some other applications. Follow RetDec’s Windows environment setup guide to get everything you need on Windows.
  • Active Perl. It needs to be the first Perl in PATH, or it has to be provided to CMake using CMAKE_PROGRAM_PATHvariable, e.g. -DCMAKE_PROGRAM_PATH=/c/perl/bin.
  • Python (version >= 3.4)

macOS

  • Full Xcode installation (Command Line Tools are untested)
  • CMake (version >= 3.6)
  • Newer versions of Bison and Flex, preferably installed via Homebrew
  • wget
  • Python (version >= 3.4, macOS has 2.7)

Process
Warning: Currently, RetDec has to be installed into a clean, dedicated directory. Do NOT install it into /usr, /usr/local, etc. because our build system is not yet ready for system-wide installations. So, when running cmake, always set -DCMAKE_INSTALL_PREFIX=<path> to a directory that will be used just by RetDec. For more details, see #12.

  • Recursively clone the repository (it contains submodules):
  • Linux:
    • cd retdec
    • mkdir build && cd build
    • cmake .. -DCMAKE_INSTALL_PREFIX=<path>
    • make && make install
  • Windows:
    • Open MSBuild command prompt, or any terminal that is configured to run the msbuild command.
    • cd retdec
    • mkdir build && cd build
    • cmake .. -DCMAKE_INSTALL_PREFIX=<path> -G<generator>
    • msbuild /m /p:Configuration=Release retdec.sln
    • msbuild /m /p:Configuration=Release INSTALL.vcxproj
    • Alternatively, you can open retdec.sln generated by cmake in Visual Studio IDE.
  • macOS:
    • cd retdec
    • mkdir build && cd build
    • # Apple ships old Flex & Bison, so Homebrew versions should be used.
export CMAKE_INCLUDE_PATH="/usr/local/opt/flex/include"
export CMAKE_LIBRARY_PATH="/usr/local/opt/flex/lib;/usr/local/opt/bison/lib"
export PATH="/usr/local/opt/flex/bin:/usr/local/opt/bison/bin:$PATH"
    • cmake .. -DCMAKE_INSTALL_PREFIX=<path>
    • make && make install

You have to pass the following parameters to cmake:

  • -DCMAKE_INSTALL_PREFIX=<path> to set the installation path to <path>.
  • (Windows only) -G<generator> is -G"Visual Studio 14 2015" for 32-bit build using Visual Studio 2015, or -G"Visual Studio 14 2015 Win64" for 64-bit build using Visual Studio 2015. Later versions of Visual Studio may be used.

You can pass the following additional parameters to cmake:

  • -DRETDEC_DOC=ON to build with API documentation (requires Doxygen and Graphviz, disabled by default).
  • -DRETDEC_TESTS=ON to build with tests, including all the tests in dependency submodules (disabled by default).
  • -DCMAKE_BUILD_TYPE=Debug to build with debugging information, which is useful during development. By default, the project is built in the Release mode. This has no effect on Windows, but the same thing can be achieved by running msbuild with the /p:Configuration=Debug parameter.
  • -DCMAKE_PROGRAM_PATH=<path> to use Perl at <path> (probably useful only on Windows).

Repository Overview
This repository contains the following libraries:

  • bin2llvmir — library of LLVM passes for translating binaries into LLVM IR modules.
  • debugformat — library for uniform representation of DWARF and PDB debugging information.
  • dwarfparser — library for high-level representation of DWARF debugging information.
  • llvm-support — set of LLVM related utility functions.
  • llvmir2hll — library for translating LLVM IR modules to high-level source codes (C, Python-like language).

This repository contains the following tools:

  • bin2llvmirtool — frontend for the bin2llvmir library.
  • llvm2hlltool — frontend for the llvmir2hll library.

This repository contains the following scripts:

  • decompile.sh — the main decompilation script binding it all together. This is the tool to use for full binary-to-C decompilations.
  • Support scripts used by decompile.sh:
    • color-c.py — decorates output C sources with IDA color tags — syntax highlighting for IDA.
    • config.sh — decompiler’s configuration file.
    • decompile-archive.sh — decompiles objects in the given AR archive.
    • fileinfo.sh — a Fileinfo tool wrapper.
    • signature-from-library.sh — extracts function signatures from the given library.
    • unpack.sh — tries to unpack the given executable file by using any of the supported unpackers.
  • Other utility scripts:
    • decompile-all.sh — decompiles all executables in the given directory and subdirectories.
    • run-unit-test.sh — run all tests in the unit test directory.
    • utils.sh — a collection of bash utilities.

Related Repositories

  • retdec-idaplugin — embeds RetDec into IDA (Interactive Disassembler) and makes its use much easier.
  • retdec-regression-tests-framework — provides means to run and create regression tests for RetDec and related tools. This is a must if you plan to contribute to the RetDec project.
  • retdec-python — Python library and tools providing easy access to our online decompilation service through its REST API.
  • vim-syntax-retdecdsm — Vim syntax-highlighting file for the output from the RetDec’s disassembler (.dsm files).

 

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