Awesome

LLVM IR Transformation Passes

LLVM pass to obfuscate the control flow of a program at the LLVM IR level. There are three different passes inside the repository:

• hello_world_example: Simple analysis pass added to test the environment and tools before running the transformation passes.
• transformation_pass: Transformation pass that splits each basic block in a function into two basic blocks and link the two with an unconditional branch.
• transformation_pass_improved: Transformation pass improved by introducing a bogus/made-up conditional branch instead of an unconditional branch when splitting basic blocks.

Development Environment

• LLVM 18
• C++ compiler that supports C++17
• CMake 3.20 or higher

Tools Needed

• clang-18 (for input generation)
• opt (to run the passes)
• FileCheck and lit (for tests)

Building the Passes

export LLVM_DIR=<installation dir of llvm18>
mkdir build
cd build
cmake -DLT_LLVM_INSTALL_DIR=$LLVM_DIR <source_dir>/LLVM_PASS/<pass directory>/
make

Generate Inputs

$LLVM_DIR/bin/clang -O1 -S -emit-llvm <input source file> -o <IR output file>

Run the Passes

$LLVM_DIR/bin/opt -load-pass-plugin=<.so library> -passes=<"pass name"> -S <IR input file> -o <IR output file>

In order to run the "transformation_pass_improved" pass with conditional branches, the flag -use-conditional needs to be specified when using opt:

$LLVM_DIR/bin/opt -load-pass-plugin=libLLVMSplitPass.so -passes="split-pass" -use-conditional -S <IR input file> -o <IR output file>

Removing the flag will use unconditional branches instead.

Automatic Test

Before doing the test, verify the paths to llvm installation and tools in run_tests.sh and the llvm binaries location in lit.cfg, then simply do:

./run_tests.sh

To get the output of the test you can also run:

lit -v ./ > ./Output/lit_output.txt 2>&1

Sample output is inside transformation_pass_improved/tests/Output directory.