UPX is a command-line utility designed to reduce the file size of compiled programs and shared libraries. It functions as an executable binary compressor that maintains the ability for files to run natively without requiring additional runtime dependencies or external decompression software.
The tool operates by parsing executable headers and applying entropy-based compression to code segments. It achieves this by injecting a self-extracting stub into the binary, which facilitates in-place memory decompression during the initial execution phase. This process includes platform-specific binary patching to ensure the modified files remain compatible with native system loaders.
Beyond compression, the utility provides integrated functionality for verifying the structural integrity of processed files. It calculates and embeds checksums to confirm that binaries remain functional and uncorrupted. These capabilities support software distribution optimization and assist in managing binary footprints for resource-constrained environments.
