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Explore how to effectively manage build configurations in CMake by passing external program results as preprocessor definitions through a structured solution.
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How to Pass External Program Results as Preprocessor Definitions with CMake

If you're new to CMake, you might find yourself facing challenges with managing build configurations, especially when it comes to compiling dependencies dynamically. A common problem is needing to pass data generated from other programs into your main application. This guide will guide you through a clear solution to streamline the process of passing external program results as preprocessor definitions in CMake.

The Problem at Hand

Suppose you have a project with the following structure:

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Your goal is to build main_program by dynamically including binary data (bindata) generated from subprograms without cluttering your command line with numerous definitions. Previously, you may have run commands like:

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Every time the subprograms change, you need to regenerate these bindata and update your CMake command. This method can quickly become unwieldy.

The Solution Overview

The ideal approach is to automate the bindata generation process directly within your CMake configuration. The solution comprises three main steps:

Compile each subprogram.

Generate shellcode from each subprogram using a dedicated program.

Pass the generated shellcode into the main program during its build.

Step-by-Step Implementation

Step 1: Create a Script for Generating a Header File

Start by creating a shell script that will generate a header file containing the definitions for your shellcode:

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This script reads the bindata from the specified files and generates a header file that you can include in your main program.

Step 2: Configure CMakeLists.txt for Automated Build

Now, let’s set up your CMakeLists.txt to automate the entire process:

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Step 3: Modify Your Main Program to Utilize the Generated Header

Finally, modify your main program to include the generated header:

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Recommendations for Reducing Compilation Times

To optimize build times, consider creating a wrapper around your shellcode functionality. This way, only the wrapper file is recompiled when shellcode changes occur.

Example of a wrapper implementation:

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Conclusion

By following these steps, you can automate the process of passing external program results as preprocessor definitions in CMake, leading to a cleaner and more efficient build workflow. This structure will not only make managing changes easier but also significantly speed up your compilation times thanks to reduced recompilation of unaffected files.

Now, you can run your builds cleanly and efficiently by simply issuing the cmake command without needing constant adjustments for your bindata. Automating these workflows will lead to a more productive development experience.