As LLVM generates code for different architectures, it seems obvious to use clang to cross-compile. The obstacle here is that LLVM does not provide all the required parts – for example, the C library is missing. Because of this, you must use a mix of LLVM and GNU tools and as a result, you need to tell CMake even more about the environment you are using. As a minimum, you need to specify the following options for clang and clang++: –target=<target-triple> (enables code generation for a different target), –sysroot=<path> (path to the root directory for the target), I (search path for header files), and –L (search path for libraries). During the CMake run, a small application is compiled and CMake complains if something is wrong with your setup. This step is sufficient to check if you have a working environment. Common problems are picking the wrong header files or link failures due to different library names or wrong search paths.
Cross-compiling is surprisingly complex. With the instructions from this section, you will be able to cross-compile your application for a target architecture of your choice.
Summary
In this chapter, you learned about creating passes that run beyond instruction selection, specifically exploring the creation behind machine function passes in the backend! You also discovered how to add a new experimental target into clang, and some of the driver, ABI, and toolchain changes that are required. Finally, while considering the supreme discipline of compiler construction, you learned how to cross-compile your application for another target architecture.
Now that we’re at the end of Learn LLVM 17, you are equipped with the knowledge to use LLVM in creative ways in your projects and have explored many interesting topics. The LLVM ecosystem is very active, and new features are added all the time, so be sure to follow its development!
As compiler developers ourselves, it was a pleasure for us to write about LLVM and discover some new features along the way. Have fun with LLVM!