Using sysroots to isolate build environments

In a nutshell, a sysroot is a directory that a build system considers to be the root directory from which to locate headers and libraries. In brief, they contain a stripped-down version of the root filesystem for the platform for which software is being compiled. They are often used when cross-compiling software for other platforms, as described in Chapter 12, Cross-Platform Compiling and Custom Toolchains. If containers for shipping whole build environments are not an option, sysroots can be an alternative to provide a defined build environment.

To use a sysroot with CMake, a toolchain file is needed. As the name suggests, these files define the tools to use to compile and link the software as well as indicating where to find any libraries. In a normal build, CMake automatically detects the toolchain by introspecting the system. Toolchain files are passed to CMake with the CMAKE_TOOLCHAIN_FILE variable like this:

cmake -S <source_dir...