What counts as an “architecture” in discussions on Linux architecture support:
For example, Linux supports the User Mode Linux “architecture”, which lets the kernel run as an unprivileged process inside an existing kernel for testing purposes. By most normal definitions, User Mode Linux isn’t really a CPU architecture, even if the code for it lives alongside the kernel’s other architecture support code. On the other hand, the kernel considers all PowerPC CPUs to be one architecture, regardless of whether they’re running in big-endian or little-endian mode; most distributions count those as two architectures because software compiled for different endiannesses must be packaged separately. Even without architecture-wide incompatibilities like that, several architectures also offer different “levels” or optional extensions that make describing a piece of software’s requirements a bit difficult. RISC-V has, at the time of writing, 48 different standards adding a larger number of extensions.