On getting supported extension status - there's a C API spec that could potentially become an option for an OS-agnostic way: https://github.com/riscv-non-isa/ri

On getting supported extension status - there's a C API spec that could potentially become an option for an OS-agnostic way: https://github.com/riscv-non-isa/riscv-c-api-doc/blob/main/src/c-api.adoc#extension-bitmask https://github.com/riscv-non-isa/riscv-c-api-doc/blob/main/s.... libc already will want to call whatever OS thing to determine what extensions it can use for memcpy etc, so taking the results from libc is "free".