Correct, actually most programs I've written for the BIO are in assembly.
The C compiler support is a relatively recent addition, mostly to showcase the possibilities of doing high-level protocol offloading into the BIO, and the tooling benefits of sticking with a "standard" instruction set.
The C compiler support is a relatively recent addition, mostly to showcase the possibilities of doing high-level protocol offloading into the BIO, and the tooling benefits of sticking with a "standard" instruction set.