What's this gregset_t gregs thing

Linux has gregset_t gregs;
https://github.com/lattera/glibc/blob/master/sysdeps/unix/sysv/linux/x86/sys/ucontext.h

Defined above, I also see it in the RISC-V glibc stuff as well.

FreeBSD doesn't seem to have this field defined, I see FreeBSD uses
/usr/include/x86/ucontext.h

but there's no gregs;

If I wanted to return mcontext.gregs

How could I implement that on FreeBSD?

Best,
Owen