Comment 5 for bug 2029382

check if :sb-thread is in your *features*.
Line #305 of src/cold/shared will add the :os-thread-stack feature for OpenBSD and then you'll get a definition for new_thread_trampoline_switch_stack in thread.c

As to register usage, according to riscv-linux-os.c, they are all sequential in the sigcontext for linux, so it can use "return (os_context_register_t*)&(context->uc_mcontext.__gregs[offset]);" for the definition of os_context_register_addr. Perhaps it works similarly easily on OpenBSD