Get the information stored in the alternate register set for the process associated with the file descriptor. The argument is a pointer to a procfs_fpreg structure (see debug_fpreg_t in <sys/debug.h>) that's filled in with the required information on return. If you provide a non-NULL extra argument, it's filled with the actual size of the register set. For example:
procfs_fpreg reg; int regsize; devctl( fd, DCMD_PROC_GETALTREG, ®, sizeof(reg), ®size);
To set the alternate register set, use DCMD_PROC_SETALTREG .