Set the alternate register set with the values provided for the process associated with the file descriptor. You must have opened the file descriptor for writing. The argument is a pointer to a procfs_fpreg structure (see debug_fpreg_t in <sys/debug.h>) that specifies to set the values of the alternate register set. For example:

procfs_fpreg reg;

/* Set the members of reg as required. */
devctl( fd, DCMD_PROC_SETALTREG, &reg, sizeof(reg), NULL);

To get the alternate register set, use DCMD_PROC_GETALTREG .