vax_boot_block
struct vax_boot_block bb;
struct vax_boot_block *bb;
__CTASSERT(offsetof(struct vax_boot_block,bb_magic1) == 0x19e);
__CTASSERT(sizeof(struct vax_boot_block) == VAX_BOOT_BLOCK_BLOCKSIZE);
offsetof(struct vax_boot_block,bb_magic1) - VAX_LABELOFFSET);
bb = (struct vax_boot_block*)bootstrapbuf;