Portfolio provides three special tag commands that have universal meanings in all system calls: TAG_END, TAG_NOP, and TAG_JUMP. By setting the ta_Tag field to these commands, you can control how TagArg arrays are processed by the system.
TAG_END
The TAG_END command tells the system that this structure marks the end of an array of TagArg structures. The system stops scanning the array and goes no further.
TAG_NOP
The TAG_NOP command tells the system to ignore the particular TagArg structure. The system just skips ahead and continues processing with the next TagArg structure.
TAG_JUMP
The TAG_JUMP command links arrays of TagArg structures together. The ta_Arg field for this command must point to another array of TagArg structures. When the system encounters such a TagArg structure, it stops scanning the current array, and resumes scanning at the address specified by ta_Arg.