A program cannot change the order of the entries on the linkage stack, nor can it change any part of an entry, except for the eight-byte modifiable area of the current entry. Three instructions copy information from the current entry or copy information to the modifiable area of the current entry:

• The extract stacked registers (EREG) instruction loads ARs and GPRs from the current linkage stack entry.
• The extract stacked state (ESTA) instruction obtains non-register information from the current linkage stack entry.
• The modify stacked state (MSTA) instruction copies the contents of an even/odd GPR pair to the modifiable area of the current linkage stack entry.