When an asynchronous exit routine (for example, an STIMER exit) gets control, it cannot access the last entry (if any) on the linkage stack, because that entry was created by the interrupted routine. The extract stacked registers (EREG) instruction, extract stacked state (ESTA) instruction, and the modify stacked state (MSTA) instruction will cause a linkage stack exception to occur.
Any routines to which the exit routine passes control are also subject to the same restriction. However, the exit routine, and any routines to which it passes control, can manipulate linkage stack entries that they add.