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Vol. 3 6-17
INTERRUPT AND EXCEPTION HANDLING
When the processor performs a call to the exception- or interrupt-handler procedure:
• If the handler procedure is going to be executed at a numerically lower privilege
level, a stack switch occurs. When the stack switch occurs:
a. The segment selector and stack pointer for the stack to be used by the
handler are obtained from the TSS for the currently executing task. On this
new stack, the processor pushes the stack segment selector and stack
pointer of the interrupted procedure.
b. The processor then saves the current state of the EFLAGS, CS, and EIP
registers on the new stack (see
Figures 6-4).
c. If an exception causes an error code to be saved, it is pushed on the new
stack after the EIP value.
• If the handler procedure is going to be executed at the same privilege level as the
interrupted procedure:
a. The processor saves the current state of the EFLAGS, CS, and EIP registers
on the current stack (see Figures 6-4).
b. If an exception causes an error code to be saved, it is pushed on the current
stack after the EIP value.