microsoft上的解释：
PUSHFD is one of the atomic components of an interrupt. When an interrupt or an exception occurs, the following code effectively executes:
PUSHFD, PUSH CS, PUSH EIP.
Following the three pushes, the EIP register changes to the interrupt handler address contained in the appropriate slot in the Interrupt Descriptor Table (IDT). Likewise, the IRETD effectively does a POPFD as part of returning from an interrupt.
IRET/IRETD - Interrupt Return
Usage: IRET
IRETD (386+)
Modifies flags: AF CF DF IF PF SF TF ZF
Returns control to point of interruption by popping IP, CS
and then the Flags from the stack and continues execution at
this location. CPU exception interrupts will return to the
instruction that cause the exception because the CS:IP placed
on the stack during the interrupt is the address of the offending
