Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1619

POPF/POPFD—Pop Stack into EFLAGS Register
Opcode
9D
9D
Description
Pops a doubleword (POPFD) from the top of the stack (if the current operand-size
attribute is 32) and stores the value in the EFLAGS register or pops a word from the top
of the stack (if the operand-size attribute is 16) and stores it in the lower 16 bits of the
EFLAGS register. (These instructions reverse the operation of the PUSHF/PUSHFD
instructions.)
The POPF (pop flags) and POPFD (pop flags double) mnemonics reference the same
opcode. The POPF instruction is intended for use when the operand-size attribute is 16
and the POPFD instruction for when the operand-size attribute is 32. Some assemblers
may force the operand size to 16 when POPF is used and to 32 when POPFD is used.
Others may treat these mnemonics as synonyms (POPF/POPFD) and use the current
setting of the operand-size attribute to determine the size of values to be popped from
the stack, regardless of the mnemonic used.
The effect of the POPF/POPFD instructions on the EFLAGS register changes slightly,
depending on the mode of operation of the processor. When the processor is operating
in protected mode at privilege level 0 (or in real-address mode, which is equivalent to
privilege level 0), all the non-reserved flags in the EFLAGS register except the VIP and
VIF flags can be modified. The VIP and VIF flags are cleared.
When operating in protected mode, but with a privilege level greater an 0, all the flags
can be modified except the IOPL field and the VIP and VIF flags. Here, the IOPL flags
are masked and the VIP and VIF flags are cleared.
When operating in virtual-8086 mode, the I/O privilege level (IOPL) must be equal to 3
to use POPF/POPFD instructions and the VM, RF, IOPL, VIP, and VIF flags are masked. If
the IOPL is less than 3, the POPF/POPFD instructions cause a general protection
exception (#GP).
The IOPL is altered only when executing at privilege level 0. The interrupt flag is altered
only when executing at a level at least as privileged as the IOPL. (Real-address mode is
equivalent to privilege level 0.) If a POPF/POPFD instruction is executed with insufficient
privilege, an exception does not occur, but the privileged bits do not change.
Operation
OLD_IF <- IF; OLD_AC <- AC; OLD_TF <- TF;
IF CR0.PE = 0 (*Real Mode *)
THEN
IF OperandSize = 32;
FI;
ELSE (*In Protected Mode *)
Volume 4: Base IA-32 Instruction Reference
Instruction
POPF
POPFD
THEN
EFLAGS  Pop();
(* All non-reserved flags except VM, RF, VIP and VIF can be modified; *)
ELSE (* OperandSize = 16 *)
EFLAGS[15:0]  Pop(); (* All non-reserved flags can be modified; *)
Description
Pop top of stack into EFLAGS
Pop top of stack into EFLAGS
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