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INSTRUCTION SET REFERENCE
POPF/POPFDPop Stack into EFLAGS Register
Description
These instructions pop 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 (that is, the FLAGS 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 deter-
mine 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, VIF, and VM flags
can be modified. The VIP and VIF flags are cleared, and the VM flag is unaffected.
When operating in protected mode, with a privilege level greater than 0, but less than or equal
to IOPL, all the flags can be modified except the IOPL field and the VIP, VIF, and VM flags.
Here, the IOPL flags are unaffected, the VIP and VIF flags are cleared, and the VM flag is unaf-
fected. The interrupt flag (IF) is altered only when executing at a level at least as privileged as
the IOPL. If a POPF/POPFD instruction is executed with insufficient privilege, an exception
does not occur, but the privileged bits do not change.
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 unaffected. If the
IOPL is less than 3, the POPF/POPFD instructions cause a general-protection exception (#GP).
Refer to Section 3.6.3. in Chapter 3, Basic Execution Environment of the Intel Architecture Soft-
ware Developers Manual, Volume 1, for information about the EFLAGS registers.
Operation
IF VM=0 (* Not in Virtual-8086 Mode *)
THEN IF CPL=0
THEN
IF OperandSize = 32;
THEN
Opcode
Instruction
Description
9D
POPF
Pop top of stack into lower 16 bits of EFLAGS
9D
POPFD
Pop top of stack into EFLAGS
