POPFD Pop Top of Stack into EFlags (386+)

Flags affected:

Legal forms:

POPFD <none>

Examples:

POPFD

Notes:

POPFD pops the double word (4 bytes) at the top of the stack into the EFlags register. In 32-bit protected mode, the top of the stack is defined as the DWORD at [ESP], and there is no way to override the SS segment with prefixes.

ESP is incremented by 4 after the word comes off the stack. Remember that ESP always points to either an empty stack or else real data. There is a separate pair of instructions, PUSH and POP, for pushing and popping other register data and memory data, in both 16-bit and 32-bit sizes.

PUSHFD and POPFD are most used in writing 32-bit interrupt service routines, where you must be able to save and restore the environment, that is, all machine registers, to avoid disrupting machine operations while servicing the interrupt.

PUSH Push Operand onto Top of Stack

Flags affected:

<none> IF: Interrupt flag ZF: Zero flag CF: Carry flag

Legal forms:

Examples:

PUSH WORD [BX]

PUSH EAX

PUSH DI

PUSH ES

PUSH DWORD 5

PUSH WORD 1000H

Notes:

It is impossible to push an 8-bit item onto the stack. Also remember that the top of the stack is defined (in 16bit modes) as the word at address SS:SP, and there's no way to override that using prefixes. In 32-bit modes the top of the stack is the DWORD at [ESP]. There is a separate pair of instructions, PUSHF and POPF, for pushing and popping the Flags register.

Also remember that SP/ESP is decremented before the push takes place; SP points to either an empty stack or else real data.

PUSHA Push All 16-Bit GP Registers (286+)

Flags affected:

Legal forms:

Examples:

PUSHA

Notes:

PUSHA pushes all 16-bit general-purpose registers onto the stack. This instruction is present on the 286 and later CPUs and is not available in the 8086/8088.

The registers are pushed in this order:

AX, CX, DX, BX, SP, BP, SI, DI

However, note that the value of SP pushed is the value SP had before the first register was pushed onto the stack. In the course of executing PUSHA, the stack pointer is decremented by 16 bytes (8 registers x 2 bytes each).

The Flags register is not pushed onto the stack by PUSHA; see PUSHF.

PUSHAD Push All 32-Bit GP Registers (386+)

Flags affected:

Legal forms:

PUSHAD 386+

Examples:

PUSHAD

Notes:

PUSHA pushes all 32-bit general-purpose registers onto the stack. This instruction is present on the 386 and later CPUs and is not available in the 8086, 8088, or 286.

The registers are pushed in this order:

EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI

However, note that the value of ESP pushed is the value SP had before the first register was pushed onto the stack. In the course of executing PUSHAD, the stack pointer is decremented by 32 bytes (8 registers x 4 bytes each).

The EFlags register is not pushed onto the stack by PUSHAD; see PUSHFD.