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Code Mnemonic Description
8F /0 POP m16 Pop top of stack into m16; increment stack pointer
8F /0 POP m32 Pop top of stack into m32; increment stack pointer
58 + rw POP r16 Pop top of stack into r16; increment stack pointer
58 + rd POP r32 Pop top of stack into r32; increment stack pointer
1F POP DS Pop top of stack into DS; increment stack pointer
07 POP ES Pop top of stack into ES; increment stack pointer
17 POP SS Pop top of stack into SS; increment stack pointer
0F A1 POP FS Pop top of stack into FS; increment stack pointer
0F A9 POP GS Pop top of stack into GS; increment stack pointer

Description
Loads the value from the top of the stack to the location specified with the destination operand and then increments the stack pointer. The destination operand can be a general-purpose register, memory location, or segment register.

The address-size attribute of the stack segment determines the stack pointer size (16 bits or 32 bits—the source address size), and the operand-size attribute of the current code segment deter-mines the amount the stack pointer is incremented (2 bytes or 4 bytes). For example, if these address- and operand-size attributes are 32, the 32-bit ESP register (stack pointer) is incre-mented by 4 and, if they are 16, the 16-bit SP register is incremented by 2. (The B flag in the stack segment's segment descriptor determines the stack's address-size attribute, and the D flag in the current code segment's segment descriptor, along with prefixes, determines the operand-size attribute and also the address-size attribute of the destination operand.)

If the destination operand is one of the segment registers DS, ES, FS, GS, or SS, the value loaded into the register must be a valid segment selector. In protected mode, popping a segment selector into a segment register automatically causes the descriptor information associated with that segment selector to be loaded into the hidden (shadow) part of the segment register and causes the selector and the descriptor information to be validated (see the "Operation" section below).

A null value (0000-0003) may be popped into the DS, ES, FS, or GS register without causing a general protection fault. However, any subsequent attempt to reference a segment whose corre-sponding segment register is loaded with a null value causes a general protection exception (#GP). In this situation, no memory reference occurs and the saved value of the segment register is null.

The POP instruction cannot pop a value into the CS register. To load the CS register from the stack, use the RET instruction.

If the ESP register is used as a base register for addressing a destination operand in memory, the POP instruction computes the effective address of the operand after it increments the ESP register.

The POP ESP instruction increments the stack pointer (ESP) before data at the old top of stack is written into the destination.

A POP SS instruction inhibits all interrupts, including the NMI interrupt, until after execution of the next instruction. This action allows sequential execution of POP SS and MOV ESP, EBP instructions without the danger of having an invalid stack during an interrupt 1 . However, use of the LSS instruction is the preferred method of loading the SS and ESP registers.
Operands Bytes Clocks
reg 1 1 UV
mem 2 + d(0 - 2) 3 NP
seg 1 3 NP
FS/GS 2 3 NP

Protected Mode
Operands Bytes Clocks
CS/DS/ES 1 3-12 NP
SS 1 8-17 NP
FS/GS 2 3-12 NP

Flags

ID unaffected DF unaffected
VIP unaffected IF unaffected
VIF unaffected TF unaffected
AC unaffected SF unaffected
VM unaffected ZF unaffected
RF unaffected AF unaffected
NT unaffected PF unaffected
IOPL unaffected CF unaffected
OF unaffected