Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

Vol. 2B 4-253
INSTRUCTION SET REFERENCE, N-Z
RET—Return from Procedure
Description
Transfers program control to a return address located on the top of the stack. The
address is usually placed on the stack by a CALL instruction, and the return is made
to the instruction that follows the CALL instruction.
The optional source operand specifies the number of stack bytes to be released after
the return address is popped; the default is none. This operand can be used to
release parameters from the stack that were passed to the called procedure and are
no longer needed. It must be used when the CALL instruction used to switch to a new
procedure uses a call gate with a non-zero word count to access the new procedure.
Here, the source operand for the RET instruction must specify the same number of
bytes as is specified in the word count field of the call gate.
The RET instruction can be used to execute three different types of returns:
• Near return—A return to a calling procedure within the current code segment
(the segment currently pointed to by the CS register), sometimes referred to as
an intrasegment return.
• Far return—A return to a calling procedure located in a different segment than
the current code segment, sometimes referred to as an intersegment return.
• Inter-privilege-level far return—A far return to a different privilege level than that
of the currently executing program or procedure.
The inter-privilege-level return type can only be executed in protected mode. See the
section titled “Calling Procedures Using Call and RET” in Chapter 6 of the Intel
®
64
and IA-32 Architectures Software Developer’s Manual, Volume 1, for detailed infor-
mation on near, far, and inter-privilege-level returns.
When executing a near return, the processor pops the return instruction pointer
(offset) from the top of the stack into the EIP register and begins program execution
at the new instruction pointer. The CS register is unchanged.
When executing a far return, the processor pops the return instruction pointer from
the top of the stack into the EIP register, then pops the segment selector from the top
of the stack into the CS register. The processor then begins program execution in the
new code segment at the new instruction pointer.
Opcode Instruction
64-Bit
Mode
Compat/
Leg Mode Description
C3 RET Valid Valid Near return to calling procedure.
CB RET Valid Valid Far return to calling procedure.
C2 iw RET imm16 Valid Valid Near return to calling procedure and
pop imm16 bytes from stack.
CA iw RET imm16 Valid Valid Far return to calling procedure and pop
imm16 bytes from stack.