Intel 253666-024US Manuel D’Utilisation
3-282 Vol. 2A
ENTER—Make Stack Frame for Procedure Parameters
INSTRUCTION SET REFERENCE, A-M
ENTER—Make Stack Frame for Procedure Parameters
Description
Creates a stack frame for a procedure. The first operand (size operand) specifies the
size of the stack frame (that is, the number of bytes of dynamic storage allocated on
the stack for the procedure). The second operand (nesting level operand) gives the
lexical nesting level (0 to 31) of the procedure. The nesting level determines the
number of stack frame pointers that are copied into the “display area” of the new
stack frame from the preceding frame. Both of these operands are immediate values.
The stack-size attribute determines whether the BP (16 bits), EBP (32 bits), or RBP
(64 bits) register specifies the current frame pointer and whether SP (16 bits), ESP
(32 bits), or RSP (64 bits) specifies the stack pointer. In 64-bit mode, stack-size
attribute is always 64-bits.
The ENTER and companion LEAVE instructions are provided to support block struc-
tured languages. The ENTER instruction (when used) is typically the first instruction
in a procedure and is used to set up a new stack frame for a procedure. The LEAVE
instruction is then used at the end of the procedure (just before the RET instruction)
to release the stack frame.
If the nesting level is 0, the processor pushes the frame pointer from the BP/EBP/RBP
register onto the stack, copies the current stack pointer from the SP/ESP/RSP
register into the BP/EBP/RBP register, and loads the SP/ESP/RSP register with the
current stack-pointer value minus the value in the size operand. For nesting levels of
1 or greater, the processor pushes additional frame pointers on the stack before
adjusting the stack pointer. These additional frame pointers provide the called proce-
dure with access points to other nested frames on the stack. See “Procedure Calls for
Block-Structured Languages” in Chapter 6 of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1, for more information about the actions of
the ENTER instruction.
The ENTER instruction causes a page fault whenever a write using the final value of
the stack pointer (within the current stack segment) would do so.
In 64-bit mode, default operation size is 64 bits; 32-bit operation size cannot be
encoded.
size of the stack frame (that is, the number of bytes of dynamic storage allocated on
the stack for the procedure). The second operand (nesting level operand) gives the
lexical nesting level (0 to 31) of the procedure. The nesting level determines the
number of stack frame pointers that are copied into the “display area” of the new
stack frame from the preceding frame. Both of these operands are immediate values.
The stack-size attribute determines whether the BP (16 bits), EBP (32 bits), or RBP
(64 bits) register specifies the current frame pointer and whether SP (16 bits), ESP
(32 bits), or RSP (64 bits) specifies the stack pointer. In 64-bit mode, stack-size
attribute is always 64-bits.
The ENTER and companion LEAVE instructions are provided to support block struc-
tured languages. The ENTER instruction (when used) is typically the first instruction
in a procedure and is used to set up a new stack frame for a procedure. The LEAVE
instruction is then used at the end of the procedure (just before the RET instruction)
to release the stack frame.
If the nesting level is 0, the processor pushes the frame pointer from the BP/EBP/RBP
register onto the stack, copies the current stack pointer from the SP/ESP/RSP
register into the BP/EBP/RBP register, and loads the SP/ESP/RSP register with the
current stack-pointer value minus the value in the size operand. For nesting levels of
1 or greater, the processor pushes additional frame pointers on the stack before
adjusting the stack pointer. These additional frame pointers provide the called proce-
dure with access points to other nested frames on the stack. See “Procedure Calls for
Block-Structured Languages” in Chapter 6 of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1, for more information about the actions of
the ENTER instruction.
The ENTER instruction causes a page fault whenever a write using the final value of
the stack pointer (within the current stack segment) would do so.
In 64-bit mode, default operation size is 64 bits; 32-bit operation size cannot be
encoded.
Opcode
Instruction
64-Bit
Mode
Compat/
Leg Mode
Description
C8 iw 00
ENTER imm16, 0
Valid
Valid
Create a stack frame for a
procedure.
C8 iw 01
ENTER imm16,1
Valid
Valid
Create a nested stack frame for a
procedure.
C8 iw ib
ENTER imm16, imm8 Valid
Valid
Create a nested stack frame for a
procedure.