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Source code

LEA

Load Effective Address

stableVMJITAOTinstruction

Encodings

OpcodeInstructionOp/En64-bitCompat/LegacyDescription
8D /rLEA r16,mRMValidValidStore effective address for m in register r16.
8D /rLEA r32,mRMValidValidStore effective address for m in register r32.
REX.W + 8D /rLEA r64,mRMValidNot encodableStore effective address for m in register r64.

Operand encoding

Each mode is a value of the Op/En column above. It says which field of the encoded instruction carries each operand, in the order they are written, and whether the instruction reads it, writes it or both.

RM

  1. modrm.reg escrituraModRM byte, reg field (bits 5-3)
  2. modrm.rm lecturaModRM byte, r/m field (bits 2-0); with the SIB byte and the displacement when the mod field asks for them

Measured cost

Loading measurements from arch-data...

Description

Computes the effective address of the second operand (the source operand) and stores it in the first operand (destination operand). The source operand is a memory address (offset part) specified with one of the processors addressing modes; the destination operand is a general-purpose register. The address-size and operand-size attributes affect the action performed by this instruction, as shown in the following table. The operand-size attribute of the instruction is determined by the chosen register; the address-size attribute is determined by the attribute of the code segment.

Non-64-bit Mode LEA Operation with Address and Operand Size Attributes

Operand SizeAddress SizeAction Performed
1616 16-bit effective address is calculated and stored in requested 16-bit register destination.
1632 32-bit effective address is calculated. requested 16-bit register destination.The lower 16 bits of the address are stored in the
3216 16-bit effective address is calculated. requested 32-bit register destination.The 16-bit address is zero-extended and stored in the

64-bit Mode LEA Operation with Address and Operand Size Attributes

Operand SizeAddress SizeAction Performed
1632 32-bit effective address is calculated (using 67H prefix). The lower 16 bits of the address are
stored in the requested 16-bit registerdestination (using 66H prefix).
1664 64-bit effective address is calculated (default address size). The lower 16 bits of the address

Operation

IF OperandSize = 16 and AddressSize = 16

    THEN
          DEST := EffectiveAddress(SRC); (* 16-bit address *)

   ELSE IF OperandSize = 16 and AddressSize = 32

          THEN
                temp := EffectiveAddress(SRC); (* 32-bit address *)
                DEST := temp[0:15]; (* 16-bit address *)

          FI;

   ELSE IF OperandSize = 32 and AddressSize = 16

          THEN
                temp := EffectiveAddress(SRC); (* 16-bit address *)
                DEST := ZeroExtend(temp); (* 32-bit address *)

          FI;

   ELSE IF OperandSize = 32 and AddressSize = 32

          THEN
                DEST := EffectiveAddress(SRC); (* 32-bit address *)

          FI;

   ELSE IF OperandSize = 16 and AddressSize = 64

          THEN
                temp := EffectiveAddress(SRC); (* 64-bit address *)
                DEST := temp[0:15]; (* 16-bit address *)

          FI;

   ELSE IF OperandSize = 32 and AddressSize = 64

          THEN
                temp := EffectiveAddress(SRC); (* 64-bit address *)
                DEST := temp[0:31]; (* 16-bit address *)

          FI;

   ELSE IF OperandSize = 64 and AddressSize = 64

          THEN
                DEST := EffectiveAddress(SRC); (* 64-bit address *)

          FI;
FI;

Flags affected

None.

Exceptions

Protected mode
#UDIf source operand is not a memory location. If the LOCK prefix is used.
Real address mode
Same exceptions as in protected mode.
Virtual-8086 mode
Same exceptions as in protected mode.
Compatibility mode
Same exceptions as in protected mode.
64-bit mode
Same exceptions as in protected mode.

Sources