aadd

Atomically Add

AADD m32, r32

Atomically adds a value to a remote memory location.

Details

Atomically adds a 32-bit register value to a memory location without acquiring a lock and without returning the old value. This is a remote atomic operation that guarantees atomicity at the hardware level via cache coherency; the instruction does not serialize the entire pipeline but may have store ordering implications. No flags are modified; this is a write-only operation to memory.

Pseudocode Operation

atomic_add([dest], src);
// Semantically: [dest] ← [dest] + src

Example

AADD [rbp-4], eax

Encoding

Binary Layout
66
+0
0F
+1
38
+2
FC
+3
 
Format VEX
Opcode NP 0F 38 FC !(11):rrr:bbb
Extension RAO-INT

Operands

  • dest
    Mem
  • src
    Reg

Reference (Intel® SDM)

Instruction Forms

Opcode Instruction Op/En 64/32-bit Mode CPUID Description
04 ib ADD AL, imm8 I Valid Valid Add imm8 to AL.
05 iw ADD AX, imm16 I Valid Valid Add imm16 to AX.
05 id ADD EAX, imm32 I Valid Valid Add imm32 to EAX.
REX.W + 05 id ADD RAX, imm32 I Valid N.E. Add imm32 sign-extended to 64-bits to RAX.
80 /0 ib ADD r/m8, imm8 MI Valid Valid Add imm8 to r/m8.
81 /0 iw ADD r/m16, imm16 MI Valid Valid Add imm16 to r/m16.
81 /0 id ADD r/m32, imm32 MI Valid Valid Add imm32 to r/m32.
REX.W + 81 /0 id ADD r/m64, imm32 MI Valid N.E. Add imm32 sign-extended to 64-bits to r/m64.
83 /0 ib ADD r/m16, imm8 MI Valid Valid Add sign-extended imm8 to r/m16.
83 /0 ib ADD r/m32, imm8 MI Valid Valid Add sign-extended imm8 to r/m32.
REX.W + 83 /0 ib ADD r/m64, imm8 MI Valid N.E. Add sign-extended imm8 to r/m64.
00 /r ADD r/m8, r8 MR Valid Valid Add r8 to r/m8.
01 /r ADD r/m16, r16 MR Valid Valid Add r16 to r/m16.
01 /r ADD r/m32, r32 MR Valid Valid Add r32 to r/m32.
REX.W + 01 /r ADD r/m64, r64 MR Valid N.E. Add r64 to r/m64.
02 /r ADD r8, r/m8 RM Valid Valid Add r/m8 to r8.
03 /r ADD r16, r/m16 RM Valid Valid Add r/m16 to r16.
03 /r ADD r32, r/m32 RM Valid Valid Add r/m32 to r32.
REX.W + 03 /r ADD r64, r/m64 RM Valid N.E. Add r/m64 to r64.

Description

Adds the destination operand (first operand) and the source operand (second operand) and then stores the result in the destination operand. The destination operand can be a register or a memory location; the source operand can be an immediate, a register, or a memory location. (However, two memory operands cannot be used in one instruction.) When an immediate value is used as an operand, it is sign-extended to the length of the destination operand format. The ADD instruction performs integer addition. It evaluates the result for both signed and unsigned integer operands and sets the OF and CF flags to indicate a carry (overflow) in the signed or unsigned result, respectively. The SF flag indicates the sign of the signed result. This instruction can be used with a LOCK prefix to allow the instruction to be executed atomically. ADD—Add Vol. 2A 3-14 In 64-bit mode, the instruction’s default operation size is 32 bits. Using a REX prefix in the form of REX.R permits access to additional registers (R8-R15). Using a REX prefix in the form of REX.W promotes operation to 64 bits. See the summary chart at the beginning of this section for encoding data and limits.

Operation

DEST := DEST + SRC;

Flags Affected

The OF, SF, ZF, AF, CF, and PF flags are set according to the result.

Exceptions

Protected Mode Exceptions

#GP(0) If the destination is located in a non-writable segment. If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. If the DS, ES, FS, or GS register is used to access memory and it contains a NULL segment selector. #SS(0) If a memory operand effective address is outside the SS segment limit. #PF(fault-code) If a page fault occurs. #AC(0) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3. #UD If the LOCK prefix is used but the destination is not a memory operand.

Real-Address Mode Exceptions

#GP If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. #SS If a memory operand effective address is outside the SS segment limit. #UD If the LOCK prefix is used but the destination is not a memory operand.

Virtual-8086 Mode Exceptions

#GP(0) If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. #SS(0) If a memory operand effective address is outside the SS segment limit. #PF(fault-code) If a page fault occurs. #AC(0) If alignment checking is enabled and an unaligned memory reference is made. #UD If the LOCK prefix is used but the destination is not a memory operand.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#SS(0) If a memory address referencing the SS segment is in a non-canonical form. #GP(0) If the memory address is in a non-canonical form. #PF(fault-code) If a page fault occurs. #AC(0) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3. #UD If the LOCK prefix is used but the destination is not a memory operand. ADD—Add Vol. 2A 3-15