ADD

Table of Contents

1. ADD (add)
   1. Basic function
   2. Instruction format
   3. Instruction execution process
   4. Example
   5. Equivalent expansion example
   6. Common uses

ADD (add)

Basic function

The ADD instruction performs addition, writing the result of x1 + x2 into x1.
At the same time, it affects multiple EFLAGS flags.

Instruction format

1
add x1, x2
2
x1 = x1 + x2

x1, x2 types:

• Register
• Memory
• Immediate value
  (the two cannot both be memory)

Instruction execution process

1
x1 ← x1 + x2
2
EFLAGS ← 根据结果更新

The affected flags include:

• OF (overflow)
• SF (sign)
• ZF (zero)
• CF (carry)
• AF, PF

Example

1
add eax, ebx      ;寄存器 寄存器
2
add rax, 0x20.    ;寄存器 立即数
3
add [rbp-0x4], 1  ; 内存 立即数

Equivalent expansion example

1
add rax, rbx
2
; 等价于
3
tmp = rax + rbx
4
rax = tmp
5
更新 EFLAGS

Common uses

• Pointer offset
• Incrementing, accumulation
• Integer arithmetic
• Constructing loop counters
• Stack address calculation (such as add rsp, 0x20)