程序生成步骤

转自：https://azeria-labs.com/writing-arm-assembly-part-1/

• 写好汇编代码到helloworld.s
• 编译文件（但是没有链接）

只编译不链接形成.o文件。里面包含了对各个函数的入口标记，描述，当程序要执行时还需要链接(link)
链接就是把多个.o文件链成一个可执行文件

as helloworld.s -o helloworld.o

• 链接文件，形成可执行文件

ld helloworld.o -o helloworld

GDB调试

程序代码

.data
var1: .word 3
var2: .word 4

.text
.global _start

_start:
    ldr r0, adr_var1         @ load the memory address of var1 via label adr_var1 to R0
    ldr r1, adr_var2         @ load the memory address of var2 via label adr_var2 to R1
    ldr r2, [r0]             @ load the value (0x03) at memory address found in R0 to R2
    str r2, [r1, r2, LSL#2]  @ address mode: offset. Store the value found in R2 (0x03) to the memory address found in R1 with the offset R2 left-shifted by 2. Base register (R1) unmodified.
    str r2, [r1, r2, LSL#2]! @ address mode: pre-indexed. Store the value found in R2 (0x03) to the memory address found in R1 with the offset R2 left-shifted by 2. Base register modified: R1 = R1 + R2<<2
    ldr r3, [r1], r2, LSL#2  @ address mode: post-indexed. Load value at memory address found in R1 to the register R3. Then modifiy base register: R1 = R1 + R2<<2
    bkpt

adr_var1: .word var1
adr_var2: .word var2

• 进入调试

gdb helloworld

• 下断点。在_start函数下好断点

break _start

• 运行。会执行到断点位置

run 或者 r

• 向下执行3步

nexti 3

• 查看下面的10条指令

x:十六进制，i:指令

x/10i $pc

• 查看所有寄存器状态数据

info registers
或者： i r

• 查看指定内存地址存储的数据

x：十六进制
w：word，字类型

x/w 0x0001009F