（三）ARM 常用汇编指令(3)之内嵌汇编-白红宇

（三）ARM 常用汇编指令(3)之内嵌汇编

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发布时间：2019-05-25

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3.5内嵌汇编

示例1 add sub mul

#include 
   
    int main(void){	//(1-(1+2))*(1+2)	int out = 0;	__asm__ __volatile__(		"nop\n\t"	//nop延时指令 \n\t 换行		"mov r0,#1\n\t"		"mov r1,#2\n\t"		"add %[out],r0,r1\n\t"//out = 1+2=3		"sub r1,r0,%[out]\n\t"//r1 = r0-out=1-3=-2		"mul %[out],r1,%[out]\n\t"//out = r1*out=-6		"nop\n\t"		:[out]"=&r"(out) //输出操作数列表 可读		:                //输入操作数列表		:"r0","r1"	 //破坏操作数列表  保护寄存器值不被修改		/*		 = 只写操作 用于输出		 + 读写操作 必须是输出操作		 & 只用做输出的寄存器（表示与输入寄存器不能用同一个寄存器）		*/	);	printf("out = %d\n",out);	return 0;}

调试结果：

root@ubuntu12:/ARM/instructions#arm-linux-gcc add_sub_mul.c -o add_sub_mul

root@ubuntu12:/ARM/instructions#cp add_sub_mul /nfsroot/

[root@ARM_Exynos4412/mnt]# ./add_sub_mul

out= -6

示例2 and orr bic eor

#include 
    
     int main(void){	int and, orr, bic, eor;	unsigned int var = 0;	printf("give a hex num:");	scanf("%x", &var);	__asm__ __volatile__(		"nop\n\t"				"and %[and], %[var], #(~0xf)\n\t"  //&		"orr %[orr], %[var], #(0xf << 28)\n\t"//|		"bic %[bic], %[var], #0xf\n\t" // &= ~		"eor %[eor], %[var], #0x11\n\t"//按位异或		"nop\n\t"		:[and]"=&r"(and),[orr]"=&r"(orr),		 [bic]"=&r"(bic),[eor]"=&r"(eor)		:[var]"r"(var)	);	printf("var = %#x\n", var);	printf("and: add = %#x & 0xfffff0 = %#x\n", var,and);	printf("orr: orr = %#x | 0xf00000 = %#x\n", var,orr);	printf("bic: bic = %#x &= ~0xf) = %#x\n",var,bic);	printf("eor = %#x\n", eor);	return 0;}

调试结果：

root@ubuntu12:/ARM/instructions# arm-linux-gcclogic.c

root@ubuntu12:/ARM/instructions#cp logic.c /nfsroot/

[root@ARM_Exynos4412 /mnt]# ./logic

givea hex num:0xff

var= 0xff

and:add = 0xff & 0xfffff0 = 0xf0

orr:orr = 0xff | 0xf00000 = 0xf00000ff

bic:bic = 0xff &= ~0xf) = 0xf0

eor= 0xee

示例3 lsl lsr asr ror

#include 
    
     int main(void){	int lsl, lsr, asr, ror;	__asm__ __volatile__(		"nop\n\t"		"mov r0,#0x96\n\t" 		"lsl %[lsl], r0,#4\n\t"		"lsr %[lsr], %[lsl],#4\n\t"		"ror %[ror], r0, #4\n\t"//循环右移  		"mov r0, #-2\n\t"  		"asr %[asr], r0, #9\n\t"//算术右移 		:[lsl]"=&r"(lsl),[lsr]"=&r"(lsr),[asr]"=&r"(asr),[ror]"=&r"(ror)	);	printf("lsl << 4 = %#x\n", lsl);   //0x960	printf("%#x >> 4 = %#x\n", lsl, lsr);//0x96	printf("0x96 ror 4 = %#x\n", ror);   //0x6000009	printf("%#x asr 4 = %#x\n", -2, asr);		return 0;}

调试结果：

root@ubuntu12:/ARM/instructions# arm-linux-gcc shift.c -o shift

root@ubuntu12:/ARM/instructions#cp shift /nfsroot/

[root@ARM_Exynos4412/mnt]# ./shift

lsl<< 4 = 0x960

0x960>> 4 = 0x96

0x96ror 4 = 0x60000009

0xfffffffeasr 4 = 0xffffffff

示例4 ldr str cmp b

#include 
    
     #if 0char *strcpy(char *dst,const char *src){	char *ret = dst;	while(*src != '\0')	{		*dst = *src;		src++;		dst++;	}	*dst = '\0';	return ret;}#endifchar *strcpy(char *dst,const char *src){	__asm__ __volatile__(		"nop\n\t"		"mov r0,%[dst]\n\t"		"mov r1,%[src]\n\t"		"while:\n\t"			"ldrb r2,[r1],#1\n\t"			"cmp r2,#0\n\t"			"beq end\n\t"			"strb r2,[r0],#1\n\t"			"b while\n\t"		"end:\n\t"			"mov r3,#0\n\t"			"strb r3,[r0]\n\t"		:[dst]"+&r"(dst)		:[src]"r"(src)		:"r0","r1","r2","r3"	);	return dst;}int main(void){	char buf[] = "hello";	char buf2[10] = {0};	printf("strcpy:%s\n",strcpy(buf2,buf));	return 0;}

调试结果：

root@ubuntu12:/ARM/instructions# arm-linux-gcc strcpy.c -ostrcpy

root@ubuntu12:/ARM/instructions#cp strcpy /nfsroot/

[root@ARM_Exynos4412 /mnt]#./strcpy

strcpy:hello

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