天书一般的gcc嵌入汇编（内联汇编），似乎没有选择，硬着脑瓜皮学下去吧！

 运行结果：（参考书籍《LInux内核完全注释》，赵炯编著）

仿照手中自己编写的代码：

#include <stdio.h>

#define mystrcpy(dest, source) \
({ \
register char *mydest __asm__("edi"); \
__asm__("cld; \
		pushl %%edi; \
		1: \
		movsb; \
		cmpb $0, (%%esi); \
		jne 1b; \
		popl %%edi" \
		:"=D"(mydest) \
		:"S"(source),"D"(dest)); \
mydest;})

int add(int x, int y);
int sub(int x, int y);
int mul(int x, int y);
int div(int x, int y);
int mod(int x, int y);

int main(void) {
	int x = 100, y = 33;
	printf("%d + %d =%d\n%d - %d =%d\n%d * %d =%d\n\
%d / %d =%d\n%d %% %d =%d\n", x, y, add(x, y), x, y, sub(x, y), \
	x, y, mul(x, y), x, y, div(x, y), x, y, mod(x, y));
	char dest[0x100] = "NULL!";
	char source[0x100] = "Hello, World!";
	printf("%s\n\n%s\n\n", source, dest);
	printf("%s\n\n", mystrcpy(dest, source));
	printf("%s\n\n%s\n\n", source, dest);
}

int add(int x, int y) {
register int __result __asm__("eax");
__asm__("addl %1, %2"
		:"=a"(__result):"b"(y),"0"(x));
return __result;
}

int sub(int x, int y) {
register int __result __asm__("eax");
__asm__("subl %1, %2"
		:"=a"(__result):"b"(y),"0"(x));
return __result;
}

int mul(int x, int y) {
register int __result __asm__("eax");
__asm__("mull %1"
		:"=a"(__result):"b"(y),"0"(x),"d"(0));
return __result;
}

int div(int x, int y) {
register int __result __asm__("eax");
__asm__("divl %1"
		:"=a"(__result):"b"(y),"0"(x),"d"(0));
return __result;	
}

int mod(int x, int y) {
register int __result __asm__("eax");
__asm__("divl %1\n"
		"movl %3, %0"
		:"=a"(__result):"b"(y),"0"(x),"d"(0));
return __result;
}