求助c语言的内嵌汇编编译时的问题

#define MEM_SIZE 15
#define LOW_MEM 0x100000
#define PAGING_MEM (MEM_SIZE*1024*1024)
#define PAGING_PAGES (PAGING_MEM>>12)

static unsigned char mem_map[PAGING_PAGES] = {0};

unsigned long get_free_page()
{
 register unsigned long __res asm("eax");

 __asm__ ("std; repne; scasb\n\t"
 "jne 1f\n\t"
 "movb $1, 1(%%edi)\n\t"

 "sall $12, %%ecx\n\t"
 "addl %2, %%ecx\n\t"
 "movl %%ecx, %%edx\n\t"

 "movl $1024, %%ecx\n\t"
 "leal 4092(%%edx), %%edi\n\t"
 "rep; stosl\n\t"
 "movl %%edx, %%eax\n"
 "1:"
 :"=a"(__res)
 :"0"(0), "i"(LOW_MEM), "c"(PAGING_PAGES),
 "D"(mem_map + PAGING_PAGES - 1)
 : "edx"
 );
 return __res;
}

 You may not write a clobber description in a way that overlaps with
an input or output operand. For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list. There is no way for you to specify that an input
operand is modified without also specifying it as an output operand.
Note that if all the output operands you specify are for this purpose
(and hence unused), you will then also need to specify `volatile' for
the `asm' construct, as described below, to prevent GCC from deleting
the `asm' statement as unused.