asm in C “too many memory references for `mov'”

Question

I\'ve seen the post about the same error but i\'m still get error :

 too many memory references for `mov\'
 junk `hCPUIDmov buffer\' after expression
         


        

Answer 1

1. Because of how C works,

   __asm(
       "mov %eax, 01h"
       "CPUID"
       "mov buffer, edx"
   );
   

   is equivalent to

   __asm("mov %eax, 01h" "CPUID" "mov buffer, edx");
   

   which is equivalent to

   __asm("mov %eax, 01hCPUIDmov buffer, edx");
   

   which isn't what you want.

2. AT&T syntax (GAS's default) puts the destination register at the end.

3. AT&T syntax requires immediates to be prefixed with $.

4. You can't reference local variables like that; you need to pass them in as operands.

Wikipedia's article gives a working example that returns eax.

The following snippet might cover your use-cases (I'm not intricately familiar with GCC inline assembly or CPUID):

int eax, ebx, ecx, edx;
eax = 1;
__asm( "cpuid"
     : "+a" (eax), "+b" (ebx), "+c" (ecx), "+d" (edx));
buffer = edx