int
asm_func (char a, char b)
{
        int d = 0;
        asm (   ".intel_syntax noprefix 
	" /* 15 */
                "mov al, a              
	"
                "add al, b              
	"
                "adc ah, b              
	"
                "mov d, ax              	"
                ".att_syntax prefix     	"
                : "=r" (d)
                : "a" (a), "b" (b), "c" (c)
                : "%eax", "%ebx", "%ecx"
            );
        return d;

}

//////////

amber >gcc -o 1 1.c
1.c: In function ‘asm_func’:
1.c:15: error: can't find a register in class ‘AREG’ while reloading ‘asm’
1.c:15: error: ‘asm’ operand has impossible constraints