outb_p

fchoo

#define outb_p(value,port) \
__asm__ ("outb %%al,%%dx\n" \
"\tjmp 1f\n" \
"1:\tjmp 1f\n" \
"1:"::"a" (value),"d" (port))
请教3，4，5行代码
1b向后,1f向前,为什么用1f?