assemblyx86attioportshardware-port

what does "outb" in AT&T asm mean?

I am reading some code of Linux. The keyboard.S has something like

outb %al,$0x61

and

inb $0x61,%al

I think the pending 'b' means 'byte', but i still cannot find what these instructions mean.

Solution

  • OUT and IN are instructions for transferring data between I/O ports. Those are a couple of links I found which provide a bit more information.

    As you mentioned, the b is the byte form of those instructions, which is appropriate since you're using the lower byte of ax (al).