C Assembly convert 0xffffffff

If there is a register, say %eax that is an integer type. If %eax is 0xffffffff, what would x be?

This is on a 64-bit machine.

Since 0xffffffff is 4 bytes, what could be a possible x type? an int or unsigned int or unsigned long, right? Also, could the value be -1 or would it be 2^32 -1? Are we treating it as signed or unsigned?

I'm just struggling to understand how to go about this.