<code>8(FP)</code> is the second (on a 64-bit machine), and so on.
However, when referring to a function argument this way, it is necessary to place a name
at the beginning, as in <code>first_arg+0(FP)</code> and <code>second_arg+8(FP)</code>.
(The meaning of the offset—offset from the frame pointer—distinct
from its use with <code>SB</code>, where it is an offset from the symbol.)