Qm.n multiplication in VHDL
1) Possibly because as you say it's easy enough to implement yourself;

2) Correct, you have to know where the "binary point" is.

I find the concept of the binary point (like decimal point, but for binary) to be very useful when dealing with fixed point. 

     aaa.aaaaa
x    bbb.bbbbb
= nnnnnn.nnnnnnnnnn


The other way of thinking of it is that everything is implicitly multiplied by (1 &lt;&lt; number of fractional bits):

A*(1&lt;&lt;5) * B*(1&lt;&lt;5) = (A*B) * (1&lt;&lt;10)