multiplication differences in HLA and gnu as

Hello :)
I was using gas for a while with a syntax like that
imull $5, %edx
However, HLA does not accept the second operand
imul (5, edx)
as far as I understood from IntegerArithmetic.html i wants second
operand as eax
There is a description of intel cpu's limitation, where destination
register is alweays eax/ax/al in case of multiplication
However, in "Programming from Ground Up" which teaches asm programming
with gas there is no word about this limiataion of intel processors,
but, however a similar note about div instructions.
So... Is that limitation of very old cpu's and HLA tries to be
compatible with them?
Or... I really do not understand what is the reason HLA do not accept
that?
May be there is a workaround? Because I do not want to change my
existing code (which was originally written for gas) so much.

Thank you

Norayr