Hi,

I actually think it shouldn't matter.  The caller should only rely on the
parts of %eax which are covered by the return type.

So problems can only arise if the caller for some reason doesn't know the
exact return type (like in the bugreport the ffi library, which simply
assumes that the return type is ffi_arg).  If we want to define something
for that case (I think outside the C standard, but the ABI doesn't need to
confine itself to only valid programs), then we can't specify either sign
or zero extension exclusively, as the extension needs to be value
preserving.

Hence I think we can only say that before returning, %eax should be sign
extended when the actual return type was a signed one, or zero extended if
not.  I don't think we should go that route, though.

Ciao,
Michael.