On 10/12/06, Juan Jose Garcia-Ripoll <[EMAIL PROTECTED]> wrote:
First of all, every time you call a function with foreign-funcall you
have to supply the types of the arguments. The aliasing of all pointer
types to :pointer means that type information is lost. Not all pointer
type are equivalent, because some types have alignment restrictions.
Can you give me an example?
Supplying the argument types is extremely tricky in some cases and
might not be enough type information. For example,
int f1(int i, ...)
is not the same function as
int f2(int i, int j)
even though when we invoke f1(1, 2) the (2) is coerced to type int.
On all platforms I have access too they seem to behave the same since
we manage to call varargs functions and the various Lisps don't know
anything about their varargs-ness. I hear that might not always be
true, so see below.
The information about "..." is taken cared of by DEFCFUN, but not by
FOREIGN-FUNCALL. That may seem useless but really, it is not the same
thing to call f1 and f2, because the C compiler does produce different
assembly code. For instance, using AMD64, in the first case it has to
push the arguments on the stack, while in the second case everything
goes into registers Similar things happen with a PPC backend.
See my comment in src/functions.lisp about foreign-funcall-varargs:
;;; ATM, the only difference between this macro and FOREIGN-FUNCALL is that
;;; it does argument promotion for that variadic argument. This could be useful
;;; to call an hypothetical %foreign-funcall-varargs on some hypothetical lisp
;;; on an hypothetical platform that has different calling conventions for
;;; varargs functions. :-)
If ECL can do something special about varargs, we can go ahead and use that!
--
Luís Oliveira
http://student.dei.uc.pt/~lmoliv/
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