Re: [9fans] calling function with (variable number of) parameters

[Latchesar Ionkov <lucho@gmx.net>]

On Wed, Jun 20, 2001 at 04:30:21PM +0000, Douglas A. Gwyn said:
> Latchesar Ionkov wrote:
> > I am trying to write a function
> >         int callf(void *f, int nargs, int *args)
> > f is a pointer to a function of a type
> >         int f(int, int, int, ..., int)
> 
> No, it isn't; at least, not as you have declared callf.
> 
> Also, that is not a proper variadic declaration for the type of f.
> I think what you mean is that the actual function definition uses
> a *fixed* number of arguments, different for different values of
> f, and you're hoping that the passed nargs happens to be
> consistent with the function that the passed f points to.

You understood what I meant, which was the purpose of the two pseudo
declarations.

> > callf should copy nargs number of ints from args to the stack and call f,
> > and then return f's return value.
> 
> > Is this possible with Plan9 C calling convention? ...
> > Do I miss something? Any ideas how to implement it?
> 
> It's an abuse of C under any linkage convention.

I know, but that knowledge doesn't help me.

> > Unfortunately I don't have any control on the requirements or the way f gets
> > its parameters. If there is no way to do it for any number of args, I'll
> > limit nargs (and hope nobody will write function with more than 15
> > arguments) and will modify SP with a constant value.
> 
> That will probably be your best bet.
> Other solutions would require changes to the interface.

The interface is called JNI and I can't change it.

	Lucho