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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: The "black magic" of ioctl
Date: Sun, 24 Oct 2010 19:36:34 +0100
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Date: 2010-10-24T19:36:34+01:00
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Florian Weimer <fw@deneb.enyo.de> writes:

> * Frank J. Lhota:
>
>> Actually, you can call a varargs function such as ioctl from
>> Ada. Declare each ioctl profile that you need, e.g.
>
> Perhaps it seems to work for you, but this is not portable.  There are
> popular targets where the varargs calling convention is markedly
> different from the non-varargs calling convention, such as amd64.  It
> might still work by accident, but all bets are off, really.

I hadn't realised this: but a quick scan of the GNAT sources confirms:
in socket.c,

* Wrapper for ioctl(2), which is a variadic function */

int
__gnat_socket_ioctl (int fd, int req, int *arg) {
#if defined (_WIN32)
  return ioctlsocket (fd, req, arg);
#else
  return ioctl (fd, req, arg);
#endif
}