From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,235855e3822c83d1
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Received: by 10.204.156.202 with SMTP id y10mr25347bkw.1.1334186682118;
        Wed, 11 Apr 2012 16:24:42 -0700 (PDT)
MIME-Version: 1.0
Path: 
 h15ni113014bkw.0!nntp.google.com!news1.google.com!volia.net!news2.volia.net!feed-A.news.volia.net!news.ecp.fr!news.jacob-sparre.dk!munin.jacob-sparre.dk!pnx.dk!.POSTED!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Importing C function with variable argument list
Date: Wed, 11 Apr 2012 18:24:33 -0500
Organization: Jacob Sparre Andersen Research & Innovation
Message-ID: <jm53rn$56b$1@munin.nbi.dk>
References: 
 <610ee323-4c7f-413d-8568-aed4955f5152@z38g2000vbu.googlegroups.com>
NNTP-Posting-Host: static-69-95-181-76.mad.choiceone.net
X-Trace: munin.nbi.dk 1334186679 5323 69.95.181.76 (11 Apr 2012 23:24:39 GMT)
X-Complaints-To: news@jacob-sparre.dk
NNTP-Posting-Date: Wed, 11 Apr 2012 23:24:39 +0000 (UTC)
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157
Date: 2012-04-11T18:24:33-05:00
List-Id: <comp.lang.ada>

"Maxim Reznik" <reznikmm@gmail.com> wrote in message 
news:610ee323-4c7f-413d-8568-aed4955f5152@z38g2000vbu.googlegroups.com...
...
> It seems it's impossible to call C function variable argument lists
> from Ada.
> Even when one knows in advace all arguments at compile time.
>
> Functions with Variable Argument Lists have their own ABI. For
> instance, in x86_64:
>
>> When a function taking variable-arguments is called, %rax must be set to 
>> the
>> total number of floating point parameters passed to the function in 
>> vector registers.

This is news to me! This is definitely not the case in the 32-bit interfaces 
with which I'm familar, so I'm not surprised that neither Ada nor 
implementers ever worried about this case. (Janus/Ada doesn't have any 
special handling for this case, and I've never seen any need for it, 
either.)

The "intended" solution would be for the language-name to be some 
implementation-defined name that specifies this ABI (much like "StdCall" 
specifies the "standard" ABI on Windows). That's necessarily not portable 
across implementations, but then again these sorts of bindings are almost 
never 100% portable.

                                       Randy.