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Newsgroups: comp.lang.ada
Subject: Re: Importing C function with variable argument list
Date: Thu, 12 Apr 2012 12:08:28 +0200
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Date: 2012-04-12T12:08:28+02:00
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Am 10.04.2012 18:47, schrieb Simon Wright:
> Markus Schöpflin<no.spam@spam.spam>  writes:
>
>> Compiling above code on an x86_64 Linux system (Debian Squeeze, using
>> GNAT 4.4.5) still works, but executing the resulting binary results
>> in: "raised PROGRAM_ERROR : unhandled signal".
>
> Worked as one would hope on Mac OS X (GNAT GPL 2011, target
> x86_64-apple-darwin10.2.0).

I tried with GNAT GPL 2011 on 64 bit Debian and it still doesn't work. Does 
Mac OS X use the same 64 bit ABI as Linux?

Meanwhile I found the following in the GNAT user manual:

<quote>
A note on interfacing to a C "varargs" function:

     In C, varargs allows a function to take a variable number of arguments. 
There is no direct equivalent in this to Ada. One approach that can be used is 
to create a C wrapper for each different profile and then interface to this C 
wrapper. For example, to print an int value using printf, create a C function 
printfi that takes two arguments, a pointer to a string and an int, and calls 
printf. Then in the Ada program, use pragma Import to interface to printfi.

     It may work on some platforms to directly interface to a varargs function 
by providing a specific Ada profile for a particular call. However, this does 
not work on all platforms, since there is no guarantee that the calling 
sequence for a two argument normal C function is the same as for calling a 
varargs C function with the same two arguments.
</quote>

So the note from the Ada RM does not seem to be followed by GNAT, and it works 
by chance only on 32 bit Linux systems.

Markus