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,FREEMAIL_FROM
	autolearn=unavailable autolearn_force=no version=3.4.4
X-Received: by 10.107.142.84 with SMTP id q81mr576911iod.51.1515100197565;
        Thu, 04 Jan 2018 13:09:57 -0800 (PST)
X-Received: by 10.157.82.108 with SMTP id q44mr37807otg.13.1515100197378; Thu,
 04 Jan 2018 13:09:57 -0800 (PST)
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!news.linkpendium.com!news.linkpendium.com!news.snarked.org!border2.nntp.dca1.giganews.com!nntp.giganews.com!g80no68537itg.0!news-out.google.com!b73ni175ita.0!nntp.google.com!g80no68532itg.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Thu, 4 Jan 2018 13:09:57 -0800 (PST)
In-Reply-To: <lypo6qd2oj.fsf@pushface.org>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=173.71.208.22;
 posting-account=okr6MwkAAAA58xM6G2PLG3lOj8tIok0v
NNTP-Posting-Host: 173.71.208.22
References: <6042baa6-7743-48aa-8237-87181ab41a02@googlegroups.com>
 <lypo6qd2oj.fsf@pushface.org>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <7c41ec78-ba73-4f85-a7a7-837c3d582fa0@googlegroups.com>
Subject: Re: Linker_Alias
From: jhb.games@gmail.com
Injection-Date: Thu, 04 Jan 2018 21:09:57 +0000
Content-Type: text/plain; charset="UTF-8"
Xref: reader02.eternal-september.org comp.lang.ada:49755
Date: 2018-01-04T13:09:57-08:00
List-Id: <comp.lang.ada>

On Wednesday, January 3, 2018 at 4:59:11 PM UTC-5, Simon Wright wrote:
> Jere writes:
> 
> > I know this is more of a GNAT question than an Ada question
> > but was hoping someone else had some insight to this pragma.
> >
> > I am trying to use pragma Linker_Alias to set up a default
> > operation for an operation defined with pragma Weak_External.  
> [...]
> > The intent is that GNAT links in a default operation unless
> > the client exports a procedure with the intended link name.
> >
> > The use case is for ZFP runtimes where I don't have access
> > to protected procedures.  I want to supply a dummy ISR
> > unless the client decides to override it.  
> >
> > I know GCC itself supports this (I tested it in another
> > language just to make sure), but I cannot figure out how
> > to get GNAT to support it.
> >
> > Am I setting up the pragma's wrong?  I've tried a few different
> > combinations, but with no luck.
> >
> > I'm on Windows 10 using GNAT GPL 2017 (same problem on 2015 and 2016).
> 
> On macOS with GCC8 it failed to link (symbol "target" missing).
> 
> I never came across pragma Linker_Alias (and the description isn't easy
> to get my head round). I had a similar problem in Cortex GNAT RTS: the
> default was
> 
>    procedure HardFault_Handler
>    with Export, Convention => Ada, External_Name => "HardFault_Handler";
>    pragma Weak_External (HardFault_Handler);
>    procedure HardFault_Handler is
>    begin
>       loop
>          null;
>       end loop;
>    end HardFault_Handler;
> 
> and then, if required, override by providing a package containing
> 
>    procedure Handler
>    with
>      Export,
>      Convention => Asm,
>      External_Name => "HardFault_Handler";
>    pragma Machine_Attribute (Handler, "naked");
> 
> whose body works out which stack is in use and sets up for debugging.


Thanks!

I tried that but ran into the same problem.  I added:

   procedure Target_Op_2
      with
         Convention => Ada,
         Export,
         External_Name => "t2",
         Link_Name => "t2";
   pragma Weak_External(Target_Op_2);

to Operations.ads, and

   procedure Target_Op_2 is
   begin
      Put_Line("t2");
   end Target_Op_2;

to Operations.adb but still got the same exception when calling
from the entry procedure:

with Ada.Text_IO; use Ada.Text_IO;
with Operations;

procedure Main is
begin
   Put_Line("Hello");
   Operations.Target_Op_2;
end Main;  

********************
Hello

raised PROGRAM_ERROR : EXCEPTION_ACCESS_VIOLATION
********************

So it looks like it still isn't defaulting the procedure.

Note
that I am testing this in the standard windows GNAT GPL
version as opposed to the cross compiler.  I'll get to
that, but I had to redo my environment for it.  I just
wanted to test out the functionality.

Any thoughts?