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=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,afb4d45672b1e262
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!news4.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local01.nntp.dca.giganews.com!nntp.pipex.net!news.pipex.net.POSTED!not-for-mail
NNTP-Posting-Date: Sat, 01 Apr 2006 11:54:14 -0600
Reply-To: "Doobs" <doobs@doobs.com>
From: "Doobs" <doobs@doobs.com>
Newsgroups: comp.lang.ada
References: <LIednWDbPNgXGbPZRVnysQ@pipex.net>
 <87odzl5ilt.fsf@mid.deneb.enyo.de>
Subject: Re: Any way of persuading GNAT/GCC to implement a true overlay and
 not a pointer?
Date: Sat, 1 Apr 2006 18:54:16 +0100
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.2527
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2527
X-RFC2646: Format=Flowed; Original
Message-ID: <SdmdndA2Z9jbI7PZnZ2dnUVZ8qWdnZ2d@pipex.net>
NNTP-Posting-Host: 85.210.60.99
X-Trace: 
 sv3-3XJF0PKhHfVyZ53G9awN11WLwkbKzDdtfzKuDlky+s4fay+P7TYptvykLHoXqcfwg18XAGJozhbamkW!DjcpudoeFmQfzdG25K4l9H2pM4vGTBruiwtrRAwZSUUcT8477bzWLXPStUTvMlzh9+FCFpoT1xnD!zpRRwavpck2csgS2bQglJUU=
X-Complaints-To: abuse@dsl.pipex.net
X-DMCA-Complaints-To: abuse@dsl.pipex.net
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint
 properly
X-Postfilter: 1.3.32
Xref: g2news1.google.com comp.lang.ada:3699
Date: 2006-04-01T18:54:16+01:00
List-Id: <comp.lang.ada>


"Florian Weimer" <fw@deneb.enyo.de> wrote in message 
news:87odzl5ilt.fsf@mid.deneb.enyo.de...
>> I was under the impression that code of the following form :
>>
>> X : <Some Type>;
>> Y : <Some Type>;
>> for Y'Address use X'Address;
>>
>> would result in an overlay in the resulting code.
>
> Could you show some more code?  Probably initialization is causing
> your problems, which can be fixed with a pragma Import.

The following is an example of the problem:

package TestPackage
is

   type MyRecordType is
   record
      element1 : Positive;
      element2 : Positive;
   end record;

   type MyArrayType is array(1..2) of Positive;

   myX : MyRecordType;
   pragma volatile(myX);
   myY : MyArrayType;
   pragma volatile(myY);
   for myY'Address use myX'Address;


end TestPackage;

The following fragments of the resulting MAP file (GCC 3.4.2 mingw32) show 
the problem...

 .data          0x00472b00       0x10 ./testpackage.o
                0x00472b00                testpackage__myy
 .data          0x00472b10       0x10 ./nextpackage.o

<..... later in the file...>

 COMMON         0x004a2770       0x20 ./testpackage.o
                0x004a2770                testpackage__myx
                0x004a2780                testpackage_E


Clearly myX and myY do NOT share the same address.  I am also puzzled as to 
why the variables have been put in differen memory sections...