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=unavailable autolearn_force=no version=3.4.4
Path: 
 border1.nntp.dca3.giganews.com!backlog3.nntp.dca3.giganews.com!border3.nntp.dca.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!news.glorb.com!feeder.erje.net!eu.feeder.erje.net!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: pragma import => pointer in mapping table ?
Date: Tue, 05 Nov 2013 12:56:36 +0000
Organization: A noiseless patient Spider
Message-ID: <lyfvrbroqj.fsf@pushface.org>
References: <2d53ec9f-1ae1-4547-ac08-6fef44ab490f@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: mx05.eternal-september.org;
 posting-host="feb3f5761668d64af19c3661aa3d3ca4";
 logging-data="8302"; mail-complaints-to="abuse@eternal-september.org";
 posting-account="U2FsdGVkX18jqXcCNxlrgf5lYej9IU95g4k009nMZno="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (darwin)
Cancel-Lock: sha1:it4d/WfG0VZnzT1NU0bCEm3XXY4=
 sha1:k/PfYZjmyycXmb1jDOboUmeHSgI=
X-Original-Bytes: 2105
Xref: number.nntp.dca.giganews.com comp.lang.ada:183781
Date: 2013-11-05T12:56:36+00:00
List-Id: <comp.lang.ada>

wkernow@gmail.com writes:

> In deed, I saw that all variables X derived from a "pragma import" are
> considered as pointers in mapping table whereas variables type of varX
> are not access types (basic types).

I expect the format of the map file depends on the version of the linker
ld used on your system.

But, what in the mapping table leads you to conclude that these
variables are treated as pointers?

If the C code contains a variable foo and the Ada code uses pragma
Import to access it, then the Ada-derived object module contains an
unsatisfied reference to the symbol foo (possibly _foo) and the
C-derived object module contains a definition of the symbol; the linker
uses the definition to satisfy the reference.

So what we have is a variable at an address which is known, and when the
Ada code reads the variable the corresponding machine code loads the
data at that address into a register (or whatever is appropriate).

You could think of this as an access via a pointer at the machine code
level, but at the Ada level this is just the same as any other variable
access.