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From: Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP>
Newsgroups: comp.lang.ada
Subject: Re: Forcing GNAT to use 32-bit load/store instructions on ARM?
Date: Tue, 1 Jul 2014 17:26:55 +0000 (UTC)
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Date: 2014-07-01T17:26:55+00:00
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On 2014-07-01, Niklas Holsti <niklas.holsti@tidorum.invalid> wrote:
> On 14-07-01 15:06 , Simon Clubley wrote:
>> On 2014-06-30, Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org> wrote:
>>> On 06/30/2014 03:11 PM, daniel.dmk@googlemail.com wrote:
>>>>
>>>> Does anyone know how I can force GNAT to generate the appropriate
>>>> instructions?
>>>
>>> If you need specific machine instructions, you should use a machine-code insertion.
>>>
>> 
>> The issue here is that Pragma Atomic should have given him the guarantee
>> he needs.
>
> Perhaps pragma Atomic did not work because the record actually had only
> 2 significant bits, fitting in one octet, and the Size = 32 bits clause
> did not make GNAT treat all 32 bits as atomic? I'm not sure if that
> would be a bug -- does a Size clause determine the extent of pragma Atomic?
>

I suppose it's possible, but then again according to the OP it did work
when using a temporary record.

> The OP should try to add components to fill all 32 bits, and also use
> pragma Atomic. If that doesn't work, then it is a GNAT bug, methinks.
>

Filling out to 32-bits would be an interesting test (and allows the OP
to set them to a known value if performing a simple 32-bit store instead
of a R/M/W operation.)

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world