From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <segher@kernel.crashing.org>
Received: from gate.crashing.org (gate.crashing.org [63.228.1.57])
 by sourceware.org (Postfix) with ESMTP id D63FB3857826
 for <gcc-help@gcc.gnu.org>; Fri,  9 Oct 2020 23:29:25 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org D63FB3857826
Authentication-Results: sourceware.org; dmarc=none (p=none dis=none)
 header.from=kernel.crashing.org
Authentication-Results: sourceware.org;
 spf=fail smtp.mailfrom=segher@kernel.crashing.org
Received: from gate.crashing.org (localhost.localdomain [127.0.0.1])
 by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 099NSPtC017533;
 Fri, 9 Oct 2020 18:28:25 -0500
Received: (from segher@localhost)
 by gate.crashing.org (8.14.1/8.14.1/Submit) id 099NSOu4017532;
 Fri, 9 Oct 2020 18:28:24 -0500
X-Authentication-Warning: gate.crashing.org: segher set sender to
 segher@kernel.crashing.org using -f
Date: Fri, 9 Oct 2020 18:28:24 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: David Brown <david.brown@hesbynett.no>
Cc: gcc-help@gcc.gnu.org
Subject: Re: Atomic accesses on ARM microcontrollers
Message-ID: <20201009232824.GM2672@gate.crashing.org>
References: <945d5e74-b449-3746-6560-996d0437db76@hesbynett.no>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <945d5e74-b449-3746-6560-996d0437db76@hesbynett.no>
User-Agent: Mutt/1.4.2.3i
X-Spam-Status: No, score=-7.0 required=5.0 tests=BAYES_00, JMQ_SPF_NEUTRAL,
 KAM_DMARC_STATUS, TXREP, T_SPF_HELO_PERMERROR,
 T_SPF_PERMERROR autolearn=no autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
X-BeenThere: gcc-help@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-help mailing list <gcc-help.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-help>,
 <mailto:gcc-help-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-help/>
List-Post: <mailto:gcc-help@gcc.gnu.org>
List-Help: <mailto:gcc-help-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-help>,
 <mailto:gcc-help-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Fri, 09 Oct 2020 23:29:26 -0000

Hi!

On Fri, Oct 09, 2020 at 08:28:05PM +0200, David Brown wrote:
> For 8-bit, 16-bit and 32-bit types, atomic accesses are just simple
> loads and stores.  These are generated fine.
> 
> But for 64-bit and above, there are library calls to a compiler-provided
> library.

> Is there any way I can replace this library with my own code here, while
> still using the language atomics?

Add something in libgcc/config/arm/ ?

You might need to add something specific to some configuration (in some
t-* file), or maybe add another command line flag.

It sounds like you have to add more constraints on what atomic can be
used for than what is specified currently.


Segher