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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Sat, 10 Oct 2020 21:18:05 +0100
Message-ID: <CAH6eHdRJxBgkhbhjuY2VSjOs5xqXdOhnOW9u3a9BqC1qs=hoUw@mail.gmail.com>
Subject: Re: Atomic accesses on ARM microcontrollers
To: David Brown <david.brown@hesbynett.no>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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On Sat, 10 Oct 2020 at 20:43, David Brown <david.brown@hesbynett.no> wrote:
> Is this strategy guaranteed to work in gcc, or is it a case of "it works
> in a simple test, but might fail in a complicated program or with
> different flags" ?

I think it works by design. My understanding is that users providing
their own implementation of those calls is fully supported. I think
that's partly why libatomic.so is a distinct library, and not just
part of libgcc_s.so. The docs aren't entirely clear about this, they
just say that if the compiler can't emit lock-free instructions for
the atomic operation "a call is made to an external routine with the
same parameters to be resolved at run time." But I think that "to be
resolved at run time" means that you can choose how those calls will
be resolved.