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From: "Alex Bennée" <alex.bennee@linaro.org>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [PATCH] qemu/atomic.h: add #ifdef guards for stdatomic.h
Date: Fri, 27 Mar 2020 09:51:17 +0000
Message-ID: <87y2rmm8h6.fsf@linaro.org> (raw)
In-Reply-To: <CAFEAcA_KSVHkVznGD=cxzLaHSbPmWLN6MSqWHBqB8_ux05gD7A@mail.gmail.com>

Peter Maydell <peter.maydell@linaro.org> writes:

> On Thu, 26 Mar 2020 at 18:05, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> On 26/03/20 18:14, Peter Maydell wrote:
>> >> +#ifndef atomic_fetch_add
>> >>  #define atomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)
>> >>  #define atomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)
>> >>  #define atomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)
>> >>  #define atomic_fetch_or(ptr, n)  __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)
>> >>  #define atomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)
>> >> +#endif
>> >
>> > This will work around FreeBSD's current implementation in particular,
>> > but I don't think there's anything in the C11 spec that mandates that
>> > atomic_fetch_add() and friends have to be macros and not simply
>> > functions...
>> That's not a problem as long as they are all functions, the macros would
>> simply override the function-based implementation.
> Oh yes, so it would. I think I was also vaguely thinking in terms
> of FreeBSD being the leading edge of "one day most or all of our
> hosts will have a full stdatomic.h", so maybe we should shift to
> use-host-stdatomic-by-default, with the use of the gcc __atomic*
> as the fallback at some point ?

At some point but I suspect not right now.

So what's the conclusion for this patch? Are people happy with it as a
sticking plaster I can apply to the bounced testing PR?

Alex Bennée

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26 17:01 Alex Bennée
2020-03-26 17:14 ` Peter Maydell
2020-03-26 17:32   ` Alex Bennée
2020-03-26 18:05   ` Paolo Bonzini
2020-03-26 20:19     ` Peter Maydell
2020-03-27  9:51       ` Alex Bennée [this message]
2020-03-27 13:35         ` Richard Henderson
2020-03-26 19:58 ` Richard Henderson
2020-03-26 20:05   ` Paolo Bonzini

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