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From: Peter Maydell <peter.maydell@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Alex Bennée" <alex.bennee@linaro.org>,
	"QEMU Developers" <qemu-devel@nongnu.org>
Subject: Re: [PATCH] qemu/atomic.h: add #ifdef guards for stdatomic.h
Date: Thu, 26 Mar 2020 20:19:44 +0000
Message-ID: <CAFEAcA_KSVHkVznGD=cxzLaHSbPmWLN6MSqWHBqB8_ux05gD7A@mail.gmail.com> (raw)
In-Reply-To: <ba33454a-6e57-960a-7114-fc71a9f09442@redhat.com>

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 ?

-- PMM

  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 [this message]
2020-03-27  9:51       ` Alex Bennée
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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