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From: Richard Henderson <richard.henderson@linaro.org>
To: "Alex Bennée" <alex.bennee@linaro.org>,
	"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 06:35:28 -0700
Message-ID: <e10f27f8-a47f-2ebe-5cab-0c4eae43667c@linaro.org> (raw)
In-Reply-To: <87y2rmm8h6.fsf@linaro.org>

On 3/27/20 2:51 AM, Alex Bennée wrote:
> 
> 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?
> 

I guess I'm happy with it.  Have a
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~


  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
2020-03-27 13:35         ` Richard Henderson [this message]
2020-03-26 19:58 ` Richard Henderson
2020-03-26 20:05   ` Paolo Bonzini

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