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Re: [PATCH] qemu/atomic.h: add #ifdef guards for stdatomic.h

From: Richard Henderson
Subject: Re: [PATCH] qemu/atomic.h: add #ifdef guards for stdatomic.h
Date: Fri, 27 Mar 2020 06:35:28 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 3/27/20 2:51 AM, Alex Bennée wrote:
> Peter Maydell <address@hidden> writes:
>> On Thu, 26 Mar 2020 at 18:05, Paolo Bonzini <address@hidden> 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, 
>>>>>  #define atomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, 
>>>>>  #define atomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, 
>>>>>  #define atomic_fetch_or(ptr, n)  __atomic_fetch_or(ptr, n, 
>>>>>  #define atomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, 
>>>>> +#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 <address@hidden>


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