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From: Richard Henderson <rth@twiddle.net>
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Date: Tue, 17 May 2016 12:19:27 -0700
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Subject: Re: [Qemu-devel] [PATCH v5 07/18] qemu-thread: add simple
 test-and-set spinlock
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To: Sergey Fedorov <serge.fdrv@gmail.com>, "Emilio G. Cota" <cota@braap.org>, QEMU Developers <qemu-devel@nongnu.org>, MTTCG Devel <mttcg@greensocs.com>
Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>

On 05/17/2016 10:13 AM, Sergey Fedorov wrote:
>> > +static inline void qemu_spin_lock(QemuSpin *spin)
>> > +{
>> > +    while (atomic_test_and_set_acquire(&spin->value)) {
>>>From gcc-4.8 info page, node "__atomic Builtins", description of
> __atomic_test_and_set():
> 
>     It should be only used for operands of type 'bool' or 'char'.
> 

Hum.  I thought I remembered all operand sizes there, but I've just re-checked
and you're right about bool (and really only bool).

Perhaps we should just stick with __sync_test_and_set then.  I'm thinking here
of e.g. armv6, a reasonable host, which can't operate on 1 byte atomic values.


r~