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From: Peter Maydell <peter.maydell@linaro.org>
Date: Mon, 4 Apr 2016 20:38:54 +0100
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Subject: Re: [Qemu-devel] [PATCH 1/2] softfloat: Enable
 run-time-configurable meaning of signaling NaN bit
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: "proljc@gmail.com" <proljc@gmail.com>, "kbastian@mail.uni-paderborn.de" <kbastian@mail.uni-paderborn.de>, "mark.cave-ayland@ilande.co.uk" <mark.cave-ayland@ilande.co.uk>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "agraf@suse.de" <agraf@suse.de>, "blauwirbel@gmail.com" <blauwirbel@gmail.com>, "jcmvbkbc@gmail.com" <jcmvbkbc@gmail.com>, Aleksandar Markovic <Aleksandar.Markovic@imgtec.com>, "qemu-arm@nongnu.org" <qemu-arm@nongnu.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, Petar Jovanovic <Petar.Jovanovic@imgtec.com>, "pbonzini@redhat.com" <pbonzini@redhat.com>, Miodrag Dinic <Miodrag.Dinic@imgtec.com>, "edgar.iglesias@gmail.com" <edgar.iglesias@gmail.com>, "gxt@mprc.pku.edu.cn" <gxt@mprc.pku.edu.cn>, Leon Alrae <Leon.Alrae@imgtec.com>, "afaerber@suse.de" <afaerber@suse.de>, "aurelien@aurel32.net" <aurelien@aurel32.net>, Richard Henderson <rth@twiddle.net>

On 4 April 2016 at 20:37, Eduardo Habkost <ehabkost@redhat.com> wrote:
> On Mon, Apr 04, 2016 at 02:31:47PM +0100, Peter Maydell wrote:
>> On 4 April 2016 at 14:21, Aleksandar Markovic
>> <Aleksandar.Markovic@imgtec.com> wrote:
>> > B. arm - explicitely sets other fields of float_status,
>> >       explicit invocation of set_snan_bit_is_one(0) added
>>
>> We zero the float_status structs on reset, because they are earlier
>> in the CPUARMState structure than the 'features' field (and so the
>> memset() in arm_cpu_reset() will clear them). So you don't
>> need to explicitly zero a field like this. I expect the other
>> architectures are the same.
>
> Even if it is not zeroed on reset, it is zeroed on object_new().
> Isn't that enough?

It must be zeroed on reset, otherwise we won't get the right
behaviour if you reset the CPU after running it for a bit.
object_new() zeroing is not sufficient.

thanks
-- PMM