Re: [Qemu-ppc] [Qemu-devel] [PATCH 1/2] softfloat: Enable run-time-configurable meaning of signaling NaN bit

[Peter Maydell]

On 4 April 2016 at 20:42, Eduardo Habkost <address@hidden> wrote:
> On Mon, Apr 04, 2016 at 08:38:54PM +0100, Peter Maydell wrote:
>> On 4 April 2016 at 20:37, Eduardo Habkost <address@hidden> wrote:
>> > On Mon, Apr 04, 2016 at 02:31:47PM +0100, Peter Maydell wrote:
>> >> On 4 April 2016 at 14:21, Aleksandar Markovic
>> >> <address@hidden> 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.
>
> The only calls to set_snan_bit_is_one() with non-zero arguments I
> see on this patch are during CPU init or reset. How exactly would
> the snan_bit_is_one field change to non-zero during runtime, to
> require zeroing it again on reset?

I meant in general for these float_status flags, not anything
specific to this particular flag.

thanks
-- PMM