Re: [PATCH v3] MIPS: Implement ieee754 NAN2008 emulation mode

Jiaxun Yang
2024-07-11T01:53:52Z

在2024年7月10日七月 下午5:21，Maciej W. Rozycki写道：
> On Wed, 10 Jul 2024, Thomas Bogendoerfer wrote:
>
>> > > I'm considering to apply your patch, how much testing/verification did
>> > > this patch see ? Do have some test binaries ?
>> >
>> > It has been tested against Debian rootfs. There is no need to test againt special binary,
>> > but you need NaN2008 hardware such as Loongson 3A4000.
>>
>> that's just one case, what about NaN2008 binaries on a legacy MIPS CPU ?
>
> It would be good to check with hard-float QEMU configured for writable
> FCSR.NAN2008 (which is one way original code was verified) that things
> have not regressed. And also what happens if once our emulation has
> triggered for the unsupported FCSR.NAN2008 mode, an attempt is made to
> flip the mode bit via ptrace(2), e.g. under GDB, which I reckon our
> emulation permits for non-legacy CPUs (and which I think should not be
> allowed under the new setting).

PTrace is working as expected (reflects emulated value).

The actual switchable NaN hardware (M5150, P5600) uses a dedicated Config7
bit rather than writable FCSR.NAN2008 to control NaN2008 mode. This is undocumented
and not present on some RTL releases. FCSR.NAN2008 is R/O as per The MIPS32 Instruction
Set Manual. This renders the purposed test pointless.

That being said, I'll catch some time later to test behaviour with purposed QEMU modification
but I think it's good to go now.

Thanks
- Jiaxun

>
> Maciej

--
- Jiaxun