Re: Math errors

[Jonathan Nieder <jrnieder@gmail.com>]

Hi,

Alistair Francis wrote:
> On Wed, Jan 8, 2020 at 4:29 AM Jim Wilson <jimw@sifive.com> wrote:
>> On Mon, Jan 6, 2020 at 5:33 PM Alistair Francis <alistair23@gmail.com> wrote:

>>> I have the latest 5.4.x kernel, I'm not sure if that has it or not.
>>
>> I don't know.  I don't follow linux kernel development that closely.
>> But the failures I sometimes see are test-fenv and test-fpucw which I
>> don't see in your list.
>>
>> I only run glibc testsuite on hardware though, and I've only been
>> testing rv64gc support.  I haven't tried qemu.  In the RISC-V software
>> meeting this morning, Palmer mentioned that there are some known
>> RISC-V qemu FP bugs, for instance fcmp doesn't set the FP reg dirty
>> bit when an exception flag is set, which could cause a testcase
>> failure if a context switch happens at the wrong time.  This could
>
> I have noticed that running the tests not in parallel gives much better results

Interesting.  Can you provide full "uname -r" output?  What Linux
distribution do you use?

I suspect the issue Jim mentioned is fixed by v5.3-rc5~12^2~1 ("riscv:
Correct the initialized flow of FP register", 2019-08-14), which you
would already have.  That said, the 5.5-rc series has some more fp reg
handling fixes.

[...]
>> Someone will have to look at the rv32gc math failures, and keep an
>> open mind that they could be glibc, qemu, gcc, linux kernel, etc
>
> Yeah, that's what I was thinking. There are only a few math tests left
> failing, so it's not too bad. Thanks for the information Jim.

That it appears more often with threading does suggest some kind of FP
register leakage.

Thanks and happy hunting,
Jonathan