Re: 3.18+: soft-float userland unusable due to .MIPS.abiflags patch

[Markos Chandras <Markos.Chandras@imgtec.com>]

On 01/19/2015 05:36 AM, Paul Burton wrote:
> On Sun, Jan 18, 2015 at 11:35:31AM +0100, Manuel Lauss wrote:
>> On Sat, Jan 17, 2015 at 8:00 PM, Matthew Fortune
>> <Matthew.Fortune@imgtec.com> wrote:
>>> Aaro Koskinen <aaro.koskinen@iki.fi> writes:
>>>> On Fri, Jan 16, 2015 at 08:36:12PM +0000, Matthew Fortune wrote:
>>>>> You are right that it is the .MIPS.abiflags patch that is causing your
>>>>> trouble. For a long time I had to put a restriction in the ABI plan
>>>>> that soft-float binaries without an ABIFLAGS pheader could not be
>>>>> linked against soft-float binaries with an ABIFLAGS pheader. We have
>>>>> since found a way to relax that restriction without reducing the
>>>>> effectiveness of the new compatibility checks. I would need to check
>>>>> the code in the kernel but I suspect that is the issue. Markos has
>>>>> done a significant update to this piece of code which he posted
>>>>> earlier today. That updated version should allow the combination of
>>>>> soft-float without ABIFLAGS and soft-float with ABIFLAGS.
>>>>
>>>> Are you referring to the series with 70 patches? I think a fix that
>>>> passes stable kernel rules is needed.
>>>
>>> Yes it was just one patch though for this issue:
>>> [PATCH RFC v2 68/70] MIPS: kernel: elf: Improve the overall ABI and FPU
>>> mode checks
>>>
>>> I wasn't trying to suggest how to fix the existing code just explaining
>>> how it came to be and what has been done about it for next release.
>>> (I'm not a kernel developer I'm just interested as I did most of the
>>> design work for the new ABI extensions.)
>>>
>>> I guess there are three options:
>>> a) revert the patch - That would remove the new ABI safety measures from
>>>    3.19 which is a shame given it has MSA support in it (I think anyway).
>>>    equally given that the new prctl FPU mode options did not make 3.19
>>>    then I suppose it doesn't lose too much either as the two features
>>>    go hand in hand to some extent.
>>
>> I favor this one.  I don't know how many systems with MSA are in the wild,
>> and if there are any, I'm sure they're using some mti/imgtec-supplied kernel
>> anyway.  Another thing I noticed last time is that companies shipping MIPS
>> products rarely upgrade their toolchains, so I'm sure the ABI safety measures
>> can wait for another release, but then function with all configurations
>> in the wild.
>>
>> Manuel
> 
> An alternative would be the patch I just submitted, which makes the mode
> checks conditional upon CONFIG_MIPS_O32_FP64_SUPPORT:
> 
>   http://marc.info/?l=linux-mips&m=142164553017027&w=2
> 
> Assuming this fixes your problem, and I believe it should, it would
> avoid the churn of reverting the patch & readding the modified logic
> again later.
> 
> Thanks,
>     Paul
> 
There is also this patch from James for 3.19 final

http://patchwork.linux-mips.org/patch/8932/

so with these two patches we should be good for 3.19.

-- 
markos