C vdso

[Michael Ellerman]

Christophe Leroy <christophe.leroy at csgroup.eu> writes:
> Quoting Michael Ellerman <mpe at ellerman.id.au>:
>
>> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
>>> Le 03/11/2020 à 19:13, Christophe Leroy a écrit :
>>>> Le 23/10/2020 à 15:24, Michael Ellerman a écrit :
>>>>> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
>>>>>> Le 24/09/2020 à 15:17, Christophe Leroy a écrit :
>>>>>>> Le 17/09/2020 à 14:33, Michael Ellerman a écrit :
>>>>>>>> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
>>>>>>>>>
>>>>>>>>> What is the status with the generic C vdso merge ?
>>>>>>>>> In some mail, you mentionned having difficulties getting it working on
>>>>>>>>> ppc64, any progress ? What's the problem ? Can I help ?
>>>>>>>>
>>>>>>>> Yeah sorry I was hoping to get time to work on it but haven't been able
>>>>>>>> to.
>>>>>>>>
>>>>>>>> It's causing crashes on ppc64 ie. big endian.
>>>>> ...
>>>>>>>
>>>>>>> Can you tell what defconfig you are using ? I have been able to  
>>>>>>> setup a full glibc PPC64 cross
>>>>>>> compilation chain and been able to test it under QEMU with  
>>>>>>> success, using Nathan's vdsotest tool.
>>>>>>
>>>>>> What config are you using ?
>>>>>
>>>>> ppc64_defconfig + guest.config
>>>>>
>>>>> Or pseries_defconfig.
>>>>>
>>>>> I'm using Ubuntu GCC 9.3.0 mostly, but it happens with other  
>>>>> toolchains too.
>>>>>
>>>>> At a minimum we're seeing relocations in the output, which is a problem:
>>>>>
>>>>>    $ readelf -r build\~/arch/powerpc/kernel/vdso64/vdso64.so
>>>>>    Relocation section '.rela.dyn' at offset 0x12a8 contains 8 entries:
>>>>>      Offset          Info           Type           Sym. Value     
>>>>> Sym. Name + Addend
>>>>>    000000001368  000000000016 R_PPC64_RELATIVE                     7c0
>>>>>    000000001370  000000000016 R_PPC64_RELATIVE                     9300
>>>>>    000000001380  000000000016 R_PPC64_RELATIVE                     970
>>>>>    000000001388  000000000016 R_PPC64_RELATIVE                     9300
>>>>>    000000001398  000000000016 R_PPC64_RELATIVE                     a90
>>>>>    0000000013a0  000000000016 R_PPC64_RELATIVE                     9300
>>>>>    0000000013b0  000000000016 R_PPC64_RELATIVE                     b20
>>>>>    0000000013b8  000000000016 R_PPC64_RELATIVE                     9300
>>>>
>>>> Looks like it's due to the OPD and relation between the function()  
>>>> and .function()
>>>>
>>>> By using DOTSYM() in the 'bl' call, that's directly the dot  
>>>> function which is called and the OPD is
>>>> not used anymore, it can get dropped.
>>>>
>>>> Now I get .rela.dyn full of 0, don't know if we should drop it explicitely.
>>>
>>> What is the status now with latest version of CVDSO ? I saw you had  
>>> it in next-test for some time,
>>> it is not there anymore today.
>>
>> Still having some trouble with the compat VDSO.
>>
>> eg:
>>
>> $ ./vdsotest clock-gettime-monotonic verify
>> timestamp obtained from kernel predates timestamp
>> previously obtained from libc/vDSO:
>> 	[1346, 821441653] (vDSO)
>> 	[570, 769440040] (kernel)
>>
>>
>> And similar for all clocks except the coarse ones.
>>
>
> Ok, I managed to get the same with QEMU. Looking at the binary, I only  
> see an mftb instead of the mftbu/mftb/mftbu triplet.
>
> Fix below. Can you carry it, or do you prefer a full patch from me ?  
> The easiest would be either to squash it into [v13,4/8]  
> ("powerpc/time: Move timebase functions into new asm/timebase.h"), or  
> to add it between patch 4 and 5 ?

I can squash it in.

cheers