C vdso

[Christophe Leroy]

Hi Michael,

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.

Thanks,
Christophe