C vdso

[Michael Ellerman]

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.

Hopefully I can find time to dig into it.

cheers