Re: C vdso

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Hi Michael,

Le 24/09/2020 à 15:17, Christophe Leroy a écrit :
> Hi Michael
> 
> Le 17/09/2020 à 14:33, Michael Ellerman a écrit :
>> Hi Christophe,
>>
>> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>>> Hi Michael,
>>>
>>> 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.
>>
> 
>>
>> As you can see from the instruction dump we have jumped into the weeds somewhere.
>>
>> We also had the report from the kbuild robot about rela.opd being
>> discarded, which I think is indicative of a bigger problem. ie. we don't
>> process relocations for the VDSO, but opds require relocations (they
>> contain an absolute pointer).
>>
>> I thought we could get away with that, because the VDSO entry points
>> aren't proper functions (so they don't have opds), and I didn't think
>> we'd be calling via function pointers in the VDSO code (which would
>> require opds). But seems something is not working right.
>>
>> Sorry I haven't got back to you with those details. Things are a bit of
>> a mess inside IBM at the moment (always?), and I've been trying to get
>> everything done before I take a holiday next week.
>>
> 
> 
> 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 ?

Christophe

> 
> I tested with both ppc64_defconfig and pseries_defconfig.
> 
> The only problem I got is with getcpu, which segfaults but both before and after applying my series, 
> so I guess this is unrelated.
> 
> Not sure we can pay too much attention to the exact measurement as it is a ppc64 QEMU running on a 
> x86 Linux which is running in a Virtual Box on a x86 windows Laptop, but at least it works:
> 
> Without the series:
> 
> clock-getres-monotonic:    vdso: 389 nsec/call
> clock-gettime-monotonic:    vdso: 781 nsec/call
> clock-getres-monotonic-coarse:    vdso: 13715 nsec/call
> clock-gettime-monotonic-coarse:    vdso: 312 nsec/call
> clock-getres-monotonic-raw:    vdso: 13589 nsec/call
> clock-getres-tai:    vdso: 13827 nsec/call
> clock-gettime-tai:    vdso: 14846 nsec/call
> clock-getres-boottime:    vdso: 13596 nsec/call
> clock-gettime-boottime:    vdso: 14758 nsec/call
> clock-getres-realtime:    vdso: 327 nsec/call
> clock-gettime-realtime:    vdso: 717 nsec/call
> clock-getres-realtime-coarse:    vdso: 14102 nsec/call
> clock-gettime-realtime-coarse:    vdso: 299 nsec/call
> gettimeofday:    vdso: 771 nsec/call
> 
> With the series:
> 
> clock-getres-monotonic:    vdso: 350 nsec/call
> clock-gettime-monotonic:    vdso: 726 nsec/call
> clock-getres-monotonic-coarse:    vdso: 356 nsec/call
> clock-gettime-monotonic-coarse:    vdso: 423 nsec/call
> clock-getres-monotonic-raw:    vdso: 349 nsec/call
> clock-getres-tai:    vdso: 419 nsec/call
> clock-gettime-tai:    vdso: 724 nsec/call
> clock-getres-boottime:    vdso: 352 nsec/call
> clock-gettime-boottime:    vdso: 752 nsec/call
> clock-getres-realtime:    vdso: 351 nsec/call
> clock-gettime-realtime:    vdso: 733 nsec/call
> clock-getres-realtime-coarse:    vdso: 356 nsec/call
> clock-gettime-realtime-coarse:    vdso: 367 nsec/call
> gettimeofday:    vdso: 796 nsec/call
> 
> 
> Thanks
> Christophe