Re: C vdso

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

Quoting Michael Ellerman <mpe@ellerman.id.au>:

> Christophe Leroy <christophe.leroy@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@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@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 ?

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index f877a576b338..c3473eb031a3 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1419,7 +1419,7 @@ static inline void msr_check_and_clear(unsigned  
long bits)
  		__msr_check_and_clear(bits);
  }

-#if defined(CONFIG_PPC_CELL) || defined(CONFIG_E500)
+#if defined(__powerpc64__) && (defined(CONFIG_PPC_CELL) ||  
defined(CONFIG_E500))
  #define mftb()		({unsigned long rval;				\
  			asm volatile(					\
  				"90:	mfspr %0, %2;\n"		\
diff --git a/arch/powerpc/include/asm/timebase.h  
b/arch/powerpc/include/asm/timebase.h
index a8eae3adaa91..7b372976f5a5 100644
--- a/arch/powerpc/include/asm/timebase.h
+++ b/arch/powerpc/include/asm/timebase.h
@@ -21,7 +21,7 @@ static inline u64 get_tb(void)
  {
  	unsigned int tbhi, tblo, tbhi2;

-	if (IS_ENABLED(CONFIG_PPC64))
+	if (IS_BUILTIN(__powerpc64__))
  		return mftb();

  	do {