linux-kernel - Re: [PATCH v1 4/9] powerpc/vdso: Remove unnecessary ifdefs in vdso

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Message-ID: <e885d2cf-4b29-95d7-38ac-bff2951e57ad@csgroup.eu>
Date:   Fri, 28 Aug 2020 07:46:04 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v1 4/9] powerpc/vdso: Remove unnecessary ifdefs in
 vdso_pagelist initialization



Le 28/08/2020 à 07:40, Christophe Leroy a écrit :
> 
> 
> Le 27/08/2020 à 15:19, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>> On 08/26/2020 02:58 PM, Michael Ellerman wrote:
>>>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>>>> diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
>>>>> index daef14a284a3..bbb69832fd46 100644
>>>>> --- a/arch/powerpc/kernel/vdso.c
>>>>> +++ b/arch/powerpc/kernel/vdso.c
>>>>> @@ -718,16 +710,14 @@ static int __init vdso_init(void)
>>>> ...
>>>>> -
>>>>> -#ifdef CONFIG_VDSO32
>>>>>        vdso32_kbase = &vdso32_start;
>>>>>        /*
>>>>> @@ -735,8 +725,6 @@ static int __init vdso_init(void)
>>>>>         */
>>>>>        vdso32_pages = (&vdso32_end - &vdso32_start) >> PAGE_SHIFT;
>>>>>        DBG("vdso32_kbase: %p, 0x%x pages\n", vdso32_kbase, 
>>>>> vdso32_pages);
>>>>> -#endif
>>>>
>>>> This didn't build for ppc64le:
>>>>
>>>>     
>>>> /opt/cross/gcc-8.20_binutils-2.32/powerpc64-unknown-linux-gnu/bin/powerpc64-unknown-linux-gnu-ld: 
>>>> arch/powerpc/kernel/vdso.o:(.toc+0x0): undefined reference to 
>>>> `vdso32_end'
>>>>     
>>>> /opt/cross/gcc-8.20_binutils-2.32/powerpc64-unknown-linux-gnu/bin/powerpc64-unknown-linux-gnu-ld: 
>>>> arch/powerpc/kernel/vdso.o:(.toc+0x8): undefined reference to 
>>>> `vdso32_start'
>>>>     make[1]: *** [/scratch/michael/build/maint/Makefile:1166: 
>>>> vmlinux] Error 1
>>>>     make: *** [Makefile:185: __sub-make] Error 2
>>>>
>>>> So I just put that ifdef back.
>>>>
>>>
>>> The problem is because is_32bit() can still return true even when
>>> CONFIG_VDSO32 is not set.
>>
>> Hmm, you're right. My config had CONFIG_COMPAT enabled.
>>
>> But that seems like a bug, if someone enables COMPAT on ppc64le they are
>> almost certainly going to want VDSO32 as well.
>>
>> So I think I'll do a lead up patch as below.
> 
> Ah yes, and with that then no need to consider the case where 
> is_32bit_task() is true and CONFIG_VDSO32 is not selected.
> 
> I'll update my leading series accordingly.

I meant follow up series.

Christophe
> 
> Christophe
> 
>>
>> cheers
>>
>> diff --git a/arch/powerpc/platforms/Kconfig.cputype 
>> b/arch/powerpc/platforms/Kconfig.cputype
>> index d4fd109f177e..cf2da1e401ef 100644
>> --- a/arch/powerpc/platforms/Kconfig.cputype
>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>> @@ -501,13 +501,12 @@ endmenu
>>   config VDSO32
>>       def_bool y
>> -    depends on PPC32 || CPU_BIG_ENDIAN
>> +    depends on PPC32 || COMPAT
>>       help
>>         This symbol controls whether we build the 32-bit VDSO. We 
>> obviously
>>         want to do that if we're building a 32-bit kernel. If we're 
>> building
>> -      a 64-bit kernel then we only want a 32-bit VDSO if we're 
>> building for
>> -      big endian. That is because the only little endian 
>> configuration we
>> -      support is ppc64le which is 64-bit only.
>> +      a 64-bit kernel then we only want a 32-bit VDSO if we're also 
>> enabling
>> +      COMPAT.
>>   choice
>>       prompt "Endianness selection"
>>