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

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Date:   Fri, 28 Aug 2020 07:40:42 +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 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.

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"
>