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

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Date:   Thu, 27 Aug 2020 23:19:44 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        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

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.

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"