linux-kernel - Re: [PATCH] random: vDSO: Redefine PAGE_SIZE and PAGE

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Message-ID: <0085b19d-bb87-45bc-8a74-7464316f86a1@csgroup.eu>
Date: Thu, 29 Aug 2024 17:00:17 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Vincenzo Frascino <vincenzo.frascino@....com>,
 Arnd Bergmann <arnd@...db.de>, "Jason A . Donenfeld" <Jason@...c4.com>
Cc: Theodore Ts'o <tytso@....edu>, Andy Lutomirski <luto@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] random: vDSO: Redefine PAGE_SIZE and PAGE_MASK

Hi Vincenzo,

Le 29/08/2024 à 14:01, Vincenzo Frascino a écrit :
> Hi Christophe,
> 
> On 27/08/2024 18:14, Christophe Leroy wrote:
>>
>>
>> Le 27/08/2024 à 18:05, Vincenzo Frascino a écrit :
>>> Hi Christophe,
>>>
>>> On 27/08/2024 11:49, Christophe Leroy wrote:
>>>
>>> ...
> 
> ...
> 
>>>
>>> Could you please clarify where minmax is needed? I tried to build Jason's master
>>> tree for x86, commenting the header and it seems building fine. I might be
>>> missing something.
>>
>> Without it:
>>
>>    VDSO32C arch/powerpc/kernel/vdso/vgetrandom-32.o
>> In file included from /home/chleroy/linux-powerpc/lib/vdso/getrandom.c:11,
>>                   from <command-line>:
> ...
> 
>>
>>
>>>
>>>> Same for ARRAY_SIZE(->reserved) by the way, easy to do opencode, we also have it
>>>> only once
>>>>
>>>
>>> I have a similar issue to figure out why linux/array_size.h and
>>> uapi/linux/random.h are needed. It seems that I can build the object without
>>> them. Could you please explain?
>>
>> Without linux/array_size.h:
>>
>>    VDSO32C arch/powerpc/kernel/vdso/vgetrandom-32.o
>> In file included from <command-line>:
>> /home/chleroy/linux-powerpc/lib/vdso/getrandom.c: In function
>> '__cvdso_getrandom_data':
>> /home/chleroy/linux-powerpc/lib/vdso/getrandom.c:89:40: error: implicit
> If this is the case, those headers should be defined for the powerpc
> implementation only. The generic implementation should be interpreted as the
> minimum common denominator in between all the architectures for what concerns
> the headers.
> 

Sorry, I disagree. You can't rely on necessary headers being included 
indirectly by other arch specific headers. getrandom.c uses 
ARRAY_SIZE(), it must include the header that defines ARRAY_SIZE().

At the moment, on x86 you get linux/array.h by change through the 
following chain, that the reason why the build doesn't break:

In file included from ./include/linux/kernel.h:16,
                  from ./include/linux/cpumask.h:11,
                  from ./arch/x86/include/asm/cpumask.h:5,
                  from ./arch/x86/include/asm/msr.h:11,
                  from ./arch/x86/include/asm/vdso/gettimeofday.h:19,
                  from ./include/vdso/datapage.h:164,
                  from 
arch/x86/entry/vdso/../../../../lib/vdso/getrandom.c:9,

 From my point of view you can't expect such a chain from each architecture.

Christophe