linux-kernel - Re: [PATCH v8 5/7] powerpc/64: make buildable without CONFIG

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Message-ID: <758324b9-203b-ec4b-affc-a30aefc9ea23@c-s.fr>
Date:   Thu, 12 Sep 2019 21:36:11 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Breno Leitao <leitao@...ian.org>,
        Michael Neuling <mikey@...ling.org>,
        Diana Craciun <diana.craciun@....com>,
        Firoz Khan <firoz.khan@...aro.org>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Joel Stanley <joel@....id.au>, Arnd Bergmann <arnd@...db.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v8 5/7] powerpc/64: make buildable without CONFIG_COMPAT



Le 12/09/2019 à 20:26, Michal Suchánek a écrit :
> On Thu, 12 Sep 2019 20:02:16 +0200
> Christophe Leroy <christophe.leroy@....fr> wrote:
> 
>> Le 12/09/2019 à 19:26, Michal Suchanek a écrit :
>>> There are numerous references to 32bit functions in generic and 64bit
>>> code so ifdef them out.
>>>
>>> Signed-off-by: Michal Suchanek <msuchanek@...e.de>
>>> ---
>>> v2:
>>> - fix 32bit ifdef condition in signal.c
>>> - simplify the compat ifdef condition in vdso.c - 64bit is redundant
>>> - simplify the compat ifdef condition in callchain.c - 64bit is redundant
>>> v3:
>>> - use IS_ENABLED and maybe_unused where possible
>>> - do not ifdef declarations
>>> - clean up Makefile
>>> v4:
>>> - further makefile cleanup
>>> - simplify is_32bit_task conditions
>>> - avoid ifdef in condition by using return
>>> v5:
>>> - avoid unreachable code on 32bit
>>> - make is_current_64bit constant on !COMPAT
>>> - add stub perf_callchain_user_32 to avoid some ifdefs
>>> v6:
>>> - consolidate current_is_64bit
>>> v7:
>>> - remove leftover perf_callchain_user_32 stub from previous series version
>>> v8:
>>> - fix build again - too trigger-happy with stub removal
>>> - remove a vdso.c hunk that causes warning according to kbuild test robot
>>> ---
>>>    arch/powerpc/include/asm/thread_info.h |  4 +--
>>>    arch/powerpc/kernel/Makefile           |  7 ++---
>>>    arch/powerpc/kernel/entry_64.S         |  2 ++
>>>    arch/powerpc/kernel/signal.c           |  3 +-
>>>    arch/powerpc/kernel/syscall_64.c       |  6 ++--
>>>    arch/powerpc/kernel/vdso.c             |  3 +-
>>>    arch/powerpc/perf/callchain.c          | 39 ++++++++++++++------------
>>>    7 files changed, 33 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
>>> index 8e1d0195ac36..c128d8a48ea3 100644
>>> --- a/arch/powerpc/include/asm/thread_info.h
>>> +++ b/arch/powerpc/include/asm/thread_info.h
>>> @@ -144,10 +144,10 @@ static inline bool test_thread_local_flags(unsigned int flags)
>>>    	return (ti->local_flags & flags) != 0;
>>>    }
>>>    
>>> -#ifdef CONFIG_PPC64
>>> +#ifdef CONFIG_COMPAT
>>>    #define is_32bit_task()	(test_thread_flag(TIF_32BIT))
>>>    #else
>>> -#define is_32bit_task()	(1)
>>> +#define is_32bit_task()	(IS_ENABLED(CONFIG_PPC32))
>>>    #endif
>>>    
>>>    #if defined(CONFIG_PPC64)
>>
>> [...]
>>
>>> +static inline int current_is_64bit(void)
>>> +{
>>> +	if (!IS_ENABLED(CONFIG_COMPAT))
>>> +		return IS_ENABLED(CONFIG_PPC64);
>>> +	/*
>>> +	 * We can't use test_thread_flag() here because we may be on an
>>> +	 * interrupt stack, and the thread flags don't get copied over
>>> +	 * from the thread_info on the main stack to the interrupt stack.
>>> +	 */
>>> +	return !test_ti_thread_flag(task_thread_info(current), TIF_32BIT);
>>> +}
>>
>>
>> Since at least commit ed1cd6deb013 ("powerpc: Activate
>> CONFIG_THREAD_INFO_IN_TASK")
>> [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ed1cd6d]
>> the above comment is wrong and current_is_64bit() is equivalent to
>> !is_32bit_task()
>>
>> See https://github.com/linuxppc/issues/issues/275
>>
>> Christophe
> 
> I aim at changing the code as little as possible here. A separate patch
> on top removing this function would be ok?

Yes I agree. By making prior to this patch a separate patch which drops 
current_is_64bit() would be good. And it would reduce the size of this 
patch by approximately one third.

Christophe

> 
> Thanks
> 
> Michal
>