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

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Date:   Thu, 12 Sep 2019 22:19:46 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     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>,
        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,
        Hari Bathini <hbathini@...ux.ibm.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v8 5/7] powerpc/64: make buildable without CONFIG_COMPAT

On Thu, 12 Sep 2019 21:36:11 +0200
Christophe Leroy <christophe.leroy@....fr> wrote:

> 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.

Indeed, removing it before makes this patch much cleaner.

Thanks

Michal