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

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Date:   Thu, 12 Sep 2019 20:02:16 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Michal Suchanek <msuchanek@...e.de>, linuxppc-dev@...ts.ozlabs.org
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Nicholas Piggin <npiggin@...il.com>,
        Breno Leitao <leitao@...ian.org>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Firoz Khan <firoz.khan@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Stanley <joel@....id.au>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Michael Neuling <mikey@...ling.org>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Russell Currey <ruscur@...sell.cc>,
        Diana Craciun <diana.craciun@....com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Hildenbrand <david@...hat.com>,
        Allison Randal <allison@...utok.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v8 5/7] powerpc/64: make buildable without CONFIG_COMPAT



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