linux-kernel - Re: [PATCH v7 5/6] powerpc/64: Make COMPAT user-selectable disabled on littleendian by default.

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Message-ID: <87ftlftpy7.fsf@mpe.ellerman.id.au>
Date:   Mon, 02 Sep 2019 12:03:12 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michal Suchanek <msuchanek@...e.de>, linuxppc-dev@...ts.ozlabs.org
Cc:     Michal Suchanek <msuchanek@...e.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        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,
        Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: [PATCH v7 5/6] powerpc/64: Make COMPAT user-selectable disabled on littleendian by default.

Michal Suchanek <msuchanek@...e.de> writes:
> On bigendian ppc64 it is common to have 32bit legacy binaries but much
> less so on littleendian.

I think the toolchain people will tell you that there is no 32-bit
little endian ABI defined at all, if anything works it's by accident.

So I think we should not make this selectable, unless someone puts their
hand up to say they want it and are willing to test it and keep it
working.

cheers

> v3: make configurable
> ---
>  arch/powerpc/Kconfig | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 5bab0bb6b833..b0339e892329 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -264,8 +264,9 @@ config PANIC_TIMEOUT
>  	default 180
>  
>  config COMPAT
> -	bool
> -	default y if PPC64
> +	bool "Enable support for 32bit binaries"
> +	depends on PPC64
> +	default y if !CPU_LITTLE_ENDIAN
>  	select COMPAT_BINFMT_ELF
>  	select ARCH_WANT_OLD_COMPAT_IPC
>  	select COMPAT_OLD_SIGACTION
> -- 
> 2.22.0