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

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Date:   Mon, 2 Sep 2019 11:42:39 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Michael Ellerman <mpe@...erman.id.au>
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>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v7 5/6] powerpc/64: Make COMPAT user-selectable disabled
 on littleendian by default.

On Mon, 02 Sep 2019 12:03:12 +1000
Michael Ellerman <mpe@...erman.id.au> wrote:

> 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.

I have seen a piece of software that workarounds code issues on 64bit
by always compiling 32bit code. So it does work in some way. Also it
has been pointed out that you can still switch to BE even with the
'fast-switch' removed.

> 
> 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.

I don't really care either way.

Thanks

Michal

> 
> 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