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

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Date:   Tue, 3 Sep 2019 05:21:49 +0000
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Michal Suchanek <msuchanek@...e.de>, linuxppc-dev@...ts.ozlabs.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        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 v7 5/6] powerpc/64: Make COMPAT user-selectable disabled
 on littleendian by default.



On 09/02/2019 11:53 PM, Michael Ellerman wrote:
> Segher Boessenkool <segher@...nel.crashing.org> writes:
>> On Mon, Sep 02, 2019 at 12:03:12PM +1000, Michael Ellerman 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.
>                  ^
>                  v2
> 
>> There of course is a lot of powerpcle-* support.  The ABI used for it
>> on linux is the SYSV ABI, just like on BE 32-bit.
> 
> I was talking about ELFv2, which is 64-bit only. But that was based on
> me thinking we had a hard assumption in the kernel that ppc64le kernels
> always expect ELFv2 userland. Looking at the code though I was wrong
> about that, it looks like we will run little endian ELFv1 binaries,
> though I don't think anyone is testing it.
> 
>> There also is specific powerpcle-linux support in GCC, and in binutils,
>> too.  Also, config.guess/config.sub supports it.  Half a year ago this
>> all built fine (no, I don't test it often either).
>>
>> I don't think glibc supports it though, so I wonder if anyone builds an
>> actual system with it?  Maybe busybox or the like?
>>
>>> 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.
>>
>> What about actual 32-bit LE systems?  Does anyone still use those?
> 
> Not that I've ever heard of.
> 

We dropped support from 32-bit LE at least with a1f3ae3fe8a1 
("powerpc/32: Use stmw/lmw for registers save/restore in asm").

Discussion about it can be found at 
https://patchwork.ozlabs.org/patch/899465/

Christophe