linux-kernel - Re: [PATCH] prctl: implement PR_GET

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Message-ID: <CAEdQ38FXam3sXKFc5-3WEgDDov0yayAWXK8hbuNjbSxJQ5QDVw@mail.gmail.com>
Date:   Sun, 5 Feb 2017 12:48:37 +0100
From:   Matt Turner <mattst88@...il.com>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Helge Deller <deller@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        Michael Kerrisk <mtk.manpages@...glemail.com>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] prctl: implement PR_GET_ENDIAN for all architectures

On Thu, Feb 2, 2017 at 12:12 AM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Tue, 2017-01-31 at 16:26 -0800, Andrew Morton wrote:
>> On Sat, 28 Jan 2017 12:13:10 +0100 Helge Deller <deller@....de>
>> wrote:
>>
>> > The prctl(PR_GET_ENDIAN) syscall was added to Kernel 2.6.18, but
>> > implemented for PowerPC only. This trivial patch adds support for
>> > this syscall for all other architectures.
>>
>> Seems reasonable.  I guess.  Why is this needed?
>
> I don't think it is other than for PPC.  If you're not variable endian
> (which is only PPC to date), then you should know a priori what endian
> you are from the #defines in userspace.

MIPS as well, but it seems strange to require the kernel to tell you
your endianness, when you can easily determine it yourself. Unless
there's something about this I don't understand.