linux-kernel - Re: [PATCH] powerpc: Make set_endian() return EINVAL when not supporting little endian

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Date:   Thu, 26 Aug 2021 06:55:49 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc: Make set_endian() return EINVAL when not
 supporting little endian

Le 26/08/2021 à 05:41, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>> There is no point in modifying MSR_LE bit on CPUs not supporting
>> little endian.
> 
> Isn't that an ABI break?

Or an ABI fix ? I don't know.

My first thought was that all other 32 bits architectures were returning -EINVAL, but looking at the 
man page of prctl, it is explicit that this is powerpc only.

> 
> set_endian(PR_ENDIAN_BIG) should work on a big endian CPU, even if it
> does nothing useful.

Fair enough. But shouldn't in that case get_endian() return PR_ENDIAN_BIG instead of returning EINVAL ?

We can do one or the other, but I think it should at least be consistant between them, shouldn't it ?

Christophe