linux-kernel - Re: [PATCH v2] Make iwmmxt.S support Clang's integrated assembler

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Message-ID: <CAKwvOdkXz5wOwKQDsi5jt21ov3xETSByAqxGLQ=7U6Gsp46zcQ@mail.gmail.com>
Date:   Tue, 10 Nov 2020 11:26:32 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Jian Cai <jiancai@...gle.com>, Manoj Gupta <manojgupta@...gle.com>,
        Luis Lozano <llozano@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <natechancellor@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Make iwmmxt.S support Clang's integrated assembler

On Mon, Nov 9, 2020 at 11:36 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> BE32 != BE8

Oh? Sorry, what does BE8 stand for?  arch/arm/mm/Kconfig says:

CONFIG_CPU_ENDIAN_BE8
Support for the BE-8 (big-endian) mode on ARMv6 and ARMv7 processors.

vs:
CPU_ENDIAN_BE32
Support for the BE-32 (big-endian) mode on pre-ARMv6 processors.

So BE8 seems newer?  It looks like in my tests, enabling
CPU_BIG_ENDIAN via menuconfig enabled CPU_ENDIAN_BE8.

>
> Please use, e.g., ixp4xx_defconfig with IWMMXT and BE enabled. It
> seems like .inst does the right thing here, i.e., the assembler knows
> that it should emit BE for BE32 and LE for BE8, but it needs to be
> confirmed.

Ah and ixp4xx_defconfig selects CPU_ENDIAN_BE32.  Yep, and the
disassemblies of those match, too.
-- 
Thanks,
~Nick Desaulniers