linux-kernel - Re: [PATCH] ARM: disallow ARM

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Message-ID: <4112999.Nl7pxYH1YF@wuerfel>
Date:   Fri, 16 Dec 2016 22:51:08 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Jonas Jensen <jonas.jensen@...il.com>
Subject: Re: [PATCH] ARM: disallow ARM_THUMB for ARMv4 builds

On Friday, December 16, 2016 5:20:22 PM CET Ard Biesheuvel wrote:
> 
> Can't we use the old
> 
> tst lr, #1
> moveq pc, lr
> bx lr
> 
> trick? (where bx lr needs to be emitted as a plain opcode to hide it
> from the assembler)
> 

Yes, that should work around the specific problem in theory, but back
when Jonas tried it, it still didn't work. There may also be other
problems in that configuration.

	Arnd