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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 1/16] ARM Add ARM 920T identifiers
Date: Tue, 26 May 2009 11:16:18 +0100
References: <20090423171503.GC4629@derik>
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To: qemu-devel@nongnu.org
Cc: Laurent Desnogues <laurent.desnogues@gmail.com>, Vincent Sanders <vince@kyllikki.org>

> > It could be a major problem if you start playing with ARM/Thumb
> > interworking.
>
> I'm curious.  How would code built for ARMv4T interworking fail on an
> ARMv5T emulator?

Usually the reverse is true - code works on v5, but fails on v4t.
However the following will work on armv4t and fail on armv5:

test:
adr r0, 1f
orr r0, r0, #1
str r0, [sp, #-4]!
ldr pc, [sp], #4
1:
bx lr

Admittedly this is a fairly contrived example, but the circumstances aren't 
completely implausible. Imagine someone using the low bit of a pointer as an 
additional flag, and relying on the hardware ignoring that bit.

Paul