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From: Peter Maydell <peter.maydell@linaro.org>
Date: Mon, 11 Dec 2017 15:37:09 +0000
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Subject: Re: [Qemu-devel] [PULL 08/13] target/arm: Pull Thumb insn word
 loads up to top level
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To: "Emilio G. Cota" <cota@braap.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Richard Henderson <richard.henderson@linaro.org>, qemu-arm <qemu-arm@nongnu.org>

On 10 December 2017 at 18:24, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 8 December 2017 at 23:09, Emilio G. Cota <cota@braap.org> wrote:
>> On Thu, Oct 12, 2017 at 17:03:31 +0100, Peter Maydell wrote:
>>> Refactor the Thumb decode to do the loads of the instruction words at
>>> the top level rather than only loading the second half of a 32-bit
>>> Thumb insn in the middle of the decode.
>
>> This commit breaks the debian-arm boot test (see [1]), boot dies at:
>>
>>> random: systemd urandom read with 4 bits of entropy available
>>> systemd[1]: Caught <SEGV>, core dump failed.
>>> systemd[1]: Freezing execution.
>>
>> Sorry I noticed this so late (-rc4), for a while I thought my development
>> was causing this and didn't pay much attention to it. However, just realised
>> the problem is present on master. Bisect log below.
>
> It's missed the deadline for getting fixed in 2.11, but I'll have
> a look at what's going on here.

This is a really bad bug -- we accidentally stopped generating UNDEF
for 32-bit Thumb2 instructions that should UNDEF (including things
like "first use of FPU with FPU disabled", which is probably why
systemd falls over). I wish we'd noticed this a week ago :-(

Patch coming in a moment, anyway.

thanks
-- PMM