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Re: [Qemu-arm] [Qemu-devel] [PULL 08/13] target/arm: Pull Thumb insn wor

From: Peter Maydell
Subject: Re: [Qemu-arm] [Qemu-devel] [PULL 08/13] target/arm: Pull Thumb insn word loads up to top level
Date: Mon, 11 Dec 2017 15:37:09 +0000

On 10 December 2017 at 18:24, Peter Maydell <address@hidden> wrote:
> On 8 December 2017 at 23:09, Emilio G. Cota <address@hidden> 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.

-- PMM

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