[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [Bug 1713066] Re: Incorrect handling of aarch64 ldp in some
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [Bug 1713066] Re: Incorrect handling of aarch64 ldp in some cases |
Date: |
Tue, 29 Aug 2017 11:47:27 -0000 |
Richard Henderson has posted a patch which should fix this:
http://patchwork.ozlabs.org/patch/806051/
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1713066
Title:
Incorrect handling of aarch64 ldp in some cases
Status in QEMU:
New
Bug description:
In some cases the ldp instruction (and presumably other multi-register
loads and stores) can behave incorrectly.
Given the following instruction:
ldp x0, x1, [x0]
This will load two 64 bit values from memory, however if each location
to load is on a different page and the second page is unmapped this
will raise an exception. When this happens x0 has already been updated
so after the exception handler has run the operating system will try
to rerun the instruction. QEMU will now try to perform an invalid load
and raise a new exception.
I believe this is incorrect as section D.1.14.5 of the ARMv8 reference
manual B.a states that, on taking an exception, registers used in the
generation of addresses are restored to their initial value, so x0
shouldn't be changed, where x1 can be un an unknown state.
I found the issue running FreeBSD with the cortex-strings
implementation of memcpy. This uses a similar instruction when copying
between 64 and 96 bytes.
I've observed this on:
QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.14), Copyright (c)
2003-2008 Fabrice Bellard
And checked I still get the same behaviour on:
QEMU emulator version 2.9.94 (v2.10.0-rc4-dirty)
Git revision: 248b23735645f7cbb503d9be6f5bf825f2a603ab
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1713066/+subscriptions