From: Alexander Richardson <1916269@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1916269] Re: TCG: QEMU raises exception on SSE4.2 CRC32 instruction in kernel
Date: Thu, 22 Apr 2021 10:41:43 -0000 [thread overview]
Message-ID: <161908810382.6637.2396062733185532941.malone@chaenomeles.canonical.com> (raw)
In-Reply-To: 161375459275.29060.15778429539023668893.malonedeb@soybean.canonical.com
Could someone familiar with the target/i386 decode logic could have a look at this? It should be a rather simple change to avoid the exception for the crc32 encoding. However, I am not familiar with x86 instruction encodings so it would take me a long time to come up with a correct patch.
Thanks!
** Summary changed:
- TCG: QEMU raises exception on SSE4.2 CRC32 instruction in kernel
+ TCG: QEMU incorrectly raises exception on SSE4.2 CRC32 instruction
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1916269
Title:
TCG: QEMU incorrectly raises exception on SSE4.2 CRC32 instruction
Status in QEMU:
New
Bug description:
If I run FreeBSD on QEMU 5.2 with TCG acceleration -cpu Nehalem, I get
a FPU exception when executing crc32
(https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253617). This is
not a problem with the default CPU (or KVM) since that does not
support SSE 4.2.
Attaching GDB shows this is triggered in
target/i386/tcg/translate.c:3067
/* simple MMX/SSE operation */
if (s->flags & HF_TS_MASK) {
gen_exception(s, EXCP07_PREX, pc_start - s->cs_base);
return;
}
However, according to
https://software.intel.com/sites/default/files/m/8/b/8/D9156103.pdf,
page 61 the CRC32 instruction works no matter what the value of the TS
bit.
The code sequence in question is:
0xffffffff8105a4de <+126>: f2 48 0f 38 f1 de crc32q %rsi,%rbx
0xffffffff8105a4e4 <+132>: f2 48 0f 38 f1 ca crc32q %rdx,%rcx.
This should work even with the FPU disabled.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1916269/+subscriptions
next prev parent reply other threads:[~2021-04-22 11:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 17:09 [Bug 1916269] [NEW] TCG: QEMU raises exception on SSE4.2 CRC32 instruction in kernel Alexander Richardson
2021-04-22 10:41 ` Alexander Richardson [this message]
2021-05-13 11:47 ` [Bug 1916269] Re: TCG: QEMU incorrectly raises exception on SSE4.2 CRC32 instruction Thomas Huth
2021-07-13 4:17 ` Launchpad Bug Tracker
2021-07-13 8:51 ` Alexander Richardson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=161908810382.6637.2396062733185532941.malone@chaenomeles.canonical.com \
--to=1916269@bugs.launchpad.net \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).