From: Alexander Richardson <1916269@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1916269] [NEW] TCG: QEMU raises exception on SSE4.2 CRC32 instruction in kernel
Date: Fri, 19 Feb 2021 17:09:52 -0000 [thread overview]
Message-ID: <161375459275.29060.15778429539023668893.malonedeb@soybean.canonical.com> (raw)
Public bug reported:
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.
** Affects: qemu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1916269
Title:
TCG: QEMU raises exception on SSE4.2 CRC32 instruction in kernel
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 reply other threads:[~2021-02-19 17:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 17:09 Alexander Richardson [this message]
2021-04-22 10:41 ` [Bug 1916269] Re: TCG: QEMU raises exception on SSE4.2 CRC32 instruction in kernel Alexander Richardson
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
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