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From: "aurelien at aurel32 dot net" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug string/29611] New: Optimized AVX2 string functions unconditionally use BMI2 instructions
Date: Sun, 25 Sep 2022 08:17:58 +0000 [thread overview]
Message-ID: <bug-29611-131@http.sourceware.org/bugzilla/> (raw)
https://sourceware.org/bugzilla/show_bug.cgi?id=29611
Bug ID: 29611
Summary: Optimized AVX2 string functions unconditionally use
BMI2 instructions
Product: glibc
Version: 2.31
Status: NEW
Severity: critical
Priority: P2
Component: string
Assignee: goldstein.w.n at gmail dot com
Reporter: aurelien at aurel32 dot net
Target Milestone: ---
Starting with commit aaa23c350715 ("x86: Optimize strlen-avx2.S"), the
optimized AVX2 string functions uses the bzhiq and sarxl instructions, causing
SIGILL on CPU which does have AVX2 instructions, but does not have BMI2
instructions.
For instance this happens on a Intel(R) Core(TM) i3-4000M CPU @ 2.40GHz:
cpu family : 6
model : 60
model name : Intel(R) Core(TM) i3-4000M CPU @ 2.40GHz
stepping : 3
microcode : 0x12
It *seems* that upgrading the microcode to level 0x28 fixes the issue. That
said why it is acceptable to have performance issues with an older microcode,
this should not prevent a system to boot.
This has been reported to affected Debian Bullseye (as the optimization have
been backported to the upstream release/2.31/master tree), Debian Sid and
Fedora Rawhide.
I think that the code should probably be reverted, or at least the IFUNC
functions using BMI2 instructions should be probably be gated by the CPU flag.
It also poses the question of backporting optimizations to stable release
trees.
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next reply other threads:[~2022-09-25 8:17 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-25 8:17 aurelien at aurel32 dot net [this message]
2022-09-25 11:40 ` [Bug string/29611] " aurelien at aurel32 dot net
2022-09-25 13:57 ` goldstein.w.n at gmail dot com
2022-09-25 14:09 ` goldstein.w.n at gmail dot com
2022-09-25 14:11 ` goldstein.w.n at gmail dot com
2022-09-26 5:18 ` aurelien at aurel32 dot net
2022-09-26 5:19 ` aurelien at aurel32 dot net
2022-09-26 14:05 ` goldstein.w.n at gmail dot com
2022-09-26 17:52 ` hjl.tools at gmail dot com
2022-09-28 14:01 ` skpgkp2 at gmail dot com
2022-09-28 14:01 ` skpgkp2 at gmail dot com
2022-09-28 15:01 ` goldstein.w.n at gmail dot com
2022-09-28 15:10 ` aurelien at aurel32 dot net
2022-09-28 15:52 ` goldstein.w.n at gmail dot com
2022-09-28 15:57 ` skpgkp2 at gmail dot com
2022-09-28 23:14 ` skpgkp2 at gmail dot com
2022-09-28 23:15 ` skpgkp2 at gmail dot com
2022-09-29 1:26 ` hjl.tools at gmail dot com
2022-09-29 1:59 ` cvs-commit at gcc dot gnu.org
2022-09-29 1:59 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:00 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:00 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:34 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:34 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:35 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:36 ` cvs-commit at gcc dot gnu.org
2022-09-29 2:36 ` cvs-commit at gcc dot gnu.org
2022-09-29 3:11 ` cvs-commit at gcc dot gnu.org
2022-09-29 3:11 ` cvs-commit at gcc dot gnu.org
2022-09-29 23:26 ` sam at gentoo dot org
2022-09-30 20:02 ` hjl.tools at gmail dot com
2022-10-01 15:23 ` aurelien at aurel32 dot net
2022-10-01 16:24 ` goldstein.w.n at gmail dot com
2022-10-01 16:51 ` goldstein.w.n at gmail dot com
2022-10-01 16:52 ` aurelien at aurel32 dot net
2022-10-03 21:46 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:46 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:47 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:47 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:47 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:47 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:47 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:51 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:55 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:55 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:55 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:56 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:56 ` cvs-commit at gcc dot gnu.org
2022-10-03 21:56 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:02 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:05 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:05 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:05 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:05 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:05 ` cvs-commit at gcc dot gnu.org
2022-10-03 22:05 ` cvs-commit at gcc dot gnu.org
2022-10-04 5:05 ` aurelien at aurel32 dot net
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