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From: "luto at mit dot edu" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug other/55307] New: libgcc's __cpu_indicator_init does not check for avx correctly Date: Tue, 13 Nov 2012 05:21:00 -0000 [thread overview] Message-ID: <bug-55307-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307 Bug #: 55307 Summary: libgcc's __cpu_indicator_init does not check for avx correctly Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: other AssignedTo: unassigned@gcc.gnu.org ReportedBy: luto@mit.edu [this is a libgcc bug, and I haven't tested it -- the test is a PITA.] One might expect that __builtin_cpu_supports("avx") would only return true if avx is usable. Unfortunately, it returns true iff avx is implemented by the cpu, regardless of whether it should be expected to work. The code should check for osxsave and then use xgetbv to see if ymm state is available. This is more or less the same bug as glibc bug 13007 [1]. There's an intel blog post on the subject at [2]. It's likely to result in crashes if old kernels are run on new hardware. Curiously, the code in gcc/testsuite/gcc.target/i386/avx-check.h appears correct. I suspect it's never been run with ymm state disabled. [1] http://sourceware.org/bugzilla/show_bug.cgi?id=13007 [2] http://software.intel.com/en-us/blogs/2011/04/14/is-avx-enabled/
next reply other threads:[~2012-11-13 5:21 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-11-13 5:21 luto at mit dot edu [this message] 2012-11-13 14:55 ` [Bug target/55307] " hjl.tools at gmail dot com 2013-03-22 14:48 ` jakub at gcc dot gnu.org 2013-05-31 10:59 ` jakub at gcc dot gnu.org 2013-10-16 9:51 ` jakub at gcc dot gnu.org 2015-06-22 14:25 ` rguenth at gcc dot gnu.org 2015-08-19 17:04 ` noloader at gmail dot com
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