[Bug other/55307] New: libgcc's __cpu_indicator_init does not check for avx correctly

[Bug other/55307] New: libgcc's __cpu_indicator_init does not check for avx correctly

[luto at mit dot edu]

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/

[Bug target/55307] libgcc's __cpu_indicator_init does not check for avx correctly

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-11-13
          Component|other                       |target
                 CC|                            |areg.melikadamyan at gmail
                   |                            |dot com, hjl.tools at gmail
                   |                            |dot com
     Ever Confirmed|0                           |1
   Target Milestone|---                         |4.8.0

[Bug target/55307] libgcc's __cpu_indicator_init does not check for avx correctly

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.0                       |4.8.1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-22 14:45:13 UTC ---
GCC 4.8.0 is being released, adjusting target milestone.

[Bug target/55307] libgcc's __cpu_indicator_init does not check for avx correctly

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.1                       |4.8.2

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.1 has been released.

[Bug target/55307] libgcc's __cpu_indicator_init does not check for avx correctly

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.2                       |4.8.3

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.2 has been released.

[Bug target/55307] libgcc's __cpu_indicator_init does not check for avx correctly

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.3                       |---

[Bug target/55307] libgcc's __cpu_indicator_init does not check for avx correctly

[noloader at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55307

Jeffrey Walton <noloader at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |noloader at gmail dot com

--- Comment #4 from Jeffrey Walton <noloader at gmail dot com> ---
Forgive my ignorance... Is __builtin_cpu_supports really __builtin_os_supports?
If we want to test CPU support (rather than OS support), then can it be done
with the built-ins?

Also, the documentation at
https://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/X86-Built-in-Functions.html does
not mention that this is in fact OS support, and not CPU support.