[Bug libc/13583] New: AVX check not done correctly for strcasecmp

["delroth at gmail dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13583

             Bug #: 13583
           Summary: AVX check not done correctly for strcasecmp
           Product: glibc
           Version: 2.15
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: delroth@gmail.com
    Classification: Unclassified


According to Intel manuals, checking for AVX has to be done by checking AVX and
OS XSAVE support in CPUID + XFEATURE_ENABLED_MASK via xgetbv. However, for
strcasecmp, AVX is checked by testing the AVX bit in the cpuid.

This makes systems using glibc-2.15 unbootable under current versions of Xen
when the CPU supports AVX because Xen does not have XSAVE support. On these
systems, strcasecmp fails with a SIGILL when executing vmovdqa.

Bad check is here:
http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86_64/multiarch/strcmp.S;h=f93c83d7d469085029018dcf0d7f2eaadb05a44f;hb=HEAD#l108

Example of a good check:
http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86_64/dl-trampoline.S;h=6523c92945a59e6a5eefa3cfb2e0c58dfa99fd44;hb=HEAD#l137

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