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From: "pageexec at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/17259] New: sysdeps/x86_64/cacheinfo.c:intel_check_word corrupts rbx and another register
Date: Mon, 11 Aug 2014 23:29:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=17259

            Bug ID: 17259
           Summary: sysdeps/x86_64/cacheinfo.c:intel_check_word corrupts
                    rbx and another register
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: pageexec at gmail dot com
                CC: drepper.fsp at gmail dot com

the inline asm invoking cpuid tries to save/restore rbx itself but unlike its
i386 version, this one will actually corrupt (zero out) the top 32 bits of both
rbx and whatever register gets assigned to %1 due to the "xchg ebx,%1". this
code was probably simply copy-pasted from the i386 version. note that the same
file actually contains a proper implementation of cpuid as the __cpuid_count
macro that had been there some 2 years before this new and buggy 'invention'.

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