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From: "hjl.tools at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/17259] sysdeps/x86_64/cacheinfo.c:intel_check_word may corrupt rbx
Date: Tue, 12 Aug 2014 16:04:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=17259

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com
            Summary|sysdeps/x86_64/cacheinfo.c: |sysdeps/x86_64/cacheinfo.c:
                   |intel_check_word corrupts   |intel_check_word may
                   |rbx and another register    |corrupt rbx

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
There are

          asm volatile ("xchgl %%ebx, %1; cpuid; xchgl %%ebx, %1"
                : "=a" (eax), "=r" (ebx), "=c" (ecx), "=d" (edx)
                : "0" (4), "2" (round));

The only register compiler is aware of is RBX.  No other registers are
impacted.  We are lucky that it doesn't cause any problems since RBX
is also used by compiler for other purposes so that RBX is saved and
restored in intel_check_word.  We should just use __cpuid_count instead.

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