[Bug libc/17259] New: sysdeps/x86_64/cacheinfo.c:intel_check_word corrupts rbx and another register

[Bug libc/17259] New: sysdeps/x86_64/cacheinfo.c:intel_check_word corrupts rbx and another register

[pageexec at gmail dot com]

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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[Bug libc/17259] sysdeps/x86_64/cacheinfo.c:intel_check_word may corrupt rbx

[hjl.tools at gmail dot com]

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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[Bug libc/17259] sysdeps/x86_64/cacheinfo.c:intel_check_word may corrupt rbx

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17259

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  b4acef1ffe2e1ba6c608f31c1954a8100d3eabb0 (commit)
      from  61b1ef6e7cc4518cdadb808dfa78980cc15a63c3 (commit)

Those revisions listed above that are new to this repository have
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b4acef1ffe2e1ba6c608f31c1954a8100d3eabb0

commit b4acef1ffe2e1ba6c608f31c1954a8100d3eabb0
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Tue Aug 12 17:02:51 2014 -0700

    Replace cpuid asm statement with __cpuid_count

    The compiler doesn't know that the cpuid asm statement in intel_check_word
    will trash RBX.  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.  This patch replaces it with __cpuid_count.

        [BZ #17259]
        * sysdeps/x86_64/cacheinfo.c (intel_check_word): Replace cpuid
        asm statement with __cpuid_count.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                  |    6 ++++++
 NEWS                       |    3 ++-
 sysdeps/x86_64/cacheinfo.c |    4 +---
 3 files changed, 9 insertions(+), 4 deletions(-)

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[Bug libc/17259] sysdeps/x86_64/cacheinfo.c:intel_check_word may corrupt rbx

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17259

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
            Version|unspecified                 |2.20
         Resolution|---                         |FIXED
   Target Milestone|---                         |2.20

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> ---
Fixed for 2.20.

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