[Bug runtime/13289] New: %m/%M printf formatting operators access memory incorrectly

["dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13289

             Bug #: 13289
           Summary: %m/%M printf formatting operators access memory
                    incorrectly
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sourceware.org
        ReportedBy: dsmith@redhat.com
    Classification: Unclassified


While working on bug #12341 on s390x, I found that running the memory1.exp test
would crash the system.  After lots of debugging, I found that the %m/%M printf
formatting operators were accessing memory incorrectly.

When the %m/%M formatting operators are used, translate.cxx emits code that
uses deref_buffer() to validate whether the memory used at the address can be
accessed safely.  If the works, the code in _stp_vsnprintf() actually reads the
memory to put in the output buffer.  However, the _stp_vsnprintf() code
accesses the memory directly, instead of using deref().

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