[Bug dyninst/15306] New: stapdyn IRPC on terminated process, child SEGV

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

http://sourceware.org/bugzilla/show_bug.cgi?id=15306

             Bug #: 15306
           Summary: stapdyn IRPC on terminated process, child SEGV
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dyninst
        AssignedTo: systemtap@sourceware.org
        ReportedBy: jistone@redhat.com
                CC: adrian.m.negreanu@intel.com
    Classification: Unclassified


Probing process(".../libc.so.6").function("*") leads to dyninst complaining
about "IRPC on terminated process" and stapdyn reports the child SEGVed.

The IRPC failure is while stapdyn is attempting the oneTimeCode to run
stp_dyninst_shm_connect in the child process.

The SEGV is from enter_dyninst_uprobe doing atomic_read(session_state()), which
gdb presents as atomic_read (v=0x0).

So it seems that this probe is firing in early glibc setup code, before that
code for shm_connect has even had a chance to run.  The session_state is in shm
since it's shared across all processes, so the pointer will be invalid this
early.  We'll need to guard against this condition in the probe prologue.

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