libunwind Cursor.step() return values

[Phil Muldoon <pmuldoon at redhat dot com>]

I've been looking at a fd 0 close when opening a corefile on x86 via 
fhpd. The last few of the console trace are:

-Dec-07 10:13:10 AM lib.unwind.Cursor <init>
FINE: lib.unwind.Cursor@54e690 Create Cursor

6-Dec-07 10:13:10 AM lib.unwind.UnwindX86 step
FINE: lib.unwind.UnwindX86@376460 step cursor: 0x1ccc00

6-Dec-07 10:13:10 AM frysk.stack.LibunwindAddressSpace findProcInfo
FINE: Entering findProcInfo, ip: 804854a

6-Dec-07 10:13:10 AM frysk.stack.LibunwindAddressSpace getElfImage
FINE: frysk.stack.LibunwindAddressSpace@28ab40 Entering getElfImage, addr: 0x804854a

6-Dec-07 10:13:10 AM frysk.stack.LibunwindAddressSpace getElfImage
FINEST: Handling regular map name: 
6-Dec-07 10:13:10 AM frysk.stack.LibunwindAddressSpace getElfImage
FINER: Leaving getElfImage
6-Dec-07 10:13:10 AM frysk.stack.LibunwindAddressSpace findProcInfo
FINEST: Obtained elfImage: Bad Elf Image, ret: -1

6-Dec-07 10:13:10 AM lib.unwind.UnwindX86 createProcInfoFromElfImage
FINE: lib.unwind.UnwindX86@376460 Pre unw_get_unwind_table

6-Dec-07 10:13:10 AM lib.unwind.UnwindX86 createProcInfoFromElfImage
FINE: lib.unwind.UnwindX86@376460 Post unw_get_unwind_table

6-Dec-07 10:13:10 AM frysk.stack.LibunwindAddressSpace findProcInfo
FINE: post procInfo ProcInfo Error: -1

6-Dec-07 10:13:10 AM lib.unwind.Cursor unwind
FINEST: lib.unwind.Cursor@42dac8, unwind, step returned: -1


And the exception returned after that is:

(fhpd) ERROR: Could not read from command line
Bad file descriptorException in thread "main" frysk.sys.Errno$Ebadf: tcsetattr: Bad file descriptor (fd 0)
  at frysk.sys.termios.Termios.set(fhpd)
  at frysk.sys.termios.Termios.set(fhpd)
  at frysk.util.PtyTerminal$1.start(fhpd)
  at java.lang.Runtime.runShutdownHooks(libgcj.so.8rh)
  at java.lang.Runtime.exitNoChecks(libgcj.so.8rh)
  at java.lang.Runtime.exitNoChecksAccessor(libgcj.so.8rh)

Looking at: ~/frysk/frysk-sys/lib/unwind/Cursor.java I see this code in question:


   public Cursor unwind() {
       logger.log(Level.FINE, "{0}, unwind\n", this);

       //XXX: Don't unwind if no more, or unknown frames.
       if (step == 0 || getIP() == 0)
           return null;

       Cursor newCursor = new Cursor(addressSpace,
                                     unwinder.copyCursor(cursor), unwinder);

       step = newCursor.step();

       logger.log(Level.FINEST, "{0}, unwind, step returned: {1}\n",
                  new Object[] {this, new Integer(step)});

       if (step > 0)
           return newCursor;

       return null;
   }

I see that step == 0 means no more or unknown frames. Further down the:

step = newCursor.step()

returns -1 in this case. What does that mean in this case?

Regards

Phil