What does "Got an error handling event: Dwarf Error: Cannot find type of die" mean?

Question

I'm trying to debug a hang on an old Apple PowerMac G5. The program is C++11, and it was created using MacPorts GCC 5.4. MacPorts also supplies the debugger, which is GDB 6.3.

Under the debugger I see:

...
Catchpoint 1 (exception thrown).
Catchpoint 1 (exception caught), throw location assert.cpp:33, catch location unknown, exception type Botan::Exception
0x009903ec      110           { ::operator delete(__p); }
(gdb) c
Continuing.
Util load/store ran 229 tests all ok
Util round_down ran 6 tests in 0.11 msec all ok
Util round_up ran 11 tests in 22.56 sec all ok
Die: DW_TAG_unspecified_type (abbrev = 3, offset = 247)
        has children: FALSE
        attributes:
                DW_AT_name (DW_FORM_string) string: "decltype(nullptr)"
warning: Got an error handling event: "Dwarf Error: Cannot find type of die [in module /Users/botan/libbotan-1.11.35.35.dylib]".

After the above, things just hang. I can CTRL+C and Continue, but I seem to flop around _Unwind_RaiseException () and _Unwind_GetIPInfo ().

What does Got an error handling event: "Dwarf Error: Cannot find type of die mean?

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I've found a couple of related questions, but they are not very satisfying and don't explain much:

• Dwarf Error: Cannot find DIE
• iceweasel: randomly crashes by receiving from X the following: ABORT: Request 155.34: BadLength

I also can't seem to get a decent backtrace:

(gdb) bt full
#0  0x009903ec in __cxa_throw () at ext/new_allocator.h:110
No symbol table info available.
Die: DW_TAG_unspecified_type (abbrev = 3, offset = 247)
        has children: FALSE
        attributes:
                DW_AT_name (DW_FORM_string) string: "decltype(nullptr)"
Dwarf Error: Cannot find type of die [in module /Users/botan/libbotan-1.11.35.35.dylib]