$ perl6-gdb-m -e 'say uniname(nqp::null_s)'
================================================================================================
This is Rakudo Perl 6 running in the GNU debugger, which often allwos to generate useful back-
traces to debug or report issues in Rakudo, the MoarVM backend or the currently running code.

The currently used MoarVM backend is not compiled with debugging symbols, you might want to
reconfigure and reinstall MoarVM with --debug enabled.

This Rakudo version is 2015.3.186.g.260.e.3.cd built on MoarVM version 2015.3.64.g.79.b.6087,
running on ubuntu (14.4.2.LTS.Trusty.Tahr) / linux (81.Ubuntu.SMP.Tue.Mar.24.19.29.48.UTC.2015)

Type `bt full` to generate a backtrace if applicable, type `q` to quite or `help` for help.
------------------------------------------------------------------------------------------------
Reading symbols from /home/froggs/dev/nqp/install/bin/moar...done.
Starting program: /home/froggs/dev/nqp/install/bin/moar --execname=/home/froggs/dev/nqp/install/bin/perl6-gdb-m --libpath=/home/froggs/dev/nqp/install/share/nqp/lib --libpath=/home/froggs/dev/nqp/install/share/perl6/lib --libpath=/home/froggs/dev/nqp/install/share/perl6/runtime /home/froggs/dev/nqp/install/share/perl6/runtime/perl6.moarvm -e say\ uniname\(nqp::null_s\)
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
MVM_interp_run (tc=tc@entry=0x6036c0, initial_invoke=0x21b5480, invoke_data=0x0) at src/core/interp.c:1488
1488	                GET_REG(cur_op, 0).i64 = MVM_string_graphs(tc, GET_REG(cur_op, 2).s);
(gdb)