Here's a backtrace that I can't make any sense of. Pay close attention to frame #30:
#0 0x00007fffed34175d in g_slice_alloc () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#1 0x00007fffed341be9 in g_slice_alloc0 () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007fffed407c57 in () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#3 0x00007fffed4086e7 in () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#4 0x00007fffed42663c in g_type_create_instance () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#5 0x00007fffed409398 in () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#6 0x00007fffed40ab15 in g_object_new_with_properties () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#7 0x00007fffed40b581 in g_object_new () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#8 0x00007fffee31fef8 in () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#9 0x00007fffee3c7779 in gtk_widget_get_style_context () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#10 0x00007fffee3c8f8d in gtk_widget_style_get_valist () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#11 0x00007fffee3c90d8 in gtk_widget_style_get () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#12 0x00007fffee1e855f in () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#13 0x00007fffee1e8658 in () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#14 0x00007fffee1e87b2 in () at /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
#15 0x00007fffed426677 in g_type_create_instance () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#16 0x00007fffed409398 in () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#17 0x00007fffed40ab15 in g_object_new_with_properties () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#18 0x00007fffed40b581 in g_object_new () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#19 0x00007fffe8caa03c in ()
#20 0x00007ffff7fcaf80 in null_args_callsite () at //home/cbwood/Projects/rakudobrew/moar-master/install/lib/libmoar.so
#21 0x000055555b7cdb10 in ()
--Type <RET> for more, q to quit, c to continue without paging--
#22 0x0000555555559ca0 in ()
#23 0x00007ffff7fcaf80 in null_args_callsite () at //home/cbwood/Projects/rakudobrew/moar-master/install/lib/libmoar.so
#24 0x000055555b7cdb10 in ()
#25 0x00007ffff7a02736 in MVM_frame_invoke
(tc=0x5555582822a0, static_frame=<optimized out>, callsite=0x7fffffffcad0, args=0x7fffeedec5b6, outer=<optimized out>, code_ref=<optimized out>, spesh_cand=<optimized out>) at src/core/frame.c:557
frame = 0x7ffff77ec0e8
chosen_bytecode = 0x33943 <error: Cannot access memory at address 0x33943>
spesh = <optimized out>
#26 0x0000555555559ca0 in ()
#27 0x00007ffff7f0e480 in inv_arg_callsite () at //home/cbwood/Projects/rakudobrew/moar-master/install/lib/libmoar.so
#28 0x0000555555559ca0 in ()
#29 0x00005555582822a8 in ()
#30 0x00007ffff79fa46d in MVM_interp_run (tc=0x10, tc@entry=0x555555559ca0, initial_invoke=0x85, invoke_data=0x7ffff7439a60, invoke_data@entry=0x7fffffffce70)
at src/core/interp.c:5241
op = 39520
LABELS =
{0x7ffff79e6565 <MVM_interp_run+229>, 0x7ffff79fb7f7 <MVM_interp_run+86903>, 0x7ffff79e67b5 <MVM_interp_run+821>, 0x7ffff79e67b5 <MVM_interp_run+821>, 0x7ffff79f7241 <MVM_interp_run+69057>, 0x7ffff79fb7e5 <MVM_interp_run+86885>, 0x7ffff79eb67a <MVM_interp_run+20986>, 0x7ffff79eeaf3 <MVM_interp_run+34419>, 0x7ffff79ee9f0 <MVM_interp_run+34160>, 0x7ffff79e9267 <MVM_interp_run+11751>, 0x7ffff79e922b <MVM_interp_run+11691>, 0x7ffff79e91f0 <MVM_interp_run+11632>, 0x7ffff79e91b3 <MVM_interp_run+11571>, 0x7ffff79e9176 <MVM_interp_run+11510>, 0x7ffff79e913a <MVM_interp_run+11450>, 0x7ffff79e90fe <MVM_interp_run+11390>, 0x7ffff79e90c2 <MVM_interp_run+11330>, 0x7ffff79ee86b <MVM_interp_run+33771>, 0x7ffff79ee82f <MVM_interp_run+33711>, 0x7ffff79ee7f3 <MVM_interp_run+33651>, 0x7ffff79ee7b8 <MVM_interp_run+33592>, 0x7ffff79ee776 <MVM_interp_run+33526>, 0x7ffff79ee734 <M--Type <RET> for more, q to quit, c to continue without paging--
VM_interp_run+33460>, 0x7ffff79ee6e7 <MVM_interp_run+33383>, 0x7ffff79ee683 <MVM_interp_run+33283>, 0x7ffff79eea2c <MVM_interp_run+34220>, 0x7ffff79ee986 <MVM_interp_run+34054>, 0x7ffff79ee923 <MVM_interp_run+33955>, 0x7ffff79ee8a6 <MVM_interp_run+33830>, 0x7ffff79eb148 <MVM_interp_run+19656>, 0x7ffff79eb0d8 <MVM_interp_run+19544>, 0x7ffff79eb061 <MVM_interp_run+19425>, 0x7ffff79eaff6 <MVM_interp_run+19318>, 0x7ffff79eb60c <MVM_interp_run+20876>, 0x7ffff79eb4f1 <MVM_interp_run+20593>, 0x7ffff79eb56d <MVM_interp_run+20717>, 0x7ffff79eb3d2 <MVM_interp_run+20306>, 0x7ffff79eb482 <MVM_interp_run+20482>, 0x7ffff79eb361 <MVM_interp_run+20193>, 0x7ffff79eb2f2 <MVM_interp_run+20082>, 0x7ffff79eb25a <MVM_interp_run+19930>, 0x7ffff79ede8d <MVM_interp_run+31245>, 0x7ffff79ede1e <MVM_interp_run+31134>, 0x7ffff79ee083 <MVM_interp_run+31747>, 0x7ffff79ee014 <MVM_interp_run+31636>, 0x7ffff79fb6df <MVM_interp_run+86623>, 0x7ffff79fb6df <MVM_interp_run+86623>, 0x7ffff79ee0f2 <MVM_interp_run+31858>, 0x7ffff79e906a <MVM_interp_run+11242>, 0x7ffff79ea4a8 <MVM_interp_run+16424>, 0x7ffff79ea431 <MVM_interp_run+16305>, 0x7ffff79ea67d <MVM_interp_run+16893>, 0x7ffff79ea3b4 <MVM_interp_run+16180>, 0x7ffff79ea338 <MVM_interp_run+16056>, 0x7ffff79ea2ac <MVM_interp_run+15916>, 0x7ffff79ea247 <MVM_interp_run+15815>, 0x7ffff79ea1fd <MVM_interp_run+15741>, 0x7ffff79ea1b3 <MVM_interp_run+15667>, 0x7ffff79ea169 <MVM_interp_run+15593>, 0x7ffff79ea11f <MVM_interp_run+15519>, 0x7ffff79ea0d5 <MVM_interp_run+15445>, 0x7ffff79ea08b <MVM_interp_run+15371>, 0x7ffff79ea031 <MVM_interp_run+15281>, 0x7ffff79e9fec <MVM_interp_run+15212>, 0x7ffff79e9fa7 <MVM_interp_run+15143>, 0x7ffff79e9f61 <MVM_interp_run+15073>, 0x7ffff79e9ee3 <MVM_interp_run+14947>, 0x7ffff79e9e9c <MVM_interp_run+14876>, 0x7ffff79e9e49 <MVM_interp_run+14793>, 0x7ffff79e9e02 <MVM_interp_run+14722>, 0x7ffff79e9dc3 <MVM_interp_run+14659>, 0x7ffff79e9d7a <MVM_interp_run+14586>, 0x7ffff79e9d45 <MVM_interp_run+14533>, 0x7ffff79e9d10 <MVM_interp_run+14480>, 0x7ffff79e9cdb <MVM_interp_run+14427>, 0x7ffff79e9ca6 <MVM_interp_run+14374>, 0x7ffff79e9c61 <MVM_interp_run+14305>, 0x7ffff79e9c1c <MVM_interp_run+14236>, 0x7ffff79e9bd7 <MVM_interp_run+14167>, 0x7ffff79e9b98 <MVM_interp_run+14104>, 0x7ffff79e9b50 <MVM_interp_run+14032>, 0x7ffff79e9b08 <MVM_interp_run+13960>, 0x7ffff79e9ab9 <MVM_interp_run+13881>, 0x7ffff79e9a74 <MVM_interp_run+13812>, 0x7ffff79e99eb <MVM_interp_run+13675>, 0x7ffff79e9979 <MVM_interp_run+13561>, 0x7ffff79e9925 <MVM_interp_run+13477>, 0x7ffff79e98d1 <MVM_interp_run+13393>, 0x7ffff79e9883 <MVM_interp_run+13315>, 0x7ffff79e9835 <MVM_interp_run+13237>, 0x7ffff79e97e7 <MVM_interp_run+13159>, 0x7ffff79e9799 <MVM_interp_run+13081>, 0x7ffff79e973b <MVM_interp_run+12987>, 0x7ffff79e96f3 <MVM_interp_run+12915>, 0x7ffff79e96ab <MVM_interp_run+12843>, 0x7ffff79e9663 <MVM_interp_run+12771>, 0x7ffff79e961c <MVM_interp_run+12700>, 0x7ffff79e9560 <MVM_interp_run+12512>, 0x7ffff79e951a <MVM_interp_run+12442>, 0x7ffff79e94b0 <MVM_interp_run+12336>, 0x7ffff79e9459 <MVM_interp_run+12249>, 0x7ffff79e93ce <MVM_interp_run+12110>, 0x7ffff79e9337 <MVM_interp_run+11959>, 0x7ffff79e92f1 <MVM_interp_run+11889>, 0x7ffff79e92a3 <MVM_interp_run+11811>, 0x7ffff79f2402 <MVM_interp_run+49026>, 0x7ffff79f23b4 <MVM_interp_run+48948>, 0x7ffff79f236e <MVM_interp_run+48878>, 0x7ffff79f2328 <MVM_interp_run+48808>, 0x7ffff79f22d1 <MVM_interp_run+48721>, 0x7ffff79f227f <MVM_interp_run+48639>, 0x7ffff79f2229 <MVM_interp_run+48553>, 0x7ffff79f21db <MVM_interp_run+48475>, 0x7ffff79f218d <MVM_interp_run+48397>, 0x7ffff79f2147 <MVM_interp_run+48327>, 0x7ffff79f20e8 <MVM_interp_run+48232>, 0x7ffff79f208d <MVM_interp_run+48141>, 0x7ffff79f203f <MVM_interp_run+48063>, 0x7ffff79f1ff1 <MVM_interp_run+47985>, 0x7ffff79f1fae <MVM_interp_run+47918>, 0x7ffff79f1f70 <MVM_interp_run+47856>, 0x7ffff79f1f20 <MVM_interp_r--Type <RET> for more, q to quit, c to continue without paging--
un+47776>, 0x7ffff79f1ecf <MVM_interp_run+47695>, 0x7ffff79f1e7f <MVM_interp_run+47615>, 0x7ffff79f1e2e <MVM_interp_run+47534>, 0x7ffff79f1dd5 <MVM_interp_run+47445>, 0x7ffff79f1d7c <MVM_interp_run+47356>, 0x7ffff79f1d2d <MVM_interp_run+47277>, 0x7ffff79f1ce1 <MVM_interp_run+47201>, 0x7ffff79f1c93 <MVM_interp_run+47123>, 0x7ffff79f1c47 <MVM_interp_run+47047>, 0x7ffff79f1bfb <MVM_interp_run+46971>, 0x7ffff79f1bbc <MVM_interp_run+46908>, 0x7ffff79f1b7b <MVM_interp_run+46843>, 0x7ffff79f1b17 <MVM_interp_run+46743>, 0x7ffff79f2cad <MVM_interp_run+51245>, 0x7ffff79f2bbb <MVM_interp_run+51003>, 0x7ffff79f304a <MVM_interp_run+52170>, 0x7ffff79f28ab <MVM_interp_run+50219>, 0x7ffff79f27b9 <MVM_interp_run+49977>, 0x7ffff79f276c <MVM_interp_run+49900>, 0x7ffff79f2710 <MVM_interp_run+49808>, 0x7ffff79f26b2 <MVM_interp_run+49714>, 0x7ffff79f313e <MVM_interp_run+52414>, 0x7ffff79f2e54 <MVM_interp_run+51668>, 0x7ffff79f2aa0 <MVM_interp_run+50720>, 0x7ffff79f2a22 <MVM_interp_run+50594>, 0x7ffff79f2dd8 <MVM_interp_run+51544>, 0x7ffff79f25db <MVM_interp_run+49499>, 0x7ffff79f255c <MVM_interp_run+49372>, 0x7ffff79f24dd <MVM_interp_run+49245>, 0x7ffff79f3262 <MVM_interp_run+52706>, 0x7ffff79f31e3 <MVM_interp_run+52579>, 0x7ffff79f32e1 <MVM_interp_run+52833>, 0x7ffff79f2b1c <MVM_interp_run+50844>, 0x7ffff79f2f4c <MVM_interp_run+51916>, 0x7ffff79f2ead <MVM_interp_run+51757>, 0x7ffff79f2feb <MVM_interp_run+52075>, 0x7ffff79f2657 <MVM_interp_run+49623>, 0x7ffff79f319a <MVM_interp_run+52506>, 0x7ffff79f299f <MVM_interp_run+50463>, 0x7ffff79f2d93 <MVM_interp_run+51475>, 0x7ffff79f1ac7 <MVM_interp_run+46663>, 0x7ffff79f1a7b <MVM_interp_run+46587>, 0x7ffff79f19ff <MVM_interp_run+46463>, 0x7ffff79f19b2 <MVM_interp_run+46386>, 0x7ffff79f1965 <MVM_interp_run+46309>, 0x7ffff79f18af <MVM_interp_run+46127>, 0x7ffff79f185f <MVM_interp_run+46047>, 0x7ffff79f190e <MVM_interp_run+46222>, 0x7ffff79f1506 <MVM_interp_run+45190>, 0x7ffff79f17ac <MVM_interp_run+45868>, 0x7ffff79f174f <MVM_interp_run+45775>, 0x7ffff79f1809 <MVM_interp_run+45961>, 0x7ffff79f1310 <MVM_interp_run+44688>, 0x7ffff79f16ae <MVM_interp_run+45614>, 0x7ffff79f1656 <MVM_interp_run+45526>, 0x7ffff79f1707 <MVM_interp_run+45703>, 0x7ffff79f145f <MVM_interp_run+45023>, 0x7ffff79f15b0 <MVM_interp_run+45360>, 0x7ffff79fb80e <MVM_interp_run+86926>, 0x7ffff79fb7fc <MVM_interp_run+86908>, 0x7ffff79f1560 <MVM_interp_run+45280>, 0x7ffff79f1607 <MVM_interp_run+45447>, 0x7ffff79f11c1 <MVM_interp_run+44353>, 0x7ffff79f14a3 <MVM_interp_run+45091>, 0x7ffff79f13e4 <MVM_interp_run+44900>, 0x7ffff79f1295 <MVM_interp_run+44565>, 0x7ffff79f1210 <MVM_interp_run+44432>, 0x7ffff79f1146 <MVM_interp_run+44230>, 0x7ffff79f108e <MVM_interp_run+44046>, 0x7ffff79f1369 <MVM_interp_run+44777>, 0x7ffff79f1021 <MVM_interp_run+43937>, 0x7ffff79f0ee9 <MVM_interp_run+43625>, 0x7ffff79f0e89 <MVM_interp_run+43529>, 0x7ffff79f0e31 <MVM_interp_run+43441>, 0x7ffff79f0df9 <MVM_interp_run+43385>, 0x7ffff79f0db4 <MVM_interp_run+43316>, 0x7ffff79f0d5c <MVM_interp_run+43228>, 0x7ffff79f0cf6 <MVM_interp_run+43126>...}
cur_op = 0x7fffef4ebee4 ""
bytecode_start = 0x7fffef4ebec6 "\214"
reg_base = 0x5555582822a0
cu = 0x55555562be58
--Type <RET> for more, q to quit, c to continue without paging--
cur_callsite = 0x7ffff7fcaf80 <null_args_callsite>
#31 0x00007ffff7a14504 in callback_handler (cb=<optimized out>, cb_args=<optimized out>, cb_result=0x7fffffffcfa8, data=0x5555587c9020) at src/core/nativecall_dyncall.c:341
backup_mark = <optimized out>
backup_interp_jump =
{{__jmpbuf = {93824992255136, -5773965049323896237, 93824992252512, 140737488347499, 93824992246944, 5, 5773965047990927955, 5773947178180362835}, __mask_was_saved = 0, __saved_mask = {__val = {0 <repeats 16 times>}}}}
backup_interp_cur_op = <optimized out>
backup_interp_bytecode_start = <optimized out>
backup_interp_reg_base = <optimized out>
backup_interp_cu = <optimized out>
backup_cur_frame = 0x55555baa93b0
backup_thread_entry_frame = 0x0
backup_jit_return_address = 0x0
cid = {invokee = 0x7fffe513c934, args = 0x55555b0fe050, cs = 0x7ffff7f0e460 <two_args_callsite>}
num_roots = <optimized out>
i = <optimized out>
res = {o = 0x6, s = 0x6, i8 = 6 '\006', u8 = 6 '\006', i16 = 6, u16 = 6, i32 = 6, u32 = 6, i64 = 6, u64 = 6, n32 = 8.40779079e-45, n64 = 2.9643938750474793e-323}
interval_id = 0
tc = 0x555555559ca0
was_blocked = 1
#32 0x00007ffff7b16dd0 in dcCallback_x64_sysv () at //home/cbwood/Projects/rakudobrew/moar-master/install/lib/libmoar.so
#33 0x00007fffed403b6d in g_closure_invoke () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
--Type <RET> for more, q to quit, c to continue without paging--
#34 0x00007fffed4168f3 in () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#35 0x00007fffed41f882 in g_signal_emit_valist () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#36 0x00007fffed41fecf in g_signal_emit () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#37 0x00007fffed5feef8 in () at /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
#38 0x00007fffed5ff0a7 in g_application_run () at /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
#39 0x00007ffff7b15f39 in dcCall_x64_sysv () at //home/cbwood/Projects/rakudobrew/moar-master/install/lib/libmoar.so
#40 0x0000000000000003 in ()
#41 0x00007fffffffd650 in ()
#42 0x00007ffff7b15e72 in dc_callvm_call_x64 () at //home/cbwood/Projects/rakudobrew/moar-master/install/lib/libmoar.so
Did I break something with NativeCall?
Turning off JIT gives me this SEGV, but it is not consistent, and there are no helpful pointers.