Here's a trace from Nicholas.
http://paste.husk.org/7347
#53700 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170736) at emitter.c:1171
#53701 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167600) at perl_syck.h:717
#53702 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170752) at perl_syck.h:596
#53703 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170752) at emitter.c:431
#53704 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170752) at emitter.c:1171
#53705 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167296) at perl_syck.h:717
#53706 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170736) at perl_syck.h:596
#53707 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170736) at emitter.c:431
#53708 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170736) at emitter.c:1171
#53709 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167600) at perl_syck.h:717
#53710 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170752) at perl_syck.h:596
#53711 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170752) at emitter.c:431
#53712 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170752) at emitter.c:1171
#53713 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167296) at perl_syck.h:717
#53714 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170736) at perl_syck.h:596
#53715 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170736) at emitter.c:431
#53716 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170736) at emitter.c:1171
#53717 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167600) at perl_syck.h:717
#53718 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170752) at perl_syck.h:596
#53719 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170752) at emitter.c:431
#53720 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170752) at emitter.c:1171
#53721 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167296) at perl_syck.h:717
#53722 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170736) at perl_syck.h:596
#53723 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170736) at emitter.c:431
#53724 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170736) at emitter.c:1171
#53725 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167600) at perl_syck.h:717
#53726 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170752) at perl_syck.h:596
#53727 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170752) at emitter.c:431
#53728 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170752) at emitter.c:1171
#53729 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167296) at perl_syck.h:717
#53730 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170736) at perl_syck.h:596
#53731 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170736) at emitter.c:431
#53732 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170736) at emitter.c:1171
#53733 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167600) at perl_syck.h:717
#53734 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170752) at perl_syck.h:596
#53735 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170752) at emitter.c:431
#53736 0x0041ffbd in syck_emit_item (e=0x1100aa0, n=25170752) at emitter.c:1171
#53737 0x004330be in json_syck_emitter_handler (e=0x1100aa0,
data=25167296) at perl_syck.h:717
#53738 0x0043290f in json_syck_emitter_handler (e=0x1100aa0,
data=25170784) at perl_syck.h:596
#53739 0x0041e0ac in syck_emit (e=0x1100aa0, n=25170784) at emitter.c:431
#53740 0x00434e09 in DumpJSON (sv=0x1801360) at perl_syck.h:873
#53741 0x0043e03a in XS_YAML__Syck_DumpJSON (cv=0x1817300) at Syck.c:109
#53742 0x000bcc23 in Perl_pp_entersub () at pp_hot.c:2900
#53743 0x00063a9e in Perl_runops_debug () at dump.c:1870
#53744 0x0009b687 in S_run_body (oldscope=1) at perl.c:2404
#53745 0x0009aa90 in perl_run (my_perl=0x11000f0) at perl.c:2324
#53746 0x00002083 in main (argc=2, argv=0xbffff0ac, env=0xbffff0b8) at
perlmain.c:113
(gdb)
--
Tatsuhiko Miyagawa