Test string_instructions-32-no-syscallbuf failing on fedora 21 ("Assertion `(pending_sig() == SIGTRAP || ReplaySession::is_ignored_signal(pending_sig()))' failed to hold. PENDING SIG IS SIGSTKFLT")

Seeing the following gdb interaction

(gdb) break string_store
break string_store
Breakpoint 1 at 0x8048841: file /home/cjones/rr/obj/32/string_instructions.c, line 36.
c
(gdb) c
Continuing.

Breakpoint 1, string_store (dest=0x55995008 "", a=1633771873, size=10485760, unit=1, dir=1) at /home/cjones/rr/obj/32/string_instructions.c:36
36    set_dir(dir);
finish
watch -l p[1000000]
(gdb) finish
Run till exit from #0  string_store (dest=0x55995008 "", a=1633771873, size=10485760, unit=1, dir=1) at /home/cjones/rr/obj/32/string_instructions.c:36
0x08048c51 in main (argc=1, argv=0xffffd5c4) at /home/cjones/rr/obj/32/string_instructions.c:254
254     string_store(p, pattern, size_units, unit, dir);
(gdb) watch -l p[1000000]
Hardware watchpoint 2: -location p[1000000]reverse-continue

(gdb) reverse-continue
Continuing.
[FATAL /home/cjones/rr/rr/src/task.cc:353:finish_emulated_syscall() errno: 0 'Success'] 
 (task 31530 (rec:31475) at time 294)
 ->  Assertion `(pending_sig() == SIGTRAP || ReplaySession::is_ignored_signal(pending_sig()))' failed to hold. PENDING SIG IS SIGSTKFLT

Seeing if I can repro.

Reproduce string_instructions-32-no-syscallbuf on Fedora 21 using the reported GDB reverse-continue interaction. Start at rr/src/task.cc:353 in finish_emulated_syscall() and trace why SIGSTKFLT remains pending; done means the failing test no longer aborts and the signal behavior is covered by an appropriate regression test.