Helping understand cause of SIGSEGV

[Pete Wright]

i was hoping someone with more experience in C and threading can help me 
better understand this SIGSEGV fault I'm hitting.  the background is I'm 
trying to get sysutils/fluent-bit working on 12.2-RELEASE as well as on 
CURRENT.

I've created the following PR and upstream github issues:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=250825
https://github.com/fluent/fluent-bit/issues/2747

so where i am at now is i am able to generate a useful core file when it 
hits the fault and can step through it in lldb.

here is the output from fluent-bit:
|[2020/11/04 22:18:12] [debug] [task] created task=0x416410a0 id=0 OK
[2020/11/04 22:18:12] [trace] [thread 0x416091c0] created (custom data 
at 0x416091e0, size=80
[2020/11/04 22:18:12] [engine] caught signal (SIGSEGV)
#0  0x406d11ee          in  thr_sighandler() at 
/lib/libthr/thread/thr_sig.c:246
Abort trap (core dumped)|


here's an example from one of the threads (the github link above has the 
full backtrace) from lldb:

| thread #1, name = 'fluent-bit', stop reason = signal SIGABRT
   * frame #0: 0x000000004087100a libc.so.7`__sys_thr_kill at thr_kill.S:4
     frame #1: 0x00000000407e6c84 libc.so.7`__raise(s=6) at raise.c:52:10
     frame #2: 0x000000004089a5d9 libc.so.7`abort at abort.c:67:8
     frame #3: 0x000000000034a7a8 
fluent-bit`flb_signal_handler(signal=11) at fluent-bit.c:418:9
     frame #4: 0x00000000406d1c20 
libthr.so.3`handle_signal(actp=0x00007fffdfffc600, sig=11, 
info=0x00007fffdfffc9f0, ucp=0x00007fffdfffc680) at thr_sig.c:303:3
     frame #5: 0x00000000406d11ef libthr.so.3`thr_sighandler(sig=11, 
info=0x00007fffdfffc9f0, _ucp=0x00007fffdfffc680) at thr_sig.c:246:2
     frame #6: 0x00007fffffffe193
     frame #7: 0x000000000036fe0c fluent-bit`tasks_start [inlined] 
output_params_set(th=0x00000000416091c0, data=0x000000004165d980, 
bytes=128, tag="random.0", tag_len=8, i_ins=0x0000000040e58000, 
out_plugin=0x0000000040e2dfc0, out_context=0x00000000416051e0, 
config=0x0000000040e19180) at flb_output.h:429:5
     frame #8: 0x000000000036fd14 fluent-bit`tasks_start [inlined] 
flb_output_thread(task=0x00000000416410a0, i_ins=0x0000000040e58000, 
o_ins=0x0000000040e5b000, config=0x0000000040e19180, 
buf=0x000000004165d980, size=128, tag="random.0", tag_len=8) at 
flb_output.h:522
     frame #9: 0x000000000036fab5 
fluent-bit`tasks_start(in=0x0000000040e58000, config=0x0000000040e19180) 
at flb_engine_dispatch.c:190
     frame #10: 0x000000000036f6fd fluent-bit`flb_engine_dispatch(id=0, 
in=0x0000000040e58000, config=0x0000000040e19180) at 
flb_engine_dispatch.c:293:5
     frame #11: 0x000000000036ce10 
fluent-bit`flb_engine_flush(config=0x0000000040e19180, 
in_force=0x0000000000000000) at flb_engine.c:85:9
     frame #12: 0x000000000036d43a fluent-bit`flb_engine_start [inlined] 
flb_engine_handle_event(fd=20, mask=1, config=0x0000000040e19180) at 
flb_engine.c:292:13
     frame #13: 0x000000000036d3e6 
fluent-bit`flb_engine_start(config=0x0000000040e19180) at flb_engine.c:559
     frame #14: 0x00000000003564ec 
fluent-bit`flb_lib_worker(data=0x0000000040e19180) at flb_lib.c:488:11
     frame #15: 0x00000000406c87db 
libthr.so.3`thread_start(curthread=0x0000000040e12500) at 
thr_create.c:292:16



I was hoping someone here could help point me in the right direction as 
i'm kinda stuck but not sure where i should start looking?

cheers,
-pete|


-- 
Pete Wright
pete at nomadlogic.org
@nomadlogicLA