Odd gdb problem

[Lars Ingebrigtsen]

I'm seeing this on the current trunk (not emacs-28) and on
Debian/bookworm (not on Debian/bullseye, the stable Debian release).  I
don't think I've ever seen something like this before:

larsi@xo:~/src/emacs/trunk$ gdb ./src/emacs 
GNU gdb (Debian 10.1-2) 10.1.90.20210103-git
Copyright (C) 2021 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.

[...]

Type "apropos word" to search for commands related to "word"...
Reading symbols from ./src/emacs...
(gdb) run -Q .
Starting program: /home/larsi/src/emacs/trunk/src/emacs -Q .
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff172b640 (LWP 823779)]
[New Thread 0x7ffff0eaf640 (LWP 823780)]
[New Thread 0x7fffebfff640 (LWP 823781)]
[New Thread 0x7fffeb7fe640 (LWP 823782)]
[Thread 0x7fffeb7fe640 (LWP 823782) exited]
[New Thread 0x7fffeb7fe640 (LWP 823783)]
[New Thread 0x7fffeaffd640 (LWP 823784)]
[Thread 0x7fffeb7fe640 (LWP 823783) exited]
[New Thread 0x7fffeb7fe640 (LWP 823785)]
[New Thread 0x7fffea7fc640 (LWP 823786)]
[Thread 0x7fffeaffd640 (LWP 823784) exited]
[Thread 0x7fffeb7fe640 (LWP 823785) exited]
[Thread 0x7fffea7fc640 (LWP 823786) exited]
[Detaching after vfork from child process 823787]
[Thread 0x7fffebfff640 (LWP 823781) exited]
[Thread 0x7ffff0eaf640 (LWP 823780) exited]
[Thread 0x7ffff172b640 (LWP 823779) exited]

Program terminated with signal SIGTRAP, Trace/breakpoint trap.
The program no longer exists.
(gdb) 

That is, if I start "emacs -Q ." (i.e., open a dired buffer), then it
exits with SIGTRAP, which is something I can't recall having seen before
ever.  (And Emacs works fine from without gdb.)

I tried googling briefly, but no.  Does anybody know what this might
mean?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no