@bmike gave me most of what I needed. A few additional clues and limitations.
Emacs is an app that lives in /Applications/Emacs.app and it has lots of stuff within that directory. I finally took it one step at a time. I created a dumpme app:
#include <unistd.h>
#include <signal.h>
int main(int argc, char *argv[])
{
pid_t pid = getpid();
kill(pid, SIGBUS);
}
and I did the codesign as suggested and I got a core file. Note that before the code side, I would get
zsh: bus error ./dumpme
and after the codesign I would get:
zsh: bus error (core dumped) ./dumpme
A preliminary step in building the Emacs app is temacs which is an executable without an initial state. I codesigned it and it produced a core too when started from the Terminal prompt. Then I did the codesign for /Applications/Emacs.app/Contents/MacOS/Emacs and I got this nastygram:
codesign -s - -f --entitlements tmp.entitlements /Applications/Emacs.app/Contents/MacOS/Emacs
/Applications/Emacs.app/Contents/MacOS/Emacs: replacing existing signature
/Applications/Emacs.app/Contents/MacOS/Emacs: code object is not signed at all
In subcomponent: /Applications/Emacs.app/Contents/MacOS/Emacs.pdmp
A search found this answer so I backed up and I did sudo codesign -s - -f --deep --entitlements tmp.entitlements /Applications/Emacs.app -- (Note the addition of --deep). Also, without the sudo I got permission problems.
If I start Emacs from the Finder or via open /Applications/Emacs.app and kill it, I do not get a core file. But if I start it from my Terminal prompt I do. e.g.
% /Applications/Emacs.app/Contents/MacOS/Emacs
I suspect there is a fix when starting from Finder as well. I'm assuming it has something to do with the ulimit -c unlimited that is suggested / required.