Eli Zaretskii <eliz@gnu.org> writes:

>> It happens when I click the "C source code" button in the *Help* buffer,
>
> "Click", as in "with a mouse"?  What kind of mouse do you have there
> -- GPM, xterm, something else?  Also, was the 'button' or 'link' face
> customized in any way?

No, by placing point on the text and hitting RET.  No mouse.  Sorry for
the confusion.  AFAICT, the faces aren't customized either (nothing to
that effect in .emacs): the closest thing to that would be:

(setq window-system-default-frame-alist
      '((x . ((background-color . "black")
              (foreground-color . "white")))
        (nil . ((background-color . "black")
                (foreground-color . "brightwhite")
                (background-mode . dark)))))

The terminal emulator is rxvt-unicode, though I have TERM set manually
to xterm-256color.  It only crashes when the terminal is the only X
window open on the workspace (it's a tiling window manager).  When it
shares space with some other window, it doesn't happen.

> I think it was trying to redisplay the "function is a special
> form in ..." line.  But to be sure, please show the contents of the
> 2nd argument to tty_write_glyphs

You're right, the array begins with "function is a special form..."  The
contents of the entire array are attached below.

> (and I'm guessing that you had the menu bar turned off in that frame,
> right?).

Yes, I shut the menu bar off globally in .emacs.