But from an uncrashed emacs, with beacon loaded as before, C-h v window-scroll-functions gives ...
(gdb) pp Vwindow_scroll_functions
xdisp.c:3047: Emacs fatal error: assertion failed: charpos == BYTE_TO_CHAR (bytepos)
Thread 1 "emacs" hit Breakpoint 1, terminate_due_to_signal (sig=sig@entry=6,
backtrace_limit=backtrace_limit@entry=2147483647) at emacs.c:375
375 {
The program being debugged stopped while in a function called from GDB.
Evaluation of the _expression_ containing the function
(safe_debug_print) will be abandoned.
When the function is done executing, GDB will silently stop.
(gdb) fr 2
#2 0x0000000000456b44 in init_iterator (it=it@entry=0x7ffffffef990, w=w@entry=0x89da880, charpos=2874,
bytepos=<optimized out>, row=<optimized out>, base_face_id=base_face_id@entry=DEFAULT_FACE_ID)
at xdisp.c:3047
3047 eassert (charpos == BYTE_TO_CHAR (bytepos));
(gdb) p w->start
$16 = XIL(0x89daa95)
(gdb) xmarker
$17 = (struct Lisp_Marker *) 0x89daa90
(gdb) p $->buffer->name_
$18 = XIL(0x7960234)
(gdb) xstring
$19 = (struct Lisp_String *) 0x7960230
"
standard-reading.org"
(gdb)