Re: 21.2.19 SEGV on null frame pointer

Kyle Jones <kyle_jones(a)wonderworks.com&gt; writes: Well, the whole reason for the SEGV is that f is 0x0. See Subject:. :-) gdb complains that it does not know of a "sym" in this context. I'm trying to chase through the twisty maze of #definitions and inline func defs to figure out how gdb would comprehend what is being called "sym" here, but so far... Er, hang on, I think I just got it. Or got something, anyway. The FRAME_TYPE_DATA whose assertion is getting horked over on a null pointer is actually the FRAME_X_XIC at the top of x_to_emacs_keysym(), line 783, assuming I've followed the twisty maze properly. (gdb) p event->window $16 = 79692505 (gdb) p event->display $17 = (Display *) 0x85074c0 (gdb) p *(event->display) $18 = <incomplete type> (gdb) p get_device_from_display (event->display) $19 = (struct device *) 0x832cf10 (gdb) p x_any_window_to_frame(get_device_from_display (event->display),event->window) $20 = (struct frame *) 0x0 I just single-stepped through that call of x_any_window_to_frame. It just plain didn't find a frame it liked. It did check a frame on the way through (which does have symbol 'x), but it didn't think that was the right one. (gdb) p x_any_window_to_frame(get_device_from_display (event->display),event->window) Breakpoint 1, x_any_window_to_frame (d=0x832cf10, wdesc=79692505) at frame-x.c:109 109 assert (DEVICE_X_P (d)); The program being debugged stopped while in a function called from GDB. When the function (x_any_window_to_frame) is done executing, GDB will silently stop (instead of continuing to evaluate the expression containing the function call). (gdb) n 145 return f; (gdb) 119 frame = XCAR (tail); (gdb) 120 f = XFRAME (frame); (gdb) 122 if (wdesc == XtWindow (FRAME_X_SHELL_WIDGET (f)) || (gdb) p frame $39 = 140188784 (gdb) p f $40 = (struct frame *) 0x85b1c70 (gdb) pobj f->framemeths->symbol $41 = (Lisp_Symbol *) 0x82ecd24 $42 = {lheader = {type = 3, mark = 0, c_readonly = 0, lisp_readonly = 0}, next = 0x0, name = 0x82ec59c, value = 136654664, function = 136654664, plist = 146629516} Symbol name: x (gdb) n 124 wdesc == XtWindow (FRAME_X_TEXT_WIDGET (f))) (gdb) 141 for (i = 0; i < FRAME_X_NUM_TOP_WIDGETS (f); i++) (gdb) 143 Widget wid = FRAME_X_TOP_WIDGETS (f)[i]; (gdb) 144 if (wid && XtIsManaged (wid) && wdesc == XtWindow (wid)) (gdb) 146 } (gdb) 259 assert (EQ (FRAME_TYPE (f), sym)); (gdb) 141 for (i = 0; i < FRAME_X_NUM_TOP_WIDGETS (f); i++) (gdb) 150 if (x_window_is_scrollbar (f, wdesc)) (gdb) 153 } (gdb) 155 return 0; (gdb) 156 } (gdb) (gdb) pobj Qt $6 = (Lisp_Symbol *) 0x82cefcc $7 = {lheader = {type = 3, mark = 0, c_readonly = 0, lisp_readonly = 0}, next = 0x0, name = 0x82ce7cc, value = 137162700, function = 136654664, plist = 145957396} Symbol name: t (gdb) pobj Qnil $8 = (Lisp_Symbol *) 0x82cefb4 $9 = {lheader = {type = 3, mark = 0, c_readonly = 0, lisp_readonly = 0}, next = 0x0, name = 0x82ce7bc, value = 137162676, function = 136654664, plist = 137162676} Symbol name: nil (gdb) pobj Qx $10 = (Lisp_Symbol *) 0x82ecd24 $11 = {lheader = {type = 3, mark = 0, c_readonly = 0, lisp_readonly = 0}, next = 0x0, name = 0x82ec59c, value = 136654664, function = 136654664, plist = 146629516} Symbol name: x --karl