bug#18140: [PATCH] macros.c: CHECK_VECTOR_OR_STRING invokes wrong_type_argument for Qnil instead of return 0

[Jan Chaloupka]

On 07/29/2014 09:52 AM, Andreas Schwab wrote:
> Jan Chaloupka <jchaloup@redhat.com> writes:
>
> > Changelog:
> >         line wrapping to 80 characters
> >
> > In function Fstart_kbd_macro (macros.c), Vlast_kbd_macro of current_kboard is
> > Qnil for the first invocation. If NILP (append) is false,
> > current_kboard->kbd_macro_ptr has random value (in our case
> > 0x5353535353535353), which after CHECK_VECTOR_OR_STRING failure (invocation
> > of wrong_type_argument) results in garbage collecting.
> > During gc, marking of objects is processed and mark_kboards (keyboard.c) is
> > invoked. Following for loop is fired:
> >
> > for (p = kb->kbd_macro_buffer; p < kb->kbd_macro_ptr; p++)
> >                    mark_object (*p);
> >
> > Since kb->kbd_macro_ptr is set to 0x5353535353535353, mark_object (*p) is
> > trying to mark object on address out of memory space (or memory that
> > cannot be accessed). Thus resulting in SIGSEGV signal.
> So the correct solution is to initialize kbd_macro_ptr together with
> kbd_macro_buffer.  Otherwise the same situation can still happen any
> time garbage collection is called.
Yes, for garbage collector. However, Vlast_kbd_macro will continue being 
Qnil.
The patch is still valid (just without comment about random value of
kbd_macro_ptr and garbage collection):

In function Fstart_kbd_macro (macros.c), Vlast_kbd_macro of 
current_kboard is
Qnil for the first invocation. If NILP (append) is false
CHECK_VECTOR_OR_STRING fails (invocation
of wrong_type_argument resulting in emacs_abort). However, it has to pass.

> Andreas.