bug#33014: 26.1.50; 27.0.50; Fatal error after re-evaluating a thread's function

[Eli Zaretskii]

> Date: Tue, 16 Oct 2018 22:25:21 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 33014@debbugs.gnu.org, schwab@linux-m68k.org
> 
> > - The value of 'fun' in Ffuncall after it is used as an argument for
> >   funcall_lambda.
> > 
> > - The value of 'fun' in funcall_lambda after it is used to calculate
> >   the arguments to exec_byte_code.
> > 
> > - The value of 'vector' in exec_byte_code after the calculation of
> >   vectorp.
> 
> There are calling frames as well.  For GC to pay attention to a Lisp
> object, it is enough to have that object _somewhere_ on the stack.

And btw, 'fun' is not the object we should be tracing in this case.
We should be tracing the bytecode that is being run, either the entire
vector or some of its elements.  AFAIU, that is the bytecode of the
thread function, which I think is the one called here:

> #11 0x00000000005cdd32 in funcall_lambda (fun=XIL(0x7fecdacdc468), 
> nargs=nargs@entry=0, arg_vector=0x16eac38 <bss_sbrk_buffer+9926040>, 
>     arg_vector@entry=0x1578c58 <bss_sbrk_buffer+8410552>) at eval.c:3057
> #12 0x00000000005ca54b in Ffuncall (nargs=nargs@entry=1, 
> args=args@entry=0x1578c50 <bss_sbrk_buffer+8410544>) at eval.c:2870
> #13 0x000000000064680b in invoke_thread_function () at thread.c:684