Re: SIGSEGV on cons_free_list in alloc.c

[Richard Stallman]

    So the question is how to intercept code that places a wrong
    address to cons_free_list.

That's not the only possibility.  Another is that something clobbers
an address in cons_free_list.

You could try this change.  It should detect such clobberage much
sooner.  It might be noticeably slower; I don't know how much slower
it will be.

*** lisp.h      22 Jan 2005 07:59:59 -0500      1.521
--- lisp.h      25 Feb 2005 13:06:54 -0500      
***************
*** 53,58 ****
--- 53,63 ----
  
  #endif /* 0 */
  
+ #ifdef GC_CHECK_CONS_LIST
+ #define CHECK_CONS_LIST() check_cons_list()
+ #else
+ #define CHECK_CONS_LIST() 0
+ #endif
  
  /* These are default choices for the types to use.  */
  #ifdef _LP64


*** eval.c      06 Feb 2005 06:22:27 -0500      1.233
--- eval.c      25 Feb 2005 13:09:13 -0500      
***************
*** 2067,2072 ****
--- 2067,2074 ----
        args_left = original_args;
        numargs = Flength (args_left);
  
+       CHECK_CONS_LIST ();
+ 
        if (XINT (numargs) < XSUBR (fun)->min_args ||
          (XSUBR (fun)->max_args >= 0 && XSUBR (fun)->max_args < XINT 
(numargs)))
        return Fsignal (Qwrong_number_of_arguments, Fcons (fun, Fcons (numargs, 
Qnil)));
***************
*** 2190,2195 ****
--- 2192,2199 ----
        return Fsignal (Qinvalid_function, Fcons (fun, Qnil));
      }
   done:
+   CHECK_CONS_LIST ();
+ 
    lisp_eval_depth--;
    if (backtrace.debug_on_exit)
      val = call_debugger (Fcons (Qexit, Fcons (val, Qnil)));
***************
*** 2746,2751 ****
--- 2750,2757 ----
  
    if (SUBRP (fun))
      {
+       CHECK_CONS_LIST ();
+ 
        if (numargs < XSUBR (fun)->min_args
          || (XSUBR (fun)->max_args >= 0 && XSUBR (fun)->max_args < numargs))
        {
***************
*** 2844,2849 ****
--- 2850,2856 ----
        return Fsignal (Qinvalid_function, Fcons (fun, Qnil));
      }
   done:
+   CHECK_CONS_LIST ();
    lisp_eval_depth--;
    if (backtrace.debug_on_exit)
      val = call_debugger (Fcons (Qexit, Fcons (val, Qnil)));