Backtrace for SystemStackError

* eval.c (setup_exception): set backtrace in system stack error
  other than the pre-allocated sysstack_error.  [Feature #6216]
* proc.c (Init_Proc): freeze the pre-allocated sysstack_error.
* vm_insnhelper.c (vm_stackoverflow): raise new instance for each
  times without calling any methods to keep the backtrace with no
  further stack overflow.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46502 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 0 deletions

diff --git a/proc.c b/proc.c
index befa8834cd..34159480e0 100644
--- a/proc.c
+++ b/proc.c
@@ -2748,6 +2748,7 @@ Init_Proc(void)
     sysstack_error = rb_exc_new3(rb_eSysStackError,
 				 rb_obj_freeze(rb_str_new2("stack level too deep")));
     OBJ_TAINT(sysstack_error);
+    OBJ_FREEZE(sysstack_error);
 
     /* utility functions */
     rb_define_global_function("proc", rb_block_proc, 0);