[ruby-core:71389] [Ruby trunk - Bug #11668] [Open] SEGV instead of SystemStackError when using the TracePoint API

Issue #11668 has been reported by David Rodr鱈guez.

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Bug #11668: SEGV instead of SystemStackError when using the TracePoint API
https://bugs.ruby-lang.org/issues/11668

* Author: David Rodr鱈guez
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.0dev (2015-11-09 trunk 52499) [x86_64-linux
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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**fixnum_monkey.rb**

~~~

class Fixnum
  define_method(:to_s) do |*args|
    to_default_s(*args)
  end

  alias_method :to_default_s, :to_s
end
~~~

If I use this code normally it gives me SystemStackError as expected

~~~
$ ruby -e "load('fixnum_monkey.rb');  5.to_s"
fixnum_monkey.rb:2:in `block in <class:Fixnum>': stack level too deep (SystemStackError)
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
    ... 5804 levels...
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from fixnum_monkey.rb:3:in `block in <class:Fixnum>'
   from -e:1:in `<main>'
~~~

But if I enable the `return` event of the TracePoint API before using it, I get a segfault

~~~
$ ruby -e "load('fixnum_monkey.rb'); TracePoint.trace(:return) { |_tp| }; 5.to_s"
Violaci坦n de segmento
~~~



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