From: "jeremyevans0 (Jeremy Evans)" <noreply@...>
Date: 2022-04-28T22:37:03+00:00
Subject: [ruby-core:108437] [Ruby master Bug#18730] Double `return` event handling with different tracepoints

Issue #18730 has been updated by jeremyevans0 (Jeremy Evans).


I've submitted a pull request to fix the use-after-free bug: https://github.com/ruby/ruby/pull/5862

----------------------------------------
Bug #18730: Double `return` event handling with different tracepoints
https://bugs.ruby-lang.org/issues/18730#change-97475

* Author: hurricup (Alexandr Evstigneev)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
I'm not sure if this is a bug or intentional behavior, but feels a bit unexpected. Ruby 3.0.x, 3.1.x affected.

Here is the script demonstrating the issue:
```
def bar
  42 #bp here
end

tp_line = TracePoint.new(:line) do |tp0|
  puts "Got line event from #{tp0.path}:#{tp0.lineno}"

  tp_multi1 = TracePoint.new(:return, :b_return, :line) do |tp|
    if tp.lineno == 3
      puts "Got first return `#{tp.event}` from #{tp.path}:#{tp.lineno}"
      tp.disable
      # tp0.disable # uncommenting this line changes things to the more expected 


      tp_multi2 = TracePoint.new(:return, :b_return, :line) do |tps|
        puts "Got second return `#{tps.event}` from #{tps.path}:#{tps.lineno}"
      end
      tp_multi2.enable(target: RubyVM::InstructionSequence.of(method :bar))
    end
  end
  tp_multi1.enable
end

tp_line.enable(target: RubyVM::InstructionSequence.of(method :bar))

bar
```
1. We set a line TP to the `bar` method `iseq` (consider it a line breakpoint)
2. When line event is triggered we setting another untargeted tracepoint for the same method, to catch `line`, `return` and `b_return` events (consider it attempt to step into something)
3. When return event of the `bar` method is triggered, we disabling second tracepoint and setting another one, targeted to the same method and multiple events.

Output i get:
```
Got line event from /home/hurricup/test.rb:2
Got first return `return` from /home/hurricup/test.rb:3
Got second return `return` from /home/hurricup/test.rb:3
```
The questions are: 
1. why return triggered on the second tracepoint, when we already handeled it?
2. why disabling line tracepoint changes behavior?




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