Why does this result in a stack overflow? #215

sebnozzi · 2023-05-15T22:53:53Z

sebnozzi
May 15, 2023

Basically I'm evaluating some Ruby code asynchronously and using a line-handler (TracePoint).

<html>
<head>
  <title>Ruby/Wasm - Infinite Recursion on Eval/Tracing</title>
  <link rel="icon" href="data:;base64,iVBORw0KGgo=">
</head>
<body>

  <script src="https://cdn.jsdelivr.net/npm/ruby-3_2-wasm-wasi@next/dist/browser.script.iife.js"></script>

  <script type="text/ruby">
    require "js"   
    
    # We boostrap the whole process once Ruby processing is in place
    JS.global[:window].bootStrapAsyncEval()
  </script>
  <script type="text/javascript">

    // This is the final code we want to evaluate
    window.CODE_TO_EVAL = `
      def print_numbers(e)
        (1..e).each do |x|
            puts "Number: #{x}"
        end
      end

      (1..5).each do |n|
          print_numbers n
      end
      `;
    
    // This contains the setup for the line-tracer
    window.TRACER_SETUP = `
      line_tracer = TracePoint.new(:line) do |tp|
        # One could remove the restriction to "(EVAL)" and the result would
        # be the same.
        puts "Line #{tp.lineno} of #{tp.path}" if tp.path == "(EVAL)"
      end
      line_tracer.enable
      `;

    // This allows us to evaluate code in JS's global scope,
    // giving the evaluation a ("file") name. By giving it a name
    // we can filter by it in the line-handler.
    window.EVAL_FN = `
      require 'js'
      def eval_code(code_name, eval_name)
        code = JS.global[:window][code_name].to_s
        scope = binding
        eval(code, scope, eval_name, 1)
      end
      `;

    window.bootStrapAsyncEval = function () {
      // I do this to rule out problems of inkoving "evalAsync" inside of
      // an already running "eval". This should take us back to the JS 
      // main event loop.
      setTimeout(async function() {
        evalCodeAsync();
      }, 0);
    }

    async function evalCodeAsync() {
      const vm = window.rubyVM;

      // Get the code snippets
      const tracerSetup = window["TRACER_SETUP"];
      const evalFn = window["EVAL_FN"];
      const codeToEval = window["CODE_TO_EVAL"];

      console.log("Setting up eval function ...");
      await vm.evalAsync(evalFn);

      console.log("Setting up line tracer ...");
      await vm.evalAsync(tracerSetup);

      console.log("Evaluating code ...");
      // Either evaluating the code directly or through one layer
      // or Ruby's eval results the same problem (too much recursion).
      // I tried running Ruby's eval to change the name of the evaluated
      // code, so that I could filter it out in the line-tracer, but the
      // problem remains.
      //await vm.evalAsync(codeToEval);
      await vm.evalAsync("eval_code('CODE_TO_EVAL','(EVAL)')")
    }

  </script>

</body>
</html>

In Chrome this results in:

Not evaluating it "async", however, runs just fine:
(the async, await on JavaScript are gone)

<html>
<head>
  <title>Ruby/Wasm - Infinite Recursion on Eval/Tracing</title>
  <link rel="icon" href="data:;base64,iVBORw0KGgo=">
</head>
<body>

  <script src="https://cdn.jsdelivr.net/npm/ruby-3_2-wasm-wasi@next/dist/browser.script.iife.js"></script>

  <script type="text/ruby">
    require "js"   
    
    # We boostrap the whole process once Ruby processing is in place
    JS.global[:window].evalCodeSync()
  </script>
  <script type="text/javascript">

    // This is the final code we want to evaluate
    window.CODE_TO_EVAL = `
      def print_numbers(e)
        (1..e).each do |x|
            puts "Number: #{x}"
        end
      end

      (1..5).each do |n|
          print_numbers n
      end
      `;
    
    // This contains the setup for the line-tracer
    window.TRACER_SETUP = `
      line_tracer = TracePoint.new(:line) do |tp|
        # One could remove the restriction to "(EVAL)" and the result would
        # be the same.
        puts "Line #{tp.lineno} of #{tp.path}" if tp.path == "(EVAL)"
      end
      line_tracer.enable
      `;

    // This allows us to evaluate code in JS's global scope,
    // giving the evaluation a ("file") name. By giving it a name
    // we can filter by it in the line-handler.
    window.EVAL_FN = `
      require 'js'
      def eval_code(code_name, eval_name)
        code = JS.global[:window][code_name].to_s
        scope = binding
        eval(code, scope, eval_name, 1)
      end
      `;

    function evalCodeSync() {
      const vm = window.rubyVM;

      // Get the code snippets
      const tracerSetup = window["TRACER_SETUP"];
      const evalFn = window["EVAL_FN"];
      const codeToEval = window["CODE_TO_EVAL"];

      console.log("Setting up eval function ...");
      vm.eval(evalFn);

      console.log("Setting up line tracer ...");
      vm.eval(tracerSetup);

      console.log("Evaluating code ...");
      vm.eval("eval_code('CODE_TO_EVAL','(EVAL)')")
    }

  </script>

</body>
</html>

What's going on? I am doing anything wrong?

Any ideas?

sebnozzi · 2023-05-15T22:58:25Z

sebnozzi
May 15, 2023
Author

In the async version (the one causing the stack-overflow) if one changes the CODE_TO_EVAL to something trivial then it works:

window.CODE_TO_EVAL_SIMPLE = `
puts "One"
puts "Two"
puts "Three"
`;

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Why does this result in a stack overflow? #215

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sebnozzi May 15, 2023 Author

sebnozzi
May 15, 2023

sebnozzi
May 15, 2023
Author