• BatmanAoD@programming.dev
    2·
    3 days ago

    …what is your point? Some software (in a language that doesn’t have tail-recursion optimization) used recursion to handle user-provided input, and indeed it broke. Someone wrote to explain that that’s a potential vulnerability, the author agreed, and fixed it. Who here is misunderstanding how computers implement recursion?

    • CanadaPlus@lemmy.sdf.org
      1·
      2 days ago

      I was answering a specific question put directly to me. There’s no “point”, exactly.

      Who here is misunderstanding how computers implement recursion?

      Taking a wild stab at how you might be reading this exchange, my original reply was about the title of the post, which implies a CompSci professor would be unhappy about someone criticising the use of recursion in code.

      (in a language that doesn’t have tail-recursion optimization)

      Wait, it doesn’t? I had kind of assumed GCC (for example) would do that at anything greater than -O0.

      • BatmanAoD@programming.dev
        1·
        2 days ago

        Okay, yeah, I was indeed reading your original reply as a criticism of one of the people involved (presumably the security researcher), rather than as a criticism of the post title. Sorry for misunderstanding.

        Apparently GCC does indeed do tail-call optimization at -O2: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-foptimize-sibling-calls

        But in that case, I’m not sure why the solution to the denial of service vulnerability isn’t just “compile with -foptimize-sibling-calls.”

        • CanadaPlus@lemmy.sdf.org
          1·
          2 days ago

          I mean, “criticism” is a little extreme even, because it’s a humour post, and I was just riffing back.

          Apparently GCC does indeed do tail-call optimization at -O2

          Hmm, I wonder why it’s considered O2 heavy. The concept of turning tail recursion into loops is simple.

          But in that case, I’m not sure why the solution to the denial of service vulnerability isn’t just “compile with -foptimize-sibling-calls.”

          Probably because some of the recursion involved is non-tail. Actually, it looks like GCC might still be able to cases of corecursion where the functions are “stack compatibale”, but presumably most functions aren’t, and who knows what little knots they tied the parsing functions in this XML library into.

            • CanadaPlus@lemmy.sdf.org
              1·
              1 day ago

              Yes, definitely. Rereading the StackOverflow, “stack compatible” just means it can mutate the stack frame in place without resizing it in the optimised code. There’s a number of ways trying to handle tail (co)recursion sucks if you try and get around that. Here’s a Dr. Dobbs about it.