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    I can’t agree with this more. While doing olin/wasmcloud stuff I have resorted to this slightly insane method of debugging:

    • debug printf the pointer of a value you want to look for
    • immediately crash the program so none of the heap gets “contaminated”
    • pray the value didn’t get overwritten somehow (in my subjective and wholly personal experience Rust does this sometimes, it’s kind of annoying)
    • dump the webassembly linear memory/heap to a binary file
    • search for that pointer using xxd(1) and less(1)
    • grab my little-endian cheat sheet
    • hopefully derive meaning from it

    WebAssembly debuggers really need to happen, but until they do we are basically stuck in the printf debugging, black magick and tarot cards stone age, but at least it’s slightly easier to make a core dump. After a few hours though you learn to read little endian integers without needing to break out graph paper.

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      I’ve used instrumentation tools like Wasabi for dynamic testing during client assessments (yes, we have clients working in WASM already). Also, we’ve extended Manticore, our symbolic executor to support WASM, and we have some symbolic debugging-like scripts for it internally.

      In general tho, I whole-heartedly agree; we’re seeing more and more of this sort of thing, and the tooling definitely needs to catch up.

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        To be fair, the changes needed on the DWARF/LLVM side are super recent; I believe I saw commits related to this in LLVM as recently as December. The debuggers will catch up, but it takes time for some of this stuff to percolate outwards, I haven’t done any testing myself in the last few months, but I suspect the browsers have experimental support on the way shortly, if not already available. It will take a bit longer for this stuff to make it into say, lldb, but not that much longer.

        The current situation does suck for those of us needing to build stuff with WebAssembly right now, but I keep myself sane by knowing that its just growing pains - we’ll get the necessary tooling sooner rather than later.

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          Call me a pessimist, but existing debugging infrastructure might not be good enough for this. We might wanna start with something like AVR debuggers or other things made for Harvard architectures.

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            Presumably there are different needs. The first need is for front end / in browser use cases. For that, foo.wasm.debug could effectively include all the debug symbols, and source map, or whatever and you use the in browser debugger. That seems fine.

            The server side is more problematic, I think, but that’s where your Harvard arch comes in. Provide a manhole cover that can be opened for the purposes of attaching a debugger to, in your execution environment, and poke and prod with step debuggers, perhaps? Still need the debug symbols and such… of course.

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              Jtag into a wasm env, really this just needs to a handful of exported fn from the env itself. One could run wasm in wasm and implement it yourself in user space.

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          What if your wasm env could visualize memory in real-time and set breakpoints in any fn call or memory write?

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            Debuggers have two sides, symbol side and target side. Breaking/resuming and reading/writing memory is done in target side, and you can implement them in your WebAssembly environments. But that only lets you to do break 123 or print 456, not break function or print variable. The article is mostly about symbol side.

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              That would solve a lot of problems, but it would also be a lot of work :)

              I’m gonna see what I can do though.

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                Here is a veritable zoo of binary visualizers


                I think the past of least friction is run wasm3 within the browser so that you can have 100% over execution, it will be slow ~25x, but provide first class access to all facets of execution of the code under debug.