Need help debugging unreachable code

[gmlewis]

While trying to learn Virgil, I've generated a .wasm with unreachable code and am interested in getting tips on how to debug this.
Here's the repo, branch, and directory: https://github.com/gmlewis/virgil/tree/extism-pdk/apps/Extism

To recreate, you first need the Extism CLI:

$ ./build.sh
...
$ ./run.sh
+ extism call greet/Greet.wasm greet --wasi --input Benjamin
Hello, Benjamin!

+ extism call count-vowels/CountVowels.wasm count_vowels --wasi --input 'Once upon a dream'
{"count":7,"total":7,"vowels":"aeiouAEIOU"}

+ extism call http-get/HttpGet.wasm http_get --wasi '--allow-host=*.typicode.com'
Error: wasm error: unreachable
wasm stack trace:
	.$40(i32,i32,i32,i32) i32
	.$31(i32,i32,i32) i32
	.$20(i32) i32
	.$14(i32,i32) i32
	.$10() i32

I've used wasm2wat but I'm thinking there must be a better way, and would love to get advice.
Thank you!

[titzer]

One thing is to add -symbols when compiling; that will give you source-level function names. The Wasm target doesn't have source lines yet, a stacktrace with just function names is the best you can do for now. Any unreachable that you hit is going to be a safety check or an out-of-memory, so look for places where a NullCheckException or a BoundsCheckException, etc could be triggered.

[gmlewis]

Thank you, @titzer !

[gmlewis]

That was the key, @titzer - thank you!

Next question - now that I've got all 3 example Extism plugins working, are you interested in a PR into your main repo, or would you like me to keep my Extism Virgil PDK separate in my own fork?

[titzer]

Sure, happy to have an example Extism plugin, if it doesn't pull in any dependencies. It could live under apps/. Does it make sense to collapse them all into one directory or prefer to keep separate subdirectories?

[gmlewis]

OK, sounds good. Yes, I think one directory is fine.
I'll send you a PR then. Thanks.

[gmlewis]

I've made one here: #258