Get the BytecodeArray of a Local<Function> on Nodejs c++ land

Question

I'm struggling a bit with the code base of nodejs + v8.

The Goal is to get the bytecode of a function / module (looking at the code they are the same) and disassemble it using the BytecodeArray::Disassemble function, possibly, without side effects, a.k.a, executing the code.

The problem is that it's not clear how to get the bytecode in the first place.

Answer 1

(V8 developer here.) V8's API does not provide access to functions' bytecode. That's intentional, because bytecode is an internal implementation detail. For inspecting bytecode, the --print-bytecode flag is the way to go.

If you insist on mucking with internal details, then of course you can circumvent the public API and poke at V8's internals. From a v8::internal::JSFunction you can get to the v8::internal::SharedFunctionInfo, check whether it HasBytecodeArray(), and if so, call GetBytecodeArray() on it. Disassembling bytecode never has side effects, and never executes the bytecode. It's entirely possible that a function doesn't have bytecode at a given moment in time -- bytecode is created lazily when it's needed, and thrown away if it hasn't been used in a while. If you dig far enough, you can interfere with those mechanisms too, but...:

Needless to say, accessing internal details is totally unsupported, not recommended, and even if you get it to work in Node version x.y, it may break in x.(y+1), because that's what "internal details" means.