Allow passing of wasm file into EXPORTED_FUNCTIONS

[Mintyboi]

I have a transitive dependency in my project.

• Main module
  -- sidey1
  --- sidey2

And Sidey1 is dependent on Sidey2.
To make sure that all the functions are exported correctly in Sidey2, we can use wasm-objdump -x --section=import to get the list of imports and parse it with regex to eventually populate csv file to pass into EXPORTED_FUNCTIONS.

Would it be easier if we are able to pass in a wasm module in while building the side module? eg.

emcc side2.cpp -sSIDE_MODULE=2 -o Sidey2.wasm [email protected]

[sbc100]

Interesting idea! So in this case you know that the only consumer of Sidey2.wasm is Sidey1.wasm so any function not needed by Sidey1.wasm can be DCE'd.

What happens if Sidey1.wasm also contains symbols from other module, e.g. libc/main module? i.e. what happens if Sidey1.wasm imports printf? Would that not result in "undefined symbol: printf" when linking Sidey2?

[Mintyboi]

Yes, that's the part I'm unsure about and seeking your input.
I see the implementation in the process_dynamic_library() function which adds functions into the export_if_define list.

Is that something that we can follow here as well?

[sbc100]

I think maybe the solution based on using wasm-objdump might make the sense. i.e. maybe we can avoid adding more magic to the core compiler.

[sbc100]

I can see that something like -sEXPORT_IF_DEFINED=@syms_needed_by_side1.txt could be useful, but against it adding more complexity so we would need to consider carefully.

[Mintyboi]

Sure, that makes sense.
Yea I'll continue to use the wasm-objdump approach. My only little complain is that wasm-objdump belongs to wabt and is not part of the toolset in emsdk.
Might you know of any other tools that'll allow me to get the imports of a wasm file?

[sbc100]

You can probably use wasm-dis from emscripten, or llvm-objdump from llvm, both of which should be part of emsdk