TypeError when loading a wasm module

[dr-matt]

I ran into the following runtime error when my app tries to load a wasm module in the browser. The same code and build process worked previously, so this may be due to a more recent version of emscripten. Also this only occurrs in Release cmake build, not Debug.

TypeError: registerType registeredInstance requires argPackAdvance

This was emitted from _embind_register_void.

Before creating a MRE, I wanted to find out what this error means, as perhaps it'll help focus debugging. Googling didn't reveal anything useful. Any ideas?

Version 3.1.69:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.69 (c55ff404dbe1eb9f263c48b584d5ba627224763a)
clang version 20.0.0git (https:/github.com/llvm/llvm-project 50866e84d1da8462aeb96607bf6d9e5bbd5869c5)
Target: wasm32-unknown-emscripten
Thread model: posix

Build line from cmake:

em++ -flto --bind --closure 1 --no-entry --gc-sections -sFILESYSTEM=0 -sEXPORT_ES6=1 -sENVIRONMENT=web -sALLOW_MEMORY_GROWTH=1 --emit-tsd MyModule.d.ts @CMakeFiles/MyModule.dir/objects1.rsp -o MyModule.js @CMakeFiles/MyModule.dir/linkLibs.rsp

[brendandahl]

I was able to reproduce with a small example and doing emcc --closure 1 -lembind main.cpp -o a.out.js. It looks like a regression from #22413. Closure is minifying argPackAdvance, but we're still checking for the string name.

Aside: The error is coming from an assertion, which should be disabled with any optimization level of -O<x>. Are you intentionally enabling assertions for your release build?

[dr-matt]

@brendandahl thanks for looking into this. I did not explicitly enable assertions in the build, and as far as I know the Release cmake build uses -O2. So from your description it seems strange that the debug build works while the release build does not.

[brendandahl]

Does your debug build enable closure?

[brendandahl]

Also, from the command you posted above there doesn't appear to be any -O flags.

[dr-matt]

When I explicitly add -sASSERTIONS=0 to the release build, then it works. I thought that was the default value - I am not setting it explicitly.

In debug build, this is the line:

em++ -flto --bind --closure 1 --no-entry --gc-sections -sFILESYSTEM=0 -sEXPORT_ES6=1 -sENVIRONMENT=web -sALLOW_MEMORY_GROWTH=1 -g2 -sASSERTIONS=2 -sNO_DISABLE_EXCEPTION_CATCHING --emit-tsd MyModule.d.ts @CMakeFiles/MyModule.dir/objects1.rsp -o MyModule.js @CMakeFiles/MyModule.dir/linkLibs.rsp

You're right about -O2 not being there, that's strange. I'll look into why optimizations are no longer being turned on via cmake.

[dr-matt]

@brendandahl thanks for addressing this.