Can't run simple hello world wasm game

[fatduckling]

Godot version

v4.6.rc2.official [78c6632eb]

godot-cpp version

e3f229e

System information

Linux Mint LMDE 6

Issue description

Hi,
I created a simple Hello World game using Godot 4.6 rc2 and GDExtension.
The game runs perfectly on Linux, but when I export it to Web (Wasm) with GDExtension and Threads support, it fails to load with error:

Uncaught (in promise) TypeError: can't access property "sig", _emscripten_glGetVertexAttribIuiv is undefined
    Godot http://localhost/game/example.js:1
    Engine http://localhost/game/example.js:719
    promise callback*SafeEngine/init/doInit/Engine< http://localhost/game/example.js:717
    doInit http://localhost/game/example.js:716
    init http://localhost/game/example.js:733
    startGame http://localhost/game/example.js:828
    <anonymous> http://localhost/game/example.html:202
    <anonymous> http://localhost/game/example.html:216
[example.js:1:279258](http://localhost/game/example.js)

And on Chrome:

Uncaught (in promise) TypeError: Cannot set properties of undefined (setting 'sig')
    at example.js:1:279295
    at example.js:719:8

It seems to be coming from here:

I'm using Apache2 Web Server with headers mod enabled and these headers:

<IfModule mod_headers.c>
    Header always set Cross-Origin-Opener-Policy "same-origin"
    Header always set Cross-Origin-Embedder-Policy "require-corp"
</IfModule>

I've attached a minimum reproducible example for you to test.

Thank you

Steps to reproduce

You can build the example code and export to Wasm

Minimal reproduction project

example.zip

[dsnopek]

What version of Emscripten are you building your extension with?

It needs to match the version that was used to build Godot, which I think for the official Godot 4.6-rc2 build is 4.0.20

[fatduckling]

Thanks @dsnopek I was originally using 4.0.23 but now I downgraded to 4.0.20.
But I'm getting a new error:

Uncaught (in promise) Error: need to see wasm magic number
    at failIf (example.js:1:7910)
    at getDylinkMetadata (example.js:1:8281)
    at loadWebAssemblyModule (example.js:1:14151)
    at example.js:1:70541
    at async loadDylibs (example.js:1:71576)

I think it's because of the way I'm compiling the GDExtension library:

$ em++ -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.20 (6913738ec5371a88c4af5a80db0ab42bad3de681)
clang version 22.0.0git (https:/github.com/llvm/llvm-project d163988dd2833f28fbca8c144265108d25ae7bd2)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /home/saleem/software/emsdk-4.0.23/upstream/bin


saleem@localhost:$ rm -rf ../build/* && emcmake cmake .. && make -j23
emcmake: cmake .. -DCMAKE_TOOLCHAIN_FILE=/home/saleem/software/emsdk-4.0.23/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/home/saleem/software/emsdk-4.0.23/node/22.16.0_64bit/bin/node in directory /home/saleem/GodotProjects/example/backend/build
CMake Warning (dev) at CMakeLists.txt:30 (add_library):
  ADD_LIBRARY called with SHARED option but the target platform does not
  support dynamic linking.  Building a STATIC library instead.  This may lead
  to problems.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Configuring done
-- Generating done
-- Build files have been written to: /home/saleem/GodotProjects/example/backend/build
[ 66%] Building CXX object CMakeFiles/example.dir/src/register_types.cpp.o
[ 66%] Building CXX object CMakeFiles/example.dir/src/scenes/example_scene.cpp.o
[ 66%] Building CXX object CMakeFiles/tests.dir/tests/example_test.cpp.o
[ 66%] Building CXX object CMakeFiles/tests.dir/third-party/pugixml/pugixml.cpp.o
[ 83%] Linking CXX static library libexample.a
[ 83%] Built target example
[100%] Linking CXX executable tests.js
[100%] Built target tests


saleem@localhost:$ xxd -l 16 /home/saleem/GodotProjects/example/backend/build/libexample.a 
00000000: 213c 6172 6368 3e0a 2f20 2020 2020 2020  !<arch>./       

Using xxd I can see that that libexample.a is an arch, not asm dyli.

This is my cmake:

cmake_minimum_required(VERSION 3.25.1)
project(example)

enable_testing()

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_FLAGS_DEBUG "-g")
set(CMAKE_CXX_FLAGS_RELEASE "-Ofast")
set(CMAKE_POSITION_INDEPENDENT_CODE ON)

# show all errors
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wno-attributes -Wpedantic -Wextra -Werror")

set(GODOT_ROOT /home/saleem/software/godot/godot-cpp CACHE PATH "Path to Godot root directory")
set(GODOT_LIBRARY ${GODOT_ROOT}/bin/libgodot-cpp.linux.template_debug.x86_64.a CACHE PATH "Path to Godot static library")

include_directories(include)

include_directories(SYSTEM
        ${GODOT_ROOT}/include
        ${GODOT_ROOT}/gdextension
        ${GODOT_ROOT}/gen/include
        third-party
)

file(GLOB_RECURSE SOURCES src/*.cpp)

set(TEST_SOURCES third-party/pugixml/pugixml.cpp)

add_library(example SHARED ${SOURCES})
target_link_libraries(example ${GODOT_LIBRARY})
...

Any idea?

[enetheru]

yeah, so there are hoops that need to be jumped through if you try to use CMake to build due to the emscripten toolchain scripts which are attached with emcmake not allowing shared libs.

I have the hack we use to get this working documented here: https://github.com/godotengine/godot-cpp/blob/master/cmake/emsdkHack.cmake

To take advantage of it you will need to consume the godot-cpp lib using "modern cmake", use the godot-cpp-template as your starting point https://github.com/godotengine/godot-cpp-template

[fatduckling]

Thanks @enetheru

Now I'm getting a new error:

ERROR: Attempt to get non-existent interface function: 'alid_html_color'. example.js:467:18
    onPrintError http://localhost/game/example.js:467
    put_char http://localhost/game/example.js:1
    write http://localhost/game/example.js:1
    write http://localhost/game/example.js:1
    doWritev http://localhost/game/example.js:1
    _fd_write http://localhost/game/example.js:1
    <anonymous> source280:509505
    <anonymous> source280:714363
    <anonymous> source280:717605
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:30818298
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:30817908
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:30817634
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:30818707
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:33499550
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:33500031
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:32995968
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:1213802
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:1215405
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:820410
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:33026682
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:33028952
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:33028238
    <anonymous> http://localhost/game/example.js line 1 > WebAssembly.instantiate:3635978
    __Z14godot_web_mainiPPc http://localhost/game/example.js:1
    <anonymous> source280:490251
    callMain http://localhost/game/example.js:1
    Engine http://localhost/game/example.js:798
    Engine http://localhost/game/example.js:793
    (Async: promise callback)
    start http://localhost/game/example.js:772
    Engine http://localhost/game/example.js:831
    (Async: promise callback)
    startGame http://localhost/game/example.js:830
    <anonymous> http://localhost/game/example.html:202
    <anonymous> http://localhost/game/example.html:216
   at: get_interface_function (core/extension/gdextension.cpp:730) example.js:467:18
 load GDExtension interface function print_error(). example.js:452:16
ERROR: GDExtension initialization function 'example_library_init' returned an error. example.js:467:18
   at: initialize (core/extension/gdextension_library_loader.cpp:235) example.js:467:18
ERROR: Error loading extension: 'res://example.gdextension'. example.js:467:18
   at: load_extensions (core/extension/gdextension_manager.cpp:329) example.js:467:18
Godot Engine v4.6.rc.custom_build.78c6632eb - https://godotengine.org example.js:452:16
OpenGL API OpenGL ES 3.0 (WebGL 2.0) - Compatibility - Using Device: Mozilla - NVIDIA GeForce GTX 980, or similar example.js:452:16
An AudioContext was prevented from starting automatically. It must be created or resumed after a user gesture on the page. example.js:1:572965
Build configuration: Emscripten 4.0.20, single-threaded, GDExtension support. example.js:452:16
ERROR: Cannot get class 'ExampleScene'. example.js:467:18
   at: _instantiate_internal (core/object/class_db.cpp:565) example.js:467:18
WARNING: Node Root of type ExampleScene cannot be created. A placeholder will be created instead. example.js:467:18
   at: instantiate (scene/resources/packed_scene.cpp:333)

EDIT I compiled godot again with threads support:

scons platform=web target=template_debug javascript_eval=no dlink_enabled=yes threads=yes

Then I also added this in my cmake:

target_compile_options(example PRIVATE -pthread -Wno-error=experimental)
target_link_options(example PRIVATE -pthread -Wno-error=experimental)

It seemed to have fixed it. Looks like a similar issue is already reported in #1830

[enetheru]

Can you please test if using the more generic way works with emscripten instead of adding flags manually?

find_package(Threads)
target_link_libraries(my_lib PRIVATE Threads::Threads)

from https://cmake.org/cmake/help/latest/module/FindThreads.html

[fatduckling]

@enetheru I tried that before, I get this error:

Uncaught (in promise) LinkError: imported shared memory but unshared required
    loadDylibs http://localhost/game/example.js:1
    AsyncFunctionThrow self-hosted:784
    (Async: async)
    receiveInstance http://localhost/game/example.js:1
    Godot http://localhost/game/example.js:1
    done http://localhost/game/example.js:540
    (Async: promise callback)
    instantiateWasm http://localhost/game/example.js:543
    Godot http://localhost/game/example.js:1
    createWasm http://localhost/game/example.js:1
    Godot http://localhost/game/example.js:1
    Engine http://localhost/game/example.js:719
    (Async: promise callback)
    Engine http://localhost/game/example.js:717
    doInit http://localhost/game/example.js:716
    init http://localhost/game/example.js:733
    startGame http://localhost/game/example.js:828
    <anonymous> http://localhost/game/example.html:202
    <anonymous> http://localhost/game/example.html:216

I have to add this to make it work:

    target_compile_options(example PRIVATE -sUSE_PTHREADS=1)
    target_link_options(example PRIVATE -sUSE_PTHREADS=1 -Wno-error=experimental)

[Zylann]

It needs to match the version that was used to build Godot, which I think for the official Godot 4.6-rc2 build is 4.0.20

@dsnopek how can users know this? If someone wants to build my extension for the web matching their Godot version, they would have to know about this quirk, and know which version of Emscripten to use exactly (In Godot docs we see 4.0.0+ but that isn't an exact version). So even if I were to document this myself it wouldn't be complete without that info.
I tried looking into Godot's Github Actions and found 4.0.11 instead of 4.0.20: https://github.com/godotengine/godot/blob/bf95b62586e31b8a3503f5903d7764d7c52bf2ab/.github/workflows/web_builds.yml#L12

I suppose this means you'd have to build Godot anyways so in a way "you would know" which version of Emscripten to use I guess? But the doc doesnt indicate the quirk.
Of am I misunderstanding what the doc says? I was told official templates actually do support extensions, but then I don't know where to look for which Emscripten version is associated with them.
(on a side note it also means it's a bit difficult to provide web builds in my release packages, since users would either have to build Godot export templates themselves, or rebuild the extension if they use a Godot version that used a different Emscripten version that was used for my extension build, forcing me to do an extension build for every version of Godot pretty much?)

[dsnopek]

It needs to match the version that was used to build Godot, which I think for the official Godot 4.6-rc2 build is 4.0.20

@dsnopek how can users know this?

So, the way I look this up, is by checking the Dockerfile.web for the right branch in Godot's build-containers project, because this is what's used to make the official Godot builds (not GitHub actions).

For example, here's for Godot 4.5:

https://github.com/godotengine/build-containers/blob/4.5/Dockerfile.web#L4

Right now, master appears to still be used for 4.6, but at some point that'll be for 4.7 and there will be a 4.6 branch.

It would be nice to have these versions documented, though!

on a side note it also means it's a bit difficult to provide web builds in my release packages, since users would either have to build Godot export templates themselves, or rebuild the extension if they use a Godot version that used a different Emscripten version that was used for my extension build, forcing me to do an extension build for every version of Godot pretty much?

Unfortunately, yes. Unless Godot sticks to a specific Emscripten version across several minor releases, there's really nothing we can do about this. Two binaries built with two different versions of Emscripten are incompatible.

[fatduckling]

Thanks @dsnopek Closing this, no further action