Emscripten port SDL 2.24.0 SDL_THREADS_DISABLED stack error

[ericoporto]

Hey, I am trying to upgrade AGS to use Emscripten 3.1.23, and it also uses SDL 2.24.0. It doesn't even start for me, I am getting the following error stack, and it's all in SDL 2. It looks like a recursive error? I curiously don't use SDL_CreateSemaphore and revealing the missing frames it's all a loop started by it.

ags.js:36 Uncaught RangeError: Maximum call stack size exceeded
    at __memcpy (emscripten_memcpy.c:29:1)
    at __fwritex (fwrite.c:23:2)
    at out (vfprintf.c:179:27)
    at printf_core (vfprintf.c:513:10)
    at __vfprintf_internal (vfprintf.c:739:13)
    at vfprintf (vfprintf.c:756:9)
    at vsnprintf (vsnprintf.c:54:9)
    at SDL_vsnprintf (SDL_string.c:1407:12)
    at SDL_SetError (SDL_error.c:40:18)
    at SDL_CreateSemaphore (SDL_syssem.c:35:5)
$__memcpy	@	emscripten_memcpy.c:29
$__fwritex	@	fwrite.c:23
$out	@	vfprintf.c:179
$printf_core	@	vfprintf.c:513
$__vfprintf_internal	@	vfprintf.c:739
$vfprintf	@	vfprintf.c:756
$vsnprintf	@	vsnprintf.c:54
$SDL_vsnprintf	@	SDL_string.c:1407
$SDL_SetError	@	SDL_error.c:40
$SDL_CreateSemaphore	@	SDL_syssem.c:35
$SDL_CreateMutex	@	SDL_sysmutex.c:44
$SDL_LogMessageV	@	SDL_log.c:319
$SDL_LogDebug	@	SDL_log.c:227
$SDL_SetError	@	SDL_error.c:58
$SDL_CreateSemaphore	@	SDL_syssem.c:35
$SDL_CreateMutex	@	SDL_sysmutex.c:44
$SDL_LogMessageV	@	SDL_log.c:319
$SDL_LogDebug	@	SDL_log.c:227
$SDL_SetError	@	SDL_error.c:58
$SDL_CreateSemaphore	@	SDL_syssem.c:35
$SDL_CreateMutex	@	SDL_sysmutex.c:44
$SDL_LogMessageV	@	SDL_log.c:319
$SDL_LogDebug	@	SDL_log.c:227
$SDL_SetError	@	SDL_error.c:58
$SDL_CreateSemaphore	@	SDL_syssem.c:35
$SDL_CreateMutex	@	SDL_sysmutex.c:44
$SDL_LogMessageV	@	SDL_log.c:319
$SDL_LogDebug	@	SDL_log.c:227
$SDL_SetError	@	SDL_error.c:58
$SDL_CreateSemaphore	@	SDL_syssem.c:35
load (async)		
agsAttachFileInput	@	ags.html:295
onchange	@	ags.html:183
Show 170 more frames

I added a breakpoint there and this revealed that the cause was just the SDL_Init call we use.

My Emsdk flags used through CMake

CMAKE_CXX_FLAGS:   -sUSE_SDL=2  -sUSE_FREETYPE=1  -sUSE_VORBIS=1  -sUSE_OGG=1           -O2         -s DISABLE_EXCEPTION_CATCHING=0          -gsource-map -fsanitize=null -fsanitize-minimal-runtime
CMAKE_C_FLAGS:   -sUSE_SDL=2  -sUSE_FREETYPE=1  -sUSE_VORBIS=1  -sUSE_OGG=1           -O2         -s DISABLE_EXCEPTION_CATCHING=0          -gsource-map -fsanitize=null -fsanitize-minimal-runtime
CMAKE_EXE_LINKER_FLAGS:   -sUSE_SDL=2  -sUSE_FREETYPE=1  -sUSE_VORBIS=1  -sUSE_OGG=1          -s ALLOW_MEMORY_GROWTH=1          -s ASYNCIFY         -s ALLOW_TABLE_GROWTH=1         -s WASM=1         -s INVOKE_RUN=0              -s EXIT_RUNTIME=1               -s EMULATE_FUNCTION_POINTER_CASTS=1          -s FULL_ES2=1         -s FORCE_FILESYSTEM=1 -lidbfs.js          -s EXPORTED_FUNCTIONS=['_main']         -s EXTRA_EXPORTED_RUNTIME_METHODS=['ccall','callMain'] --emit-symbol-map --source-map-base http://127.0.0.1:8000/../  --shell-file C:/Users/user/launcher_index.html

The SDL2 I am using is built by emscripten own ports feature, built without threads.

[ericoporto]

SDL/CMakeLists.txt

Lines 2768 to 2773 in 33050fe

	if (EMSCRIPTEN)
	set(SDL_THREADS_DISABLED 1)
	file(GLOB THREADS_SOURCES ${SDL2_SOURCE_DIR}/src/thread/generic/*.c)
	list(APPEND SOURCE_FILES ${THREADS_SOURCES})
	else()
	message_error("Threads are needed by many SDL subsystems and may not be disabled")

SDL can only be built without threads in Emscripten platform, so it's hard to track this in other platform. It would be nice if it was possible to build and run SDL without threads in other platform, at least to be able to more easily debug an emscripten like logic.

[slouken]

We've had many problems reported by people who have disabled threads expecting everything to work, so we're not going to do that in default builds. We can potentially do a custom build and test in CI, but we're not removing that check in general.

[slouken]

I think I fixed this, can you try now?

[ericoporto]

@slouken that does fix it! Any chance this makes into a 2.24.2 release? The SDL2 from Emscripten ports is useless so far since it was upgraded to 2.24.0 there...

I also found it is missing a symbol there, so a PR is needed, it doesn't have the stdlib/SDL_crc16.c included in it's sources so the built SDL2 will fail to link for missing symbols.

If this makes it, just hit me up and I PR it there.

[slouken]

Great! Yes, I merged this over for 2.24.2.

[ericoporto]

emscripten-core/emscripten#18026 leaving as draft until 2.24.2 is released