Main module initialization order

[allsey87]

The main module's constructor seems to be called by the runtime before its thread local storage has been initialized. Should this be the case? Perhaps it is just my ignorance, but this seems a bit off to me.

[sbc100]

That certainly should not be the case no. TLS initialization should happen before any code (including static constructors) run.

Perhaps I'm not understanding correctly.. what do you mean by "main module's constructor"

[allsey87]

Hi Sam, by main module's constructor, I mean Module["asm"]["__wasm_call_ctors"] seems to be getting called before Module["asm"]["_emscripten_tls_init"] (based on wrapping the two in a function that also prints to Console.log).

[allsey87]

@sbc100 do you also observe this on your end?

[sbc100]

TLS init is performed by the PThread.threadInitTLS() function.

For the main thread this is called by __emscripten_init_main_thread_js, which itself is called from a static constructor using a system level priority to put it first above all user static constructor:

emscripten/system/lib/pthread/library_pthread.c

Lines 576 to 579 in 68ae550

	// See system/lib/README.md for static constructor ordering.
	__attribute__((constructor(48)))
	void __emscripten_init_main_thread(void) {
	__emscripten_init_main_thread_js(&__main_pthread);

The list of system-level static constructors is here:

emscripten/system/lib/README.md

Lines 19 to 24 in 68ae550

	- 1: `emscripten_stack_init` (stack_limits.S)
	- 47: `initialize_emmalloc_heap` (emmalloc.c)
	- 48: `__emscripten_init_main_thread` (pthread/library_pthread.c)
	- 49: `init_file_data` (generated by file_packager.py)
	- 50: asan init (??)
	- 100: `WasmFS wasmFS` (wasmfs/wasmfs.cpp)

[sbc100]

In order works __wasm_call_ctors is the thing that actually calls _emscripten_tls_init .. but this is by design.