Code change:
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runs successfully
Also is broken on ubuntu with the same error message (at least windows subsystem for linux)
rustc 1.53.0-nightly ( 2021-04-24) emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 2.0.12 () Here's some info I gathered: Rust tries to . I think Rust is assuming that this symbol comes from emscripten. emscripten has a : libc++abi.a: emscripten exceptions: this is what rustc is trying to use; libc++abi-noexcept.a: no exceptions: does not compile libc++abi-except.a: wasm exceptions: experimental; in emscripten's repo shows that was never compiled into libc++abi.a by This commit looks suspicious: Prior to emscripten SDK version 2.0.10, I think has been and never did anything. Rust probably shouldn't be calling a stubbed function. seems untested if you ask me because I don't know how it could ever have worked. I successfully compiled hello world with emscripten SDK version 2.0.9. That version still has the stub.
label I-prioritize T-compiler O-wasm
thanks for the analysis. Assigning priority as discussed in the of the Prioritization Working Group. Let's find someone who can have a look at this. label -I-prioritize +P-high +I-nominated
I recall with the LLVM 11 upgrade, the compat notes mentioned which version of Emscripten to use when compiling with the target. Once this bug is resolved, can we add a similar note for the releases that upgrade Rust to LLVM 12?
As mentioned the panic=unwind strategy is broken on wasm32-unknown-emscripten. I recommend to switch default to panic=abort. Note that also rust std lib has to be rebuilt with panic=abort to fix the undefined symbol errors. Testing on my side showed that the problem could be fixed by changing TargetOptions on line 38 to "panicstrategy: PanicStrategy::Abort," in file. Unfortunatelly I do not have experience in preparing pull request and have no capacity to get into it now.
This issue can be solved by setting the env var which will override any flags passed to emcc. See this comment - Passing these flags using the won't work, as they are not passed to the linker. I received this error in two places, one for symbol and one for , hence the flag.
Reported this on Emscripten:

Related discussion:
text: } } <ins> // This is required by the compiler to exist (e.g., it's a lang item), but it's // never actually called by the compiler.  Emscripten EH doesn't use a // personality function at all, it instead uses __cxa_find_matching_catch. // Wasm error handling would use __gxx_personality_wasm0. </ins> #[lang = "eh_personality"] unsafe extern "C" fn rust_eh_personality( <del> version: c_int, actions: uw::_Unwind_Action, exception_class: uw::_Unwind_Exception_Class, exception_object: *mut uw::_Unwind_Exception, context: *mut uw::_Unwind_Context, </del> <ins> _version: c_int, _actions: uw::_Unwind_Action, _exception_class: uw::_Unwind_Exception_Class, _exception_object: *mut uw::_Unwind_Exception, _context: *mut uw::_Unwind_Context, </ins> ) -> uw::_Unwind_Reason_Code { <del> __gxx_personality_v0(version, actions, exception_class, exception_object, context) </del> <ins> core::intrinsics::abort() </ins> } extern "C" {