[wasm coreclr] exception handling #113694

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1. ghost added

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3. jkotas

   changed the title [-]exception handling[/-] [+][wasm coreclr] exception handling[/+] on Mar 19, 2025
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5. radekdoulik

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   arch-wasmWebAssembly architectureWebAssembly architecture

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7. dotnet-policy-service commented on Mar 19, 2025

   

   dotnet-policy-serviceBot

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   Tagging subscribers to 'arch-wasm': @lewing
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8. pavelsavara

   added this to the 10.0.0 milestone on Apr 1, 2025
9. lewing

   modified the milestones: 10.0.0, 11.0.0 on Aug 5, 2025
10. pavelsavara commented on Aug 29, 2025

    

    pavelsavara

    on Aug 29, 2025

    Last edited by pavelsavara

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    In transitions to native code in Mono we use C++ catch via LLVM, that translates to WASM catch instruction/block.

    This would not be necessary for JSImport/JSExport interop, because we catch and marshal exceptions in JS.

    But any exceptions in native code called by P/Invoke/Qcall/Fcall/Icall (including emscripten and browser errors) would trap if not handled. So I think we will need something similar when we call out.

    runtime/src/mono/mono/mini/llvm-runtime.cpp

    Lines 42 to 50 in 2562b73

    	mono_llvm_cpp_catch_exception (MonoLLVMInvokeCallback cb, gpointer arg, gboolean *out_thrown)
    	{
    	*out_thrown = FALSE;
    	try {
    	cb (arg);
    	} catch (int*) {
    	*out_thrown = TRUE;
    	}
    	}

    runtime/src/mono/mono/mini/llvm-runtime.cpp

    Lines 58 to 66 in 2562b73

    	EMSCRIPTEN_KEEPALIVE void
    	mono_jiterp_begin_catch (void *exception_object) {
    	__cxa_begin_catch (exception_object);
    	}
    	EMSCRIPTEN_KEEPALIVE void
    	mono_jiterp_end_catch (void) {
    	return __cxa_end_catch ();
    	}
11. pavelsavara commented on Apr 10, 2026

    

    pavelsavara

    on Apr 10, 2026

    Last edited by pavelsavara

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    @janvorli said JS exception in DLLImport is undefined behavior - he is right
    but the lived reality is that people have native code that calls JS directly and propagates JS exceptions.
    The key trick there is to abort posix/"process" when it happens, so that you don't get crazy behavior from subsequent calls into broken/corrupted system and silly bug reports.
12. lewing

    added a commit that references this issue on Apr 10, 2026

    Set interpreter context for WASM exception dispatch

    ...

    91e51f8
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16. pavelsavara commented on Jul 14, 2026

    

    pavelsavara

    on Jul 14, 2026

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    Is there anything remaining for this one @radekdoulik ?
17. pavelsavara

    modified the milestones: 11.0.0, 12.0.0 on Jul 15, 2026