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It also happens on Net9

the Itanium demangle is just C++ name mangling on unix systems, used on other architectures than itanium.

it is linked away in out publish .wasm, so I think we don't need to do anything here.

> wa-info -d -f itanium_demangle artifacts/obj/mono/Wasm.Browser.Bench.Sample/browser.wasm.Release/browser-wasm/wasm/for-publish/dotnet.native.wasm | grep func | wc -l
     268
> wa-info -d -f itanium_demangle src/mono/sample/wasm/browser-bench/bin/browser-wasm/publish/dotnet.native.wasm | grep func | wc -l
       0

I can reproduce it out of tree with 9.0.101 vanilla template

dotnet new wasmbrowser
dotnet publish -c Release

Adding <EmccExtraLDFlags>-Wl,--print-map</EmccExtraLDFlags> shows the source as

C:\Dev\.dotnet\packs\Microsoft.NET.Runtime.Emscripten.3.1.56.Cache.win-x64\9.0.0\tools\emscripten\cache\sysroot\lib\wasm32-emscripten\libc++abi-except.a(cxa_demangle.o)

Interestingly it doesn't happen in intree build in main, but happens in net9 template. I was able to reproduce it locally in net9 and wasmbrowser template.

With Pavel we tried to use main's clang and wasm-ld to see if main's linker might behave differently. it still reproduced in net9 template.

with <EmccExtraLDFlags>-Wl,--trace-symbol=__cxa_demangle</EmccExtraLDFlags>

    C:\Dev\.dotnet\packs\Microsoft.NET.Runtime.Emscripten.3.1.56.Cache.win-x64\9.0.0\tools\emscripten\cache\sysroot\lib\wasm32-emscripten\libc++abi-except.a(cxa_demangle.o): lazy definition of __cxa_demangle
    C:\Dev\.dotnet\packs\Microsoft.NET.Runtime.Emscripten.3.1.56.Cache.win-x64\9.0.0\tools\emscripten\cache\sysroot\lib\wasm32-emscripten\libc++abi-except.a(cxa_exception_js_utils.o): reference to __cxa_demangle
    C:\Dev\.dotnet\packs\Microsoft.NET.Runtime.Emscripten.3.1.56.Cache.win-x64\9.0.0\tools\emscripten\cache\sysroot\lib\wasm32-emscripten\libc++abi-except.a(cxa_demangle.o): definition of __cxa_demangle

Meanwhile we traced it back to -s EXPORT_EXCEPTION_HANDLING_HELPERS=1 option, which pulls the demangle symbols in.

@kg do we still need this setting? It was added in #91364

I'm testing without it here #111033

I believe these are still needed for proper exception handling integration. Not specifically the demangle stuff but the other bits that come with the exception handling helpers.

It's possible something has changed and they aren't needed, but you would need to manually test to verify that the relevant configurations haven't regressed, as they aren't tested by CI. I don't remember how to test it anymore, to be honest.