[wasm-mt] Emscripten SDK runtime pack is missing multi-threaded static libraries

[lambdageek]

In dotnet/emsdk#43 we removed *-mt.a from the emscripten sysroot.

Unfortunately this means that /p:WasmBuildNative=true does not work for multi-threaded builds.

We should either put the libraries back in the main SDK, or figure out how to provide an additional nuget with the threaded libs along with required build flags to make emcc look for them in another directory.

$ dotnet build
MSBuild version 17.4.0-preview-22416-02+5d102ae37 for .NET
Determining projects to restore...
Restored /Users/alklig/work/net7-playground/hithread/browser.csproj (in 2 ms).
/Users/alklig/work/net7-nightly/sdk/7.0.100-rc.2.22425.5/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.RuntimeIdentifierInference.targets(219,5): message NETSDK1057: You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy [/Users/alklig/work/net7-playground/hithread/browser.csproj]
browser -> /Users/alklig/work/net7-playground/hithread/bin/Debug/net7.0/browser-wasm/browser.dll
Compiling native assets with emcc with -O0. This may take a while ...
[2/3] corebindings.c -> corebindings.o [took 0.384s]
[1/3] pinvoke.c -> pinvoke.o [took 0.384s]
[3/3] driver.c -> driver.o [took 0.416s]
Linking for initial memory $(EmccInitialHeapSize)=536870912 bytes. Set this msbuild property to change the value.
Linking with emcc with -O0. This may take a while ...
...
Exception: FROZEN_CACHE is set, but cache file is missing: "sysroot/lib/wasm32-emscripten/libGL-mt.a" (in cache root path "/Users/alklig/work/net7-nightly/packs/Microsoft.NET.Runtime.Emscripten.3.1.12.Sdk.osx-x64/8.0.0-alpha.1.22415.5/tools/emscripten/cache")
/Users/alklig/work/net7-nightly/packs/Microsoft.NET.Runtime.WebAssembly.Sdk/7.0.0-rc.1.22422.12/Sdk/WasmApp.Native.targets(422,5): error MSB3073: The command "emcc "@/Users/alklig/work/net7-nightly/packs/Microsoft.NETCore.App.Runtime.Mono.multithread.browser-wasm/7.0.0-rc.1.22422.12/runtimes/browser-wasm/native/src/emcc-default.rsp" "@/Users/alklig/work/net7-nightly/packs/Microsoft.NETCore.App.Runtime.Mono.multithread.browser-wasm/7.0.0-rc.1.22422.12/runtimes/browser-wasm/native/src/emcc-link.rsp" "@/Users/alklig/work/net7-playground/hithread/obj/Debug/net7.0/browser-wasm/wasm/for-build/emcc-link.rsp"" exited with code 1. [/Users/alklig/work/net7-playground/hithread/browser.csproj]

Part of #74654

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

In dotnet/emsdk#43 we removed *-mt.a from the emscripten sysroot.

Unfortunately this means that /p:WasmBuildNative=true does not work for multi-threaded builds.

We should either put the libraries back in the main SDK, or figure out how to provide an additional nuget with the threaded libs along with required build flags to make emcc look for them in another directory.

$ dotnet build
MSBuild version 17.4.0-preview-22416-02+5d102ae37 for .NET
Determining projects to restore...
Restored /Users/alklig/work/net7-playground/hithread/browser.csproj (in 2 ms).
/Users/alklig/work/net7-nightly/sdk/7.0.100-rc.2.22425.5/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.RuntimeIdentifierInference.targets(219,5): message NETSDK1057: You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy [/Users/alklig/work/net7-playground/hithread/browser.csproj]
browser -> /Users/alklig/work/net7-playground/hithread/bin/Debug/net7.0/browser-wasm/browser.dll
Compiling native assets with emcc with -O0. This may take a while ...
[2/3] corebindings.c -> corebindings.o [took 0.384s]
[1/3] pinvoke.c -> pinvoke.o [took 0.384s]
[3/3] driver.c -> driver.o [took 0.416s]
Linking for initial memory $(EmccInitialHeapSize)=536870912 bytes. Set this msbuild property to change the value.
Linking with emcc with -O0. This may take a while ...
...
Exception: FROZEN_CACHE is set, but cache file is missing: "sysroot/lib/wasm32-emscripten/libGL-mt.a" (in cache root path "/Users/alklig/work/net7-nightly/packs/Microsoft.NET.Runtime.Emscripten.3.1.12.Sdk.osx-x64/8.0.0-alpha.1.22415.5/tools/emscripten/cache")
/Users/alklig/work/net7-nightly/packs/Microsoft.NET.Runtime.WebAssembly.Sdk/7.0.0-rc.1.22422.12/Sdk/WasmApp.Native.targets(422,5): error MSB3073: The command "emcc "@/Users/alklig/work/net7-nightly/packs/Microsoft.NETCore.App.Runtime.Mono.multithread.browser-wasm/7.0.0-rc.1.22422.12/runtimes/browser-wasm/native/src/emcc-default.rsp" "@/Users/alklig/work/net7-nightly/packs/Microsoft.NETCore.App.Runtime.Mono.multithread.browser-wasm/7.0.0-rc.1.22422.12/runtimes/browser-wasm/native/src/emcc-link.rsp" "@/Users/alklig/work/net7-playground/hithread/obj/Debug/net7.0/browser-wasm/wasm/for-build/emcc-link.rsp"" exited with code 1. [/Users/alklig/work/net7-playground/hithread/browser.csproj]

Part of #74654

Author:	lambdageek
Assignees:	-
Labels:	arch-wasm, area-Build-mono
Milestone:	-

[lambdageek]

Not sure if we will be able to do this in time for 7, or if it will have to wait until 8

[lambdageek]

A workaround is for users to manually copy the required libraries from an EMSDK install

cp ~/work/dotnet-runtime/runtime/src/mono/wasm/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/*-mt.a ~/work/net7-nightly/packs/Microsoft.NET.Runtime.Emscripten.3.1.12.Sdk.osx-x64/8.0.0-alpha.1.22415.5/tools/emscripten/cache/sysroot/lib/wasm32-emscripten

[lambdageek]

Report from

% du -c -h ~/work/dotnet-runtime/runtime/src/mono/wasm/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/*-mt.a

Size	Library	Required	Notes
40K	libGL-mt.a
1.6M	libasan_rt-mt.a
6.3M	libc++-mt.a	✅
916K	libc++abi-mt.a	✅
3.4M	libc-mt.a	✅
528K	libcompiler_rt-mt.a	✅
532K	libcompiler_rt-wasm-sjlj-mt.a	❓	not sure what this is
80K	libdlmalloc-mt.a	✅
68K	libemmalloc-memvalidate-mt.a
80K	libemmalloc-memvalidate-verbose-mt.a
52K	libemmalloc-mt.a
76K	libemmalloc-verbose-mt.a
16K	libfetch-mt.a	❓
220K	liblsan_common_rt-mt.a
496K	liblsan_rt-mt.a
36K	libprintf_long_double-mt.a	❓
10M	libsanitizer_common_rt-mt.a
40K	libsockets-mt.a	❓
36K	libsockets_proxy-mt.a	❓
32K	libubsan_minimal_rt-mt.a
604K	libubsan_rt-mt.a
4.0K	libunwind-mt.a	✅
6.2M	libwasmfs-asan-debug-mt.a
6.1M	libwasmfs-asan-mt.a
5.0M	libwasmfs-debug-mt.a
5.0M	libwasmfs-mt.a	❓
184K	libwebgpu_cpp-mt.a	❓
48M	total

Just the ✅ total is around 11 megabytes

Adding the ❓is near 17 with libwasmfs making up the bulk of the extra space

[lambdageek]

@lewing what do you think about a separate (OOB) nuget that just has the mt libs and some SDK.props that injects emscipten linker flags?

So to do a multi-threaded native build one would have to do something like this:

<PropertyGroup>
  <WasmEnableThread>true</WasmEnableThread>
  <WasmBuildNative>true</WasmBuildNative>
</PropertyGroup>

<ItemGroup>
  <PackageReference Include="Microsoft.NET.Runtime.Emscripten.3.0.12.Threading.Sdk" Version="7.0.0" IncludeAssets="build" />
</ItemGroup>

[lewing]

no need, we can do all that in the workload invisibly, the complicated part is packaging it and setting the appropriate compiler options.

[lewing]

The steps are essentially adding the threading package to the emsdk build, and referencing it in the emscripten manifest when WasmEnableThreads is set. It's props should add the required flags and paths to the emcc options.

[lambdageek]

no need, we can do all that in the workload invisibly, the complicated part is packaging it and setting the appropriate compiler options.

@lewing I was thinking OOB in case we don't make it by RTM 😁

[lambdageek]

I'm looking at the emsdk build right now - moving the -mt.a files out of the way (instead of deleting) and making a new nuget seems straightforward. I'll try to have something to show by tomorrow or Monday