Build wasm JIT and crossgen2 R2R of System.Private.CoreLib for browser target by davidwrighton · Pull Request #127935 · dotnet/runtime

davidwrighton · 2026-05-07T23:38:15Z

Note

This PR was created with assistance from GitHub Copilot.

Enable build.cmd clr+libs -os browser to:

Build clrjit_universal_wasm_x64 (the wasm-targeting JIT for the host platform)
Build crossgen2 that can use the wasm JIT
Run crossgen2 on System.Private.CoreLib to produce a .wasm R2R output

Changes

eng/Subsets.props: Remove wasm exclusion from _BuildAnyCrossArch; use ClrWasmJitSubset for wasm targets
src/coreclr/CMakeLists.txt: Early-return for wasm cross-component builds (only configure JIT + dependencies)
src/coreclr/jit/CMakeLists.txt: Create clrjit_universal_wasm_* when target=wasm
src/coreclr/gcinfo/CMakeLists.txt: Create gcinfo_universal_wasm library
src/coreclr/crossgen-corelib.proj: Enable crossgen2 for browser with --obj-format:wasm and --codegenopt:JitWasmNyiToR2RUnsupported=1; output as System.Private.CoreLib.NotReadyYet.wasm
eng/native/configureplatform.cmake: Guard emscripten link/compile options from cross-component builds
src/coreclr/jit/compiler.cpp & codegenwasm.cpp: Add missing #ifdef PROFILING_SUPPORTED guards
src/coreclr/utilcode/CMakeLists.txt: Guard natvis for wasm target
src/coreclr/tools/aot/crossgen2/crossgen2.props: Allow jitinterface pickup for wasm when CrossHostArch is set

…r target Enable 'build.cmd clr+libs -os browser' to: 1. Build clrjit_universal_wasm_x64 (the wasm-targeting JIT for the host platform) 2. Build crossgen2 that can use the wasm JIT 3. Run crossgen2 on System.Private.CoreLib to produce a .wasm R2R output Key changes: - eng/Subsets.props: Remove wasm exclusion from cross-arch build; use ClrWasmJitSubset - src/coreclr/CMakeLists.txt: Early-return for wasm cross-component (only JIT+deps) - src/coreclr/jit/CMakeLists.txt: Create clrjit_universal_wasm_* target - src/coreclr/gcinfo/CMakeLists.txt: Create gcinfo_universal_wasm library - src/coreclr/crossgen-corelib.proj: Enable crossgen2 for browser with wasm format - eng/native/configureplatform.cmake: Guard emscripten flags from cross-component builds - Fix missing PROFILING_SUPPORTED guards in JIT wasm codegen Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-05-07T23:39:39Z

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
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Copilot

Pull request overview

This PR updates the CoreCLR build and crossgen plumbing to enable a browser/wasm-targeting “cross-components” build that produces a wasm-targeting standalone JIT (clrjit_universal_wasm_*), builds a crossgen2 that can consume that JIT, and runs crossgen2 over System.Private.CoreLib to emit a wasm object/container output.

Changes:

Enable building the wasm-targeting standalone JIT and its gcinfo dependency under wasm targeting.
Adjust subset/build logic so wasm targets build only the needed cross-component pieces (wasm JIT subset) rather than all cross-arch JITs.
Enable browser corelib crossgen2 invocation with --obj-format:wasm and a wasm-specific codegen option; tighten a few wasm/cross-component guards (profiling, natvis, emscripten flags).

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
eng/Subsets.props	Enables cross-component builds for wasm targets and selects `ClrWasmJitSubset` instead of `ClrAllJitsSubset` when targeting wasm.
eng/native/configureplatform.cmake	Avoids applying emscripten-specific compile/link flags to cross-component builds.
src/coreclr/CMakeLists.txt	Adds an early-return path for wasm cross-components builds and ensures jitinterface is configured for browser when cross-component building.
src/coreclr/crossgen-corelib.proj	Enables browser crossgen2 with wasm obj-format and a wasm-specific codegen opt; sets wasm output path.
src/coreclr/gcinfo/CMakeLists.txt	Adds `gcinfo_universal_wasm` library creation for wasm-targeting builds.
src/coreclr/jit/CMakeLists.txt	Creates `clrjit_universal_wasm_${ARCH_HOST_NAME}` when targeting wasm.
src/coreclr/jit/compiler.cpp	Guards verbose printing of profiler-hook state behind `PROFILING_SUPPORTED`.
src/coreclr/jit/codegenwasm.cpp	Guards `genProfilingLeaveCallback` definition behind `PROFILING_SUPPORTED`.
src/coreclr/tools/aot/crossgen2/crossgen2.props	Allows shipping/picking up `jitinterface` content for wasm scenarios when `CrossHostArch` is set.
src/coreclr/utilcode/CMakeLists.txt	Skips linking natvis into `utilcode_dac` when targeting wasm (where that target isn’t built).

The wasm cross-component build (host=x64, target=wasm) produces libclrjit_universal_wasm_x64.so for crossgen2. Several CMake files used CLR_CMAKE_TARGET_ARCH_WASM where CLR_CMAKE_HOST_ARCH_WASM is correct, since the PAL and minipal code runs on the host, not the target. Changes: - pal/src/CMakeLists.txt: Use HOST_ARCH_WASM for libunwind, arch source selection, and multithreading guards. - clrfeatures.cmake: Disable FEATURE_EVENT_TRACE and FEATURE_EVENTSOURCE_XPLAT for wasm cross-builds (not needed for crossgen2, and eventing dependencies are unavailable). - CMakeLists.txt: Add build_resources(), nativeresources, and dlls/mscorrc to the wasm cross-build early-return block so the JIT can link mscorrc and coreclrpal. - native/minipal/CMakeLists.txt: Include ospagesize.c in cross-builds where host is not wasm (the POSIX implementation is needed on x64). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use setBBProfileWeight(BB_ZERO_WEIGHT) instead of bbSetRunRarely() for the switch and rethrow blocks created by the wasm EH pass. bbSetRunRarely() only scales the weight to zero without setting the BBF_PROF_WEIGHT flag, which causes a checked build assertion when PGO data (.mibc) is applied. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

NYI_WASM was always fatal in release builds because: 1. The JitWasmNyiToR2RUnsupported config was CONFIG_INTEGER (debug-only) 2. The NYI_WASM macro had an #if DEBUG guard that fell back to NYIRAW Change CONFIG_INTEGER to RELEASE_CONFIG_INTEGER and remove the #if DEBUG split so NYI_WASM can gracefully skip unsupported methods via implReadyToRunUnsupported() in all build configurations. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Address review feedback: use inheritWeightPercentage(regionEntryBlock, 0) instead of setBBProfileWeight(BB_ZERO_WEIGHT). This properly propagates the BBF_PROF_WEIGHT flag from the source block and handles both PGO and non-PGO cases correctly. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

kg · 2026-05-12T19:01:28Z

JIT changes LGTM but I don't know the build system well enough to greencheck the build parts

agocke

LGTM although I'm not sure that there's a circumstance where we could ever be running CMake with wasm as the host target

- Add --help output for `--obj-format` switch to crossgen2. - Minor tweak to R2RTest, if anyone is still using that - Add support for the detail that R2R on wasm targets produces .wasm files instead of .dll files - When tests are built with RuntimeFlavor=coreclr, then they will default to setting RunWithNodeJS to true - Copy crossgen2 from a cross-build directory on Wasm - Enable bash and batch precommands when building wasm tests - Disable a few tests that had problematic precommands for testing When this PR and PR #127935 are merged, it will be straightforward enough to run tests. The process will be something like: ``` Commands to run tests, starting from a fresh build ; Build runtime+libs ./build.sh clr+libs -rc debug -c release -os browser ; Build TestRoot ./src/tests/build.sh skipmanaged browser ; Build test project from the test tree ./dotnet.sh /p:TargetArchitecture=wasm /p:TargetOS=browser /p:RuntimeFlavor=coreclr src/tests/GC/API/GCSettings/InducedGen0GC.csproj export CORE_ROOT=/home/davidwr/git/runtime/artifacts/tests/coreclr/browser.wasm.Debug/Tests/Core_Root export RunCrossGen2=1 /home/davidwr/git/runtime/artifacts/tests/coreclr/browser.wasm.Debug/GC/API/GCSettings/InducedGen0GC/InducedGen0GC.sh ``` --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings May 7, 2026 23:38

Copilot started reviewing on behalf of davidwrighton May 7, 2026 23:38 View session

github-actions Bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label May 7, 2026

davidwrighton requested a review from agocke May 7, 2026 23:38

dotnet-policy-service Bot assigned davidwrighton May 7, 2026

Copilot AI reviewed May 7, 2026

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Comment thread src/coreclr/CMakeLists.txt

build-analysis Bot mentioned this pull request May 8, 2026

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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davidwrighton and others added 2 commits May 11, 2026 10:42

davidwrighton commented May 11, 2026

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Copilot AI review requested due to automatic review settings May 11, 2026 20:12

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davidwrighton requested a review from AndyAyersMS May 11, 2026 20:22

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Comment thread src/coreclr/pal/src/CMakeLists.txt

davidwrighton mentioned this pull request May 13, 2026

Test harness and assorted changes for R2R testing in Wasm #128156

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agocke reviewed May 13, 2026

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agocke approved these changes May 13, 2026

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davidwrighton merged commit a7cda92 into dotnet:main May 13, 2026
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dotnet-maestro Bot mentioned this pull request May 14, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#6573

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Build wasm JIT and crossgen2 R2R of System.Private.CoreLib for browser target#127935

Build wasm JIT and crossgen2 R2R of System.Private.CoreLib for browser target#127935
davidwrighton merged 5 commits into
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davidwrighton:Build_CrossGen_andR2R_SPC

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