[wasm][coreclr] Fix browser-wasm library tests broken by webcil V1 version bump by radekdoulik · Pull Request #126698 · dotnet/runtime

radekdoulik · 2026-04-09T11:16:09Z

Note

This PR description was AI/Copilot-generated.

PR #126388 bumped WC_VERSION_MAJOR from 0 to 1 in Webcil.cs. That constant is shared by both the crossgen2 R2R path (fully updated for V1) and the WebcilConverter build task (still writes V0 28-byte headers). The mismatch caused the C++ webcildecoder to misparse section headers at offset 32 instead of 28, breaking all browser-wasm library tests with COR_E_ASSEMBLYEXPECTED.

Pin WebcilConverter and WebcilReader to V0 until full V1 support is added to the managed converter and wasm wrapper.

WebcilConverter and WebcilReader still use the V0 28-byte header format but were picking up WC_VERSION_MAJOR=1 from the shared Webcil.cs constant, causing webcildecoder to misparse section headers. Pin both to V0. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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radekdoulik · 2026-04-09T11:17:55Z

@pavelsavara this is quick fix for the libraries test regression to unblock the libraries tests work, could I leave the V1 support to you?

Copilot

Pull request overview

Pins the managed Webcil build-task tooling back to Webcil v0 to avoid generating/accepting “v1-labeled” images that still use the v0 (28-byte) header layout, which breaks browser-wasm library tests after WC_VERSION_MAJOR was bumped to 1 elsewhere.

Changes:

Force WebcilReader to only accept Webcil major version 0 (reject v1 for now).
Force WebcilConverter to emit Webcil major version 0 in the header.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilReader.cs	Pins header validation to Webcil v0 major version.
src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilConverter.cs	Pins emitted header major version to Webcil v0.

Copilot · 2026-04-09T11:22:01Z

src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilReader.cs

        if (header.Id != WebcilConstants.WEBCIL_MAGIC
-            || header.VersionMajor != WebcilConstants.WC_VERSION_MAJOR
+            || header.VersionMajor != 0 // WASM-TODO: add webcil V1 support
            || header.VersionMinor != WebcilConstants.WC_VERSION_MINOR)
        {
            return false;


ReadHeader() returning false on a version mismatch causes the constructor to throw "Stream does not contain a valid Webcil file". With Webcil v1 now existing, a v1 image is valid but unsupported here, so the exception is misleading. Consider detecting the version mismatch explicitly and throwing a BadImageFormatException (or similar) that reports the unsupported version (e.g., major/minor) to make failures actionable.

Copilot · 2026-04-09T11:22:01Z

src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilConverter.cs

        WebcilHeader header = default;
        header.Id = WebcilConstants.WEBCIL_MAGIC;
-        header.VersionMajor = WebcilConstants.WC_VERSION_MAJOR;
+        header.VersionMajor = 0; // WASM-TODO: add webcil V1 support
        header.VersionMinor = WebcilConstants.WC_VERSION_MINOR;
        header.CoffSections = (ushort)coffHeader.NumberOfSections;


Hard-coding 0 for VersionMajor here works, but it introduces a magic number that’s now duplicated with WebcilReader. To keep this easier to update when v1 support is added, consider introducing a named constant in this project (e.g., const ushort SupportedWebcilVersionMajor = 0) and using it in both reader and converter.

Copilot · 2026-04-09T11:22:01Z

src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilReader.cs

        if (header.Id != WebcilConstants.WEBCIL_MAGIC
-            || header.VersionMajor != WebcilConstants.WC_VERSION_MAJOR
+            || header.VersionMajor != 0 // WASM-TODO: add webcil V1 support
            || header.VersionMinor != WebcilConstants.WC_VERSION_MINOR)


Hard-coding 0 for VersionMajor is intentional for now, but it creates a duplicated magic number (also in WebcilConverter). Consider using a shared named constant (within this project) for the supported major version to reduce the chance of future inconsistencies when v1 support is implemented.

pavelsavara · 2026-04-09T11:29:35Z

@radekdoulik let's revert the offending PR instead
@davidwrighton would know what needs to be fixed in the webcildecoder before merging his PR again

davidwrighton · 2026-04-09T12:19:13Z

I'd rather see a PR which just moves WC_VERSION_MAJOR back to zero. Or this PR. The only change I'm going to do after a revert would likely be to make these tasks be version 0 specific, since I don't think they are relevant in the Coreclr path.

pavelsavara · 2026-04-09T12:37:01Z

R2R is not the only scenario.
The webCIL wrapper/covertor is used by WASM SDK to conver IL only assemblies for both VMs.
a) we could give it a version parameter to produce different layouts for each VM
b) teach both VMs to accept the new layout

radekdoulik · 2026-04-09T12:49:58Z

We discussed it with @pavelsavara offline before and we will try to add V1 support to the rest of webcil ecosystem. I will open another PR for it.

radekdoulik · 2026-04-09T12:52:40Z

It is implemented and I am now testing it.

Remaining question is whether to let mono write and use V1 files now, or whether leave it at V0. @lewing @pavelsavara what is your opinion on that?

pavelsavara · 2026-04-09T12:56:13Z

It is implemented and I am now testing it.

Remaining question is whether to let mono write and use V1 files now, or whether leave it at V0. @lewing @pavelsavara what is your opinion on that?

Keep mono on V0 is easier because it would not force re-wrapping of existing (CDN) deployed binaries in Net11.

radekdoulik · 2026-04-09T14:31:39Z

ok, the library tests pass here, which is good. lets close it now and wait for #126709

…aders (#126709) PR #126388 bumped the shared webcil version from 0 to 1, we need to update the rest of webcil ecosystem ## Changes - **Webcil.cs**: Add `TableBase` field to managed `WebcilHeader` struct (32 bytes for V1) - **WebcilConverter.cs**: Parameterize version (default V0), write V0 (28-byte) or V1 (32-byte) header based on `webcilVersion` parameter. Add version validation and WriteStructure bounds checks. - **WebcilReader.cs**: Read V0 header first (28 bytes), then conditionally read extra 4-byte TableBase for V1. Version-aware `SectionDirectoryOffset`. - **webcil-loader.c** (Mono): Accept both V0 and V1 headers with proper bounds checking, use correct header size for section offset calculation. The WebcilConverter defaults to V0, which is what non-R2R builds use. The R2R/crossgen2 path (WasmObjectWriter + WebcilEncoder) produces V1 independently. Both CoreCLR and Mono decoders now handle V0 and V1. ## Testing - CoreCLR browser-wasm library tests: 474/476 passed (2 skipped, 0 failed) - Mono browser-wasm library tests: 469/476 passed (5 pre-existing DateTime failures, 0 webcil-related) Supersedes #126698 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

radekdoulik added this to the Future milestone Apr 9, 2026

radekdoulik added arch-wasm WebAssembly architecture area-Infrastructure-coreclr labels Apr 9, 2026

Copilot AI review requested due to automatic review settings April 9, 2026 11:16

radekdoulik added the area-Infrastructure-coreclr label Apr 9, 2026

github-project-automation bot added this to Runtime Infra Apr 9, 2026

dotnet-policy-service bot assigned radekdoulik Apr 9, 2026

Copilot started reviewing on behalf of radekdoulik April 9, 2026 11:18 View session

radekdoulik changed the title ~~Fix browser-wasm library tests broken by webcil V1 version bump~~ [wasm][coreclr] Fix browser-wasm library tests broken by webcil V1 version bump Apr 9, 2026

radekdoulik requested review from adamperlin, davidwrighton and pavelsavara April 9, 2026 11:18

Copilot AI reviewed Apr 9, 2026

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radekdoulik mentioned this pull request Apr 9, 2026

[wasm][coreclr] Implement webcil V1 support in WebcilConverter and readers #126709

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radekdoulik closed this Apr 9, 2026

github-project-automation bot moved this to Done in Runtime Infra Apr 9, 2026

This was referenced Apr 9, 2026

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build-analysis bot mentioned this pull request Apr 9, 2026

Known Build Error: Blazor SimpleRunTests/BlazorBuildRunTest Playwright timeout on Counter click #126489

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