[browser] host improvements #123726

pavelsavara · 2026-01-28T18:59:13Z

Filesystem

simplified coreRun to never exit
replace cwd() in coreRun to pretend that NODERAWFS on Windows is Unix
introduce browserVirtualAppBase constant(s) and unify the app directory to /managed.
- for Mono too!
make virtual path of VFS resources in the loader config relative to browserVirtualAppBase, unless explicitly absolute. WasmFilesToIncludeInFileSystem
use browserVirtualAppBase for TPA
create virtualWorkingDirectory and change current directory to it

Fail fast

always assert and fail PortableEntryPoint::GetActualCode if the function is NULL
detect attached debugger. Kill the process if it is not attached, like int3 does elsewhere
quit on V8
wrap all timers with catch -> abort
abortPosix implemented as emscripten ___trap(), so that we don't run C++ finalizers on exit()

Other

implement PAL_ProbeMemory for browser
-sALLOW_TABLE_GROWTH=1 for R2R
move some code to browserhost/host/assets.ts
trim sockets
feedback from [browser][coreCLR] node and v8 CLI support for default browser runtime #123501
- drop support for CLI self-configuration on NodeJS
- globalThisAny
- code formating
make browserHost to run on V8/D8 shell
- optional TextDecoder

dotnet-policy-service · 2026-01-28T19:00:40Z

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

Copilot

Pull request overview

Updates the WASM browser host/loader to unify the virtual app base (/managed), improve runtime startup/exit behavior across browser/Node/V8 shells, and tighten fail-fast/debug behavior.

Changes:

Standardize the virtual app base/working directory to /managed across CoreCLR/Mono tooling and runtime.
Refactor browserhost asset/wasm instantiation and loader startup flow (polyfills/config validation/modules hooks).
Adjust fail-fast/exit/debug behavior (probe memory, debugbreak behavior, abort/trap paths, syscall trimming).

Reviewed changes

Copilot reviewed 51 out of 52 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/native/minipal/getexepath.h	Align WASM exe path convention to `/managed`.
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/libSystem.Runtime.InteropServices.JavaScript.Native.footer.js	Formatting/dep list cleanup.
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/utils.ts	Add TextDecoder fallback for V8 via Module helper.
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/http.ts	Centralize debug-only asserts in `commonAsserts`.
src/native/libs/System.Native.Browser/utils/strings.ts	Use `globalThis.TextDecoder/TextEncoder` checks.
src/native/libs/System.Native.Browser/utils/runtime-list.ts	Use shared `globalThisAny` helper.
src/native/libs/System.Native.Browser/utils/host.ts	Wrap timers; revise abort/exit path for browser.
src/native/libs/System.Native.Browser/native/scheduling.ts	Fail-fast wrapper around timer/background callbacks.
src/native/libs/System.Native.Browser/native/crypto.ts	Adjust crypto warning-once behavior/logging.
src/native/libs/System.Native.Browser/libSystem.Native.Browser.footer.js	Formatting/dep list cleanup.
src/native/libs/System.Native.Browser/libSystem.Native.Browser.Utils.footer.js	Add deps for trap support; formatting cleanup.
src/native/libs/Common/JavaScript/types/internal.ts	Add Emscripten `preInit/preRun/postRun` typing.
src/native/libs/Common/JavaScript/types/exchange.ts	Move host asset functions into `host/assets`.
src/native/libs/Common/JavaScript/types/ems-ambient.ts	Extend ambient types (FS.chdir, ENV, abort, trap).
src/native/libs/Common/JavaScript/per-module/index.ts	Add `globalThisAny` and `browserVirtualAppBase`.
src/native/libs/Common/JavaScript/cross-module/index.ts	Plumb `instantiateWasm` through internals table.
src/native/libs/Common/JavaScript/CMakeLists.txt	Include new browserhost host module sources.
src/native/corehost/browserhost/loader/run.ts	Restructure startup flow; add config validation + polyfills init.
src/native/corehost/browserhost/loader/polyfills.ts	Make polyfills async; restructure Node/V8 fetch handling.
src/native/corehost/browserhost/loader/index.ts	Rename/route instantiate hook to `instantiateMainWasm`.
src/native/corehost/browserhost/loader/host-builder.ts	Validate config when reusing an existing HostBuilder.
src/native/corehost/browserhost/loader/exit.ts	Track runtime state; improve shell quit + abort handling.
src/native/corehost/browserhost/loader/dotnet.ts	Remove Node auto-self-hosting; init polyfills async.
src/native/corehost/browserhost/loader/config.ts	Default virtual working directory to `/managed`.
src/native/corehost/browserhost/loader/bootstrap.ts	Remove Node/Shell auto resource probing logic.
src/native/corehost/browserhost/loader/assets.ts	Refactor wasm instantiation + register bytes API.
src/native/corehost/browserhost/libBrowserHost.footer.js	Remove NodeFS mounting; trim unsupported socket syscalls.
src/native/corehost/browserhost/host/per-module.ts	Re-export shared per-module environment helpers.
src/native/corehost/browserhost/host/index.ts	Centralize Emscripten setup and export table wiring.
src/native/corehost/browserhost/host/host.ts	Use `/managed` base for TPA and app context paths.
src/native/corehost/browserhost/host/cross-module.ts	Re-export shared cross-module glue.
src/native/corehost/browserhost/host/assets.ts	New asset registry + instantiateWasm implementation.
src/native/corehost/browserhost/CMakeLists.txt	Enable table growth; drop nodefs link option.
src/mono/wasm/testassets/WasmBasicTestApp/App/FilesToIncludeInFileSystemTest.cs	Update VFS file checks to relative paths.
src/mono/wasm/Wasm.Build.Tests/FilesToIncludeInFileSystemTests.cs	Update expected output for relative VFS paths.
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Clarify Webcil TODO with issue link.
src/mono/sample/wasm/console-v8/wwwroot/main.mjs	Add V8 console sample entrypoint module.
src/mono/sample/wasm/Directory.Build.targets	Run V8 using `--module`.
src/mono/sample/mbr/browser/WasmDelta.csproj	Fix TargetPath to be relative (no leading backslash).
src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets	Make default VFS TargetPath relative.
src/mono/browser/test-main.js	Default working directory to `/managed`.
src/mono/browser/runtime/startup.ts	Ensure `/managed` + working dir exists; `chdir` accordingly.
src/mono/browser/runtime/loader/globals.ts	Add `browserVirtualAppBase` constant.
src/mono/browser/runtime/loader/config.ts	Default virtual working directory to `/managed`.
src/mono/browser/runtime/globals.ts	Add `browserVirtualAppBase` constant.
src/mono/browser/runtime/assets.ts	Install VFS assets under `/managed` by default.
src/libraries/Common/tests/TestUtilities/System/AssemblyPathHelper.cs	Use `/managed` base for browser assembly paths.
src/coreclr/vm/precode_portable.cpp	Assert in all builds for NULL actual code.
src/coreclr/pal/src/debug/debug.cpp	Add browser PAL_ProbeMemory implementation.
src/coreclr/pal/src/arch/wasm/stubs.cpp	Fail-fast if debugger not attached (heuristic).
src/coreclr/hosts/corerun/wasm/libCorerun.extpost.js	Normalize Node cwd on Windows for Unix-like VFS.
src/coreclr/hosts/corerun/corerun.cpp	Keep browser runtime alive (no shutdown/exit).

src/native/corehost/browserhost/loader/polyfills.ts

src/native/corehost/browserhost/loader/assets.ts

src/native/corehost/browserhost/host/assets.ts

src/native/corehost/browserhost/loader/run.ts

src/coreclr/pal/src/debug/debug.cpp

src/native/corehost/browserhost/host/assets.ts

src/native/corehost/browserhost/loader/polyfills.ts

src/coreclr/pal/src/arch/wasm/stubs.cpp

src/native/corehost/browserhost/host/assets.ts

radekdoulik · 2026-01-29T10:21:00Z

src/coreclr/hosts/corerun/corerun.cpp

-    }
-#endif // TARGET_BROWSER
+    // In browser we don't shutdown the runtime here as we want to keep it alive
+    return 0;


I think this would break runtime tests on nodeJS as they depend on the exit code resolution.

Ok, this needs bit more work

radekdoulik

Besides the exit code change, it LGTM.

Copilot

Pull request overview

Copilot reviewed 53 out of 54 changed files in this pull request and generated 4 comments.

Copilot · 2026-01-29T23:09:36Z

src/native/corehost/browserhost/libBrowserHost.footer.js

+    function trim() {
+        return 138; // EOPNOTSUPP;
+    }
+
+    // TODO-WASM: fix PAL https://github.com/dotnet/runtime/issues/122506
+    LibraryManager.library.__syscall_pipe = trim;
+    delete LibraryManager.library.__syscall_pipe__deps;
+
+    LibraryManager.library.__syscall_connect = trim;
+    delete LibraryManager.library.__syscall_connect__deps;
+
+    LibraryManager.library.__syscall_sendto = trim;
+    delete LibraryManager.library.__syscall_sendto__deps;
+
+    LibraryManager.library.__syscall_socket = trim;
+    delete LibraryManager.library.__syscall_socket__deps;


These syscall stubs return a positive errno value (138). Emscripten/musl syscall shims typically expect negative errno return values (or setting errno and returning -1). Returning a positive value risks being interpreted as a successful return (e.g., a valid fd) and can lead to incorrect behavior. Please adjust the stub to follow the expected error-return convention for _syscall* (e.g., return -EOPNOTSUPP / -138, or set errno appropriately and return -1).

Copilot · 2026-01-29T23:09:36Z

src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Reflection/ModuleTests.cs

            {
-                loc = loc.Substring(1);
+                const string browserVirtualAppBase = "/managed"; // keep in sync other places that define browserVirtualAppBase
+                loc = loc.Replace(browserVirtualAppBase, "");


The comment says we need to strip the leading '/', but the new logic removes all occurrences of "/managed" via Replace and can leave a leading '/' (e.g., "/managed/Foo.dll" -> "/Foo.dll"). This is both inconsistent with the comment and potentially fragile (Replace can remove occurrences beyond the prefix). Consider normalizing by removing only the expected prefix ("/managed/") and/or trimming the leading '/' in a prefix-safe way so the comparison matches the intended Module.FullyQualifiedName format.

Suggested change

loc = loc.Replace(browserVirtualAppBase, "");

if (loc.StartsWith(browserVirtualAppBase, StringComparison.Ordinal))

{

int prefixLength = browserVirtualAppBase.Length;

if (loc.Length > prefixLength && loc[prefixLength] == '/')

{

prefixLength++;

}

loc = loc[prefixLength..];

}

else if (loc[0] == '/')

{

loc = loc[1..];

}

Copilot · 2026-01-29T23:09:36Z

src/native/corehost/browserhost/loader/assets.ts

+export const mainModulePromiseController = createPromiseCompletionSource<WebAssembly.Instance>();
 export const nativeModulePromiseController = createPromiseCompletionSource<EmscriptenModuleInternal>(() => {


mainModulePromiseController is created and resolved, but it isn’t referenced anywhere else in the repo (only defined/resolved in this file). If it’s not part of a planned public surface, consider removing it (and the corresponding resolve call) to avoid dead code; otherwise add the missing consumer so it’s clear why it exists.

Copilot · 2026-01-29T23:09:36Z

src/native/corehost/browserhost/loader/assets.ts

-        return res;
-    }
+export async function instantiateMainWasm(imports: WebAssembly.Imports, successCallback: InstantiateWasmSuccessCallback): Promise<void> {
+    //asset


Leftover comment //asset doesn’t convey intent and looks like a temporary note. Please remove it or replace it with a descriptive comment about why instantiation is delegated via dotnetBrowserHostExports.

Suggested change

//asset

// Delegate instantiation to the browser host so it can configure and track the main WebAssembly module consistently across environments.

pavelsavara added 4 commits January 28, 2026 16:39

wip

bd9700f

wip

657eb98

fail faster

c28568a

Merge branch 'main' into v8_poly

a2de51a

pavelsavara added this to the 11.0.0 milestone Jan 28, 2026

pavelsavara self-assigned this Jan 28, 2026

pavelsavara added arch-wasm WebAssembly architecture area-Host os-browser Browser variant of arch-wasm labels Jan 28, 2026

pavelsavara added 2 commits January 28, 2026 20:11

more

3e2a287

vfs assets and virtualWorkingDirectory

6ee3b41

fix tests

67dcece

pavelsavara mentioned this pull request Jan 29, 2026

[browser][coreCLR] node and v8 CLI support for default browser runtime #123501

Closed

pavelsavara marked this pull request as ready for review January 29, 2026 08:45

pavelsavara requested review from ilonatommy and maraf as code owners January 29, 2026 08:45

Copilot AI review requested due to automatic review settings January 29, 2026 08:46

pavelsavara requested review from akoeplinger, lewing, steveisok and vitek-karas as code owners January 29, 2026 08:46

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build-analysis bot mentioned this pull request Jan 29, 2026

[browser][coreCLR] SocketsHttpHandler_ResponseStreamTest.BrowserHttpHandler_StreamingRequest timeout #123747

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campersau reviewed Jan 29, 2026

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src/native/corehost/browserhost/loader/polyfills.ts Outdated Show resolved Hide resolved

maraf approved these changes Jan 29, 2026

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src/coreclr/pal/src/arch/wasm/stubs.cpp Outdated Show resolved Hide resolved

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radekdoulik reviewed Jan 29, 2026

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build-analysis bot mentioned this pull request Jan 29, 2026

iOS.Device test WorkItemExecutions #122874

Open

pavelsavara added 2 commits January 29, 2026 21:45

feedback

a8e14b7

fix test

83f4958

Copilot AI review requested due to automatic review settings January 29, 2026 22:58

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Copilot AI reviewed Jan 29, 2026

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feedback

180585c

build-analysis bot mentioned this pull request Jan 30, 2026

XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

Open

-                loc = loc.Replace(browserVirtualAppBase, "");
+                if (loc.StartsWith(browserVirtualAppBase, StringComparison.Ordinal))
+                {
+                    int prefixLength = browserVirtualAppBase.Length;
+                    if (loc.Length > prefixLength && loc[prefixLength] == '/')
+                    {
+                        prefixLength++;
+                    }
+                    loc = loc[prefixLength..];
+                }
+                else if (loc[0] == '/')
+                {
+                    loc = loc[1..];
+                }

		export const mainModulePromiseController = createPromiseCompletionSource<WebAssembly.Instance>();
		export const nativeModulePromiseController = createPromiseCompletionSource<EmscriptenModuleInternal>(() => {

	//asset
	// Delegate instantiation to the browser host so it can configure and track the main WebAssembly module consistently across environments.

[browser] host improvements #123726

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[browser] host improvements #123726

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pavelsavara commented Jan 28, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Filesystem

Fail fast

Other

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dotnet-policy-service bot commented Jan 28, 2026

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pavelsavara commented Jan 28, 2026 •

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