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[browser] Fix Debug-only startup failures: stack-first assert, incoming Module API, preRun function form #134527

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[browser] Fix Debug-only startup failures: stack-first assert, incoming Module API, preRun function form #134527

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e03f7ed
--stack-first
pavelsavara Sep 23, 2026
01aa2d4
INCOMING_MODULE_JS_API
pavelsavara Sep 23, 2026
33c23b8
more
pavelsavara Sep 23, 2026
8370487
Accept the function form of Module.preInit and Module.preRun on CoreCLR
pavelsavara Sep 23, 2026
0e89d24
Declare emscripten's full default INCOMING_MODULE_JS_API
pavelsavara Sep 23, 2026
435912e
Keep Module callback normalization in serialized scope
pavelsavara Sep 25, 2026
25b5c8e
Dedupe INCOMING_MODULE_JS_API to one source per runtime flavor
pavelsavara Sep 25, 2026
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32 changes: 32 additions & 0 deletions eng/native.wasm.targets
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Expand Up @@ -147,14 +147,46 @@
<EmccExportedFunction Include="___coreclr_wasm_rtlrestorecontext_tag" />
<EmccExportedFunction Include="___async_continuation" />
</ItemGroup>

<!-- Emscripten's default INCOMING_MODULE_JS_API, kept explicit so a Module property we don't declare aborts a debug build early. -->
<ItemGroup>
<EmccIncomingModuleJSAPI Include="ENVIRONMENT" />
<EmccIncomingModuleJSAPI Include="arguments" />
<EmccIncomingModuleJSAPI Include="canvas" />
<EmccIncomingModuleJSAPI Include="dynamicLibraries" />
<EmccIncomingModuleJSAPI Include="elementPointerLock" />
<EmccIncomingModuleJSAPI Include="instantiateWasm" />
<EmccIncomingModuleJSAPI Include="locateFile" />
<EmccIncomingModuleJSAPI Include="monitorRunDependencies" />
<EmccIncomingModuleJSAPI Include="noExitRuntime" />
<EmccIncomingModuleJSAPI Include="noInitialRun" />
<EmccIncomingModuleJSAPI Include="onAbort" />
<EmccIncomingModuleJSAPI Include="onExit" />
<EmccIncomingModuleJSAPI Include="onRuntimeInitialized" />
<EmccIncomingModuleJSAPI Include="postRun" />
<EmccIncomingModuleJSAPI Include="preInit" />
<EmccIncomingModuleJSAPI Include="preRun" />
<EmccIncomingModuleJSAPI Include="print" />
<EmccIncomingModuleJSAPI Include="printErr" />
<EmccIncomingModuleJSAPI Include="setStatus" />
<EmccIncomingModuleJSAPI Include="statusMessage" />
<EmccIncomingModuleJSAPI Include="stderr" />
<EmccIncomingModuleJSAPI Include="stdin" />
<EmccIncomingModuleJSAPI Include="stdout" />
<EmccIncomingModuleJSAPI Include="thisProgram" />
<EmccIncomingModuleJSAPI Include="wasm" />
<EmccIncomingModuleJSAPI Include="websocket" />
</ItemGroup>
<PropertyGroup>
<_EmccExportedRuntimeMethods>@(EmccExportedRuntimeMethod -> '%(Identity)',',')</_EmccExportedRuntimeMethods>
<_EmccExportedFunctions>@(EmccExportedFunction -> '%(Identity)',',')</_EmccExportedFunctions>
<_EmccIncomingModuleJSAPI>@(EmccIncomingModuleJSAPI -> '%(Identity)',',')</_EmccIncomingModuleJSAPI>
</PropertyGroup>

<ItemGroup>
<NativeCMakeArg Condition="'$(TargetsBrowser)' == 'true'" Include="-cmakeargs &quot;-DCMAKE_EMCC_EXPORTED_RUNTIME_METHODS=$(_EmccExportedRuntimeMethods)&quot;" />
<NativeCMakeArg Condition="'$(TargetsBrowser)' == 'true'" Include="-cmakeargs &quot;-DCMAKE_EMCC_EXPORTED_FUNCTIONS=$(_EmccExportedFunctions)&quot;" />
<NativeCMakeArg Condition="'$(TargetsBrowser)' == 'true'" Include="-cmakeargs &quot;-DCMAKE_EMCC_INCOMING_MODULE_JS_API=$(_EmccIncomingModuleJSAPI)&quot;" />
</ItemGroup>

</Target>
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36 changes: 36 additions & 0 deletions src/mono/browser/browser.proj
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Expand Up @@ -208,9 +208,43 @@
<ItemGroup Condition="'$(WasmEnableThreads)' == 'true'">
<EmccExportedFunction Include="_emscripten_main_runtime_thread_id" />
</ItemGroup>
<!-- Emscripten's default INCOMING_MODULE_JS_API, kept explicit so a Module property we don't declare aborts a debug build early. -->
<ItemGroup>
<EmccIncomingModuleJSAPI Include="ENVIRONMENT" />
<EmccIncomingModuleJSAPI Include="arguments" />
<EmccIncomingModuleJSAPI Include="canvas" />
<EmccIncomingModuleJSAPI Include="dynamicLibraries" />
<EmccIncomingModuleJSAPI Include="elementPointerLock" />
<EmccIncomingModuleJSAPI Include="instantiateWasm" />
<EmccIncomingModuleJSAPI Include="locateFile" />
<EmccIncomingModuleJSAPI Include="monitorRunDependencies" />
<EmccIncomingModuleJSAPI Include="noExitRuntime" />
<EmccIncomingModuleJSAPI Include="noInitialRun" />
<EmccIncomingModuleJSAPI Include="onAbort" />
<EmccIncomingModuleJSAPI Include="onExit" />
<EmccIncomingModuleJSAPI Include="onRuntimeInitialized" />
<EmccIncomingModuleJSAPI Include="postRun" />
<EmccIncomingModuleJSAPI Include="preInit" />
<EmccIncomingModuleJSAPI Include="preRun" />
<EmccIncomingModuleJSAPI Include="print" />
<EmccIncomingModuleJSAPI Include="printErr" />
<EmccIncomingModuleJSAPI Include="setStatus" />
<EmccIncomingModuleJSAPI Include="statusMessage" />
<EmccIncomingModuleJSAPI Include="stderr" />
<EmccIncomingModuleJSAPI Include="stdin" />
<EmccIncomingModuleJSAPI Include="stdout" />
<EmccIncomingModuleJSAPI Include="thisProgram" />
<EmccIncomingModuleJSAPI Include="wasm" />
<EmccIncomingModuleJSAPI Include="websocket" />
</ItemGroup>
<ItemGroup Condition="'$(WasmEnableThreads)' == 'true'">
<!-- not an emscripten default; set on the worker from the message which starts a pthread -->
<EmccIncomingModuleJSAPI Include="wasmMemory" />
</ItemGroup>
<PropertyGroup>
<_EmccExportedLibraryFunction>"[@(EmccExportedLibraryFunction -> '%27%(Identity)%27', ',')]"</_EmccExportedLibraryFunction>
<_EmccExportedRuntimeMethods>"[@(EmccExportedRuntimeMethod -> '%27%(Identity)%27', ',')]"</_EmccExportedRuntimeMethods>
<_EmccIncomingModuleJSAPI>"[@(EmccIncomingModuleJSAPI -> '%27%(Identity)%27', ',')]"</_EmccIncomingModuleJSAPI>
<_EmccExportedFunctions>@(EmccExportedFunction -> '%(Identity)',',')</_EmccExportedFunctions>
<!-- reserve at least enough space to complete initializing sgen without growing the heap -->
<EmccInitialHeapSize>33554432</EmccInitialHeapSize>
Expand All @@ -232,6 +266,7 @@
<_EmccLinkFlags Include="-s FORCE_FILESYSTEM=1" />
<_EmccLinkFlags Condition="'$(_EmccExportedLibraryFunction)' != ''" Include="-s DEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$(_EmccExportedLibraryFunction)" />
<_EmccLinkFlags Include="-s EXPORTED_RUNTIME_METHODS=$(_EmccExportedRuntimeMethods)" />
<_EmccLinkFlags Include="-s INCOMING_MODULE_JS_API=$(_EmccIncomingModuleJSAPI)" />
<_EmccLinkFlags Include="-s EXPORTED_FUNCTIONS=$(_EmccExportedFunctions)" />
<_EmccLinkFlags Include="--source-map-base http://example.com" />
<_EmccLinkFlags Include="-s WASM_BIGINT=1" />
Expand Down Expand Up @@ -271,6 +306,7 @@
"WasmOptConfigurationFlags": [@(WasmOptConfigurationFlags -> '%22%(Identity)%22', ',')],
"EmccDefaultExportedFunctions": [@(EmccExportedFunction -> '%22%(Identity)%22', ',')],
"EmccDefaultExportedRuntimeMethods": [@(EmccExportedRuntimeMethod -> '%22%(Identity)%22', ',')],
"EmccDefaultIncomingModuleJSAPI": [@(EmccIncomingModuleJSAPI -> '%22%(Identity)%22', ',')],
"PropertiesThatTriggerRelinking": [
{ "identity": "InvariantTimezone", "defaultValueInRuntimePack": "$(InvariantTimezone)" },
{ "identity": "InvariantGlobalization", "defaultValueInRuntimePack": "$(InvariantGlobalization)" },
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32 changes: 32 additions & 0 deletions src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
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Expand Up @@ -161,6 +161,36 @@
<EmccExportedFunction Include="___coreclr_wasm_rtlrestorecontext_tag" />
<EmccExportedFunction Include="___async_continuation" />
</ItemGroup>

<!-- Emscripten's default INCOMING_MODULE_JS_API, kept explicit so a Module property we don't declare aborts a debug build early. -->
<ItemGroup>
<EmccIncomingModuleJSAPI Include="ENVIRONMENT" />
<EmccIncomingModuleJSAPI Include="arguments" />
<EmccIncomingModuleJSAPI Include="canvas" />
<EmccIncomingModuleJSAPI Include="dynamicLibraries" />
<EmccIncomingModuleJSAPI Include="elementPointerLock" />
<EmccIncomingModuleJSAPI Include="instantiateWasm" />
<EmccIncomingModuleJSAPI Include="locateFile" />
<EmccIncomingModuleJSAPI Include="monitorRunDependencies" />
<EmccIncomingModuleJSAPI Include="noExitRuntime" />
<EmccIncomingModuleJSAPI Include="noInitialRun" />
<EmccIncomingModuleJSAPI Include="onAbort" />
<EmccIncomingModuleJSAPI Include="onExit" />
<EmccIncomingModuleJSAPI Include="onRuntimeInitialized" />
<EmccIncomingModuleJSAPI Include="postRun" />
<EmccIncomingModuleJSAPI Include="preInit" />
<EmccIncomingModuleJSAPI Include="preRun" />
<EmccIncomingModuleJSAPI Include="print" />
<EmccIncomingModuleJSAPI Include="printErr" />
<EmccIncomingModuleJSAPI Include="setStatus" />
<EmccIncomingModuleJSAPI Include="statusMessage" />
<EmccIncomingModuleJSAPI Include="stderr" />
<EmccIncomingModuleJSAPI Include="stdin" />
<EmccIncomingModuleJSAPI Include="stdout" />
<EmccIncomingModuleJSAPI Include="thisProgram" />
<EmccIncomingModuleJSAPI Include="wasm" />
<EmccIncomingModuleJSAPI Include="websocket" />
</ItemGroup>
</Target>

<!-- Import shared native.wasm.targets for Emscripten SDK, ICU, exported functions/methods.
Expand Down Expand Up @@ -856,6 +886,7 @@

<PropertyGroup>
<_EmccExportedRuntimeMethods>"[BROWSER_HOST,@(EmccExportedRuntimeMethod -> '%27%(Identity)%27', ',')]"</_EmccExportedRuntimeMethods>
<_EmccIncomingModuleJSAPI>"[@(EmccIncomingModuleJSAPI -> '%27%(Identity)%27', ',')]"</_EmccIncomingModuleJSAPI>

@pavelsavara pavelsavara Sep 25, 2026

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Structurally addressed: the items now come from the GenerateEmccExports dependency, so the ItemGroup-before-PropertyGroup ordering hazard this flags is gone. The CoreCLR in-tree browserhost link was rebuilt and its checkIncomingModuleAPI is unchanged (rejects wasmMemory/wasmBinary, accepts the 26 defaults). A full Wasm.Build.Tests/xharness Debug startup run is still pending, so I'm leaving this open until that runs.

Note: written with GitHub Copilot.

<_EmccExportedFunctions>@(EmccExportedFunction -> '%(Identity)',',')</_EmccExportedFunctions>
</PropertyGroup>

Expand Down Expand Up @@ -935,6 +966,7 @@

<!-- Exported functions and runtime methods -->
<_EmccLinkStepArgs Include="-s EXPORTED_RUNTIME_METHODS=$(_EmccExportedRuntimeMethods)" />
<_EmccLinkStepArgs Include="-s INCOMING_MODULE_JS_API=$(_EmccIncomingModuleJSAPI)" />
<_EmccLinkStepArgs Include="-s EXPORTED_FUNCTIONS=$(_EmccExportedFunctions)" />

<!-- JS library files -->
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4 changes: 4 additions & 0 deletions src/mono/browser/build/BrowserWasmApp.targets
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Expand Up @@ -313,6 +313,8 @@
<Target Name="_BrowserWasmWriteRspForLinking" BeforeTargets="_WasmWriteRspForLinking">
<ItemGroup>
<EmccExportedRuntimeMethod Include="PThread" Condition="'$(WasmEnableThreads)' == 'true'" />
<!-- EmccIncomingModuleJSAPI defaults (incl. wasmMemory when threads are enabled) come from wasm-props.json
via _ReadWasmProps, written by src/mono/browser/browser.proj. -->
</ItemGroup>
<PropertyGroup>
<_WasmEHLib Condition="'$(WasmEnableExceptionHandling)' == 'true'">libmono-wasm-eh-wasm.a</_WasmEHLib>
Expand All @@ -325,6 +327,7 @@
<_WasmSIMDLibToExclude Condition="'$(WasmEnableSIMD)' == 'true'">libmono-wasm-nosimd.a</_WasmSIMDLibToExclude>
<_EmccExportedLibraryFunction>"[@(EmccExportedLibraryFunction -> '%27%(Identity)%27', ',')]"</_EmccExportedLibraryFunction>
<_EmccExportedRuntimeMethods>"[@(EmccExportedRuntimeMethod -> '%27%(Identity)%27', ',')]"</_EmccExportedRuntimeMethods>
<_EmccIncomingModuleJSAPI>"[@(EmccIncomingModuleJSAPI -> '%27%(Identity)%27', ',')]"</_EmccIncomingModuleJSAPI>
<_EmccExportedFunctions>@(EmccExportedFunction -> '%(Identity)',',')</_EmccExportedFunctions>
</PropertyGroup>

Expand Down Expand Up @@ -373,6 +376,7 @@

<_EmccLinkStepArgs Include="-s DEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$(_EmccExportedLibraryFunction)" Condition="'$(_EmccExportedLibraryFunction)' != ''" />
<_EmccLinkStepArgs Include="-s EXPORTED_RUNTIME_METHODS=$(_EmccExportedRuntimeMethods)" />
<_EmccLinkStepArgs Include="-s INCOMING_MODULE_JS_API=$(_EmccIncomingModuleJSAPI)" />
<_EmccLinkStepArgs Include="-s EXPORTED_FUNCTIONS=$(_EmccExportedFunctions)" />

<_EmccLinkStepArgs Include="$(EmccExtraLDFlags)" />
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2 changes: 1 addition & 1 deletion src/mono/mono/utils/mono-threads-wasm.c
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Expand Up @@ -198,7 +198,7 @@ mono_threads_platform_get_stack_bounds (guint8 **staddr, size_t *stsize)
if (G_UNLIKELY (res != 0))
g_error ("%s: pthread_attr_destroy failed with \"%s\" (%d)", __func__, g_strerror (res), res);

g_assert (*staddr != NULL);
// emscripten links with --stack-first at -O0, which puts the stack at the start of the linear memory, so staddr can legitimately be NULL

@akoeplinger akoeplinger Sep 25, 2026

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we should probably backport this to 11.0 (we could argue it's a test-only change since it happens in Debug only) since it will get lost in main soon

@pavelsavara pavelsavara Sep 25, 2026

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Nobody in the world ever builds mono+MT+wasm+debug. And I'm not going to do it any time soon again.

g_assert (*stsize != (size_t)-1);
Comment on lines +201 to 202
#elif defined(HOST_WASI) && !defined(DISABLE_THREADS)
// TODO: this will need changes for WASI multithreading as the stack will be allocated per thread at different addresses
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2 changes: 2 additions & 0 deletions src/mono/wasm/build/WasmApp.Common.targets
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Expand Up @@ -399,6 +399,7 @@
<WasmOptConfigurationFlags ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="false" Output="true" />
<EmccDefaultExportedFunctions ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="false" Output="true" />
<EmccDefaultExportedRuntimeMethods ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="false" Output="true" />
<EmccDefaultIncomingModuleJSAPI ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="false" Output="true" />
<PropertiesThatTriggerRelinking ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="false" Output="true" />
</ParameterGroup>
</UsingTask>
Expand All @@ -408,6 +409,7 @@
<Output TaskParameter="EmccProperties" ItemName="_EmccPropItems" />
<Output TaskParameter="EmccDefaultExportedFunctions" ItemName="EmccExportedFunction" />
<Output TaskParameter="EmccDefaultExportedRuntimeMethods" ItemName="EmccExportedRuntimeMethod" />
<Output TaskParameter="EmccDefaultIncomingModuleJSAPI" ItemName="EmccIncomingModuleJSAPI" />

<!-- shared by browser/wasi -->
<Output TaskParameter="WasmOptConfigurationFlags" ItemName="_DefaulWasmOptConfigurationFlags" />
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2 changes: 2 additions & 0 deletions src/native/corehost/browserhost/CMakeLists.txt
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Expand Up @@ -132,6 +132,8 @@ target_link_options(browserhost PRIVATE
-sEXIT_RUNTIME=1
-sALLOW_TABLE_GROWTH=1
-sEXPORTED_RUNTIME_METHODS=BROWSER_HOST,${CMAKE_EMCC_EXPORTED_RUNTIME_METHODS}
# Emscripten's default INCOMING_MODULE_JS_API, kept explicit so a Module property we don't declare aborts a debug build early. Value comes from GenerateEmccExports in eng/native.wasm.targets.
-sINCOMING_MODULE_JS_API=${CMAKE_EMCC_INCOMING_MODULE_JS_API}
-sEXPORTED_FUNCTIONS=${CMAKE_EMCC_EXPORTED_FUNCTIONS}
-sEXPORT_NAME=createDotnetRuntime
-sENVIRONMENT=web,webview,worker,node,shell
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6 changes: 3 additions & 3 deletions src/native/libs/Common/JavaScript/types/internal.ts
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Expand Up @@ -51,9 +51,9 @@ export type EmscriptenModuleInternal = EmscriptenModule & DotnetModuleConfig & {
instantiateWasm?: InstantiateWasmCallBack;
onAbort?: (reason: any, extraJson?: string) => void;
onExit?: (code: number) => void;
preInit?: (() => any)[];
preRun?: (() => any)[];
postRun?: (() => any)[];
preInit?: (() => any)[] | (() => any);
preRun?: (() => any)[] | (() => any);
postRun?: (() => any)[] | (() => any);
}

export interface AssetEntryInternal extends AssetEntry {
Expand Down
9 changes: 7 additions & 2 deletions src/native/libs/System.Native.Browser/native/index.ts
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Expand Up @@ -54,14 +54,19 @@ export function dotnetInitializeModule(internals: InternalExchange): void {
return _ems_.wasmTable;
}

function asCallbackArray(callbacks: undefined | (() => any) | (() => any)[]): (() => any)[] {
if (!callbacks) return [];
return typeof callbacks === "function" ? [callbacks] : callbacks;
}

function setupEmscripten() {
_ems_.Module.preInit = [() => {
if (_ems_.dotnetApi.getConfig) {
const virtualWorkingDirectory = _ems_.dotnetApi.getConfig().virtualWorkingDirectory;
_ems_.FS.createPath("/", virtualWorkingDirectory!, true, true);
_ems_.FS.chdir(virtualWorkingDirectory!);
}
}, ...(_ems_.Module.preInit || [])];
}, ...asCallbackArray(_ems_.Module.preInit)];

// preInit runs before Emscripten assigns the native WASM exports.
_ems_.Module.preRun = [() => {
Expand All @@ -80,6 +85,6 @@ export function dotnetInitializeModule(internals: InternalExchange): void {
// silently ignore any error during shutdown
}
};
}, ...(_ems_.Module.preRun || [])];
}, ...asCallbackArray(_ems_.Module.preRun)];
}
}
4 changes: 3 additions & 1 deletion src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/http.ts
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Expand Up @@ -97,7 +97,9 @@ export function httpAbort(controller: HttpController): void {
// Never resolves; rejects as soon as the fetch does. A failed fetch abandons the readable end of the
// TransformStream, which leaves an in-flight write() pending forever, so writes race against this.
function rejectWhenFetchFails(controller: HttpController): Promise<never> {
return controller.responsePromise!.then(() => new Promise<never>(() => { }), (err) => { throw err; });
return controller.responsePromise!.then(() => new Promise<never>(() => { }), (err) => {
throw err;
});
}

export function httpTransformStreamWrite(controller: HttpController, bufferPtr: VoidPtr, bufferLength: number): ControllablePromise<void> {
Expand Down