Add AssemblyLoadContext.SetAssemblyLocationOverride by cdmazom · Pull Request #129773 · dotnet/runtime

cdmazom · 2026-06-23T21:58:07Z

Adds a static, set-once callback that overrides the value returned by Assembly.Location. The callback is stored in the shared AssemblyLoadContext and applied by RuntimeAssembly.Location on CoreCLR, Mono, and NativeAOT.

Updates the System.Runtime.Loader reference assembly and adds tests covering the override, the set-once guard, and null handling.

Fix #127097

Adds a static, set-once callback that overrides the value returned by Assembly.Location. The callback is stored in the shared AssemblyLoadContext and applied by RuntimeAssembly.Location on CoreCLR, Mono, and NativeAOT. Updates the System.Runtime.Loader reference assembly and adds tests covering the override, the set-once guard, and null handling. Fix dotnet#127097

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dotnet-policy-service · 2026-06-23T21:59:17Z

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Pull request overview

This PR introduces a new public API, AssemblyLoadContext.SetAssemblyLocationOverride, which allows a process-wide, set-once callback to override the value returned by Assembly.Location. The override is applied consistently across CoreCLR, Mono, and NativeAOT by routing each runtime’s RuntimeAssembly.Location implementation through a shared resolver in AssemblyLoadContext.

Changes:

Adds AssemblyLoadContext.SetAssemblyLocationOverride(Func<Assembly, string, string>) and an internal ResolveAssemblyLocation helper in System.Private.CoreLib.
Updates CoreCLR/Mono/NativeAOT Assembly.Location implementations to apply the override.
Updates the System.Runtime.Loader reference assembly and adds tests for null argument, override behavior, and set-once enforcement.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs	Adds the set-once callback storage, public setter API, and internal location resolver used by all runtimes.
src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs	Applies the location override when returning `Assembly.Location` on CoreCLR.
src/mono/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs	Applies the location override when returning `Assembly.Location` on Mono.
src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/ThunkedApis.cs	Applies the location override when returning `Assembly.Location` on NativeAOT.
src/libraries/System.Runtime.Loader/ref/System.Runtime.Loader.cs	Adds the new public API to the reference assembly surface.
src/libraries/System.Runtime.Loader/tests/AssemblyLoadContextTest.cs	Adds tests for null argument, stream-loaded override behavior, and set-once guard (RemoteExecutor isolation).
src/libraries/System.Private.CoreLib/src/Resources/Strings.resx	Adds SR string for the “already set” exception message.

Co-authored-by: Theodore Tsirpanis <teo@tsirpanis.gr>

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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

jkotas

Thanks!

jkotas · 2026-06-25T22:54:40Z

Could you please sign the Contributor License Agreement? This is good to go otherwise.

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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

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Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

+                string asmPath = ExtractEmbeddedAssembly("System.Runtime.Loader.Tests.AssemblyVersion1");
+                try
+                {
+                    // Loading from a stream means the runtime has no location, so the override kicks in.
+                    var streamAlc = new AssemblyLoadContext("LocationOverride_Stream", isCollectible: true);
+                    Assembly streamLoaded;
+                    using (FileStream fs = File.OpenRead(asmPath))
+                    {
+                        streamLoaded = streamAlc.LoadFromStream(fs);
+                    }
+                    Assert.Equal($"/overridden/{streamLoaded.GetName().Name}.dll", streamLoaded.Location);
+
+                    // The same assembly loaded from a path (into a separate context) has a real location,
+                    // so the callback leaves it untouched.
+                    var pathAlc = new AssemblyLoadContext("LocationOverride_Path", isCollectible: true);
+                    Assembly fileLoaded = pathAlc.LoadFromAssemblyPath(asmPath);
+                    Assert.False(string.IsNullOrEmpty(fileLoaded.Location));
+                    Assert.DoesNotContain("/overridden/", fileLoaded.Location);
+                }
+                finally
+                {
+                    try { File.Delete(asmPath); } catch { }
+                }


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cdmazom requested review from MichalStrehovsky, steveisok and vitek-karas as code owners June 23, 2026 21:58

github-actions Bot added the area-System.Reflection label Jun 23, 2026

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Comment thread src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs

Comment thread src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs Outdated

Comment thread src/libraries/System.Runtime.Loader/tests/AssemblyLoadContextTest.cs

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build-analysis Bot mentioned this pull request Jun 24, 2026

DiagnosticsTest Http2 SendAsync_Success_ConnectionSetupActivityGraphRecorded: Unexpected EOF trying to read request header #129771

Open

Apply suggestions from code review

8fd076f

Co-authored-by: Theodore Tsirpanis <teo@tsirpanis.gr>

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Comment thread src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs

Copilot AI mentioned this pull request Jun 24, 2026

Fix flaky SendAsync_Success_ConnectionSetupActivityGraphRecorded test (Http1.1 + Http2) #129822

Closed

cdmazom added 2 commits June 24, 2026 15:28

Added remark to SEtAssemblyLocationOverride

641781f

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Comment thread src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs

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jkotas mentioned this pull request Jun 25, 2026

System.Threading.Tasks.Tests.AsyncProfilerTests.StateMachineAsync_CallstackStressWithVaryingDepths test failure #129871

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Comment thread src/libraries/System.Private.CoreLib/src/Resources/Strings.resx Outdated

Update src/libraries/System.Private.CoreLib/src/Resources/Strings.resx

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Comment thread src/libraries/System.Private.CoreLib/src/Resources/Strings.resx

Potential fix for pull request finding

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