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[xabt] Move AddKeepAlives trimmer step to standalone MSBuild task (#10952)
Migrate AddKeepAlivesStep out of the ILLink custom step pipeline into a standalone MSBuild task that runs AfterTargets="ILLink", following the same pattern established by StripEmbeddedLibraries in #10894. Core IL-rewriting logic is extracted into AddKeepAlivesHelper, shared by both the new task (trimmed builds) and the existing pipeline step (non-trimmed builds via LinkAssembliesNoShrink). Replace DefaultAssemblyResolver with DirectoryAssemblyResolver (ReadWrite=true) to avoid file handle conflicts on Windows. The directory resolver caches all assemblies (both explicit and dependency-resolved), preventing duplicate file opens that caused IOException when the same assembly was opened as both a dependency and a primary target. ## [xabt] Combine post-trimming steps into single PostTrimmingPipeline task Replace standalone AddKeepAlives and StripEmbeddedLibraries MSBuild tasks with a single PostTrimmingPipeline task that opens assemblies once (via DirectoryAssemblyResolver with ReadWrite) and runs both modifications in a single pass. Extract StripEmbeddedLibrariesStep as an IAssemblyModifierPipelineStep for reuse. ## [xabt] Refactor PostTrimmingPipeline to use IAssemblyModifierPipelineStep pattern Use List<IAssemblyModifierPipelineStep> with StripEmbeddedLibrariesStep and PostTrimmingAddKeepAlivesStep instead of calling helpers directly. Move the IsFrameworkAssembly check into StripEmbeddedLibrariesStep.ProcessAssembly and remove all outer-loop filtering so each step handles its own guards internally. Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: sbomer <787361+sbomer@users.noreply.github.com> Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
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9 files changed

Lines changed: 327 additions & 283 deletions

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‎src/Microsoft.Android.Sdk.ILLink/Microsoft.Android.Sdk.ILLink.csproj‎

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<!--Include shared linker sources-->
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<Compile Include="..\Xamarin.Android.Build.Tasks\Linker\External\Linker\BaseMarkHandler.cs" Link="External\BaseMarkHandler.cs" />
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<Compile Include="..\Xamarin.Android.Build.Tasks\Linker\MonoDroid.Tuner\AddKeepAlivesStep.cs" Link="MonoDroid.Tuner\AddKeepAlivesStep.cs" />
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<Compile Include="..\Xamarin.Android.Build.Tasks\Linker\MonoDroid.Tuner\AndroidLinkConfiguration.cs" Link="MonoDroid.Tuner\AndroidLinkConfiguration.cs" />
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<Compile Include="..\Xamarin.Android.Build.Tasks\Linker\MonoDroid.Tuner\Extensions.cs" Link="MonoDroid.Tuner\Extensions.cs" />
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<Compile Include="..\Xamarin.Android.Build.Tasks\Linker\MonoDroid.Tuner\FixAbstractMethodsStep.cs" Link="MonoDroid.Tuner\FixAbstractMethodsStep.cs" />

‎src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/AddKeepAlivesHelper.cs‎

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using System;
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using System.Linq;
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using Java.Interop.Tools.Cecil;
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using Mono.Cecil;
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using Mono.Cecil.Cil;
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using Xamarin.Android.Tasks;
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namespace MonoDroid.Tuner
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{
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static class AddKeepAlivesHelper
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{
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internal static bool AddKeepAlives (AssemblyDefinition assembly, IMetadataResolver resolver, Func<AssemblyDefinition?> getCorlibAssembly, Action<string> logMessage)
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{
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if (!assembly.MainModule.HasTypeReference ("Java.Lang.Object"))
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return false;
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// Anything that was built against .NET for Android will have
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// keep-alives already compiled in.
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if (MonoAndroidHelper.IsDotNetAndroidAssembly (assembly))
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return false;
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MethodDefinition? methodKeepAlive = null;
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bool changed = false;
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foreach (TypeDefinition type in assembly.MainModule.Types)
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changed |= ProcessType (type, resolver, ref methodKeepAlive, getCorlibAssembly, logMessage);
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return changed;
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}
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static bool ProcessType (TypeDefinition type, IMetadataResolver resolver, ref MethodDefinition? methodKeepAlive, Func<AssemblyDefinition?> getCorlibAssembly, Action<string> logMessage)
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{
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bool changed = false;
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if (MightNeedFix (type, resolver))
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changed |= AddKeepAlives (type, ref methodKeepAlive, getCorlibAssembly, logMessage);
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if (type.HasNestedTypes) {
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foreach (var t in type.NestedTypes) {
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changed |= ProcessType (t, resolver, ref methodKeepAlive, getCorlibAssembly, logMessage);
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}
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}
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return changed;
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}
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static bool MightNeedFix (TypeDefinition type, IMetadataResolver resolver)
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{
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return !type.IsAbstract && type.IsSubclassOf ("Java.Lang.Object", resolver);
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}
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static bool AddKeepAlives (TypeDefinition type, ref MethodDefinition? methodKeepAlive, Func<AssemblyDefinition?> getCorlibAssembly, Action<string> logMessage)
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{
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bool changed = false;
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foreach (MethodDefinition method in type.Methods) {
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if (method.Parameters.Count == 0)
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continue;
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if (!method.CustomAttributes.Any (a => a.AttributeType.FullName == "Android.Runtime.RegisterAttribute"))
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continue;
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var instructions = method.Body.Instructions;
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var found = false;
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for (int off = Math.Max (0, instructions.Count - 6); off < instructions.Count; off++) {
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var current = instructions [off];
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if (current.OpCode == OpCodes.Call && current.Operand.ToString ().Contains ("System.GC::KeepAlive")) {
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found = true;
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break;
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}
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}
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if (found)
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continue;
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var processor = method.Body.GetILProcessor ();
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var module = method.DeclaringType.Module;
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var end = instructions.Last ();
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if (end.Previous.OpCode == OpCodes.Endfinally)
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end = end.Previous;
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for (int i = 0; i < method.Parameters.Count; i++) {
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if (method.Parameters [i].ParameterType.IsValueType || method.Parameters [i].ParameterType.FullName == "System.String")
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continue;
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if (methodKeepAlive == null)
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methodKeepAlive = GetKeepAliveMethod (getCorlibAssembly, logMessage);
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if (methodKeepAlive == null) {
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logMessage ("Unable to add KeepAlive call, did not find System.GC.KeepAlive method.");
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break;
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}
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processor.InsertBefore (end, GetLoadArgumentInstruction (method.IsStatic ? i : i + 1, method.Parameters [i]));
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processor.InsertBefore (end, Instruction.Create (OpCodes.Call, module.ImportReference (methodKeepAlive)));
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changed = true;
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}
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}
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return changed;
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}
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static MethodDefinition? GetKeepAliveMethod (Func<AssemblyDefinition?> getCorlibAssembly, Action<string> logMessage)
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{
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var corlibAssembly = getCorlibAssembly ();
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if (corlibAssembly == null)
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return null;
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var gcType = Extensions.GetType (corlibAssembly, "System.GC");
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if (gcType == null)
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return null;
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return Extensions.GetMethod (gcType, "KeepAlive", new string [] { "System.Object" });
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}
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// Adapted from src/Mono.Android.Export/Mono.CodeGeneration/CodeArgumentReference.cs
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static Instruction GetLoadArgumentInstruction (int argNum, ParameterDefinition parameter)
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{
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switch (argNum) {
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case 0: return Instruction.Create (OpCodes.Ldarg_0);
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case 1: return Instruction.Create (OpCodes.Ldarg_1);
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case 2: return Instruction.Create (OpCodes.Ldarg_2);
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case 3: return Instruction.Create (OpCodes.Ldarg_3);
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default: return Instruction.Create (OpCodes.Ldarg, parameter);
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}
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}
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}
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}

‎src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/AddKeepAlivesStep.cs‎

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using System;
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using System.Linq;
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using Java.Interop.Tools.Cecil;
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using Mono.Cecil;
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using Mono.Cecil.Cil;
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using Mono.Linker;
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using Mono.Linker.Steps;
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using Xamarin.Android.Tasks;
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namespace MonoDroid.Tuner
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{
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public class AddKeepAlivesStep : BaseStep
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#if !ILLINK
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, IAssemblyModifierPipelineStep
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#endif // !ILLINK
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public class AddKeepAlivesStep : BaseStep, IAssemblyModifierPipelineStep
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{
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protected override void ProcessAssembly (AssemblyDefinition assembly)
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{
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var action = Annotations.HasAction (assembly) ? Annotations.GetAction (assembly) : AssemblyAction.Skip;
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if (action == AssemblyAction.Delete)
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return;
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if (AddKeepAlives (assembly)) {
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if (action == AssemblyAction.Skip || action == AssemblyAction.Copy)
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Annotations.SetAction (assembly, AssemblyAction.Save);
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}
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}
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#if !ILLINK
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public void ProcessAssembly (AssemblyDefinition assembly, StepContext context)
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{
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// Only run this step on user Android assemblies
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if (!context.IsAndroidUserAssembly)
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return;
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context.IsAssemblyModified |= AddKeepAlives (assembly);
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}
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#endif // !ILLINK
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internal bool AddKeepAlives (AssemblyDefinition assembly)
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{
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if (!assembly.MainModule.HasTypeReference ("Java.Lang.Object"))
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return false;
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// Anything that was built against .NET for Android will have
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// keep-alives already compiled in.
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if (MonoAndroidHelper.IsDotNetAndroidAssembly (assembly))
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return false;
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bool changed = false;
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foreach (TypeDefinition type in assembly.MainModule.Types)
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changed |= ProcessType (type);
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return changed;
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}
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bool ProcessType (TypeDefinition type)
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{
60-
bool changed = false;
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if (MightNeedFix (type))
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changed |= AddKeepAlives (type);
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if (type.HasNestedTypes) {
65-
foreach (var t in type.NestedTypes) {
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changed |= ProcessType (t);
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}
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}
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return changed;
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}
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bool MightNeedFix (TypeDefinition type)
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{
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return !type.IsAbstract && type.IsSubclassOf ("Java.Lang.Object", Context);
76-
}
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78-
MethodDefinition? methodKeepAlive = null;
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80-
bool AddKeepAlives (TypeDefinition type)
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{
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bool changed = false;
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foreach (MethodDefinition method in type.Methods) {
84-
if (method.Parameters.Count == 0)
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continue;
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if (!method.CustomAttributes.Any (a => a.AttributeType.FullName == "Android.Runtime.RegisterAttribute"))
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continue;
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var instructions = method.Body.Instructions;
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var found = false;
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for (int off = Math.Max (0, instructions.Count - 6); off < instructions.Count; off++) {
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var current = instructions [off];
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if (current.OpCode == OpCodes.Call && current.Operand.ToString ().Contains ("System.GC::KeepAlive")) {
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found = true;
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break;
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}
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}
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if (found)
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continue;
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var processor = method.Body.GetILProcessor ();
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var module = method.DeclaringType.Module;
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var end = instructions.Last ();
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if (end.Previous.OpCode == OpCodes.Endfinally)
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end = end.Previous;
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for (int i = 0; i < method.Parameters.Count; i++) {
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if (method.Parameters [i].ParameterType.IsValueType || method.Parameters [i].ParameterType.FullName == "System.String")
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continue;
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if (methodKeepAlive == null)
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methodKeepAlive = GetKeepAliveMethod ();
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117-
if (methodKeepAlive == null) {
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LogMessage ("Unable to add KeepAlive call, did not find System.GC.KeepAlive method.");
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break;
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}
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processor.InsertBefore (end, GetLoadArgumentInstruction (method.IsStatic ? i : i + 1, method.Parameters [i]));
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processor.InsertBefore (end, Instruction.Create (OpCodes.Call, module.ImportReference (methodKeepAlive)));
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changed = true;
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}
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}
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return changed;
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}
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protected virtual AssemblyDefinition GetCorlibAssembly ()
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{
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return Context.GetAssembly ("System.Private.CoreLib");
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}
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135-
MethodDefinition? GetKeepAliveMethod ()
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{
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var corlibAssembly = GetCorlibAssembly ();
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if (corlibAssembly == null)
139-
return null;
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141-
var gcType = Extensions.GetType (corlibAssembly, "System.GC");
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if (gcType == null)
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return null;
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145-
return Extensions.GetMethod (gcType, "KeepAlive", new string [] { "System.Object" });
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}
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148-
public
149-
#if !ILLINK
150-
override
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#endif
152-
void LogMessage (string message)
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{
154-
Context.LogMessage (message);
155-
}
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157-
// Adapted from src/Mono.Android.Export/Mono.CodeGeneration/CodeArgumentReference.cs
158-
static Instruction GetLoadArgumentInstruction (int argNum, ParameterDefinition parameter)
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{
160-
switch (argNum) {
161-
case 0: return Instruction.Create (OpCodes.Ldarg_0);
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case 1: return Instruction.Create (OpCodes.Ldarg_1);
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case 2: return Instruction.Create (OpCodes.Ldarg_2);
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case 3: return Instruction.Create (OpCodes.Ldarg_3);
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default: return Instruction.Create (OpCodes.Ldarg, parameter);
166-
}
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context.IsAssemblyModified |= AddKeepAlivesHelper.AddKeepAlives (
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assembly,
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Context,
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() => Context.GetAssembly ("System.Private.CoreLib"),
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(msg) => LogMessage (msg));
16721
}
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}
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}

‎src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/PostTrimmingAddKeepAlivesStep.cs‎

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using System;
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using Java.Interop.Tools.Cecil;
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using Mono.Cecil;
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using Xamarin.Android.Tasks;
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6+
namespace MonoDroid.Tuner;
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/// <summary>
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/// Post-trimming version of AddKeepAlives that calls AddKeepAlivesHelper directly,
10+
/// matching the original ILLink behavior (no IsAndroidUserAssembly pre-filter).
11+
/// The helper has its own assembly-level guards (HasTypeReference, IsDotNetAndroidAssembly).
12+
/// </summary>
13+
class PostTrimmingAddKeepAlivesStep : IAssemblyModifierPipelineStep
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{
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readonly IMetadataResolver cache;
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readonly Func<AssemblyDefinition?> getCorlibAssembly;
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readonly Action<string> logMessage;
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19+
public PostTrimmingAddKeepAlivesStep (IMetadataResolver cache, Func<AssemblyDefinition?> getCorlibAssembly, Action<string> logMessage)
20+
{
21+
this.cache = cache;
22+
this.getCorlibAssembly = getCorlibAssembly;
23+
this.logMessage = logMessage;
24+
}
25+
26+
public void ProcessAssembly (AssemblyDefinition assembly, StepContext context)
27+
{
28+
context.IsAssemblyModified |= AddKeepAlivesHelper.AddKeepAlives (assembly, cache, getCorlibAssembly, logMessage);
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}
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}

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