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[cDAC][wasm] Register platform GC-info decoding
Co-authored-by: Copilot App <[email protected]>
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‎docs/design/datacontracts/GCInfo.md‎

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@@ -4,6 +4,15 @@ This contract is for fetching information related to GCInfo associated with nati
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The GCInfo contract has platform specific implementations as GCInfo differs per architecture. With the exception of x86, all platforms have a common encoding scheme with different encoding lengths and normalization functions for data. x86 uses an entirely different scheme which is partially supported by this contract.
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WebAssembly uses the common decoder with `Wasm32GcInfoEncoding` traits from
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`src/coreclr/inc/gcinfotypes.h`: code lengths/offsets and stack offsets are
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unscaled, the code-length encoding base is 6, and there is no fixed stack
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parameter scratch area. The platform encoding has no interruptible-range
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count in its fat header (`HAS_INTERRUPTIBLE_RANGES` is false).
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`DecodeInterpreterGCInfo` uses the separate interpreter traits even on
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WebAssembly, including its code-length encoding base of 8 and its
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interruptible-range count field.
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## APIs of contract
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```csharp

‎src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/PlatformTraits/WasmGCInfoTraits.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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namespace Microsoft.Diagnostics.DataContractReader.Contracts.GCInfoHelpers;
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// Mirrors Wasm32GcInfoEncoding in src/coreclr/inc/gcinfotypes.h.
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internal sealed class WasmGCInfoTraits : IGCInfoTraits
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{
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public static uint DenormalizeStackBaseRegister(uint reg) => reg;
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public static uint DenormalizeCodeLength(uint len) => len;
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public static uint NormalizeCodeLength(uint len) => len;
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public static uint DenormalizeCodeOffset(uint offset) => offset;
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public static uint NormalizeCodeOffset(uint offset) => offset;
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public static int DenormalizeStackSlot(int value) => value;
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public static uint DenormalizeSizeOfStackArea(uint size) => size;
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public static int GENERICS_INST_CONTEXT_STACK_SLOT_ENCBASE => 6;
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public static int GS_COOKIE_STACK_SLOT_ENCBASE => 6;
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public static int CODE_LENGTH_ENCBASE => 6;
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public static int STACK_BASE_REGISTER_ENCBASE => 3;
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public static int SIZE_OF_STACK_AREA_ENCBASE => 6;
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public static int SIZE_OF_EDIT_AND_CONTINUE_PRESERVED_AREA_ENCBASE => 3;
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public static int SIZE_OF_EDIT_AND_CONTINUE_FIXED_STACK_FRAME_ENCBASE => 0;
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public static int REVERSE_PINVOKE_FRAME_ENCBASE => 6;
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public static int NUM_REGISTERS_ENCBASE => 3;
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public static int NUM_STACK_SLOTS_ENCBASE => 5;
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public static int NUM_UNTRACKED_SLOTS_ENCBASE => 5;
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public static int NORM_PROLOG_SIZE_ENCBASE => 4;
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public static int NORM_EPILOG_SIZE_ENCBASE => 3;
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public static int INTERRUPTIBLE_RANGE_DELTA1_ENCBASE => 5;
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public static int INTERRUPTIBLE_RANGE_DELTA2_ENCBASE => 5;
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public static int REGISTER_ENCBASE => 3;
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public static int REGISTER_DELTA_ENCBASE => 3;
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public static int STACK_SLOT_ENCBASE => 6;
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public static int STACK_SLOT_DELTA_ENCBASE => 4;
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public static int NUM_SAFE_POINTS_ENCBASE => 4;
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public static int NUM_INTERRUPTIBLE_RANGES_ENCBASE => 1;
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public static bool HAS_FIXED_STACK_PARAMETER_SCRATCH_AREA => false;
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public static bool HAS_INTERRUPTIBLE_RANGES => false;
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public static bool IsScratchRegister(uint regNum) => false;
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}

‎src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/CoreCLRContracts.cs‎

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RuntimeInfoArchitecture.Arm => new GCInfo_1<ARMGCInfoTraits>(t),
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RuntimeInfoArchitecture.LoongArch64 => new GCInfo_1<LoongArch64GCInfoTraits>(t),
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RuntimeInfoArchitecture.RiscV64 => new GCInfo_1<RISCV64GCInfoTraits>(t),
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RuntimeInfoArchitecture.Wasm => new GCInfo_1<WasmGCInfoTraits>(t),
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_ => default(GCInfo),
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};
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});

‎src/native/managed/cdac/tests/UnitTests/StackWalkTests.cs‎

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public unsafe class StackWalkTests
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{
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[Theory]
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[InlineData(false, new byte[] { 0x04, 0x05, 0x21, 0x02 }, uint.MaxValue)]
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[InlineData(false, new byte[] { 0x81, 0x08, 0x0a, 0x30, 0x42, 0x04 }, 8u)]
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[InlineData(true, new byte[] { 0x04, 0x4a, 0x04 }, uint.MaxValue)]
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[InlineData(true, new byte[] { 0x81, 0x08, 0x84, 0x11, 0x22, 0x00 }, 8u)]
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public void GCInfo_Wasm_DecodesPlatformAndInterpreterFormats(
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bool interpreter, byte[] encoded, uint stackBaseRegister)
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{
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MockTarget.Architecture arch = new() { IsLittleEndian = true, Is64Bit = false };
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TestPlaceholderTarget.Builder builder = new(arch);
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// Length 129 and safe point 17 distinguish the platform's six-bit encoding
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// from the interpreter's eight-bit encoding and exercise header alignment.
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byte[] gcInfo = new byte[32];
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encoded.CopyTo(gcInfo, 0);
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builder.MemoryBuilder.AddHeapFragment(new MockMemorySpace.HeapFragment
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{
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Address = 0x1000,
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Data = gcInfo,
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Name = "Wasm GC info"
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});
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Mock<IRuntimeInfo> runtimeInfo = new();
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runtimeInfo.Setup(r => r.GetTargetArchitecture()).Returns(RuntimeInfoArchitecture.Wasm);
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IGCInfo contract = builder
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.AddMockContract(runtimeInfo)
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.AddContract<IGCInfo>(version: "c1")
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.Build().Contracts.GCInfo;
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IGCInfoHandle handle = interpreter
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? contract.DecodeInterpreterGCInfo(new TargetPointer(0x1000), 4)
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: contract.DecodePlatformSpecificGCInfo(new TargetPointer(0x1000), 4);
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GCInfoHeader header = contract.GetHeader(handle);
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Assert.Equal(129u, contract.GetCodeLength(handle));
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Assert.Equal(129u, header.CodeSize);
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Assert.Equal(stackBaseRegister, header.StackBaseRegister);
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Assert.Equal(0u, header.SizeOfStackParameterArea);
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Assert.Equal(new uint[] { 17 }, contract.GetSafePoints(handle));
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Assert.Empty(contract.GetInterruptibleRanges(handle));
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Assert.Equal(interpreter, contract.TryGetGenericContextStorage(
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handle, GenericContextLoc.ThisPtr, 0, out GenericContextStorage storage));
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if (interpreter)
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{
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Assert.Equal(GenericContextStorageKind.InterpreterArgumentRelative, storage.Kind);
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Assert.Equal(0, storage.Offset);
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}
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}
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[Fact]
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public void LoongArch64Unwind_EpilogReturn_DoesNotRepeatStackAdjustment()
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{

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