[cDAC] Remove DT_CONTEXT from DBI layer by rcj1 · Pull Request #130367 · dotnet/runtime

rcj1 · 2026-07-08T17:53:40Z

In order to encapsulate the target-specific knowledge within the DacDbi and therefore within the cDAC, it is necessary to remove the DT_CONTEXT struct, which represents the target context, from the DBI layer. This PR accomplishes this by:

Creating 10 new DacDbi APIs that provide target-specific information especially pertaining to contexts

    int GetTargetContextSize(ContextSizeFlags flags, uint* pSize);
    int WriteRegistersToContext(byte* ctxBuf, uint cb, CorDebugRegister* regs, uint nRegs, ulong* values);
    int ReadRegistersFromContext(byte* ctxBuf, uint cb, CorDebugRegister* regs, uint nRegs, ulong* pValues);
    int GetAvailableRegistersMask(Interop.BOOL fActive, Interop.BOOL fQuickUnwind, uint regCount, byte* pAvailable);
    int ConvertJitRegNumToCorDebugRegister(uint jitRegNum, CorDebugRegister* pReg);
    int ReadFloatRegistersFromContext(byte* ctxBuf, uint cb, uint maxValues, double* values, uint* pValuesCount, int* pFirstFloatReg, uint* pFloatStackTop);
    int GetTargetInfo(TargetInfo* pTargetInfo);
    int ContextHasExtendedRegisters(byte* ctxBuf, uint cb, Interop.BOOL* pResult);
    int CompareControlRegisters(byte* ctxBuf1, uint cb1, byte* ctxBuf2, uint cb2, Interop.BOOL* pResult);
    int CopyContext(byte* dstCtxBuf, uint cbDst, byte* srcCtxBuf, uint cbSrc, uint flags);

Using said new DacDbi APIs to replace the architecture-specific reading in (arch)/cordbregisterset.cpp
Implementing DacDbi APIs in cDAC
Where we are interop live debugging, that is where we know the host is the same as the target, replacing DT_CONTEXT with T_CONTEXT
Where target and host context may vary, switching from context structs to opaque byte buffers that are queried through DacDbi

dotnet-policy-service · 2026-07-08T17:57:19Z

Tagging subscribers to this area: @steveisok, @tommcdon, @dotnet/dotnet-diag
See info in area-owners.md if you want to be subscribed.

Copilot

Pull request overview

This PR refactors the DBI / cDAC boundary so the DBI layer no longer depends on a DT_CONTEXT struct, moving context-layout knowledge behind new IDacDbiInterface APIs and using opaque target-sized byte buffers where host/target layouts may differ.

Changes:

Extends IDacDbiInterface (IDL + managed projection) with new context/query/register APIs and switches multiple stackwalk/context entrypoints from DT_CONTEXT* to BYTE*.
Updates CoreCLR debugger right-side stackwalking and register-set plumbing to work over opaque context buffers and DAC-provided helpers (e.g., CopyContext, Read/WriteRegistersFromContext).
Updates managed contract context models to describe register copy sets/spans and adds an “Extended” register category.

Show a summary per file

File	Description
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/IDacDbiInterface.cs	Updates STRData ctx to `BYTE*` and adds new DacDbi APIs + related enums/structs for context/register operations.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/X86Context.cs	Adds scalar/wide register copy metadata; adjusts register classifications and extended-reg handling.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/RISCV64Context.cs	Adds scalar/wide register copy metadata; adjusts control/general register typing.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/RegisterAttribute.cs	Adds `RegisterType.Extended`.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/LoongArch64Context.cs	Updates context sizing and floating-point layout; adds scalar/wide register copy metadata and register typing changes.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/IPlatformContext.cs	Adds default properties for extended-register sizing and new register copy metadata accessors.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/IPlatformAgnosticContext.cs	Adds abstract extended-register properties and register copy metadata accessors used for flag-gated copies.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/ContextHolder.cs	Forwards new extended-register properties and register copy metadata accessors.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/ARMContext.cs	Adds scalar/wide register copy metadata; adjusts register typing.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/ARM64Context.cs	Adds scalar/wide register copy metadata; adjusts register typing.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/Context/AMD64Context.cs	Adds scalar/wide register copy metadata and explicit XMM span; adjusts register typing and FP/debug tagging.
src/coreclr/inc/dacdbi.idl	Removes `DT_CONTEXT` typedef; switches context parameters to `BYTE*`; adds new DacDbi context/register APIs and `TargetInfo`.
src/coreclr/debug/shared/riscv64/primitives.cpp	Switches `CORDbgCopyThreadContext` to `T_CONTEXT` and uses `CONTEXT_*` flags.
src/coreclr/debug/shared/loongarch64/primitives.cpp	Switches `CORDbgCopyThreadContext` to `T_CONTEXT` and uses `CONTEXT_*` flags; updates FP span sizing.
src/coreclr/debug/shared/i386/primitives.cpp	Switches `CORDbgCopyThreadContext` to `T_CONTEXT` and uses `CONTEXT_*` flags.
src/coreclr/debug/shared/arm64/primitives.cpp	Switches `CORDbgCopyThreadContext` to `T_CONTEXT` and uses `CONTEXT_*` flags.
src/coreclr/debug/shared/arm/primitives.cpp	Switches `CORDbgCopyThreadContext` to `T_CONTEXT` and uses `CONTEXT_*` flags; updates debug span constant.
src/coreclr/debug/shared/amd64/primitives.cpp	Switches `CORDbgCopyThreadContext` to `T_CONTEXT`.
src/coreclr/debug/inc/riscv64/primitives.h	Switches helpers to `T_CONTEXT`.
src/coreclr/debug/inc/loongarch64/primitives.h	Switches helpers to `T_CONTEXT`.
src/coreclr/debug/inc/i386/primitives.h	Switches helpers to `T_CONTEXT`.
src/coreclr/debug/inc/dbgipcevents.h	Removes arch-specific float count and SP/FP address helpers; introduces `CORDB_MAX_FLOAT_REGISTERS`.
src/coreclr/debug/inc/dacdbistructures.h	Changes `Debugger_STRData::ctx` to `BYTE*` and documents as opaque target context bytes.
src/coreclr/debug/inc/dacdbiinterface.h	Switches various context params to `BYTE*`; adds new DacDbi context/register APIs and target info enums/struct.
src/coreclr/debug/inc/common.h	Updates `CORDbgCopyThreadContext` signature to `T_CONTEXT`.
src/coreclr/debug/inc/arm64/primitives.h	Switches helpers to `T_CONTEXT`; removes unused typedef.
src/coreclr/debug/inc/arm/primitives.h	Switches helpers to `T_CONTEXT`; removes unused typedef.
src/coreclr/debug/inc/arm_primitives.h	Switches helpers to `T_CONTEXT` and adjusts breakpoint-PC logic preprocessor condition.
src/coreclr/debug/inc/amd64/primitives.h	Switches helpers to `T_CONTEXT`; removes unused typedef.
src/coreclr/debug/ee/debugger.cpp	Removes `DT_CONTEXT` casts when calling breakpoint-PC and SS-flag helpers.
src/coreclr/debug/ee/controller.cpp	Removes `DT_CONTEXT` casts when calling SS-flag and IP helpers.
src/coreclr/debug/di/valuehome.cpp	Replaces architecture-specific context/register mutations with DAC register read/write and target-sized buffers.
src/coreclr/debug/di/stdafx.h	Replaces per-arch thread-context macros with unified `DbiGet/SetThreadContext(T_CONTEXT*)` declarations.
src/coreclr/debug/di/shimstackwalk.cpp	Uses DAC register reads for SP and converts shim contexts to opaque target-sized buffers.
src/coreclr/debug/di/shimpriv.h	Updates shim stackwalk state to own target-sized context buffers and passes sizes through.
src/coreclr/debug/di/shimlocaldatatarget.cpp	Switches local datatarget thread-context casts from `DT_CONTEXT` to `T_CONTEXT`.
src/coreclr/debug/di/rsstackwalk.cpp	Converts stackwalk internal state from `DT_CONTEXT` to opaque buffers and uses DAC `CopyContext`.
src/coreclr/debug/di/rsregsetcommon.cpp	Converts register-set state from cached `DT_CONTEXT` to opaque buffers and uses DAC `CopyContext`.
src/coreclr/debug/di/rspriv.h	Updates many signatures/fields from `DT_CONTEXT` to `BYTE*`/`T_CONTEXT`; adds context-size caching and DAC register helpers.
src/coreclr/debug/di/process.cpp	Adds target-context-size caching via DAC; switches SafeRead/WriteThreadContext to operate on opaque buffers and target info queries.
src/coreclr/debug/di/platformspecific.cpp	Stops including per-arch `cordbregisterset.cpp` implementations; keeps per-arch primitives.
src/coreclr/debug/di/module.cpp	Routes JIT-reg-num → CorDebugRegister mapping through DAC-backed helper on `CordbProcess`.
src/coreclr/debug/di/cordb.cpp	Unifies `DbiGet/SetThreadContext` implementation around `T_CONTEXT` and updated alignment logic.
src/coreclr/debug/di/CMakeLists.txt	Adds a shared `cordbregisterset.cpp` (new common register-set impl) and removes floatconversion ASM wiring.
src/coreclr/debug/daccess/dacdbiimplstackwalk.cpp	Switches DacDbi stackwalk context entrypoints to `BYTE*` but reinterprets to `DT_CONTEXT` internally.
src/coreclr/debug/daccess/dacdbiimpl.h	Updates interface signatures for `BYTE*` contexts and declares new DacDbi context/register APIs.
src/coreclr/debug/di/riscv64/floatconversion.S	Removes unused float conversion assembly.
src/coreclr/debug/di/riscv64/cordbregisterset.cpp	Removes per-arch register-set implementation.
src/coreclr/debug/di/loongarch64/floatconversion.S	Removes unused float conversion assembly.
src/coreclr/debug/di/loongarch64/cordbregisterset.cpp	Removes per-arch register-set implementation.
src/coreclr/debug/di/i386/cordbregisterset.cpp	Removes per-arch register-set implementation.
src/coreclr/debug/di/arm64/floatconversion.S	Removes unused float conversion assembly.
src/coreclr/debug/di/arm64/floatconversion.asm	Removes unused float conversion assembly.
src/coreclr/debug/di/arm64/cordbregisterset.cpp	Removes per-arch register-set implementation.
src/coreclr/debug/di/arm/floatconversion.S	Removes unused float conversion assembly.
src/coreclr/debug/di/arm/cordbregisterset.cpp	Removes per-arch register-set implementation.
src/coreclr/debug/di/amd64/floatconversion.S	Removes unused float conversion assembly.
src/coreclr/debug/di/amd64/FloatConversion.asm	Removes unused float conversion assembly.
src/coreclr/debug/di/amd64/cordbregisterset.cpp	Removes per-arch register-set implementation.

Copilot's findings

Files reviewed: 62/62 changed files
Comments generated: 5

Copilot

Copilot's findings

Files reviewed: 65/65 changed files
Comments generated: 5

Copilot

Copilot's findings

Files reviewed: 65/65 changed files
Comments generated: 3

+    HRESULT hr = S_OK;
+    DWORD sizeToWrite = sizeof(T_CONTEXT);

-    if (contextSize < sizeof(DT_CONTEXT))
+    BYTE * pRemoteContext = (BYTE*) pContext.UnsafeGet();
+    BYTE * pCtxSource = (BYTE*) pCtx;
+
+
+#if defined(CONTEXT_EXTENDED_REGISTERS)
+    if ((pCtx->ContextFlags & CONTEXT_EXTENDED_REGISTERS) != CONTEXT_EXTENDED_REGISTERS)
    {
-        LOG((LF_CORDB, LL_INFO10000, "CP::GTC: thread=0x%x, context size is invalid.\n", threadID));
-        return E_INVALIDARG;
+        sizeToWrite = offsetof(T_CONTEXT, SegSs) + sizeof(pCtx->SegSs);
    }
+#endif

-    pContext = reinterpret_cast<DT_CONTEXT *>(context);
+    EX_TRY
+    {
+        TargetBuffer tb(pRemoteContext, sizeToWrite);
+        SafeWriteBuffer(tb, (const BYTE*) pCtxSource);
+    }


Copilot

Copilot's findings

Files reviewed: 69/69 changed files
Comments generated: 3

+        // Load the float cache up front so its register range can classify the
+        // requested bits into GPR and float batches.
+        HRESULT hr = EnsureFloatStateLoaded(pThread);
+        bool areFloatsValid = !!SUCCEEDED(hr);
+
+        int firstFloat = -1;
+        int lastFloat  = -1;
+        if (pThread->m_floatValuesCount > 0 && pThread->m_firstFloatReg >= 0 && areFloatsValid)
+        {
+            firstFloat = pThread->m_firstFloatReg;
+            lastFloat  = firstFloat + (int)pThread->m_floatValuesCount - 1;
+        }


@@ -166,7 +166,7 @@ HRESULT STDMETHODCALLTYPE DacDbiInterfaceImpl::GetStackWalkCurrentContext(StackW

        StackFrameIterator * pIter = GetIteratorFromHandle(pSFIHandle);

-        GetStackWalkCurrentContext(pIter, pContext);
+        GetStackWalkCurrentContext(pIter, reinterpret_cast<DT_CONTEXT *>(pContext));


Copilot

Copilot's findings

Files reviewed: 69/69 changed files
Comments generated: 2

    if (m_pDacPrimitives != NULL)
    {
        m_pDacPrimitives->Release();
        m_pDacPrimitives = NULL;
    }

    if (m_hDacModule != NULL)
    {
        LOG((LF_CORDB, LL_INFO1000, "Unloading DAC\n"));
        m_hDacModule.Free();
    }
 }


+    ULONG32 cbCtx = GetProcess()->GetTargetContextSize();
+    NewArrayHolder<BYTE> tmpCtx(new BYTE[cbCtx]);
+    memcpy(tmpCtx, m_pContextBuffer, cbCtx);
+    // flags == 0: tmpCtx already carries the desired ContextFlags (copied above).
+    IfFailThrow(pDAC->CopyContext(tmpCtx, cbCtx, context, contextSize, 0));
+    IfFailThrow(pDAC->CheckContext(m_pCordbThread->m_vmThreadToken, tmpCtx));
+
+    memcpy(m_pContextBuffer, tmpCtx, cbCtx);


Copilot

Copilot's findings

Files reviewed: 70/70 changed files
Comments generated: 2

+        // Load the float cache up front so its register range can classify the
+        // requested bits into GPR and float batches.
+        HRESULT hr = EnsureFloatStateLoaded(pThread);
+        bool areFloatsValid = !!SUCCEEDED(hr);
+
+        int firstFloat = -1;
+        int lastFloat  = -1;
+        if (pThread->m_floatValuesCount > 0 && pThread->m_firstFloatReg >= 0 && areFloatsValid)
+        {
+            firstFloat = pThread->m_firstFloatReg;
+            lastFloat  = firstFloat + (int)pThread->m_floatValuesCount - 1;
+        }


        // allocate a new CordbRegisterSet object
-        RSInitHolder<CordbRegisterSet> pRegisterSet(new CordbRegisterSet(m_pThread,
-                                                                         &m_context,
+        RSInitHolder<CordbRegisterSet> pRegisterSet(new CordbRegisterSet(m_pContextBuffer,
+                                                                         GetProcess()->GetTargetContextSize(),
+                                                                         m_pThread,
                                                                         IsLeafFrame(),
                                                                         false));



Copilot

Copilot's findings

Files reviewed: 70/70 changed files
Comments generated: 4

+        IDacDbiInterface * pDAC = GetProcess()->GetDAC();
+        ULONG32 targetContextSize = GetProcess()->GetTargetContextSize();

-        // Just to be safe, zero out the buffer we got in while preserving the ContextFlags.
-        // On X64 the ContextFlags field is not the first 4 bytes of the DT_CONTEXT.
-        DWORD dwContextFlags = pInputContext->ContextFlags;
-        ZeroMemory(context, contextSize);
-        pInputContext->ContextFlags = dwContextFlags;
-
-        // Augment the leafmost (active) register w/ information from the current context.
-        DT_CONTEXT * pLeafContext = NULL;
+        BYTE * pLeafContext = NULL;
        if (m_active)
        {


    HRESULT hr = S_OK;
-    DWORD sizeToWrite = sizeof(DT_CONTEXT);
+    ULONG32 sizeToWrite;
+    BOOL hasExtendedRegisters = FALSE;
+    IfFailThrow(GetDAC()->ContextHasExtendedRegisters(const_cast<BYTE *>(pCtx), GetTargetContextSize(), &hasExtendedRegisters));
+    IfFailThrow(GetDAC()->GetTargetContextSize(
+        hasExtendedRegisters ? IDacDbiInterface::kContextSizeExtendedRegisters : IDacDbiInterface::kContextSizeBase,
+        &sizeToWrite));
+    IDacDbiInterface::TargetInfo targetInfo;

    BYTE * pRemoteContext = (BYTE*) pContext.UnsafeGet();
    BYTE * pCtxSource = (BYTE*) pCtx;
-
-
-#if defined(DT_CONTEXT_EXTENDED_REGISTERS)
-    // If our context has extended registers, then write the whole thing. Otherwise, just write the minimum part.
-    if ((pCtx->ContextFlags & DT_CONTEXT_EXTENDED_REGISTERS) != DT_CONTEXT_EXTENDED_REGISTERS)
-    {
-        sizeToWrite = offsetof(DT_CONTEXT, ExtendedRegisters);
-    }
-#endif
+    IfFailThrow(GetDAC()->GetTargetInfo(&targetInfo));



+        // Load the float cache up front so its register range can classify the
+        // requested bits into GPR and float batches.
+        HRESULT hr = EnsureFloatStateLoaded(pThread);
+        bool areFloatsValid = !!SUCCEEDED(hr);
+
+        int firstFloat = -1;
+        int lastFloat  = -1;
+        if (pThread->m_floatValuesCount > 0 && pThread->m_firstFloatReg >= 0 && areFloatsValid)
+        {
+            firstFloat = pThread->m_firstFloatReg;
+            lastFloat  = firstFloat + (int)pThread->m_floatValuesCount - 1;
+        }


+        IDacDbiInterface * pDAC = pThread->GetProcess()->GetDAC();
+        IfFailThrow(pDAC->ReadRegistersFromContext(
+            const_cast<BYTE *>(pCtx),
+            ctxSize,


Copilot

Copilot's findings

Files reviewed: 70/70 changed files
Comments generated: 2

    if (m_hDacModule != NULL)
    {
        LOG((LF_CORDB, LL_INFO1000, "Unloading DAC\n"));
        m_hDacModule.Free();
    }
 }


+    if (targetInfo.arch == IDacDbiInterface::kArchAMD64)
+    {
+        pRemoteContext += offsetof(CONTEXT, ContextFlags); // immediately follows the 6 parameters P1-P6
+        pCtxSource += offsetof(CONTEXT, ContextFlags);
+        sizeToWrite -= offsetof(CONTEXT, ContextFlags);
+    }


remove dt context

f60b349

Copilot AI review requested due to automatic review settings July 8, 2026 17:53

github-actions Bot added the area-Diagnostics-coreclr label Jul 8, 2026

dotnet-policy-service Bot assigned rcj1 Jul 8, 2026

Copilot started reviewing on behalf of rcj1 July 8, 2026 17:55 View session

rcj1 added the area-Diagnostics-cdac label Jul 8, 2026