Fix GC reporting for slow tail call arguments of type `Span<T>` (#14826)

Fix GC reporting for slow tail call arguments of type `Span<T>`

Fixes https://github.com/dotnet/coreclr/issues/9032:
- Refactored by-ref-like method table walking to find offsets of by-ref pointers in siginfo.hpp/cpp
- Reused that for appending GC layout when creating the copy-args helper for a slow tail call

4 files changed, 56 insertions, 39 deletions

diff --git a/src/vm/i386/stublinkerx86.cpp b/src/vm/i386/stublinkerx86.cpp
index e07b6e1c37..14b9701a29 100644
--- a/src/vm/i386/stublinkerx86.cpp
+++ b/src/vm/i386/stublinkerx86.cpp
@@ -5925,6 +5925,17 @@ static void AppendGCLayout(ULONGARRAY &gcLayout, size_t baseOffset, BOOL fIsType
         _ASSERTE(pMT);
         _ASSERTE(pMT->IsValueType());
 
+        if (pMT->IsByRefLike())
+        {
+            FindByRefPointerOffsetsInByRefLikeObject(
+                pMT,
+                baseOffset,
+                [&](size_t pointerOffset)
+                {
+                    *gcLayout.AppendThrowing() = (ULONG)(pointerOffset | 1); // "| 1" to mark it as an interior pointer
+                });
+        }
+
         // walk the GC descriptors, reporting the correct offsets
         if (pMT->ContainsPointers())
         {
diff --git a/src/vm/object.inl b/src/vm/object.inl
index 5dc3d6d116..495f7bff71 100644
--- a/src/vm/object.inl
+++ b/src/vm/object.inl
@@ -325,4 +325,41 @@ inline TypeHandle Object::GetGCSafeTypeHandle() const
         return TypeHandle(pMT);
 }
 
+template<class F>
+inline void FindByRefPointerOffsetsInByRefLikeObject(PTR_MethodTable pMT, SIZE_T baseOffset, const F processPointerOffset)
+{
+    WRAPPER_NO_CONTRACT;
+    _ASSERTE(pMT != nullptr);
+    _ASSERTE(pMT->IsByRefLike());
+
+    // TODO: TypedReference should ideally be implemented as a by-ref-like struct containing a ByReference<T> field,
+    // in which case the check for g_TypedReferenceMT below would not be necessary
+    if (pMT == g_TypedReferenceMT || pMT->HasSameTypeDefAs(g_pByReferenceClass))
+    {
+        processPointerOffset(baseOffset);
+        return;
+    }
+
+    ApproxFieldDescIterator fieldIterator(pMT, ApproxFieldDescIterator::INSTANCE_FIELDS);
+    for (FieldDesc *pFD = fieldIterator.Next(); pFD != NULL; pFD = fieldIterator.Next())
+    {
+        if (pFD->GetFieldType() != ELEMENT_TYPE_VALUETYPE)
+        {
+            continue;
+        }
+
+        // TODO: GetApproxFieldTypeHandleThrowing may throw. This is a potential stress problem for fragile NGen of non-CoreLib
+        // assemblies. It won't ever throw for CoreCLR with R2R. Figure out if anything needs to be done to deal with the
+        // exception.
+        PTR_MethodTable pFieldMT = pFD->GetApproxFieldTypeHandleThrowing().AsMethodTable();
+        if (!pFieldMT->IsByRefLike())
+        {
+            continue;
+        }
+
+        SIZE_T fieldStartIndex = pFD->GetOffset() / sizeof(void *);
+        FindByRefPointerOffsetsInByRefLikeObject(pFieldMT, baseOffset + fieldStartIndex, processPointerOffset);
+    }
+}
+
 #endif  // _OBJECT_INL_
diff --git a/src/vm/siginfo.cpp b/src/vm/siginfo.cpp
index be919c8b7e..bc16bdffda 100644
--- a/src/vm/siginfo.cpp
+++ b/src/vm/siginfo.cpp
@@ -4946,50 +4946,20 @@ void PromoteCarefully(promote_func   fn,
     (*fn) (ppObj, sc, flags);
 }
 
-void ReportByRefPointersFromByRefLikeObject(promote_func *fn, ScanContext *sc, PTR_MethodTable pMT, PTR_VOID pSrc)
-{
-    WRAPPER_NO_CONTRACT;
-
-    _ASSERTE(pMT->IsByRefLike());
-
-    // TODO: TypedReference should ideally be implemented as a by-ref-like struct containing a ByReference<T> field,
-    // in which case the check for g_TypedReferenceMT below would not be necessary
-    if (pMT == g_TypedReferenceMT || pMT->HasSameTypeDefAs(g_pByReferenceClass))
-    {
-        (*fn)(dac_cast<PTR_PTR_Object>(pSrc), sc, GC_CALL_INTERIOR);
-        return;
-    }
-
-    ApproxFieldDescIterator fieldIterator(pMT, ApproxFieldDescIterator::INSTANCE_FIELDS);
-    for (FieldDesc *pFD = fieldIterator.Next(); pFD != NULL; pFD = fieldIterator.Next())
-    {
-        if (pFD->GetFieldType() != ELEMENT_TYPE_VALUETYPE)
-        {
-            continue;
-        }
-
-        // TODO: GetApproxFieldTypeHandleThrowing may throw. This is a potential stress problem for fragile NGen of non-CoreLib
-        // assemblies. It won't ever throw for CoreCLR with R2R. Figure out if anything needs to be done to deal with the
-        // exception.
-        PTR_MethodTable pFieldMT = pFD->GetApproxFieldTypeHandleThrowing().AsMethodTable();
-        if (!pFieldMT->IsByRefLike())
-        {
-            continue;
-        }
-
-        int fieldStartIndex = pFD->GetOffset() / sizeof(void *);
-        PTR_PTR_Object fieldRef = dac_cast<PTR_PTR_Object>(PTR_BYTE(pSrc) + fieldStartIndex);
-        ReportByRefPointersFromByRefLikeObject(fn, sc, pFieldMT, fieldRef);
-    }
-}
-
 void ReportPointersFromValueType(promote_func *fn, ScanContext *sc, PTR_MethodTable pMT, PTR_VOID pSrc)
 {
     WRAPPER_NO_CONTRACT;
 
     if (pMT->IsByRefLike())
     {
-        ReportByRefPointersFromByRefLikeObject(fn, sc, pMT, pSrc);
+        FindByRefPointerOffsetsInByRefLikeObject(
+            pMT,
+            0 /* baseOffset */,
+            [&](SIZE_T pointerOffset)
+            {
+                PTR_PTR_Object fieldRef = dac_cast<PTR_PTR_Object>(PTR_BYTE(pSrc) + pointerOffset);
+                (*fn)(fieldRef, sc, GC_CALL_INTERIOR);
+            });
     }
 
     if (!pMT->ContainsPointers())
diff --git a/src/vm/siginfo.hpp b/src/vm/siginfo.hpp
index 52b05928db..4cfa548270 100644
--- a/src/vm/siginfo.hpp
+++ b/src/vm/siginfo.hpp
@@ -1191,4 +1191,3 @@ BOOL IsTypeDefExternallyVisible(mdToken tk, Module *pModule, DWORD dwAttrs);
 void ReportPointersFromValueType(promote_func *fn, ScanContext *sc, PTR_MethodTable pMT, PTR_VOID pSrc);
 
 #endif /* _H_SIGINFO */
-