Fix GC interfaces versioning (#81188)

* Fix GC interfaces versioning

The change that introduced GC interfaces versioning had a bug preventing
it from using .NET 8 GC being used with .NET 7 runtime. The
GC_VersionInfo return value should have been the minimum supported
version, not the current one. But more importantly there was also
some confusion on what interface the GC_INTERFACE_MAJOR_VERSION
represents. While the change considered it to be a version of the
IGCToCLR interface, it really means the version of the IGCHeap
interface. This change creates a separate version,
EE_INTERFACE_MAJOR_VERSION for versioning o the IGCToCLR interface to
rectify that.
@Maoni0 also didn't like the way of creating a new version of
IGCToCLR interface for each major version change, so I am changing it to
single IGCToCLR interface.

src/coreclr/gc/gccommon.cpp

@@ -17,7 +17,7 @@ IGCHeapInternal* g_theGCHeap;
 IGCHandleManager* g_theGCHandleManager;
 
 #ifdef BUILD_AS_STANDALONE
-IGCToCLR2* g_theGCToCLR;
+IGCToCLR* g_theGCToCLR;
 VersionInfo g_runtimeSupportedVersion;
 #endif // BUILD_AS_STANDALONE
 

src/coreclr/gc/gcenv.ee.standalone.inl

@@ -9,7 +9,7 @@
 
 // The singular interface instance. All calls in GCToEEInterface
 // will be forwarded to this interface instance.
-extern IGCToCLR2* g_theGCToCLR;
+extern IGCToCLR* g_theGCToCLR;
 
 // GC version that the current runtime supports
 extern VersionInfo g_runtimeSupportedVersion;
@@ -316,7 +316,7 @@ inline void GCToEEInterface::DiagAddNewRegion(int generation, uint8_t* rangeStar
 
 inline void GCToEEInterface::LogErrorToHost(const char *message)
 {
-    if (g_runtimeSupportedVersion.MajorVersion >= GC_INTERFACE2_MAJOR_VERSION)
+    if (g_runtimeSupportedVersion.MajorVersion >= 1)
     {
         g_theGCToCLR->LogErrorToHost(message);
     }

src/coreclr/gc/gcinterface.ee.h

@@ -446,11 +446,8 @@ class IGCToCLR {
 
     virtual
     void DiagAddNewRegion(int generation, uint8_t* rangeStart, uint8_t* rangeEnd, uint8_t* rangeEndReserved) = 0;
-};
-
-class IGCToCLR2 : public IGCToCLR {
-public:
 
+    // The following method is available only with EE_INTERFACE_MAJOR_VERSION >= 1
     virtual
     void LogErrorToHost(const char *message) = 0;
 };

src/coreclr/gc/gcinterface.h

@@ -4,18 +4,18 @@
 #ifndef _GC_INTERFACE_H_
 #define _GC_INTERFACE_H_
 
-// The major version of the GC/EE interface. Breaking changes to this interface
+// The major version of the IGCHeap interface. Breaking changes to this interface
 // require bumps in the major version number.
-#define GC_INTERFACE_MAJOR_VERSION 6
+#define GC_INTERFACE_MAJOR_VERSION 5
 
-// The minor version of the GC/EE interface. Non-breaking changes are required
+// The minor version of the IGCHeap interface. Non-breaking changes are required
 // to bump the minor version number. GCs and EEs with minor version number
-// mismatches can still interopate correctly, with some care.
+// mismatches can still interoperate correctly, with some care.
 #define GC_INTERFACE_MINOR_VERSION 1
 
-// The major version of the GC/EE interface. Breaking changes to this interface
+// The major version of the IGCToCLR interface. Breaking changes to this interface
 // require bumps in the major version number.
-#define GC_INTERFACE2_MAJOR_VERSION 6
+#define EE_INTERFACE_MAJOR_VERSION 1
 
 struct ScanContext;
 struct gc_alloc_context;

src/coreclr/gc/gcload.cpp

@@ -75,7 +75,7 @@ GC_Initialize(
 
 #ifdef BUILD_AS_STANDALONE
     assert(clrToGC != nullptr);
-    g_theGCToCLR = (IGCToCLR2*)clrToGC;
+    g_theGCToCLR = clrToGC;
 #else
     UNREFERENCED_PARAMETER(clrToGC);
     assert(clrToGC == nullptr);

src/coreclr/vm/gcheaputilities.cpp

@@ -214,8 +214,8 @@ HRESULT LoadAndInitializeGC(LPCWSTR standaloneGcLocation)
     }
 
     g_gc_load_status = GC_LOAD_STATUS_GET_VERSIONINFO;
-    g_gc_version_info.MajorVersion = GC_INTERFACE_MAJOR_VERSION;
-    g_gc_version_info.MinorVersion = GC_INTERFACE_MINOR_VERSION;
+    g_gc_version_info.MajorVersion = EE_INTERFACE_MAJOR_VERSION;
+    g_gc_version_info.MinorVersion = 0;
     g_gc_version_info.BuildVersion = 0;
     versionInfo(&g_gc_version_info);
     g_gc_load_status = GC_LOAD_STATUS_CALL_VERSIONINFO;