Fix setting of DacpHeapSegmentData::highAllocMark on DAC side. (#69670)

Fix setting of DacpHeapSegmentData::highAllocMark on DAC side. Keep some logic for backward compat in dacprivate.h, the copy here and the one in the Diagnostics repo, so that a new SOS can work correctly with an older DAC.

The PR in the diagnostics repo is this: dotnet/diagnostics#3062.

src/coreclr/debug/daccess/request.cpp

@@ -2855,6 +2855,15 @@ ClrDataAccess::GetHeapSegmentData(CLRDATA_ADDRESS seg, struct DacpHeapSegmentDat
             heapSegment->flags = pSegment->flags;
             heapSegment->gc_heap = NULL;
             heapSegment->background_allocated = (CLRDATA_ADDRESS)(ULONG_PTR)pSegment->background_allocated;
+
+            if (seg == (CLRDATA_ADDRESS)*g_gcDacGlobals->ephemeral_heap_segment)
+            {
+                heapSegment->highAllocMark = (CLRDATA_ADDRESS)*g_gcDacGlobals->alloc_allocated;
+            }
+            else
+            {
+                heapSegment->highAllocMark = heapSegment->allocated;
+            }
         }
     }
 

src/coreclr/debug/daccess/request_svr.cpp

@@ -48,6 +48,18 @@ HRESULT GetServerHeapData(CLRDATA_ADDRESS addr, DacpHeapSegmentData *pSegment)
     pSegment->next = (CLRDATA_ADDRESS)dac_cast<TADDR>(pHeapSegment->next);
     pSegment->gc_heap = (CLRDATA_ADDRESS)pHeapSegment->heap;
 
+    TADDR heapAddress = TO_TADDR(pSegment->gc_heap);
+    dac_gc_heap heap = LoadGcHeapData(heapAddress);
+
+    if (pSegment->segmentAddr == heap.ephemeral_heap_segment.GetAddr())
+    {
+        pSegment->highAllocMark = (CLRDATA_ADDRESS)(ULONG_PTR)heap.alloc_allocated;
+    }
+    else
+    {
+        pSegment->highAllocMark = pSegment->allocated;
+    }
+
     return S_OK;
 }
 

src/coreclr/inc/dacprivate.h

@@ -789,13 +789,15 @@ struct MSLAYOUT DacpHeapSegmentData
 
     HRESULT Request(ISOSDacInterface *sos, CLRDATA_ADDRESS addr, const DacpGcHeapDetails& heap)
     {
+        // clear this here to make sure we don't get stale values
+        this->highAllocMark = 0;
+
         HRESULT hr = sos->GetHeapSegmentData(addr, this);
 
-        // if this is the start segment, set highAllocMark too.
-        if (SUCCEEDED(hr))
+        // if this is the start segment, and the Dac hasn't set highAllocMark, set it here.
+        if (SUCCEEDED(hr) && this->highAllocMark == 0)
         {
-            // TODO:  This needs to be put on the Dac side.
-            if (this->segmentAddr == heap.generation_table[0].start_segment)
+            if (this->segmentAddr == heap.ephemeral_heap_segment)
                 highAllocMark = heap.alloc_allocated;
             else
                 highAllocMark = allocated;