properly enumerate uninstrumented bounds (#119965)

* properly enumerate uninstrumented bounds
* use alignup to account for multi-byte reads

Author: max-charlamb

src/coreclr/vm/debuginfostore.cpp

@@ -1406,12 +1406,23 @@ void CompressDebugInfo::EnumMemoryRegions(CLRDataEnumMemoryFlags flags, PTR_BYTE
         _ASSERTE(flagByte == 0);
     }
 
-    NibbleReader r(pDebugInfo, 12 /* maximum size of compressed 2 UINT32s */);
+    NibbleReader r(pDebugInfo, 24 /* maximum size of compressed 4 UINT32s */);
 
     ULONG cbBounds = r.ReadEncodedU32();
+    ULONG cbUninstrumentedBounds = 0;
+    if (cbBounds == DebugInfoBoundsHasInstrumentedBounds)
+    {
+        // This means we have instrumented bounds.
+        cbBounds = r.ReadEncodedU32();
+        cbUninstrumentedBounds = r.ReadEncodedU32();
+    }
     ULONG cbVars   = r.ReadEncodedU32();
 
-    pDebugInfo += r.GetNextByteIndex() + cbBounds + cbVars;
+    pDebugInfo += r.GetNextByteIndex() + cbBounds + cbUninstrumentedBounds + cbVars;
+
+    // NibbleReader reads in units of sizeof(NibbleChunkType)
+    // So we need to account for any partial chunk at the end.
+    pDebugInfo = AlignUp(dac_cast<TADDR>(pDebugInfo), sizeof(NibbleReader::NibbleChunkType));
 
     DacEnumMemoryRegion(dac_cast<TADDR>(pStart), pDebugInfo - pStart);
 }