Index: lib/esan/cache_frag.cpp
===================================================================
--- lib/esan/cache_frag.cpp
+++ lib/esan/cache_frag.cpp
@@ -16,14 +16,34 @@
 
 namespace __esan {
 
+// This should be kept consistent with LLVM's EfficiencySanitizer StructInfo.
+struct StructInfo {
+  const char *StructName;
+  u32 NumOfFields;
+  u64 *FieldCounters;
+  const char **FieldTypeNames;
+};
+
+// This should be kept consistent with LLVM's EfficiencySanitizer CacheFragInfo.
+// The tool-specific information per compilation unit (module).
+struct CacheFragInfo {
+  const char *UnitName;
+  u32 NumOfStructs;
+  StructInfo *Structs;
+};
+
 //===-- Init/exit functions -----------------------------------------------===//
 
 void processCacheFragCompilationUnitInit(void *Ptr) {
-  VPrintf(2, "in esan::%s\n", __FUNCTION__);
+  CacheFragInfo *CFI = (CacheFragInfo *)Ptr;
+  VPrintf(2, "in esan::%s: %s with %u class(es)/struct(s)\n",
+          __FUNCTION__, CFI->UnitName, CFI->NumOfStructs);
 }
 
 void processCacheFragCompilationUnitExit(void *Ptr) {
-  VPrintf(2, "in esan::%s\n", __FUNCTION__);
+  CacheFragInfo *CFI = (CacheFragInfo *)Ptr;
+  VPrintf(2, "in esan::%s: %s with %u class(es)/struct(s)\n",
+          __FUNCTION__, CFI->UnitName, CFI->NumOfStructs);
 }
 
 void initializeCacheFrag() {
Index: lib/esan/esan.cpp
===================================================================
--- lib/esan/esan.cpp
+++ lib/esan/esan.cpp
@@ -197,7 +197,10 @@
 void processCompilationUnitInit(void *Ptr) {
   VPrintf(2, "in esan::%s\n", __FUNCTION__);
   if (WhichTool == ESAN_CacheFrag) {
+    DCHECK(Ptr != nullptr);
     processCacheFragCompilationUnitInit(Ptr);
+  } else {
+    DCHECK(Ptr == nullptr);
   }
 }
 
@@ -206,7 +209,10 @@
 void processCompilationUnitExit(void *Ptr) {
   VPrintf(2, "in esan::%s\n", __FUNCTION__);
   if (WhichTool == ESAN_CacheFrag) {
+    DCHECK(Ptr != nullptr);
     processCacheFragCompilationUnitExit(Ptr);
+  } else {
+    DCHECK(Ptr == nullptr);
   }
 }
 
Index: test/esan/TestCases/struct-simple.cpp
===================================================================
--- test/esan/TestCases/struct-simple.cpp
+++ test/esan/TestCases/struct-simple.cpp
@@ -28,17 +28,17 @@
   // CHECK:      in esan::initializeLibrary
   // CHECK:      in esan::initializeCacheFrag
   // CHECK-NEXT: in esan::processCompilationUnitInit
-  // CHECK-NEXT: in esan::processCacheFragCompilationUnitInit
+  // CHECK-NEXT: in esan::processCacheFragCompilationUnitInit: {{.*}}struct-simple.cpp with 0 class(es)/struct(s)
   // CHECK-NEXT: in esan::processCompilationUnitInit
-  // CHECK-NEXT: in esan::processCacheFragCompilationUnitInit
+  // CHECK-NEXT: in esan::processCacheFragCompilationUnitInit: {{.*}}struct-simple.cpp with 0 class(es)/struct(s)
   part();
   return 0;
   // CHECK:      in esan::finalizeLibrary
   // CHECK-NEXT: in esan::finalizeCacheFrag
   // CHECK-NEXT: {{.*}}EfficiencySanitizer is not finished: nothing yet to report
   // CHECK-NEXT: in esan::processCompilationUnitExit
-  // CHECK-NEXT: in esan::processCacheFragCompilationUnitExit
+  // CHECK-NEXT: in esan::processCacheFragCompilationUnitExit: {{.*}}struct-simple.cpp with 0 class(es)/struct(s)
   // CHECK-NEXT: in esan::processCompilationUnitExit
-  // CHECK-NEXT: in esan::processCacheFragCompilationUnitExit
+  // CHECK-NEXT: in esan::processCacheFragCompilationUnitExit: {{.*}}struct-simple.cpp with 0 class(es)/struct(s)
 }
 #endif // MAIN