[DFSan] Add __dfsan_load_callback.

[morehouse]

Summary

When -dfsan-event-callbacks is specified, insert a call to
__dfsan_load_callback() on every load.

compiler-rt/test/dfsan/event_callbacks.c

-// RUN: %clang_dfsan -fno-sanitize=dataflow -fPIE -DCALLBACKS -c %s -o %t-callbacks.o
-// RUN: %clang_dfsan -mllvm -dfsan-event-callbacks %s %t-callbacks.o -o %t
+// RUN: %clang_dfsan -fno-sanitize=dataflow -O2 -fPIE -DCALLBACKS -c %s -o %t-callbacks.o
+// RUN: %clang_dfsan -O2 -mllvm -dfsan-event-callbacks %s %t-callbacks.o -o %t
 // RUN: %run %t 2>&1 | FileCheck %s
 
 // Tests that callbacks are inserted for store events when
 // -dfsan-event-callbacks is specified.
 
 #include <assert.h>
 #include <sanitizer/dfsan_interface.h>
 #include <stdio.h>
case 1:
     break;
   case 2:
     assert(Label == LabelIJ);
     break;
   default:
     assert(0);
   }
 
-  // CHECK: Label 1 stored to memory
-  // CHECK: Label 2 stored to memory
-  // CHECK: Label 3 stored to memory
   fprintf(stderr, "Label %u stored to memory\n", Label);
 }
 
+void __dfsan_load_callback(dfsan_label Label) {
+  if (!Label)
+    return;
+
+  fprintf(stderr, "Label %u loaded from memory\n", Label);
+}
+
 #else
 // Compile this code with DFSan and -dfsan-event-callbacks to insert the
 // callbacks.
 
 dfsan_label LabelI;
 dfsan_label LabelJ;
 dfsan_label LabelIJ;
 
 int main(void) {
   int I = 1, J = 2;
   LabelI = dfsan_create_label("I", 0);
   dfsan_set_label(LabelI, &I, sizeof(I));
   LabelJ = dfsan_create_label("J", 0);
   dfsan_set_label(LabelJ, &J, sizeof(J));
   LabelIJ = dfsan_union(LabelI, LabelJ);
 
+  // CHECK: Label 1 stored to memory
   volatile int Sink = I;
+
+  // CHECK: Label 1 loaded from memory
+  assert(Sink == 1);
+
+  // CHECK: Label 2 stored to memory
   Sink = J;
+
+  // CHECK: Label 2 loaded from memory
+  assert(Sink == 2);
+
+  // CHECK: Label 2 loaded from memory
+  // CHECK: Label 3 stored to memory
   Sink += I;
 
+  // CHECK: Label 3 loaded from memory
+  assert(Sink == 3);
+
   return 0;
 }
 
 #endif // #ifdef CALLBACKS

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

 
 static cl::opt<bool> ClDebugNonzeroLabels(
     "dfsan-debug-nonzero-labels",
     cl::desc("Insert calls to __dfsan_nonzero_label on observing a parameter, "
              "load or return with a nonzero label"),
     cl::Hidden);
 
 // Experimental feature that inserts callbacks for certain data events.
-// Currently callbacks are only inserted for stores.
+// Currently callbacks are only inserted for loads and stores.
 //
 // If this flag is set to true, the user must provide definitions for the
 // following callback functions:
+//   void __dfsan_load_callback(dfsan_label Label);
 //   void __dfsan_store_callback(dfsan_label Label);
 static cl::opt<bool> ClEventCallbacks(
     "dfsan-event-callbacks",
     cl::desc("Insert calls to __dfsan_*_callback functions on data events."),
     cl::Hidden, cl::init(false));
 
 static StringRef GetGlobalTypeString(const GlobalValue &G) {
   // Types of GlobalVariables are always pointer types.
class DataFlowSanitizer : public ModulePass {
   Constant *GetRetvalTLS;
   Constant *ExternalShadowMask;
   FunctionType *DFSanUnionFnTy;
   FunctionType *DFSanUnionLoadFnTy;
   FunctionType *DFSanUnimplementedFnTy;
   FunctionType *DFSanSetLabelFnTy;
   FunctionType *DFSanNonzeroLabelFnTy;
   FunctionType *DFSanVarargWrapperFnTy;
-  FunctionType *DFSanStoreCallbackFnTy;
+  FunctionType *DFSanLoadStoreCallbackFnTy;
   FunctionCallee DFSanUnionFn;
   FunctionCallee DFSanCheckedUnionFn;
   FunctionCallee DFSanUnionLoadFn;
   FunctionCallee DFSanUnimplementedFn;
   FunctionCallee DFSanSetLabelFn;
   FunctionCallee DFSanNonzeroLabelFn;
   FunctionCallee DFSanVarargWrapperFn;
+  FunctionCallee DFSanLoadCallbackFn;
   FunctionCallee DFSanStoreCallbackFn;
   MDNode *ColdCallWeights;
   DFSanABIList ABIList;
   DenseMap<Value *, Function *> UnwrappedFnMap;
   AttrBuilder ReadOnlyNoneAttrs;
   bool DFSanRuntimeShadowMask = false;
 
   Value *getShadowAddress(Value *Addr, Instruction *Pos);
DFSanUnimplementedFnTy = FunctionType::get(
       Type::getVoidTy(*Ctx), Type::getInt8PtrTy(*Ctx), /*isVarArg=*/false);
   Type *DFSanSetLabelArgs[3] = { ShadowTy, Type::getInt8PtrTy(*Ctx), IntptrTy };
   DFSanSetLabelFnTy = FunctionType::get(Type::getVoidTy(*Ctx),
                                         DFSanSetLabelArgs, /*isVarArg=*/false);
   DFSanNonzeroLabelFnTy = FunctionType::get(
       Type::getVoidTy(*Ctx), None, /*isVarArg=*/false);
   DFSanVarargWrapperFnTy = FunctionType::get(
       Type::getVoidTy(*Ctx), Type::getInt8PtrTy(*Ctx), /*isVarArg=*/false);
-  DFSanStoreCallbackFnTy =
+  DFSanLoadStoreCallbackFnTy =
       FunctionType::get(Type::getVoidTy(*Ctx), ShadowTy, /*isVarArg=*/false);
 
   if (GetArgTLSPtr) {
     Type *ArgTLSTy = ArrayType::get(ShadowTy, 64);
     ArgTLS = nullptr;
     GetArgTLSTy = FunctionType::get(PointerType::getUnqual(ArgTLSTy), false);
     GetArgTLS = ConstantExpr::getIntToPtr(
         ConstantInt::get(IntptrTy, uintptr_t(GetArgTLSPtr)),
DFSanUnimplementedFn =
     DFSanSetLabelFn =
         Mod->getOrInsertFunction("__dfsan_set_label", DFSanSetLabelFnTy, AL);
   }
   DFSanNonzeroLabelFn =
       Mod->getOrInsertFunction("__dfsan_nonzero_label", DFSanNonzeroLabelFnTy);
   DFSanVarargWrapperFn = Mod->getOrInsertFunction("__dfsan_vararg_wrapper",
                                                   DFSanVarargWrapperFnTy);
 
+  DFSanLoadCallbackFn = Mod->getOrInsertFunction("__dfsan_load_callback",
+                                                 DFSanLoadStoreCallbackFnTy);
   DFSanStoreCallbackFn = Mod->getOrInsertFunction("__dfsan_store_callback",
-                                                  DFSanStoreCallbackFnTy);
+                                                  DFSanLoadStoreCallbackFnTy);
 
   std::vector<Function *> FnsToInstrument;
   SmallPtrSet<Function *, 2> FnsWithNativeABI;
   for (Function &i : M) {
     if (!i.isIntrinsic() &&
         &i != DFSanUnionFn.getCallee()->stripPointerCasts() &&
         &i != DFSanCheckedUnionFn.getCallee()->stripPointerCasts() &&
         &i != DFSanUnionLoadFn.getCallee()->stripPointerCasts() &&
         &i != DFSanUnimplementedFn.getCallee()->stripPointerCasts() &&
         &i != DFSanSetLabelFn.getCallee()->stripPointerCasts() &&
         &i != DFSanNonzeroLabelFn.getCallee()->stripPointerCasts() &&
         &i != DFSanVarargWrapperFn.getCallee()->stripPointerCasts() &&
+        &i != DFSanLoadCallbackFn.getCallee()->stripPointerCasts() &&
         &i != DFSanStoreCallbackFn.getCallee()->stripPointerCasts())
       FnsToInstrument.push_back(&i);
   }
 
   // Give function aliases prefixes when necessary, and build wrappers where the
   // instrumentedness is inconsistent.
   for (Module::alias_iterator i = M.alias_begin(), e = M.alias_end(); i != e;) {
     GlobalAlias *GA = &*i;
void DFSanVisitor::visitLoadInst(LoadInst &LI) {
   if (ClCombinePointerLabelsOnLoad) {
     Value *PtrShadow = DFSF.getShadow(LI.getPointerOperand());
     Shadow = DFSF.combineShadows(Shadow, PtrShadow, &LI);
   }
   if (Shadow != DFSF.DFS.ZeroShadow)
     DFSF.NonZeroChecks.push_back(Shadow);
 
   DFSF.setShadow(&LI, Shadow);
+  if (ClEventCallbacks) {
+    IRBuilder<> IRB(&LI);
+    IRB.CreateCall(DFSF.DFS.DFSanLoadCallbackFn, Shadow);
+  }
 }
 
 void DFSanFunction::storeShadow(Value *Addr, uint64_t Size, Align Alignment,
                                 Value *Shadow, Instruction *Pos) {
   if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
     const auto i = AllocaShadowMap.find(AI);
     if (i != AllocaShadowMap.end()) {
       IRBuilder<> IRB(Pos);