Autoselect

clang/include/clang/AST/RandstructSeed.h

@@ -3,5 +3,6 @@
 #include <string>
 namespace clang {
 extern std::string RandstructSeed;
+extern bool RandstructAutoSelect;
 }
 #endif

clang/include/clang/AST/RecordFieldReorganizer.h

@@ -37,6 +37,9 @@ class RecordFieldReorganizer {
 };
 
 class Randstruct : public RecordFieldReorganizer {
+public:  
+/// Determines if the Record can be safely and easily randomized based on certain criteria (see implementation).
+  static bool isTriviallyRandomizable(const RecordDecl *D);
 protected:
   virtual void reorganize(const ASTContext &C, const RecordDecl *D,
                           SmallVector<Decl *, 64> &NewOrder) const override;

clang/include/clang/Driver/Options.td

@@ -1751,6 +1751,9 @@ def freroll_loops : Flag<["-"], "freroll-loops">, Group<f_Group>,
   HelpText<"Turn on loop reroller">, Flags<[CC1Option]>;
 def fno_reroll_loops : Flag<["-"], "fno-reroll-loops">, Group<f_Group>,
   HelpText<"Turn off loop reroller">;
+def randstruct_auto : Flag<["-"], "randstruct-auto">,
+  HelpText<"Enable automatic structure selection for field randomization; "
+           "Disable for specific structures with attribute no_randomize_layout">, Flags<[CC1Option]>;
 def ftrigraphs : Flag<["-"], "ftrigraphs">, Group<f_Group>,
   HelpText<"Process trigraph sequences">, Flags<[CC1Option]>;
 def fno_trigraphs : Flag<["-"], "fno-trigraphs">, Group<f_Group>,

clang/lib/AST/RecordFieldReorganizer.cpp

@@ -25,6 +25,7 @@
 
 namespace clang {
 std::string RandstructSeed = "";
+bool RandstructAutoSelect = false;
 
 void RecordFieldReorganizer::reorganizeFields(const ASTContext &C,
                                               const RecordDecl *D) const {
@@ -37,7 +38,6 @@ void RecordFieldReorganizer::reorganizeFields(const ASTContext &C,
     mutateGuard.insert(f);
     fields.push_back(f);
   }
-
   // Now allow subclass implementations to reorder the fields
   reorganize(C, D, fields);
 
@@ -52,7 +52,6 @@ void RecordFieldReorganizer::reorganizeFields(const ASTContext &C,
 
   commit(D, fields);
 }
-
 void RecordFieldReorganizer::commit(
     const RecordDecl *D, SmallVectorImpl<Decl *> &NewFieldOrder) const {
   Decl *First, *Last;
@@ -254,5 +253,12 @@ void Randstruct::reorganize(const ASTContext &C, const RecordDecl *D,
   SmallVector<Decl *, 64> randomized = perfrandomize(C, NewOrder);
   NewOrder = randomized;
 }
-
+bool Randstruct::isTriviallyRandomizable(const RecordDecl *D) {
+  for (auto f : D->fields()){
+    //If an element of the structure does not have a 
+    //function type is not a function pointer
+    if(f->getFunctionType() == nullptr){ return false; }
+  }
+  return true;
+}
 } // namespace clang

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -2987,8 +2987,8 @@ ASTContext::getASTRecordLayout(const RecordDecl *D) const {
   if (Entry) return *Entry;
 
   const ASTRecordLayout *NewEntry = nullptr;
-  
-  bool ShouldBeRandomized = D->getAttr<RandomizeLayoutAttr>() != nullptr;
+
+  bool ShouldBeRandomized = (RandstructAutoSelect && Randstruct::isTriviallyRandomizable(D)) || D->getAttr<RandomizeLayoutAttr>() != nullptr;
   if (ShouldBeRandomized) {
     // There is no technical benefit to randomizing the fields of a union
     // since they all share the same offset of zero.

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4411,6 +4411,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(A->getValue(0));
   }
 
+  if (Arg *A = Args.getLastArg(options::OPT_randstruct_auto)) {
+    CmdArgs.push_back( "-randstruct-auto" );
+  }
+
   // -fvisibility= and -fvisibility-ms-compat are of a piece.
   if (const Arg *A = Args.getLastArg(options::OPT_fvisibility_EQ,
                                      options::OPT_fvisibility_ms_compat)) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1674,6 +1674,9 @@ static InputKind ParseFrontendArgs(FrontendOptions &Opts, ArgList &Args,
   if (const Arg* A = Args.getLastArg(OPT_randstruct_seed)) {
     RandstructSeed = A->getValue(0);
   }
+  if (const Arg* A = Args.getLastArg(OPT_randstruct_auto)) {
+    RandstructAutoSelect = true;
+  }
   Opts.AddPluginActions = Args.getAllArgValues(OPT_add_plugin);
   for (const auto *AA : Args.filtered(OPT_plugin_arg))
     Opts.PluginArgs[AA->getValue(0)].emplace_back(AA->getValue(1));