Set CSVs linkage to internal

This simple commit should improve performance of the generated program
sensibly. Basically all the global variables will have internal linkage
from now on (unless the `--external` parameter is specified on the
command line). This way, the compiler will be able to avoid load/store
instructions when leaving code in the current translation unit.

codegenerator.cpp

@@ -73,7 +73,8 @@ CodeGenerator::CodeGenerator(BinaryFile &Binary,
                              std::string BBSummary,
                              bool EnableOSRA,
                              bool DetectFunctionBoundaries,
-                             bool EnableLinking) :
+                             bool EnableLinking,
+                             bool ExternalCSVs) :
   TargetArchitecture(Target),
   Context(getGlobalContext()),
   TheModule((new Module("top", Context))),
@@ -82,7 +83,8 @@ CodeGenerator::CodeGenerator(BinaryFile &Binary,
   Binary(Binary),
   EnableOSRA(EnableOSRA),
   DetectFunctionBoundaries(DetectFunctionBoundaries),
-  EnableLinking(EnableLinking)
+  EnableLinking(EnableLinking),
+  ExternalCSVs(ExternalCSVs)
 {
   OriginalInstrMDKind = Context.getMDKindID("oi");
   PTCInstrMDKind = Context.getMDKindID("pi");
@@ -910,6 +912,9 @@ void CodeGenerator::translate(uint64_t VirtualAddress) {
   JumpTargets.noReturn().cleanup();
 
   Translator.finalizeNewPCMarkers(CoveragePath);
+
+  Variables.finalize(ExternalCSVs);
+
   Debug->generateDebugInfo();
 
 }

codegenerator.h

@@ -73,7 +73,8 @@ public:
                 std::string BBSummary,
                 bool EnableOSRA,
                 bool DetectFunctionBoundaries,
-                bool EnableLinking);
+                bool EnableLinking,
+                bool ExternalCSVs);
 
   ~CodeGenerator();
 
@@ -121,6 +122,7 @@ private:
   std::string FunctionListPath;
   bool DetectFunctionBoundaries;
   bool EnableLinking;
+  bool ExternalCSVs;
 };
 
 #endif // _CODEGENERATOR_H

docs/RevambUsage.rst

@@ -70,6 +70,11 @@ are described:
                         appear as calls to extern functions. This option makes
                         the resulting module non-functioncal but it's useful for
                         analysis-only purposes.
+:``-E``, ``--external``: Set the linkage of global variables representing the
+                         CPU state (aka CSVs) to `external` instead of
+                         `internal`. This degrades performances of the produced
+                         binary sensibly but makes debugging the generated code
+                         easier.
 :``-S``, ``--use-sections``: If they are available, ELF sections are employed to
                              identify executable code. This options is useful to
                              evaluate `revamb` ignoring the code identification

main.cpp

@@ -52,6 +52,7 @@ struct ProgramParameters {
   bool UseSections;
   bool DetectFunctionsBoundaries;
   bool NoLink;
+  bool External;
 };
 
 using LibraryDestructor = GenericFunctor<decltype(&dlclose), &dlclose>;
@@ -181,6 +182,8 @@ static int parseArgs(int Argc, const char *Argv[],
                 "disable OSRA."),
     OPT_BOOLEAN('L', "no-link", &Parameters->NoLink,
                 "do not link the output to QEMU helpers."),
+    OPT_BOOLEAN('E', "external", &Parameters->External,
+                "set CSVs linkage to external, useful for debugging purposes."),
     OPT_BOOLEAN('S', "use-sections", &Parameters->UseSections,
                 "use section informations, if available."),
     OPT_STRING('b', "bb-summary",
@@ -287,7 +290,8 @@ int main(int argc, const char *argv[]) {
                           std::string(Parameters.BBSummaryPath),
                           !Parameters.NoOSRA,
                           Parameters.DetectFunctionsBoundaries,
-                          !Parameters.NoLink);
+                          !Parameters.NoLink,
+                          Parameters.External);
 
   Generator.translate(Parameters.EntryPointAddress);
 

variablemanager.h

@@ -167,6 +167,18 @@ public:
     return storeToCPUStateOffset(Builder, StoreSize, ActualOffset, ToStore);
   }
 
+  /// \brief Perform finalization steps on variables
+  ///
+  /// \param ExternalCSVs true if CSVs linkage should not be turned into static.
+  void finalize(bool ExternalCSVs) {
+    if (!ExternalCSVs) {
+      for (auto P : CPUStateGlobals)
+        P.second->setLinkage(llvm::GlobalValue::InternalLinkage);
+      for (auto P : OtherGlobals)
+        P.second->setLinkage(llvm::GlobalValue::InternalLinkage);
+    }
+  }
+
 private:
   llvm::Value *loadFromCPUStateOffset(llvm::IRBuilder<> &Builder,
                                       unsigned LoadSize,