[BOLT][NFC] Add BOLTError and return it from passes (1/2) (#81522)

As part of the effort to refactor old error handling code that
would directly call exit(1), in this patch we add a new class
BOLTError and auxiliary functions `createFatalBOLTError()` and
`createNonFatalBOLTError()` that allow BOLT code to bubble up the
problem to the caller by using the Error class as a return
type (or Expected). Also changes passes to use these.

Co-authored-by: Rafael Auler <rafaelauler@fb.com>

Test Plan: NFC

bolt/include/bolt/Core/BinaryContext.h

@@ -145,6 +145,29 @@ public:
   }
 };
 
+/// BOLT-exclusive errors generated in core BOLT libraries, optionally holding a
+/// string message and whether it is fatal or not. In case it is fatal and if
+/// BOLT is running as a standalone process, the process might be killed as soon
+/// as the error is checked.
+class BOLTError : public ErrorInfo<BOLTError> {
+public:
+  static char ID;
+
+  BOLTError(bool IsFatal, const Twine &S = Twine());
+  void log(raw_ostream &OS) const override;
+  bool isFatal() const { return IsFatal; }
+
+  const std::string &getMessage() const { return Msg; }
+  std::error_code convertToErrorCode() const override;
+
+private:
+  bool IsFatal;
+  std::string Msg;
+};
+
+Error createNonFatalBOLTError(const Twine &S);
+Error createFatalBOLTError(const Twine &S);
+
 class BinaryContext {
   BinaryContext() = delete;
 

bolt/lib/Core/BinaryContext.cpp

@@ -83,6 +83,37 @@ cl::opt<std::string> CompDirOverride(
 namespace llvm {
 namespace bolt {
 
+char BOLTError::ID = 0;
+
+BOLTError::BOLTError(bool IsFatal, const Twine &S)
+    : IsFatal(IsFatal), Msg(S.str()) {}
+
+void BOLTError::log(raw_ostream &OS) const {
+  if (IsFatal)
+    OS << "FATAL ";
+  StringRef ErrMsg = StringRef(Msg);
+  // Prepend our error prefix if it is missing
+  if (ErrMsg.empty()) {
+    OS << "BOLT-ERROR\n";
+  } else {
+    if (!ErrMsg.starts_with("BOLT-ERROR"))
+      OS << "BOLT-ERROR: ";
+    OS << ErrMsg << "\n";
+  }
+}
+
+std::error_code BOLTError::convertToErrorCode() const {
+  return inconvertibleErrorCode();
+}
+
+Error createNonFatalBOLTError(const Twine &S) {
+  return make_error<BOLTError>(/*IsFatal*/ false, S);
+}
+
+Error createFatalBOLTError(const Twine &S) {
+  return make_error<BOLTError>(/*IsFatal*/ true, S);
+}
+
 BinaryContext::BinaryContext(std::unique_ptr<MCContext> Ctx,
                              std::unique_ptr<DWARFContext> DwCtx,
                              std::unique_ptr<Triple> TheTriple,

bolt/lib/Passes/ADRRelaxationPass.cpp

@@ -110,7 +110,7 @@ Error ADRRelaxationPass::runOnFunctions(BinaryContext &BC) {
       "ADRRelaxationPass");
 
   if (PassFailed)
-    exit(1);
+    return createFatalBOLTError("");
   return Error::success();
 }
 

bolt/lib/Passes/BinaryPasses.cpp

@@ -528,12 +528,14 @@ Error FixupBranches::runOnFunctions(BinaryContext &BC) {
 }
 
 Error FinalizeFunctions::runOnFunctions(BinaryContext &BC) {
+  std::atomic<bool> HasFatal{false};
   ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
     if (!BF.finalizeCFIState()) {
       if (BC.HasRelocations) {
         errs() << "BOLT-ERROR: unable to fix CFI state for function " << BF
                << ". Exiting.\n";
-        exit(1);
+        HasFatal = true;
+        return;
       }
       BF.setSimple(false);
       return;
@@ -552,6 +554,8 @@ Error FinalizeFunctions::runOnFunctions(BinaryContext &BC) {
   ParallelUtilities::runOnEachFunction(
       BC, ParallelUtilities::SchedulingPolicy::SP_CONSTANT, WorkFun,
       SkipPredicate, "FinalizeFunctions");
+  if (HasFatal)
+    return createFatalBOLTError("finalize CFI state failure");
   return Error::success();
 }
 

bolt/lib/Passes/Instrumentation.cpp

@@ -567,10 +567,9 @@ Error Instrumentation::runOnFunctions(BinaryContext &BC) {
 
       ErrorOr<BinarySection &> SetupSection =
           BC.getUniqueSectionByName("I__setup");
-      if (!SetupSection) {
-        llvm::errs() << "Cannot find I__setup section\n";
-        exit(1);
-      }
+      if (!SetupSection)
+        return createFatalBOLTError("Cannot find I__setup section\n");
+
       MCSymbol *Target = BC.registerNameAtAddress(
           "__bolt_instr_setup", SetupSection->getAddress(), 0, 0);
       MCInst NewInst;
@@ -586,10 +585,9 @@ Error Instrumentation::runOnFunctions(BinaryContext &BC) {
       BinaryBasicBlock &BB = Ctor->front();
       ErrorOr<BinarySection &> FiniSection =
           BC.getUniqueSectionByName("I__fini");
-      if (!FiniSection) {
-        llvm::errs() << "Cannot find I__fini section\n";
-        exit(1);
-      }
+      if (!FiniSection)
+        return createFatalBOLTError("Cannot find I__fini section");
+
       MCSymbol *Target = BC.registerNameAtAddress(
           "__bolt_instr_fini", FiniSection->getAddress(), 0, 0);
       auto IsLEA = [&BC](const MCInst &Inst) { return BC.MIB->isLEA64r(Inst); };

bolt/lib/Passes/PatchEntries.cpp

@@ -103,7 +103,7 @@ Error PatchEntries::runOnFunctions(BinaryContext &BC) {
         if (opts::ForcePatch) {
           errs() << "BOLT-ERROR: unable to patch entries in " << Function
                  << "\n";
-          exit(1);
+          return createFatalBOLTError("");
         }
 
         continue;

bolt/lib/Passes/ReorderFunctions.cpp

@@ -444,7 +444,7 @@ Error ReorderFunctions::runOnFunctions(BinaryContext &BC) {
     if (!FuncsFile) {
       errs() << "BOLT-ERROR: ordered functions file "
              << opts::GenerateFunctionOrderFile << " cannot be opened\n";
-      exit(1);
+      return createFatalBOLTError("");
     }
   }
 
@@ -455,7 +455,7 @@ Error ReorderFunctions::runOnFunctions(BinaryContext &BC) {
     if (!LinkSectionsFile) {
       errs() << "BOLT-ERROR: link sections file " << opts::LinkSectionsFile
              << " cannot be opened\n";
-      exit(1);
+      return createFatalBOLTError("");
     }
   }
 

bolt/lib/Passes/VeneerElimination.cpp

@@ -79,8 +79,8 @@ Error VeneerElimination::runOnFunctions(BinaryContext &BC) {
         VeneerCallers++;
         if (!BC.MIB->replaceBranchTarget(
                 Instr, VeneerDestinations[TargetSymbol], BC.Ctx.get())) {
-          errs() << "BOLT-ERROR: updating veneer call destination failed\n";
-          exit(1);
+          return createFatalBOLTError(
+              "BOLT-ERROR: updating veneer call destination failed\n");
         }
       }
     }