Add PNaClSjLjEH pass to implement C++ exception handling using setjmp()+longjmp()

lib/Transforms/NaCl/PNaClSjLjEH.cpp

+//===- PNaClSjLjEH.cpp - Lower C++ exception handling to use setjmp()------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The PNaClSjLjEH pass is part of an implementation of C++ exception
+// handling for PNaCl that uses setjmp() and longjmp() to handle C++
+// exceptions.  The pass lowers LLVM "invoke" instructions to use
+// setjmp().
+//
+// For example, consider the following C++ code fragment:
+//
+//   int catcher_func() {
+//     try {
+//       int result = external_func();
+//       return result + 100;
+//     } catch (MyException &exc) {
+//       return exc.value + 200;
+//     }
+//   }
+//
+// PNaClSjLjEH converts the IR for that function to the following
+// pseudo-code:
+//
+//   struct LandingPadResult {
+//     void *exception_obj;  // For passing to __cxa_begin_catch()
+//     int matched_clause_id;  // See ExceptionInfoWriter.cpp
+//   };
+//
+//   struct ExceptionFrame {
+//     union {
+//       jmp_buf jmpbuf;  // Context for jumping to landingpad block
+//       struct LandingPadResult result;  // Data returned to landingpad block
+//     };
+//     struct ExceptionFrame *next;  // Next frame in linked list
+//     int clause_list_id;  // Reference to landingpad's exception info
+//   };
+//
+//   // Thread-local exception state
+//   __thread struct ExceptionFrame *__pnacl_eh_stack;
+//
+//   int catcher_func() {
+//     struct ExceptionFrame frame;
+//     int result;
+//     if (!setjmp(&frame.jmpbuf)) {  // Save context
+//       frame.next = __pnacl_eh_stack;
+//       frame.clause_list_id = 123;
+//       __pnacl_eh_stack = &frame;  // Add frame to stack
+//       result = external_func();
+//       __pnacl_eh_stack = frame.next;  // Remove frame from stack
+//     } else {
+//       // Handle exception.  This is a simplification.  Real code would
+//       // call __cxa_begin_catch() to extract the thrown object.
+//       MyException &exc = *(MyException *) frame.result.exception;

[Derek Schuff, 2013/10/15 17:39:26]

frame.result.exception_obj

[Mark Seaborn, 2013/10/15 21:41:18]

Done.

+//       return exc.value + 200;
+//     }
+//     return result + 100;
+//   }
+//
+// The pass makes the following changes to IR:
+//
+//  * Convert "invoke" and "landingpad" instructions.
+//  * Convert "resume" instructions into __pnacl_eh_resume() calls.
+//  * Replace each call to llvm.eh.typeid.for() with an integer
+//    constant representing the exception type.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/NaCl.h"
+#include "ExceptionInfoWriter.h"
+
+using namespace llvm;
+
+namespace {
+  // This is a ModulePass so that it can introduce new global variables.
+  class PNaClSjLjEH : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    PNaClSjLjEH() : ModulePass(ID) {
+      initializePNaClSjLjEHPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+
+  class FuncRewriter {
+    Type *ExceptionFrameTy;
+    ExceptionInfoWriter *ExcInfoWriter;
+    Function *Func;
+
+    // FrameInitialized indicates whether the following variables have
+    // been initialized.
+    bool FrameInitialized;
+    Function *SetjmpIntrinsic;  // setjmp() intrinsic function
+    Instruction *EHStackTlsVar;  // __pnacl_eh_stack thread-local variable

[Derek Schuff, 2013/10/15 17:39:26]

maybe mention that this is a bitcast, since it looks odd that it's an
Instruction instead of a GlobalVariable

[Mark Seaborn, 2013/10/15 21:41:18]

Done.

+    Instruction *Frame;  // Frame allocated for this function
+    Instruction *FrameJmpBuf;  // Frame's jmp_buf field
+    Instruction *FrameNextPtr;  // Frame's next field
+    Instruction *FrameExcInfo;  // Frame's clause_list_id field
+
+    Function *EHResumeFunc;  // __pnacl_eh_resume() function
+
+    // Initialize values that are shared across all "invoke"
+    // instructions within the function.
+    void initializeFrame();
+
+  public:
+    FuncRewriter(Type *ExceptionFrameTy, ExceptionInfoWriter *ExcInfoWriter,
+                 Function *Func):
+        ExceptionFrameTy(ExceptionFrameTy),
+        ExcInfoWriter(ExcInfoWriter),
+        Func(Func),
+        FrameInitialized(false),
+        SetjmpIntrinsic(NULL), EHStackTlsVar(NULL),
+        Frame(NULL), FrameJmpBuf(NULL), FrameNextPtr(NULL), FrameExcInfo(NULL),
+        EHResumeFunc(NULL) {}
+
+    void expandInvokeInst(InvokeInst *Invoke);
+    void expandResumeInst(ResumeInst *Resume);
+    void expandFunc();
+  };
+}
+
+char PNaClSjLjEH::ID = 0;
+INITIALIZE_PASS(PNaClSjLjEH, "pnacl-sjlj-eh",
+                "Lower C++ exception handling to use setjmp()",
+                false, false)
+
+static const int kPNaClJmpBufSize = 1024;
+static const int kPNaClJmpBufAlign = 8;
+
+void FuncRewriter::initializeFrame() {
+  if (FrameInitialized)
+    return;
+  FrameInitialized = true;
+  Module *M = Func->getParent();
+
+  SetjmpIntrinsic = Intrinsic::getDeclaration(M, Intrinsic::nacl_setjmp);
+
+  Value *EHStackTlsVarUncast = M->getGlobalVariable("__pnacl_eh_stack");
+  if (!EHStackTlsVarUncast)
+    report_fatal_error("__pnacl_eh_stack not defined");
+  EHStackTlsVar = new BitCastInst(
+      EHStackTlsVarUncast, ExceptionFrameTy->getPointerTo()->getPointerTo(),
+      "pnacl_eh_stack");
+  Func->getEntryBlock().getInstList().push_front(EHStackTlsVar);
+
+  // Allocate the new exception frame.  This is reused across all
+  // invoke instructions in the function.
+  Type *I32 = Type::getInt32Ty(M->getContext());
+  Frame = new AllocaInst(ExceptionFrameTy, ConstantInt::get(I32, 1),
+                         kPNaClJmpBufAlign, "invoke_frame");
+  Func->getEntryBlock().getInstList().push_front(Frame);
+
+  // Calculate addresses of fields in the exception frame.
+  Value *JmpBufIndexes[] = { ConstantInt::get(I32, 0),
+                             ConstantInt::get(I32, 0),
+                             ConstantInt::get(I32, 0) };
+  FrameJmpBuf = GetElementPtrInst::Create(Frame, JmpBufIndexes,
+                                          "invoke_jmp_buf");
+  FrameJmpBuf->insertAfter(Frame);
+
+  Value *NextPtrIndexes[] = { ConstantInt::get(I32, 0),
+                              ConstantInt::get(I32, 1) };
+  FrameNextPtr = GetElementPtrInst::Create(Frame, NextPtrIndexes,
+                                           "invoke_next");
+  FrameNextPtr->insertAfter(Frame);
+
+  Value *ExcInfoIndexes[] = { ConstantInt::get(I32, 0),
+                              ConstantInt::get(I32, 2) };
+  FrameExcInfo = GetElementPtrInst::Create(Frame, ExcInfoIndexes,
+                                           "exc_info_ptr");
+  FrameExcInfo->insertAfter(Frame);
+}
+
+static void updateEdge(BasicBlock *Dest,
+                       BasicBlock *OldIncoming,
+                       BasicBlock *NewIncoming) {
+  for (BasicBlock::iterator Inst = Dest->begin(); Inst != Dest->end(); ++Inst) {
+    PHINode *Phi = dyn_cast<PHINode>(Inst);
+    if (!Phi)
+      break;
+    for (unsigned I = 0, E = Phi->getNumIncomingValues(); I < E; ++I) {
+      if (Phi->getIncomingBlock(I) == OldIncoming)
+        Phi->setIncomingBlock(I, NewIncoming);
+    }
+  }
+}
+
+void FuncRewriter::expandInvokeInst(InvokeInst *Invoke) {
+  initializeFrame();
+
+  LandingPadInst *LP = Invoke->getLandingPadInst();
+  Type *I32 = Type::getInt32Ty(Func->getContext());
+  Value *ExcInfo = ConstantInt::get(
+      I32, ExcInfoWriter->getIDForLandingPadClauseList(LP));
+
+  // Create setjmp() call.
+  Value *SetjmpArgs[] = { FrameJmpBuf };
+  Value *SetjmpCall = CopyDebug(CallInst::Create(SetjmpIntrinsic, SetjmpArgs,
+                                                 "invoke_sj", Invoke), Invoke);
+  // Check setjmp()'s result.
+  Value *IsZero = CopyDebug(new ICmpInst(Invoke, CmpInst::ICMP_EQ, SetjmpCall,
+                                         ConstantInt::get(I32, 0),
+                                         "invoke_sj_is_zero"), Invoke);
+
+  BasicBlock *CallBB = BasicBlock::Create(Func->getContext(), "invoke_do_call",
+                                          Func);
+  CallBB->moveAfter(Invoke->getParent());
+
+  // Append the new frame to the list.
+  Value *OldList = CopyDebug(
+      new LoadInst(EHStackTlsVar, "old_eh_stack", CallBB), Invoke);
+  CopyDebug(new StoreInst(OldList, FrameNextPtr, CallBB), Invoke);
+  CopyDebug(new StoreInst(ExcInfo, FrameExcInfo, CallBB), Invoke);
+  CopyDebug(new StoreInst(Frame, EHStackTlsVar, CallBB), Invoke);
+
+  SmallVector<Value *, 10> CallArgs;
+  for (unsigned I = 0, E = Invoke->getNumArgOperands(); I < E; ++I)
+    CallArgs.push_back(Invoke->getArgOperand(I));
+  CallInst *NewCall = CallInst::Create(Invoke->getCalledValue(), CallArgs, "",
+                                       CallBB);
+  CopyDebug(NewCall, Invoke);
+  NewCall->takeName(Invoke);
+  NewCall->setAttributes(Invoke->getAttributes());
+  NewCall->setCallingConv(Invoke->getCallingConv());
+  // Restore the old frame list.  We only need to do this on the
+  // non-exception code path.  If an exception is raised, the frame
+  // list state will be restored for us.
+  CopyDebug(new StoreInst(OldList, EHStackTlsVar, CallBB), Invoke);
+
+  CopyDebug(BranchInst::Create(CallBB, Invoke->getUnwindDest(), IsZero, Invoke),
+            Invoke);
+  CopyDebug(BranchInst::Create(Invoke->getNormalDest(), CallBB), Invoke);
+
+  updateEdge(Invoke->getNormalDest(), Invoke->getParent(), CallBB);
+
+  Invoke->replaceAllUsesWith(NewCall);
+  Invoke->eraseFromParent();
+}
+
+void FuncRewriter::expandResumeInst(ResumeInst *Resume) {
+  if (!EHResumeFunc) {
+    EHResumeFunc = Func->getParent()->getFunction("__pnacl_eh_resume");
+    if (!EHResumeFunc)
+      report_fatal_error("__pnacl_eh_resume() not defined");
+  }
+
+  // The "resume" instruction gets passed the landingpad's full result
+  // (struct LandingPadResult above).  Extract the exception_obj field
+  // to pass to __pnacl_eh_resume(), which doesn't need the
+  // matched_clause_id field.
+  unsigned Indexes[] = { 0 };
+  Value *ExceptionPtr =
+      CopyDebug(ExtractValueInst::Create(Resume->getValue(), Indexes,
+                                         "resume_exc", Resume), Resume);
+
+  // Cast to the pointer type that __pnacl_eh_resume() expects.
+  if (EHResumeFunc->getFunctionType()->getFunctionNumParams() != 1)
+    report_fatal_error("Bad type for __pnacl_eh_resume()");
+  Type *ArgType = EHResumeFunc->getFunctionType()->getFunctionParamType(0);
+  ExceptionPtr = new BitCastInst(ExceptionPtr, ArgType, "resume_cast", Resume);
+
+  Value *Args[] = { ExceptionPtr };
+  CopyDebug(CallInst::Create(EHResumeFunc, Args, "", Resume), Resume);
+  new UnreachableInst(Func->getContext(), Resume);
+  Resume->eraseFromParent();
+}
+
+void FuncRewriter::expandFunc() {
+  Type *I32 = Type::getInt32Ty(Func->getContext());
+
+  // We need to do two passes: When we process an invoke we need to
+  // look at its landingpad, so we can't remove the landingpads until
+  // all the invokes have been processed.
+  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) {
+    for (BasicBlock::iterator Iter = BB->begin(), E = BB->end(); Iter != E; ) {
+      Instruction *Inst = Iter++;
+      if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
+        expandInvokeInst(Invoke);
+      } else if (ResumeInst *Resume = dyn_cast<ResumeInst>(Inst)) {
+        expandResumeInst(Resume);
+      } else if (IntrinsicInst *Intrinsic = dyn_cast<IntrinsicInst>(Inst)) {
+        if (Intrinsic->getIntrinsicID() == Intrinsic::eh_typeid_for) {
+          Value *ExcType = Intrinsic->getArgOperand(0);
+          Value *Val = ConstantInt::get(
+              I32, ExcInfoWriter->getIDForExceptionType(ExcType));
+          Intrinsic->replaceAllUsesWith(Val);
+          Intrinsic->eraseFromParent();
+        }
+      }
+    }
+  }
+  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) {
+    for (BasicBlock::iterator Iter = BB->begin(), E = BB->end(); Iter != E; ) {
+      Instruction *Inst = Iter++;
+      if (LandingPadInst *LP = dyn_cast<LandingPadInst>(Inst)) {
+        initializeFrame();
+        Value *LPPtr = new BitCastInst(
+            FrameJmpBuf, LP->getType()->getPointerTo(), "landingpad_ptr", LP);
+        Value *LPVal = CopyDebug(new LoadInst(LPPtr, "", LP), LP);
+        LPVal->takeName(LP);
+        LP->replaceAllUsesWith(LPVal);
+        LP->eraseFromParent();
+      }
+    }
+  }
+}
+
+bool PNaClSjLjEH::runOnModule(Module &M) {
+  Type *JmpBufTy = ArrayType::get(Type::getInt8Ty(M.getContext()),
+                                  kPNaClJmpBufSize);
+
+  // Define "struct ExceptionFrame".
+  StructType *ExceptionFrameTy = StructType::create(M.getContext(),
+                                                    "ExceptionFrame");
+  Type *ExceptionFrameFields[] = {
+    JmpBufTy,  // jmp_buf
+    ExceptionFrameTy->getPointerTo(),  // struct ExceptionFrame *next
+    Type::getInt32Ty(M.getContext())  // Exception info (clause list ID)
+  };
+  ExceptionFrameTy->setBody(ExceptionFrameFields);
+
+  ExceptionInfoWriter ExcInfoWriter(&M.getContext());
+  for (Module::iterator Func = M.begin(), E = M.end(); Func != E; ++Func) {
+    FuncRewriter Rewriter(ExceptionFrameTy, &ExcInfoWriter, Func);
+    Rewriter.expandFunc();
+  }
+  ExcInfoWriter.defineGlobalVariables(&M);
+  return true;
+}
+
+ModulePass *llvm::createPNaClSjLjEHPass() {
+  return new PNaClSjLjEH();
+}