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      1 //===-- JIT.cpp - LLVM Just in Time Compiler ------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This tool implements a just-in-time compiler for LLVM, allowing direct
     11 // execution of LLVM bitcode in an efficient manner.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "JIT.h"
     16 #include "llvm/ADT/SmallPtrSet.h"
     17 #include "llvm/CodeGen/JITCodeEmitter.h"
     18 #include "llvm/CodeGen/MachineCodeInfo.h"
     19 #include "llvm/Config/config.h"
     20 #include "llvm/ExecutionEngine/GenericValue.h"
     21 #include "llvm/ExecutionEngine/JITEventListener.h"
     22 #include "llvm/ExecutionEngine/JITMemoryManager.h"
     23 #include "llvm/IR/Constants.h"
     24 #include "llvm/IR/DataLayout.h"
     25 #include "llvm/IR/DerivedTypes.h"
     26 #include "llvm/IR/Function.h"
     27 #include "llvm/IR/GlobalVariable.h"
     28 #include "llvm/IR/Instructions.h"
     29 #include "llvm/IR/Module.h"
     30 #include "llvm/Support/Dwarf.h"
     31 #include "llvm/Support/DynamicLibrary.h"
     32 #include "llvm/Support/ErrorHandling.h"
     33 #include "llvm/Support/ManagedStatic.h"
     34 #include "llvm/Support/MutexGuard.h"
     35 #include "llvm/Target/TargetJITInfo.h"
     36 #include "llvm/Target/TargetMachine.h"
     37 
     38 using namespace llvm;
     39 
     40 #ifdef __APPLE__
     41 // Apple gcc defaults to -fuse-cxa-atexit (i.e. calls __cxa_atexit instead
     42 // of atexit). It passes the address of linker generated symbol __dso_handle
     43 // to the function.
     44 // This configuration change happened at version 5330.
     45 # include <AvailabilityMacros.h>
     46 # if defined(MAC_OS_X_VERSION_10_4) && \
     47      ((MAC_OS_X_VERSION_MIN_REQUIRED > MAC_OS_X_VERSION_10_4) || \
     48       (MAC_OS_X_VERSION_MIN_REQUIRED == MAC_OS_X_VERSION_10_4 && \
     49        __APPLE_CC__ >= 5330))
     50 #  ifndef HAVE___DSO_HANDLE
     51 #   define HAVE___DSO_HANDLE 1
     52 #  endif
     53 # endif
     54 #endif
     55 
     56 #if HAVE___DSO_HANDLE
     57 extern void *__dso_handle __attribute__ ((__visibility__ ("hidden")));
     58 #endif
     59 
     60 namespace {
     61 
     62 static struct RegisterJIT {
     63   RegisterJIT() { JIT::Register(); }
     64 } JITRegistrator;
     65 
     66 }
     67 
     68 extern "C" void LLVMLinkInJIT() {
     69 }
     70 
     71 /// createJIT - This is the factory method for creating a JIT for the current
     72 /// machine, it does not fall back to the interpreter.  This takes ownership
     73 /// of the module.
     74 ExecutionEngine *JIT::createJIT(Module *M,
     75                                 std::string *ErrorStr,
     76                                 JITMemoryManager *JMM,
     77                                 bool GVsWithCode,
     78                                 TargetMachine *TM) {
     79   // Try to register the program as a source of symbols to resolve against.
     80   //
     81   // FIXME: Don't do this here.
     82   sys::DynamicLibrary::LoadLibraryPermanently(nullptr, nullptr);
     83 
     84   // If the target supports JIT code generation, create the JIT.
     85   if (TargetJITInfo *TJ = TM->getJITInfo()) {
     86     return new JIT(M, *TM, *TJ, JMM, GVsWithCode);
     87   } else {
     88     if (ErrorStr)
     89       *ErrorStr = "target does not support JIT code generation";
     90     return nullptr;
     91   }
     92 }
     93 
     94 namespace {
     95 /// This class supports the global getPointerToNamedFunction(), which allows
     96 /// bugpoint or gdb users to search for a function by name without any context.
     97 class JitPool {
     98   SmallPtrSet<JIT*, 1> JITs;  // Optimize for process containing just 1 JIT.
     99   mutable sys::Mutex Lock;
    100 public:
    101   void Add(JIT *jit) {
    102     MutexGuard guard(Lock);
    103     JITs.insert(jit);
    104   }
    105   void Remove(JIT *jit) {
    106     MutexGuard guard(Lock);
    107     JITs.erase(jit);
    108   }
    109   void *getPointerToNamedFunction(const char *Name) const {
    110     MutexGuard guard(Lock);
    111     assert(JITs.size() != 0 && "No Jit registered");
    112     //search function in every instance of JIT
    113     for (SmallPtrSet<JIT*, 1>::const_iterator Jit = JITs.begin(),
    114            end = JITs.end();
    115          Jit != end; ++Jit) {
    116       if (Function *F = (*Jit)->FindFunctionNamed(Name))
    117         return (*Jit)->getPointerToFunction(F);
    118     }
    119     // The function is not available : fallback on the first created (will
    120     // search in symbol of the current program/library)
    121     return (*JITs.begin())->getPointerToNamedFunction(Name);
    122   }
    123 };
    124 ManagedStatic<JitPool> AllJits;
    125 }
    126 extern "C" {
    127   // getPointerToNamedFunction - This function is used as a global wrapper to
    128   // JIT::getPointerToNamedFunction for the purpose of resolving symbols when
    129   // bugpoint is debugging the JIT. In that scenario, we are loading an .so and
    130   // need to resolve function(s) that are being mis-codegenerated, so we need to
    131   // resolve their addresses at runtime, and this is the way to do it.
    132   void *getPointerToNamedFunction(const char *Name) {
    133     return AllJits->getPointerToNamedFunction(Name);
    134   }
    135 }
    136 
    137 JIT::JIT(Module *M, TargetMachine &tm, TargetJITInfo &tji,
    138          JITMemoryManager *jmm, bool GVsWithCode)
    139   : ExecutionEngine(M), TM(tm), TJI(tji),
    140     JMM(jmm ? jmm : JITMemoryManager::CreateDefaultMemManager()),
    141     AllocateGVsWithCode(GVsWithCode), isAlreadyCodeGenerating(false) {
    142   setDataLayout(TM.getDataLayout());
    143 
    144   jitstate = new JITState(M);
    145 
    146   // Initialize JCE
    147   JCE = createEmitter(*this, JMM, TM);
    148 
    149   // Register in global list of all JITs.
    150   AllJits->Add(this);
    151 
    152   // Add target data
    153   MutexGuard locked(lock);
    154   FunctionPassManager &PM = jitstate->getPM();
    155   M->setDataLayout(TM.getDataLayout());
    156   PM.add(new DataLayoutPass(M));
    157 
    158   // Turn the machine code intermediate representation into bytes in memory that
    159   // may be executed.
    160   if (TM.addPassesToEmitMachineCode(PM, *JCE, !getVerifyModules())) {
    161     report_fatal_error("Target does not support machine code emission!");
    162   }
    163 
    164   // Initialize passes.
    165   PM.doInitialization();
    166 }
    167 
    168 JIT::~JIT() {
    169   // Cleanup.
    170   AllJits->Remove(this);
    171   delete jitstate;
    172   delete JCE;
    173   // JMM is a ownership of JCE, so we no need delete JMM here.
    174   delete &TM;
    175 }
    176 
    177 /// addModule - Add a new Module to the JIT.  If we previously removed the last
    178 /// Module, we need re-initialize jitstate with a valid Module.
    179 void JIT::addModule(Module *M) {
    180   MutexGuard locked(lock);
    181 
    182   if (Modules.empty()) {
    183     assert(!jitstate && "jitstate should be NULL if Modules vector is empty!");
    184 
    185     jitstate = new JITState(M);
    186 
    187     FunctionPassManager &PM = jitstate->getPM();
    188     M->setDataLayout(TM.getDataLayout());
    189     PM.add(new DataLayoutPass(M));
    190 
    191     // Turn the machine code intermediate representation into bytes in memory
    192     // that may be executed.
    193     if (TM.addPassesToEmitMachineCode(PM, *JCE, !getVerifyModules())) {
    194       report_fatal_error("Target does not support machine code emission!");
    195     }
    196 
    197     // Initialize passes.
    198     PM.doInitialization();
    199   }
    200 
    201   ExecutionEngine::addModule(M);
    202 }
    203 
    204 /// removeModule - If we are removing the last Module, invalidate the jitstate
    205 /// since the PassManager it contains references a released Module.
    206 bool JIT::removeModule(Module *M) {
    207   bool result = ExecutionEngine::removeModule(M);
    208 
    209   MutexGuard locked(lock);
    210 
    211   if (jitstate && jitstate->getModule() == M) {
    212     delete jitstate;
    213     jitstate = nullptr;
    214   }
    215 
    216   if (!jitstate && !Modules.empty()) {
    217     jitstate = new JITState(Modules[0]);
    218 
    219     FunctionPassManager &PM = jitstate->getPM();
    220     M->setDataLayout(TM.getDataLayout());
    221     PM.add(new DataLayoutPass(M));
    222 
    223     // Turn the machine code intermediate representation into bytes in memory
    224     // that may be executed.
    225     if (TM.addPassesToEmitMachineCode(PM, *JCE, !getVerifyModules())) {
    226       report_fatal_error("Target does not support machine code emission!");
    227     }
    228 
    229     // Initialize passes.
    230     PM.doInitialization();
    231   }
    232   return result;
    233 }
    234 
    235 /// run - Start execution with the specified function and arguments.
    236 ///
    237 GenericValue JIT::runFunction(Function *F,
    238                               const std::vector<GenericValue> &ArgValues) {
    239   assert(F && "Function *F was null at entry to run()");
    240 
    241   void *FPtr = getPointerToFunction(F);
    242   assert(FPtr && "Pointer to fn's code was null after getPointerToFunction");
    243   FunctionType *FTy = F->getFunctionType();
    244   Type *RetTy = FTy->getReturnType();
    245 
    246   assert((FTy->getNumParams() == ArgValues.size() ||
    247           (FTy->isVarArg() && FTy->getNumParams() <= ArgValues.size())) &&
    248          "Wrong number of arguments passed into function!");
    249   assert(FTy->getNumParams() == ArgValues.size() &&
    250          "This doesn't support passing arguments through varargs (yet)!");
    251 
    252   // Handle some common cases first.  These cases correspond to common `main'
    253   // prototypes.
    254   if (RetTy->isIntegerTy(32) || RetTy->isVoidTy()) {
    255     switch (ArgValues.size()) {
    256     case 3:
    257       if (FTy->getParamType(0)->isIntegerTy(32) &&
    258           FTy->getParamType(1)->isPointerTy() &&
    259           FTy->getParamType(2)->isPointerTy()) {
    260         int (*PF)(int, char **, const char **) =
    261           (int(*)(int, char **, const char **))(intptr_t)FPtr;
    262 
    263         // Call the function.
    264         GenericValue rv;
    265         rv.IntVal = APInt(32, PF(ArgValues[0].IntVal.getZExtValue(),
    266                                  (char **)GVTOP(ArgValues[1]),
    267                                  (const char **)GVTOP(ArgValues[2])));
    268         return rv;
    269       }
    270       break;
    271     case 2:
    272       if (FTy->getParamType(0)->isIntegerTy(32) &&
    273           FTy->getParamType(1)->isPointerTy()) {
    274         int (*PF)(int, char **) = (int(*)(int, char **))(intptr_t)FPtr;
    275 
    276         // Call the function.
    277         GenericValue rv;
    278         rv.IntVal = APInt(32, PF(ArgValues[0].IntVal.getZExtValue(),
    279                                  (char **)GVTOP(ArgValues[1])));
    280         return rv;
    281       }
    282       break;
    283     case 1:
    284       if (FTy->getParamType(0)->isIntegerTy(32)) {
    285         GenericValue rv;
    286         int (*PF)(int) = (int(*)(int))(intptr_t)FPtr;
    287         rv.IntVal = APInt(32, PF(ArgValues[0].IntVal.getZExtValue()));
    288         return rv;
    289       }
    290       if (FTy->getParamType(0)->isPointerTy()) {
    291         GenericValue rv;
    292         int (*PF)(char *) = (int(*)(char *))(intptr_t)FPtr;
    293         rv.IntVal = APInt(32, PF((char*)GVTOP(ArgValues[0])));
    294         return rv;
    295       }
    296       break;
    297     }
    298   }
    299 
    300   // Handle cases where no arguments are passed first.
    301   if (ArgValues.empty()) {
    302     GenericValue rv;
    303     switch (RetTy->getTypeID()) {
    304     default: llvm_unreachable("Unknown return type for function call!");
    305     case Type::IntegerTyID: {
    306       unsigned BitWidth = cast<IntegerType>(RetTy)->getBitWidth();
    307       if (BitWidth == 1)
    308         rv.IntVal = APInt(BitWidth, ((bool(*)())(intptr_t)FPtr)());
    309       else if (BitWidth <= 8)
    310         rv.IntVal = APInt(BitWidth, ((char(*)())(intptr_t)FPtr)());
    311       else if (BitWidth <= 16)
    312         rv.IntVal = APInt(BitWidth, ((short(*)())(intptr_t)FPtr)());
    313       else if (BitWidth <= 32)
    314         rv.IntVal = APInt(BitWidth, ((int(*)())(intptr_t)FPtr)());
    315       else if (BitWidth <= 64)
    316         rv.IntVal = APInt(BitWidth, ((int64_t(*)())(intptr_t)FPtr)());
    317       else
    318         llvm_unreachable("Integer types > 64 bits not supported");
    319       return rv;
    320     }
    321     case Type::VoidTyID:
    322       rv.IntVal = APInt(32, ((int(*)())(intptr_t)FPtr)());
    323       return rv;
    324     case Type::FloatTyID:
    325       rv.FloatVal = ((float(*)())(intptr_t)FPtr)();
    326       return rv;
    327     case Type::DoubleTyID:
    328       rv.DoubleVal = ((double(*)())(intptr_t)FPtr)();
    329       return rv;
    330     case Type::X86_FP80TyID:
    331     case Type::FP128TyID:
    332     case Type::PPC_FP128TyID:
    333       llvm_unreachable("long double not supported yet");
    334     case Type::PointerTyID:
    335       return PTOGV(((void*(*)())(intptr_t)FPtr)());
    336     }
    337   }
    338 
    339   // Okay, this is not one of our quick and easy cases.  Because we don't have a
    340   // full FFI, we have to codegen a nullary stub function that just calls the
    341   // function we are interested in, passing in constants for all of the
    342   // arguments.  Make this function and return.
    343 
    344   // First, create the function.
    345   FunctionType *STy=FunctionType::get(RetTy, false);
    346   Function *Stub = Function::Create(STy, Function::InternalLinkage, "",
    347                                     F->getParent());
    348 
    349   // Insert a basic block.
    350   BasicBlock *StubBB = BasicBlock::Create(F->getContext(), "", Stub);
    351 
    352   // Convert all of the GenericValue arguments over to constants.  Note that we
    353   // currently don't support varargs.
    354   SmallVector<Value*, 8> Args;
    355   for (unsigned i = 0, e = ArgValues.size(); i != e; ++i) {
    356     Constant *C = nullptr;
    357     Type *ArgTy = FTy->getParamType(i);
    358     const GenericValue &AV = ArgValues[i];
    359     switch (ArgTy->getTypeID()) {
    360     default: llvm_unreachable("Unknown argument type for function call!");
    361     case Type::IntegerTyID:
    362         C = ConstantInt::get(F->getContext(), AV.IntVal);
    363         break;
    364     case Type::FloatTyID:
    365         C = ConstantFP::get(F->getContext(), APFloat(AV.FloatVal));
    366         break;
    367     case Type::DoubleTyID:
    368         C = ConstantFP::get(F->getContext(), APFloat(AV.DoubleVal));
    369         break;
    370     case Type::PPC_FP128TyID:
    371     case Type::X86_FP80TyID:
    372     case Type::FP128TyID:
    373         C = ConstantFP::get(F->getContext(), APFloat(ArgTy->getFltSemantics(),
    374                                                      AV.IntVal));
    375         break;
    376     case Type::PointerTyID:
    377       void *ArgPtr = GVTOP(AV);
    378       if (sizeof(void*) == 4)
    379         C = ConstantInt::get(Type::getInt32Ty(F->getContext()),
    380                              (int)(intptr_t)ArgPtr);
    381       else
    382         C = ConstantInt::get(Type::getInt64Ty(F->getContext()),
    383                              (intptr_t)ArgPtr);
    384       // Cast the integer to pointer
    385       C = ConstantExpr::getIntToPtr(C, ArgTy);
    386       break;
    387     }
    388     Args.push_back(C);
    389   }
    390 
    391   CallInst *TheCall = CallInst::Create(F, Args, "", StubBB);
    392   TheCall->setCallingConv(F->getCallingConv());
    393   TheCall->setTailCall();
    394   if (!TheCall->getType()->isVoidTy())
    395     // Return result of the call.
    396     ReturnInst::Create(F->getContext(), TheCall, StubBB);
    397   else
    398     ReturnInst::Create(F->getContext(), StubBB);           // Just return void.
    399 
    400   // Finally, call our nullary stub function.
    401   GenericValue Result = runFunction(Stub, std::vector<GenericValue>());
    402   // Erase it, since no other function can have a reference to it.
    403   Stub->eraseFromParent();
    404   // And return the result.
    405   return Result;
    406 }
    407 
    408 void JIT::RegisterJITEventListener(JITEventListener *L) {
    409   if (!L)
    410     return;
    411   MutexGuard locked(lock);
    412   EventListeners.push_back(L);
    413 }
    414 void JIT::UnregisterJITEventListener(JITEventListener *L) {
    415   if (!L)
    416     return;
    417   MutexGuard locked(lock);
    418   std::vector<JITEventListener*>::reverse_iterator I=
    419       std::find(EventListeners.rbegin(), EventListeners.rend(), L);
    420   if (I != EventListeners.rend()) {
    421     std::swap(*I, EventListeners.back());
    422     EventListeners.pop_back();
    423   }
    424 }
    425 void JIT::NotifyFunctionEmitted(
    426     const Function &F,
    427     void *Code, size_t Size,
    428     const JITEvent_EmittedFunctionDetails &Details) {
    429   MutexGuard locked(lock);
    430   for (unsigned I = 0, S = EventListeners.size(); I < S; ++I) {
    431     EventListeners[I]->NotifyFunctionEmitted(F, Code, Size, Details);
    432   }
    433 }
    434 
    435 void JIT::NotifyFreeingMachineCode(void *OldPtr) {
    436   MutexGuard locked(lock);
    437   for (unsigned I = 0, S = EventListeners.size(); I < S; ++I) {
    438     EventListeners[I]->NotifyFreeingMachineCode(OldPtr);
    439   }
    440 }
    441 
    442 /// runJITOnFunction - Run the FunctionPassManager full of
    443 /// just-in-time compilation passes on F, hopefully filling in
    444 /// GlobalAddress[F] with the address of F's machine code.
    445 ///
    446 void JIT::runJITOnFunction(Function *F, MachineCodeInfo *MCI) {
    447   MutexGuard locked(lock);
    448 
    449   class MCIListener : public JITEventListener {
    450     MachineCodeInfo *const MCI;
    451    public:
    452     MCIListener(MachineCodeInfo *mci) : MCI(mci) {}
    453     void NotifyFunctionEmitted(const Function &, void *Code, size_t Size,
    454                                const EmittedFunctionDetails &) override {
    455       MCI->setAddress(Code);
    456       MCI->setSize(Size);
    457     }
    458   };
    459   MCIListener MCIL(MCI);
    460   if (MCI)
    461     RegisterJITEventListener(&MCIL);
    462 
    463   runJITOnFunctionUnlocked(F);
    464 
    465   if (MCI)
    466     UnregisterJITEventListener(&MCIL);
    467 }
    468 
    469 void JIT::runJITOnFunctionUnlocked(Function *F) {
    470   assert(!isAlreadyCodeGenerating && "Error: Recursive compilation detected!");
    471 
    472   jitTheFunctionUnlocked(F);
    473 
    474   // If the function referred to another function that had not yet been
    475   // read from bitcode, and we are jitting non-lazily, emit it now.
    476   while (!jitstate->getPendingFunctions().empty()) {
    477     Function *PF = jitstate->getPendingFunctions().back();
    478     jitstate->getPendingFunctions().pop_back();
    479 
    480     assert(!PF->hasAvailableExternallyLinkage() &&
    481            "Externally-defined function should not be in pending list.");
    482 
    483     jitTheFunctionUnlocked(PF);
    484 
    485     // Now that the function has been jitted, ask the JITEmitter to rewrite
    486     // the stub with real address of the function.
    487     updateFunctionStubUnlocked(PF);
    488   }
    489 }
    490 
    491 void JIT::jitTheFunctionUnlocked(Function *F) {
    492   isAlreadyCodeGenerating = true;
    493   jitstate->getPM().run(*F);
    494   isAlreadyCodeGenerating = false;
    495 
    496   // clear basic block addresses after this function is done
    497   getBasicBlockAddressMap().clear();
    498 }
    499 
    500 /// getPointerToFunction - This method is used to get the address of the
    501 /// specified function, compiling it if necessary.
    502 ///
    503 void *JIT::getPointerToFunction(Function *F) {
    504 
    505   if (void *Addr = getPointerToGlobalIfAvailable(F))
    506     return Addr;   // Check if function already code gen'd
    507 
    508   MutexGuard locked(lock);
    509 
    510   // Now that this thread owns the lock, make sure we read in the function if it
    511   // exists in this Module.
    512   std::string ErrorMsg;
    513   if (F->Materialize(&ErrorMsg)) {
    514     report_fatal_error("Error reading function '" + F->getName()+
    515                       "' from bitcode file: " + ErrorMsg);
    516   }
    517 
    518   // ... and check if another thread has already code gen'd the function.
    519   if (void *Addr = getPointerToGlobalIfAvailable(F))
    520     return Addr;
    521 
    522   if (F->isDeclaration() || F->hasAvailableExternallyLinkage()) {
    523     bool AbortOnFailure = !F->hasExternalWeakLinkage();
    524     void *Addr = getPointerToNamedFunction(F->getName(), AbortOnFailure);
    525     addGlobalMapping(F, Addr);
    526     return Addr;
    527   }
    528 
    529   runJITOnFunctionUnlocked(F);
    530 
    531   void *Addr = getPointerToGlobalIfAvailable(F);
    532   assert(Addr && "Code generation didn't add function to GlobalAddress table!");
    533   return Addr;
    534 }
    535 
    536 void JIT::addPointerToBasicBlock(const BasicBlock *BB, void *Addr) {
    537   MutexGuard locked(lock);
    538 
    539   BasicBlockAddressMapTy::iterator I =
    540     getBasicBlockAddressMap().find(BB);
    541   if (I == getBasicBlockAddressMap().end()) {
    542     getBasicBlockAddressMap()[BB] = Addr;
    543   } else {
    544     // ignore repeats: some BBs can be split into few MBBs?
    545   }
    546 }
    547 
    548 void JIT::clearPointerToBasicBlock(const BasicBlock *BB) {
    549   MutexGuard locked(lock);
    550   getBasicBlockAddressMap().erase(BB);
    551 }
    552 
    553 void *JIT::getPointerToBasicBlock(BasicBlock *BB) {
    554   // make sure it's function is compiled by JIT
    555   (void)getPointerToFunction(BB->getParent());
    556 
    557   // resolve basic block address
    558   MutexGuard locked(lock);
    559 
    560   BasicBlockAddressMapTy::iterator I =
    561     getBasicBlockAddressMap().find(BB);
    562   if (I != getBasicBlockAddressMap().end()) {
    563     return I->second;
    564   } else {
    565     llvm_unreachable("JIT does not have BB address for address-of-label, was"
    566                      " it eliminated by optimizer?");
    567   }
    568 }
    569 
    570 void *JIT::getPointerToNamedFunction(const std::string &Name,
    571                                      bool AbortOnFailure){
    572   if (!isSymbolSearchingDisabled()) {
    573     void *ptr = JMM->getPointerToNamedFunction(Name, false);
    574     if (ptr)
    575       return ptr;
    576   }
    577 
    578   /// If a LazyFunctionCreator is installed, use it to get/create the function.
    579   if (LazyFunctionCreator)
    580     if (void *RP = LazyFunctionCreator(Name))
    581       return RP;
    582 
    583   if (AbortOnFailure) {
    584     report_fatal_error("Program used external function '"+Name+
    585                       "' which could not be resolved!");
    586   }
    587   return nullptr;
    588 }
    589 
    590 
    591 /// getOrEmitGlobalVariable - Return the address of the specified global
    592 /// variable, possibly emitting it to memory if needed.  This is used by the
    593 /// Emitter.
    594 void *JIT::getOrEmitGlobalVariable(const GlobalVariable *GV) {
    595   MutexGuard locked(lock);
    596 
    597   void *Ptr = getPointerToGlobalIfAvailable(GV);
    598   if (Ptr) return Ptr;
    599 
    600   // If the global is external, just remember the address.
    601   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage()) {
    602 #if HAVE___DSO_HANDLE
    603     if (GV->getName() == "__dso_handle")
    604       return (void*)&__dso_handle;
    605 #endif
    606     Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(GV->getName());
    607     if (!Ptr) {
    608       report_fatal_error("Could not resolve external global address: "
    609                         +GV->getName());
    610     }
    611     addGlobalMapping(GV, Ptr);
    612   } else {
    613     // If the global hasn't been emitted to memory yet, allocate space and
    614     // emit it into memory.
    615     Ptr = getMemoryForGV(GV);
    616     addGlobalMapping(GV, Ptr);
    617     EmitGlobalVariable(GV);  // Initialize the variable.
    618   }
    619   return Ptr;
    620 }
    621 
    622 /// recompileAndRelinkFunction - This method is used to force a function
    623 /// which has already been compiled, to be compiled again, possibly
    624 /// after it has been modified. Then the entry to the old copy is overwritten
    625 /// with a branch to the new copy. If there was no old copy, this acts
    626 /// just like JIT::getPointerToFunction().
    627 ///
    628 void *JIT::recompileAndRelinkFunction(Function *F) {
    629   void *OldAddr = getPointerToGlobalIfAvailable(F);
    630 
    631   // If it's not already compiled there is no reason to patch it up.
    632   if (!OldAddr) return getPointerToFunction(F);
    633 
    634   // Delete the old function mapping.
    635   addGlobalMapping(F, nullptr);
    636 
    637   // Recodegen the function
    638   runJITOnFunction(F);
    639 
    640   // Update state, forward the old function to the new function.
    641   void *Addr = getPointerToGlobalIfAvailable(F);
    642   assert(Addr && "Code generation didn't add function to GlobalAddress table!");
    643   TJI.replaceMachineCodeForFunction(OldAddr, Addr);
    644   return Addr;
    645 }
    646 
    647 /// getMemoryForGV - This method abstracts memory allocation of global
    648 /// variable so that the JIT can allocate thread local variables depending
    649 /// on the target.
    650 ///
    651 char* JIT::getMemoryForGV(const GlobalVariable* GV) {
    652   char *Ptr;
    653 
    654   // GlobalVariable's which are not "constant" will cause trouble in a server
    655   // situation. It's returned in the same block of memory as code which may
    656   // not be writable.
    657   if (isGVCompilationDisabled() && !GV->isConstant()) {
    658     report_fatal_error("Compilation of non-internal GlobalValue is disabled!");
    659   }
    660 
    661   // Some applications require globals and code to live together, so they may
    662   // be allocated into the same buffer, but in general globals are allocated
    663   // through the memory manager which puts them near the code but not in the
    664   // same buffer.
    665   Type *GlobalType = GV->getType()->getElementType();
    666   size_t S = getDataLayout()->getTypeAllocSize(GlobalType);
    667   size_t A = getDataLayout()->getPreferredAlignment(GV);
    668   if (GV->isThreadLocal()) {
    669     MutexGuard locked(lock);
    670     Ptr = TJI.allocateThreadLocalMemory(S);
    671   } else if (TJI.allocateSeparateGVMemory()) {
    672     if (A <= 8) {
    673       Ptr = (char*)malloc(S);
    674     } else {
    675       // Allocate S+A bytes of memory, then use an aligned pointer within that
    676       // space.
    677       Ptr = (char*)malloc(S+A);
    678       unsigned MisAligned = ((intptr_t)Ptr & (A-1));
    679       Ptr = Ptr + (MisAligned ? (A-MisAligned) : 0);
    680     }
    681   } else if (AllocateGVsWithCode) {
    682     Ptr = (char*)JCE->allocateSpace(S, A);
    683   } else {
    684     Ptr = (char*)JCE->allocateGlobal(S, A);
    685   }
    686   return Ptr;
    687 }
    688 
    689 void JIT::addPendingFunction(Function *F) {
    690   MutexGuard locked(lock);
    691   jitstate->getPendingFunctions().push_back(F);
    692 }
    693 
    694 
    695 JITEventListener::~JITEventListener() {}
    696