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      1 //===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
      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 // The StripSymbols transformation implements code stripping. Specifically, it
     11 // can delete:
     12 //
     13 //   * names for virtual registers
     14 //   * symbols for internal globals and functions
     15 //   * debug information
     16 //
     17 // Note that this transformation makes code much less readable, so it should
     18 // only be used in situations where the 'strip' utility would be used, such as
     19 // reducing code size or making it harder to reverse engineer code.
     20 //
     21 //===----------------------------------------------------------------------===//
     22 
     23 #include "llvm/Transforms/IPO.h"
     24 #include "llvm/ADT/DenseMap.h"
     25 #include "llvm/ADT/SmallPtrSet.h"
     26 #include "llvm/DebugInfo.h"
     27 #include "llvm/IR/Constants.h"
     28 #include "llvm/IR/DerivedTypes.h"
     29 #include "llvm/IR/Instructions.h"
     30 #include "llvm/IR/Module.h"
     31 #include "llvm/IR/TypeFinder.h"
     32 #include "llvm/IR/ValueSymbolTable.h"
     33 #include "llvm/Pass.h"
     34 #include "llvm/Transforms/Utils/Local.h"
     35 using namespace llvm;
     36 
     37 namespace {
     38   class StripSymbols : public ModulePass {
     39     bool OnlyDebugInfo;
     40   public:
     41     static char ID; // Pass identification, replacement for typeid
     42     explicit StripSymbols(bool ODI = false)
     43       : ModulePass(ID), OnlyDebugInfo(ODI) {
     44         initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
     45       }
     46 
     47     virtual bool runOnModule(Module &M);
     48 
     49     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     50       AU.setPreservesAll();
     51     }
     52   };
     53 
     54   class StripNonDebugSymbols : public ModulePass {
     55   public:
     56     static char ID; // Pass identification, replacement for typeid
     57     explicit StripNonDebugSymbols()
     58       : ModulePass(ID) {
     59         initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
     60       }
     61 
     62     virtual bool runOnModule(Module &M);
     63 
     64     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     65       AU.setPreservesAll();
     66     }
     67   };
     68 
     69   class StripDebugDeclare : public ModulePass {
     70   public:
     71     static char ID; // Pass identification, replacement for typeid
     72     explicit StripDebugDeclare()
     73       : ModulePass(ID) {
     74         initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
     75       }
     76 
     77     virtual bool runOnModule(Module &M);
     78 
     79     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     80       AU.setPreservesAll();
     81     }
     82   };
     83 
     84   class StripDeadDebugInfo : public ModulePass {
     85   public:
     86     static char ID; // Pass identification, replacement for typeid
     87     explicit StripDeadDebugInfo()
     88       : ModulePass(ID) {
     89         initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
     90       }
     91 
     92     virtual bool runOnModule(Module &M);
     93 
     94     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     95       AU.setPreservesAll();
     96     }
     97   };
     98 }
     99 
    100 char StripSymbols::ID = 0;
    101 INITIALIZE_PASS(StripSymbols, "strip",
    102                 "Strip all symbols from a module", false, false)
    103 
    104 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
    105   return new StripSymbols(OnlyDebugInfo);
    106 }
    107 
    108 char StripNonDebugSymbols::ID = 0;
    109 INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
    110                 "Strip all symbols, except dbg symbols, from a module",
    111                 false, false)
    112 
    113 ModulePass *llvm::createStripNonDebugSymbolsPass() {
    114   return new StripNonDebugSymbols();
    115 }
    116 
    117 char StripDebugDeclare::ID = 0;
    118 INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
    119                 "Strip all llvm.dbg.declare intrinsics", false, false)
    120 
    121 ModulePass *llvm::createStripDebugDeclarePass() {
    122   return new StripDebugDeclare();
    123 }
    124 
    125 char StripDeadDebugInfo::ID = 0;
    126 INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
    127                 "Strip debug info for unused symbols", false, false)
    128 
    129 ModulePass *llvm::createStripDeadDebugInfoPass() {
    130   return new StripDeadDebugInfo();
    131 }
    132 
    133 /// OnlyUsedBy - Return true if V is only used by Usr.
    134 static bool OnlyUsedBy(Value *V, Value *Usr) {
    135   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
    136     User *U = *I;
    137     if (U != Usr)
    138       return false;
    139   }
    140   return true;
    141 }
    142 
    143 static void RemoveDeadConstant(Constant *C) {
    144   assert(C->use_empty() && "Constant is not dead!");
    145   SmallPtrSet<Constant*, 4> Operands;
    146   for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
    147     if (OnlyUsedBy(C->getOperand(i), C))
    148       Operands.insert(cast<Constant>(C->getOperand(i)));
    149   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
    150     if (!GV->hasLocalLinkage()) return;   // Don't delete non static globals.
    151     GV->eraseFromParent();
    152   }
    153   else if (!isa<Function>(C))
    154     if (isa<CompositeType>(C->getType()))
    155       C->destroyConstant();
    156 
    157   // If the constant referenced anything, see if we can delete it as well.
    158   for (SmallPtrSet<Constant*, 4>::iterator OI = Operands.begin(),
    159          OE = Operands.end(); OI != OE; ++OI)
    160     RemoveDeadConstant(*OI);
    161 }
    162 
    163 // Strip the symbol table of its names.
    164 //
    165 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
    166   for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
    167     Value *V = VI->getValue();
    168     ++VI;
    169     if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
    170       if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
    171         // Set name to "", removing from symbol table!
    172         V->setName("");
    173     }
    174   }
    175 }
    176 
    177 // Strip any named types of their names.
    178 static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
    179   TypeFinder StructTypes;
    180   StructTypes.run(M, false);
    181 
    182   for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
    183     StructType *STy = StructTypes[i];
    184     if (STy->isLiteral() || STy->getName().empty()) continue;
    185 
    186     if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
    187       continue;
    188 
    189     STy->setName("");
    190   }
    191 }
    192 
    193 /// Find values that are marked as llvm.used.
    194 static void findUsedValues(GlobalVariable *LLVMUsed,
    195                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
    196   if (LLVMUsed == 0) return;
    197   UsedValues.insert(LLVMUsed);
    198 
    199   ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
    200 
    201   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
    202     if (GlobalValue *GV =
    203           dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
    204       UsedValues.insert(GV);
    205 }
    206 
    207 /// StripSymbolNames - Strip symbol names.
    208 static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
    209 
    210   SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
    211   findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
    212   findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
    213 
    214   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
    215        I != E; ++I) {
    216     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
    217       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
    218         I->setName("");     // Internal symbols can't participate in linkage
    219   }
    220 
    221   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
    222     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
    223       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
    224         I->setName("");     // Internal symbols can't participate in linkage
    225     StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
    226   }
    227 
    228   // Remove all names from types.
    229   StripTypeNames(M, PreserveDbgInfo);
    230 
    231   return true;
    232 }
    233 
    234 // StripDebugInfo - Strip debug info in the module if it exists.
    235 // To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and
    236 // llvm.dbg.region.end calls, and any globals they point to if now dead.
    237 static bool StripDebugInfo(Module &M) {
    238 
    239   bool Changed = false;
    240 
    241   // Remove all of the calls to the debugger intrinsics, and remove them from
    242   // the module.
    243   if (Function *Declare = M.getFunction("llvm.dbg.declare")) {
    244     while (!Declare->use_empty()) {
    245       CallInst *CI = cast<CallInst>(Declare->use_back());
    246       CI->eraseFromParent();
    247     }
    248     Declare->eraseFromParent();
    249     Changed = true;
    250   }
    251 
    252   if (Function *DbgVal = M.getFunction("llvm.dbg.value")) {
    253     while (!DbgVal->use_empty()) {
    254       CallInst *CI = cast<CallInst>(DbgVal->use_back());
    255       CI->eraseFromParent();
    256     }
    257     DbgVal->eraseFromParent();
    258     Changed = true;
    259   }
    260 
    261   for (Module::named_metadata_iterator NMI = M.named_metadata_begin(),
    262          NME = M.named_metadata_end(); NMI != NME;) {
    263     NamedMDNode *NMD = NMI;
    264     ++NMI;
    265     if (NMD->getName().startswith("llvm.dbg.")) {
    266       NMD->eraseFromParent();
    267       Changed = true;
    268     }
    269   }
    270 
    271   for (Module::iterator MI = M.begin(), ME = M.end(); MI != ME; ++MI)
    272     for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE;
    273          ++FI)
    274       for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE;
    275            ++BI) {
    276         if (!BI->getDebugLoc().isUnknown()) {
    277           Changed = true;
    278           BI->setDebugLoc(DebugLoc());
    279         }
    280       }
    281 
    282   return Changed;
    283 }
    284 
    285 bool StripSymbols::runOnModule(Module &M) {
    286   bool Changed = false;
    287   Changed |= StripDebugInfo(M);
    288   if (!OnlyDebugInfo)
    289     Changed |= StripSymbolNames(M, false);
    290   return Changed;
    291 }
    292 
    293 bool StripNonDebugSymbols::runOnModule(Module &M) {
    294   return StripSymbolNames(M, true);
    295 }
    296 
    297 bool StripDebugDeclare::runOnModule(Module &M) {
    298 
    299   Function *Declare = M.getFunction("llvm.dbg.declare");
    300   std::vector<Constant*> DeadConstants;
    301 
    302   if (Declare) {
    303     while (!Declare->use_empty()) {
    304       CallInst *CI = cast<CallInst>(Declare->use_back());
    305       Value *Arg1 = CI->getArgOperand(0);
    306       Value *Arg2 = CI->getArgOperand(1);
    307       assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
    308       CI->eraseFromParent();
    309       if (Arg1->use_empty()) {
    310         if (Constant *C = dyn_cast<Constant>(Arg1))
    311           DeadConstants.push_back(C);
    312         else
    313           RecursivelyDeleteTriviallyDeadInstructions(Arg1);
    314       }
    315       if (Arg2->use_empty())
    316         if (Constant *C = dyn_cast<Constant>(Arg2))
    317           DeadConstants.push_back(C);
    318     }
    319     Declare->eraseFromParent();
    320   }
    321 
    322   while (!DeadConstants.empty()) {
    323     Constant *C = DeadConstants.back();
    324     DeadConstants.pop_back();
    325     if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
    326       if (GV->hasLocalLinkage())
    327         RemoveDeadConstant(GV);
    328     } else
    329       RemoveDeadConstant(C);
    330   }
    331 
    332   return true;
    333 }
    334 
    335 bool StripDeadDebugInfo::runOnModule(Module &M) {
    336   bool Changed = false;
    337 
    338   // Debugging infomration is encoded in llvm IR using metadata. This is designed
    339   // such a way that debug info for symbols preserved even if symbols are
    340   // optimized away by the optimizer. This special pass removes debug info for
    341   // such symbols.
    342 
    343   // llvm.dbg.gv keeps track of debug info for global variables.
    344   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
    345     SmallVector<MDNode *, 8> MDs;
    346     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
    347       if (NMD->getOperand(i)) {
    348         assert(DIGlobalVariable(NMD->getOperand(i)).isGlobalVariable() &&
    349           "A MDNode in llvm.dbg.gv should be a DIGlobalVariable.");
    350         MDs.push_back(NMD->getOperand(i));
    351       }
    352       else
    353         Changed = true;
    354     NMD->eraseFromParent();
    355     NMD = NULL;
    356 
    357     for (SmallVectorImpl<MDNode *>::iterator I = MDs.begin(),
    358            E = MDs.end(); I != E; ++I) {
    359       GlobalVariable *GV = DIGlobalVariable(*I).getGlobal();
    360       if (GV && M.getGlobalVariable(GV->getName(), true)) {
    361         if (!NMD)
    362           NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
    363         NMD->addOperand(*I);
    364       }
    365       else
    366         Changed = true;
    367     }
    368   }
    369 
    370   // llvm.dbg.sp keeps track of debug info for subprograms.
    371   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
    372     SmallVector<MDNode *, 8> MDs;
    373     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
    374       if (NMD->getOperand(i)) {
    375         assert(DISubprogram(NMD->getOperand(i)).isSubprogram() &&
    376           "A MDNode in llvm.dbg.sp should be a DISubprogram.");
    377         MDs.push_back(NMD->getOperand(i));
    378       }
    379       else
    380         Changed = true;
    381     NMD->eraseFromParent();
    382     NMD = NULL;
    383 
    384     for (SmallVectorImpl<MDNode *>::iterator I = MDs.begin(),
    385            E = MDs.end(); I != E; ++I) {
    386       bool FnIsLive = false;
    387       if (Function *F = DISubprogram(*I).getFunction())
    388         if (M.getFunction(F->getName()))
    389           FnIsLive = true;
    390       if (FnIsLive) {
    391           if (!NMD)
    392             NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
    393           NMD->addOperand(*I);
    394       } else {
    395         // Remove llvm.dbg.lv.fnname named mdnode which may have been used
    396         // to hold debug info for dead function's local variables.
    397         StringRef FName = DISubprogram(*I).getLinkageName();
    398         if (FName.empty())
    399           FName = DISubprogram(*I).getName();
    400         if (NamedMDNode *LVNMD = M.getNamedMetadata(
    401                 "llvm.dbg.lv." + Function::getRealLinkageName(FName)))
    402           LVNMD->eraseFromParent();
    403       }
    404     }
    405   }
    406 
    407   return Changed;
    408 }
    409