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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/Constants.h"
     25 #include "llvm/DerivedTypes.h"
     26 #include "llvm/Instructions.h"
     27 #include "llvm/Module.h"
     28 #include "llvm/Pass.h"
     29 #include "llvm/Analysis/DebugInfo.h"
     30 #include "llvm/ValueSymbolTable.h"
     31 #include "llvm/Transforms/Utils/Local.h"
     32 #include "llvm/ADT/DenseMap.h"
     33 #include "llvm/ADT/SmallPtrSet.h"
     34 using namespace llvm;
     35 
     36 namespace {
     37   class StripSymbols : public ModulePass {
     38     bool OnlyDebugInfo;
     39   public:
     40     static char ID; // Pass identification, replacement for typeid
     41     explicit StripSymbols(bool ODI = false)
     42       : ModulePass(ID), OnlyDebugInfo(ODI) {
     43         initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
     44       }
     45 
     46     virtual bool runOnModule(Module &M);
     47 
     48     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     49       AU.setPreservesAll();
     50     }
     51   };
     52 
     53   class StripNonDebugSymbols : public ModulePass {
     54   public:
     55     static char ID; // Pass identification, replacement for typeid
     56     explicit StripNonDebugSymbols()
     57       : ModulePass(ID) {
     58         initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
     59       }
     60 
     61     virtual bool runOnModule(Module &M);
     62 
     63     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     64       AU.setPreservesAll();
     65     }
     66   };
     67 
     68   class StripDebugDeclare : public ModulePass {
     69   public:
     70     static char ID; // Pass identification, replacement for typeid
     71     explicit StripDebugDeclare()
     72       : ModulePass(ID) {
     73         initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
     74       }
     75 
     76     virtual bool runOnModule(Module &M);
     77 
     78     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     79       AU.setPreservesAll();
     80     }
     81   };
     82 
     83   class StripDeadDebugInfo : public ModulePass {
     84   public:
     85     static char ID; // Pass identification, replacement for typeid
     86     explicit StripDeadDebugInfo()
     87       : ModulePass(ID) {
     88         initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
     89       }
     90 
     91     virtual bool runOnModule(Module &M);
     92 
     93     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     94       AU.setPreservesAll();
     95     }
     96   };
     97 }
     98 
     99 char StripSymbols::ID = 0;
    100 INITIALIZE_PASS(StripSymbols, "strip",
    101                 "Strip all symbols from a module", false, false)
    102 
    103 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
    104   return new StripSymbols(OnlyDebugInfo);
    105 }
    106 
    107 char StripNonDebugSymbols::ID = 0;
    108 INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
    109                 "Strip all symbols, except dbg symbols, from a module",
    110                 false, false)
    111 
    112 ModulePass *llvm::createStripNonDebugSymbolsPass() {
    113   return new StripNonDebugSymbols();
    114 }
    115 
    116 char StripDebugDeclare::ID = 0;
    117 INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
    118                 "Strip all llvm.dbg.declare intrinsics", false, false)
    119 
    120 ModulePass *llvm::createStripDebugDeclarePass() {
    121   return new StripDebugDeclare();
    122 }
    123 
    124 char StripDeadDebugInfo::ID = 0;
    125 INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
    126                 "Strip debug info for unused symbols", false, false)
    127 
    128 ModulePass *llvm::createStripDeadDebugInfoPass() {
    129   return new StripDeadDebugInfo();
    130 }
    131 
    132 /// OnlyUsedBy - Return true if V is only used by Usr.
    133 static bool OnlyUsedBy(Value *V, Value *Usr) {
    134   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
    135     User *U = *I;
    136     if (U != Usr)
    137       return false;
    138   }
    139   return true;
    140 }
    141 
    142 static void RemoveDeadConstant(Constant *C) {
    143   assert(C->use_empty() && "Constant is not dead!");
    144   SmallPtrSet<Constant*, 4> Operands;
    145   for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
    146     if (OnlyUsedBy(C->getOperand(i), C))
    147       Operands.insert(cast<Constant>(C->getOperand(i)));
    148   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
    149     if (!GV->hasLocalLinkage()) return;   // Don't delete non static globals.
    150     GV->eraseFromParent();
    151   }
    152   else if (!isa<Function>(C))
    153     if (isa<CompositeType>(C->getType()))
    154       C->destroyConstant();
    155 
    156   // If the constant referenced anything, see if we can delete it as well.
    157   for (SmallPtrSet<Constant*, 4>::iterator OI = Operands.begin(),
    158          OE = Operands.end(); OI != OE; ++OI)
    159     RemoveDeadConstant(*OI);
    160 }
    161 
    162 // Strip the symbol table of its names.
    163 //
    164 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
    165   for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
    166     Value *V = VI->getValue();
    167     ++VI;
    168     if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
    169       if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
    170         // Set name to "", removing from symbol table!
    171         V->setName("");
    172     }
    173   }
    174 }
    175 
    176 // Strip any named types of their names.
    177 static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
    178   std::vector<StructType*> StructTypes;
    179   M.findUsedStructTypes(StructTypes);
    180 
    181   for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
    182     StructType *STy = StructTypes[i];
    183     if (STy->isLiteral() || STy->getName().empty()) continue;
    184 
    185     if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
    186       continue;
    187 
    188     STy->setName("");
    189   }
    190 }
    191 
    192 /// Find values that are marked as llvm.used.
    193 static void findUsedValues(GlobalVariable *LLVMUsed,
    194                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
    195   if (LLVMUsed == 0) return;
    196   UsedValues.insert(LLVMUsed);
    197 
    198   ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
    199   if (Inits == 0) return;
    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 /// getRealLinkageName - If special LLVM prefix that is used to inform the asm
    336 /// printer to not emit usual symbol prefix before the symbol name is used then
    337 /// return linkage name after skipping this special LLVM prefix.
    338 static StringRef getRealLinkageName(StringRef LinkageName) {
    339   char One = '\1';
    340   if (LinkageName.startswith(StringRef(&One, 1)))
    341     return LinkageName.substr(1);
    342   return LinkageName;
    343 }
    344 
    345 bool StripDeadDebugInfo::runOnModule(Module &M) {
    346   bool Changed = false;
    347 
    348   // Debugging infomration is encoded in llvm IR using metadata. This is designed
    349   // such a way that debug info for symbols preserved even if symbols are
    350   // optimized away by the optimizer. This special pass removes debug info for
    351   // such symbols.
    352 
    353   // llvm.dbg.gv keeps track of debug info for global variables.
    354   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
    355     SmallVector<MDNode *, 8> MDs;
    356     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
    357       if (DIGlobalVariable(NMD->getOperand(i)).Verify())
    358         MDs.push_back(NMD->getOperand(i));
    359       else
    360         Changed = true;
    361     NMD->eraseFromParent();
    362     NMD = NULL;
    363 
    364     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
    365            E = MDs.end(); I != E; ++I) {
    366       GlobalVariable *GV = DIGlobalVariable(*I).getGlobal();
    367       if (GV && M.getGlobalVariable(GV->getName(), true)) {
    368         if (!NMD)
    369           NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
    370         NMD->addOperand(*I);
    371       }
    372       else
    373         Changed = true;
    374     }
    375   }
    376 
    377   // llvm.dbg.sp keeps track of debug info for subprograms.
    378   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
    379     SmallVector<MDNode *, 8> MDs;
    380     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
    381       if (DISubprogram(NMD->getOperand(i)).Verify())
    382         MDs.push_back(NMD->getOperand(i));
    383       else
    384         Changed = true;
    385     NMD->eraseFromParent();
    386     NMD = NULL;
    387 
    388     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
    389            E = MDs.end(); I != E; ++I) {
    390       bool FnIsLive = false;
    391       if (Function *F = DISubprogram(*I).getFunction())
    392         if (M.getFunction(F->getName()))
    393           FnIsLive = true;
    394       if (FnIsLive) {
    395           if (!NMD)
    396             NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
    397           NMD->addOperand(*I);
    398       } else {
    399         // Remove llvm.dbg.lv.fnname named mdnode which may have been used
    400         // to hold debug info for dead function's local variables.
    401         StringRef FName = DISubprogram(*I).getLinkageName();
    402         if (FName.empty())
    403           FName = DISubprogram(*I).getName();
    404         if (NamedMDNode *LVNMD =
    405             M.getNamedMetadata(Twine("llvm.dbg.lv.",
    406                                      getRealLinkageName(FName))))
    407           LVNMD->eraseFromParent();
    408       }
    409     }
    410   }
    411 
    412   return Changed;
    413 }
    414