//===- StripSymbols.cpp - Strip symbols and debug info from a module ------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // The StripSymbols transformation implements code stripping. Specifically, it // can delete: // // * names for virtual registers // * symbols for internal globals and functions // * debug information // // Note that this transformation makes code much less readable, so it should // only be used in situations where the 'strip' utility would be used, such as // reducing code size or making it harder to reverse engineer code. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/IPO.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/DebugInfo.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/Module.h" #include "llvm/IR/TypeFinder.h" #include "llvm/IR/ValueSymbolTable.h" #include "llvm/Pass.h" #include "llvm/Transforms/Utils/Local.h" using namespace llvm; namespace { class StripSymbols : public ModulePass { bool OnlyDebugInfo; public: static char ID; // Pass identification, replacement for typeid explicit StripSymbols(bool ODI = false) : ModulePass(ID), OnlyDebugInfo(ODI) { initializeStripSymbolsPass(*PassRegistry::getPassRegistry()); } virtual bool runOnModule(Module &M); virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); } }; class StripNonDebugSymbols : public ModulePass { public: static char ID; // Pass identification, replacement for typeid explicit StripNonDebugSymbols() : ModulePass(ID) { initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry()); } virtual bool runOnModule(Module &M); virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); } }; class StripDebugDeclare : public ModulePass { public: static char ID; // Pass identification, replacement for typeid explicit StripDebugDeclare() : ModulePass(ID) { initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry()); } virtual bool runOnModule(Module &M); virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); } }; class StripDeadDebugInfo : public ModulePass { public: static char ID; // Pass identification, replacement for typeid explicit StripDeadDebugInfo() : ModulePass(ID) { initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry()); } virtual bool runOnModule(Module &M); virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); } }; } char StripSymbols::ID = 0; INITIALIZE_PASS(StripSymbols, "strip", "Strip all symbols from a module", false, false) ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) { return new StripSymbols(OnlyDebugInfo); } char StripNonDebugSymbols::ID = 0; INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug", "Strip all symbols, except dbg symbols, from a module", false, false) ModulePass *llvm::createStripNonDebugSymbolsPass() { return new StripNonDebugSymbols(); } char StripDebugDeclare::ID = 0; INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare", "Strip all llvm.dbg.declare intrinsics", false, false) ModulePass *llvm::createStripDebugDeclarePass() { return new StripDebugDeclare(); } char StripDeadDebugInfo::ID = 0; INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info", "Strip debug info for unused symbols", false, false) ModulePass *llvm::createStripDeadDebugInfoPass() { return new StripDeadDebugInfo(); } /// OnlyUsedBy - Return true if V is only used by Usr. static bool OnlyUsedBy(Value *V, Value *Usr) { for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) { User *U = *I; if (U != Usr) return false; } return true; } static void RemoveDeadConstant(Constant *C) { assert(C->use_empty() && "Constant is not dead!"); SmallPtrSet Operands; for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) if (OnlyUsedBy(C->getOperand(i), C)) Operands.insert(cast(C->getOperand(i))); if (GlobalVariable *GV = dyn_cast(C)) { if (!GV->hasLocalLinkage()) return; // Don't delete non static globals. GV->eraseFromParent(); } else if (!isa(C)) if (isa(C->getType())) C->destroyConstant(); // If the constant referenced anything, see if we can delete it as well. for (SmallPtrSet::iterator OI = Operands.begin(), OE = Operands.end(); OI != OE; ++OI) RemoveDeadConstant(*OI); } // Strip the symbol table of its names. // static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) { for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) { Value *V = VI->getValue(); ++VI; if (!isa(V) || cast(V)->hasLocalLinkage()) { if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg")) // Set name to "", removing from symbol table! V->setName(""); } } } // Strip any named types of their names. static void StripTypeNames(Module &M, bool PreserveDbgInfo) { TypeFinder StructTypes; StructTypes.run(M, false); for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) { StructType *STy = StructTypes[i]; if (STy->isLiteral() || STy->getName().empty()) continue; if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg")) continue; STy->setName(""); } } /// Find values that are marked as llvm.used. static void findUsedValues(GlobalVariable *LLVMUsed, SmallPtrSet &UsedValues) { if (LLVMUsed == 0) return; UsedValues.insert(LLVMUsed); ConstantArray *Inits = cast(LLVMUsed->getInitializer()); for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) if (GlobalValue *GV = dyn_cast(Inits->getOperand(i)->stripPointerCasts())) UsedValues.insert(GV); } /// StripSymbolNames - Strip symbol names. static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) { SmallPtrSet llvmUsedValues; findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues); findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues); for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I) { if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0) if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg")) I->setName(""); // Internal symbols can't participate in linkage } for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0) if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg")) I->setName(""); // Internal symbols can't participate in linkage StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo); } // Remove all names from types. StripTypeNames(M, PreserveDbgInfo); return true; } // StripDebugInfo - Strip debug info in the module if it exists. // To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and // llvm.dbg.region.end calls, and any globals they point to if now dead. static bool StripDebugInfo(Module &M) { bool Changed = false; // Remove all of the calls to the debugger intrinsics, and remove them from // the module. if (Function *Declare = M.getFunction("llvm.dbg.declare")) { while (!Declare->use_empty()) { CallInst *CI = cast(Declare->use_back()); CI->eraseFromParent(); } Declare->eraseFromParent(); Changed = true; } if (Function *DbgVal = M.getFunction("llvm.dbg.value")) { while (!DbgVal->use_empty()) { CallInst *CI = cast(DbgVal->use_back()); CI->eraseFromParent(); } DbgVal->eraseFromParent(); Changed = true; } for (Module::named_metadata_iterator NMI = M.named_metadata_begin(), NME = M.named_metadata_end(); NMI != NME;) { NamedMDNode *NMD = NMI; ++NMI; if (NMD->getName().startswith("llvm.dbg.")) { NMD->eraseFromParent(); Changed = true; } } for (Module::iterator MI = M.begin(), ME = M.end(); MI != ME; ++MI) for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE; ++FI) for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { if (!BI->getDebugLoc().isUnknown()) { Changed = true; BI->setDebugLoc(DebugLoc()); } } return Changed; } bool StripSymbols::runOnModule(Module &M) { bool Changed = false; Changed |= StripDebugInfo(M); if (!OnlyDebugInfo) Changed |= StripSymbolNames(M, false); return Changed; } bool StripNonDebugSymbols::runOnModule(Module &M) { return StripSymbolNames(M, true); } bool StripDebugDeclare::runOnModule(Module &M) { Function *Declare = M.getFunction("llvm.dbg.declare"); std::vector DeadConstants; if (Declare) { while (!Declare->use_empty()) { CallInst *CI = cast(Declare->use_back()); Value *Arg1 = CI->getArgOperand(0); Value *Arg2 = CI->getArgOperand(1); assert(CI->use_empty() && "llvm.dbg intrinsic should have void result"); CI->eraseFromParent(); if (Arg1->use_empty()) { if (Constant *C = dyn_cast(Arg1)) DeadConstants.push_back(C); else RecursivelyDeleteTriviallyDeadInstructions(Arg1); } if (Arg2->use_empty()) if (Constant *C = dyn_cast(Arg2)) DeadConstants.push_back(C); } Declare->eraseFromParent(); } while (!DeadConstants.empty()) { Constant *C = DeadConstants.back(); DeadConstants.pop_back(); if (GlobalVariable *GV = dyn_cast(C)) { if (GV->hasLocalLinkage()) RemoveDeadConstant(GV); } else RemoveDeadConstant(C); } return true; } /// Remove any debug info for global variables/functions in the given module for /// which said global variable/function no longer exists (i.e. is null). /// /// Debugging information is encoded in llvm IR using metadata. This is designed /// such a way that debug info for symbols preserved even if symbols are /// optimized away by the optimizer. This special pass removes debug info for /// such symbols. bool StripDeadDebugInfo::runOnModule(Module &M) { bool Changed = false; LLVMContext &C = M.getContext(); // Find all debug info in F. This is actually overkill in terms of what we // want to do, but we want to try and be as resilient as possible in the face // of potential debug info changes by using the formal interfaces given to us // as much as possible. DebugInfoFinder F; F.processModule(M); // For each compile unit, find the live set of global variables/functions and // replace the current list of potentially dead global variables/functions // with the live list. SmallVector LiveGlobalVariables; SmallVector LiveSubprograms; DenseSet VisitedSet; for (DebugInfoFinder::iterator CI = F.compile_unit_begin(), CE = F.compile_unit_end(); CI != CE; ++CI) { // Create our compile unit. DICompileUnit DIC(*CI); assert(DIC.Verify() && "DIC must verify as a DICompileUnit."); // Create our live subprogram list. DIArray SPs = DIC.getSubprograms(); bool SubprogramChange = false; for (unsigned i = 0, e = SPs.getNumElements(); i != e; ++i) { DISubprogram DISP(SPs.getElement(i)); assert(DISP.Verify() && "DISP must verify as a DISubprogram."); // Make sure we visit each subprogram only once. if (!VisitedSet.insert(DISP).second) continue; // If the function referenced by DISP is not null, the function is live. if (DISP.getFunction()) LiveSubprograms.push_back(DISP); else SubprogramChange = true; } // Create our live global variable list. DIArray GVs = DIC.getGlobalVariables(); bool GlobalVariableChange = false; for (unsigned i = 0, e = GVs.getNumElements(); i != e; ++i) { DIGlobalVariable DIG(GVs.getElement(i)); assert(DIG.Verify() && "DIG must verify as DIGlobalVariable."); // Make sure we only visit each global variable only once. if (!VisitedSet.insert(DIG).second) continue; // If the global variable referenced by DIG is not null, the global // variable is live. if (DIG.getGlobal()) LiveGlobalVariables.push_back(DIG); else GlobalVariableChange = true; } // If we found dead subprograms or global variables, replace the current // subprogram list/global variable list with our new live subprogram/global // variable list. if (SubprogramChange) { // Make sure that 9 is still the index of the subprograms. This is to make // sure that an assert is hit if the location of the subprogram array // changes. This is just to make sure that this is updated if such an // event occurs. assert(DIC->getNumOperands() >= 10 && SPs == DIC->getOperand(9) && "DICompileUnits is expected to store Subprograms in operand " "9."); DIC->replaceOperandWith(9, MDNode::get(C, LiveSubprograms)); Changed = true; } if (GlobalVariableChange) { // Make sure that 10 is still the index of global variables. This is to // make sure that an assert is hit if the location of the subprogram array // changes. This is just to make sure that this index is updated if such // an event occurs. assert(DIC->getNumOperands() >= 11 && GVs == DIC->getOperand(10) && "DICompileUnits is expected to store Global Variables in operand " "10."); DIC->replaceOperandWith(10, MDNode::get(C, LiveGlobalVariables)); Changed = true; } // Reset lists for the next iteration. LiveSubprograms.clear(); LiveGlobalVariables.clear(); } return Changed; }