1 //===-- Internalize.cpp - Mark functions internal -------------------------===// 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 pass loops over all of the functions and variables in the input module. 11 // If the function or variable is not in the list of external names given to 12 // the pass it is marked as internal. 13 // 14 // This transformation would not be legal in a regular compilation, but it gets 15 // extra information from the linker about what is safe. 16 // 17 // For example: Internalizing a function with external linkage. Only if we are 18 // told it is only used from within this module, it is safe to do it. 19 // 20 //===----------------------------------------------------------------------===// 21 22 #include "llvm/Transforms/IPO.h" 23 #include "llvm/ADT/SmallPtrSet.h" 24 #include "llvm/ADT/Statistic.h" 25 #include "llvm/Analysis/CallGraph.h" 26 #include "llvm/IR/Module.h" 27 #include "llvm/Pass.h" 28 #include "llvm/Support/CommandLine.h" 29 #include "llvm/Support/Debug.h" 30 #include "llvm/Support/raw_ostream.h" 31 #include "llvm/Transforms/Utils/GlobalStatus.h" 32 #include "llvm/Transforms/Utils/ModuleUtils.h" 33 #include <fstream> 34 #include <set> 35 using namespace llvm; 36 37 #define DEBUG_TYPE "internalize" 38 39 STATISTIC(NumAliases , "Number of aliases internalized"); 40 STATISTIC(NumFunctions, "Number of functions internalized"); 41 STATISTIC(NumGlobals , "Number of global vars internalized"); 42 43 // APIFile - A file which contains a list of symbols that should not be marked 44 // external. 45 static cl::opt<std::string> 46 APIFile("internalize-public-api-file", cl::value_desc("filename"), 47 cl::desc("A file containing list of symbol names to preserve")); 48 49 // APIList - A list of symbols that should not be marked internal. 50 static cl::list<std::string> 51 APIList("internalize-public-api-list", cl::value_desc("list"), 52 cl::desc("A list of symbol names to preserve"), 53 cl::CommaSeparated); 54 55 namespace { 56 class InternalizePass : public ModulePass { 57 std::set<std::string> ExternalNames; 58 public: 59 static char ID; // Pass identification, replacement for typeid 60 explicit InternalizePass(); 61 explicit InternalizePass(ArrayRef<const char *> ExportList); 62 void LoadFile(const char *Filename); 63 bool runOnModule(Module &M) override; 64 65 void getAnalysisUsage(AnalysisUsage &AU) const override { 66 AU.setPreservesCFG(); 67 AU.addPreserved<CallGraphWrapperPass>(); 68 } 69 }; 70 } // end anonymous namespace 71 72 char InternalizePass::ID = 0; 73 INITIALIZE_PASS(InternalizePass, "internalize", 74 "Internalize Global Symbols", false, false) 75 76 InternalizePass::InternalizePass() : ModulePass(ID) { 77 initializeInternalizePassPass(*PassRegistry::getPassRegistry()); 78 if (!APIFile.empty()) // If a filename is specified, use it. 79 LoadFile(APIFile.c_str()); 80 ExternalNames.insert(APIList.begin(), APIList.end()); 81 } 82 83 InternalizePass::InternalizePass(ArrayRef<const char *> ExportList) 84 : ModulePass(ID) { 85 initializeInternalizePassPass(*PassRegistry::getPassRegistry()); 86 for(ArrayRef<const char *>::const_iterator itr = ExportList.begin(); 87 itr != ExportList.end(); itr++) { 88 ExternalNames.insert(*itr); 89 } 90 } 91 92 void InternalizePass::LoadFile(const char *Filename) { 93 // Load the APIFile... 94 std::ifstream In(Filename); 95 if (!In.good()) { 96 errs() << "WARNING: Internalize couldn't load file '" << Filename 97 << "'! Continuing as if it's empty.\n"; 98 return; // Just continue as if the file were empty 99 } 100 while (In) { 101 std::string Symbol; 102 In >> Symbol; 103 if (!Symbol.empty()) 104 ExternalNames.insert(Symbol); 105 } 106 } 107 108 static bool shouldInternalize(const GlobalValue &GV, 109 const std::set<std::string> &ExternalNames) { 110 // Function must be defined here 111 if (GV.isDeclaration()) 112 return false; 113 114 // Available externally is really just a "declaration with a body". 115 if (GV.hasAvailableExternallyLinkage()) 116 return false; 117 118 // Assume that dllexported symbols are referenced elsewhere 119 if (GV.hasDLLExportStorageClass()) 120 return false; 121 122 // Already has internal linkage 123 if (GV.hasLocalLinkage()) 124 return false; 125 126 // Marked to keep external? 127 if (ExternalNames.count(GV.getName())) 128 return false; 129 130 return true; 131 } 132 133 bool InternalizePass::runOnModule(Module &M) { 134 CallGraphWrapperPass *CGPass = getAnalysisIfAvailable<CallGraphWrapperPass>(); 135 CallGraph *CG = CGPass ? &CGPass->getCallGraph() : nullptr; 136 CallGraphNode *ExternalNode = CG ? CG->getExternalCallingNode() : nullptr; 137 bool Changed = false; 138 139 SmallPtrSet<GlobalValue *, 8> Used; 140 collectUsedGlobalVariables(M, Used, false); 141 142 // We must assume that globals in llvm.used have a reference that not even 143 // the linker can see, so we don't internalize them. 144 // For llvm.compiler.used the situation is a bit fuzzy. The assembler and 145 // linker can drop those symbols. If this pass is running as part of LTO, 146 // one might think that it could just drop llvm.compiler.used. The problem 147 // is that even in LTO llvm doesn't see every reference. For example, 148 // we don't see references from function local inline assembly. To be 149 // conservative, we internalize symbols in llvm.compiler.used, but we 150 // keep llvm.compiler.used so that the symbol is not deleted by llvm. 151 for (GlobalValue *V : Used) { 152 ExternalNames.insert(V->getName()); 153 } 154 155 // Mark all functions not in the api as internal. 156 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { 157 if (!shouldInternalize(*I, ExternalNames)) 158 continue; 159 160 I->setVisibility(GlobalValue::DefaultVisibility); 161 I->setLinkage(GlobalValue::InternalLinkage); 162 163 if (ExternalNode) 164 // Remove a callgraph edge from the external node to this function. 165 ExternalNode->removeOneAbstractEdgeTo((*CG)[I]); 166 167 Changed = true; 168 ++NumFunctions; 169 DEBUG(dbgs() << "Internalizing func " << I->getName() << "\n"); 170 } 171 172 // Never internalize the llvm.used symbol. It is used to implement 173 // attribute((used)). 174 // FIXME: Shouldn't this just filter on llvm.metadata section?? 175 ExternalNames.insert("llvm.used"); 176 ExternalNames.insert("llvm.compiler.used"); 177 178 // Never internalize anchors used by the machine module info, else the info 179 // won't find them. (see MachineModuleInfo.) 180 ExternalNames.insert("llvm.global_ctors"); 181 ExternalNames.insert("llvm.global_dtors"); 182 ExternalNames.insert("llvm.global.annotations"); 183 184 // Never internalize symbols code-gen inserts. 185 // FIXME: We should probably add this (and the __stack_chk_guard) via some 186 // type of call-back in CodeGen. 187 ExternalNames.insert("__stack_chk_fail"); 188 ExternalNames.insert("__stack_chk_guard"); 189 190 // Mark all global variables with initializers that are not in the api as 191 // internal as well. 192 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 193 I != E; ++I) { 194 if (!shouldInternalize(*I, ExternalNames)) 195 continue; 196 197 I->setVisibility(GlobalValue::DefaultVisibility); 198 I->setLinkage(GlobalValue::InternalLinkage); 199 Changed = true; 200 ++NumGlobals; 201 DEBUG(dbgs() << "Internalized gvar " << I->getName() << "\n"); 202 } 203 204 // Mark all aliases that are not in the api as internal as well. 205 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 206 I != E; ++I) { 207 if (!shouldInternalize(*I, ExternalNames)) 208 continue; 209 210 I->setVisibility(GlobalValue::DefaultVisibility); 211 I->setLinkage(GlobalValue::InternalLinkage); 212 Changed = true; 213 ++NumAliases; 214 DEBUG(dbgs() << "Internalized alias " << I->getName() << "\n"); 215 } 216 217 return Changed; 218 } 219 220 ModulePass *llvm::createInternalizePass() { return new InternalizePass(); } 221 222 ModulePass *llvm::createInternalizePass(ArrayRef<const char *> ExportList) { 223 return new InternalizePass(ExportList); 224 } 225