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> 35using namespace llvm; 36 37#define DEBUG_TYPE "internalize" 38 39STATISTIC(NumAliases , "Number of aliases internalized"); 40STATISTIC(NumFunctions, "Number of functions internalized"); 41STATISTIC(NumGlobals , "Number of global vars internalized"); 42 43// APIFile - A file which contains a list of symbols that should not be marked 44// external. 45static cl::opt<std::string> 46APIFile("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. 50static cl::list<std::string> 51APIList("internalize-public-api-list", cl::value_desc("list"), 52 cl::desc("A list of symbol names to preserve"), 53 cl::CommaSeparated); 54 55namespace { 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 72char InternalizePass::ID = 0; 73INITIALIZE_PASS(InternalizePass, "internalize", 74 "Internalize Global Symbols", false, false) 75 76InternalizePass::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 83InternalizePass::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 92void 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 108static 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 133bool 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 (SmallPtrSet<GlobalValue *, 8>::iterator I = Used.begin(), E = Used.end(); 152 I != E; ++I) { 153 GlobalValue *V = *I; 154 ExternalNames.insert(V->getName()); 155 } 156 157 // Mark all functions not in the api as internal. 158 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { 159 if (!shouldInternalize(*I, ExternalNames)) 160 continue; 161 162 I->setVisibility(GlobalValue::DefaultVisibility); 163 I->setLinkage(GlobalValue::InternalLinkage); 164 165 if (ExternalNode) 166 // Remove a callgraph edge from the external node to this function. 167 ExternalNode->removeOneAbstractEdgeTo((*CG)[I]); 168 169 Changed = true; 170 ++NumFunctions; 171 DEBUG(dbgs() << "Internalizing func " << I->getName() << "\n"); 172 } 173 174 // Never internalize the llvm.used symbol. It is used to implement 175 // attribute((used)). 176 // FIXME: Shouldn't this just filter on llvm.metadata section?? 177 ExternalNames.insert("llvm.used"); 178 ExternalNames.insert("llvm.compiler.used"); 179 180 // Never internalize anchors used by the machine module info, else the info 181 // won't find them. (see MachineModuleInfo.) 182 ExternalNames.insert("llvm.global_ctors"); 183 ExternalNames.insert("llvm.global_dtors"); 184 ExternalNames.insert("llvm.global.annotations"); 185 186 // Never internalize symbols code-gen inserts. 187 // FIXME: We should probably add this (and the __stack_chk_guard) via some 188 // type of call-back in CodeGen. 189 ExternalNames.insert("__stack_chk_fail"); 190 ExternalNames.insert("__stack_chk_guard"); 191 192 // Mark all global variables with initializers that are not in the api as 193 // internal as well. 194 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 195 I != E; ++I) { 196 if (!shouldInternalize(*I, ExternalNames)) 197 continue; 198 199 I->setVisibility(GlobalValue::DefaultVisibility); 200 I->setLinkage(GlobalValue::InternalLinkage); 201 Changed = true; 202 ++NumGlobals; 203 DEBUG(dbgs() << "Internalized gvar " << I->getName() << "\n"); 204 } 205 206 // Mark all aliases that are not in the api as internal as well. 207 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 208 I != E; ++I) { 209 if (!shouldInternalize(*I, ExternalNames)) 210 continue; 211 212 I->setVisibility(GlobalValue::DefaultVisibility); 213 I->setLinkage(GlobalValue::InternalLinkage); 214 Changed = true; 215 ++NumAliases; 216 DEBUG(dbgs() << "Internalized alias " << I->getName() << "\n"); 217 } 218 219 return Changed; 220} 221 222ModulePass *llvm::createInternalizePass() { return new InternalizePass(); } 223 224ModulePass *llvm::createInternalizePass(ArrayRef<const char *> ExportList) { 225 return new InternalizePass(ExportList); 226} 227