llvm/lib/Transforms/Utils/MetaRenamer.cpp

   1 //===- MetaRenamer.cpp - Rename everything with metasyntatic names --------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This pass renames everything with metasyntatic names. The intent is to use
  10 // this pass after bugpoint reduction to conceal the nature of the original
  11 // program.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Transforms/Utils/MetaRenamer.h"
  16 #include "llvm/ADT/STLExtras.h"
  17 #include "llvm/ADT/SmallString.h"
  18 #include "llvm/ADT/StringRef.h"
  19 #include "llvm/ADT/Twine.h"
  20 #include "llvm/Analysis/TargetLibraryInfo.h"
  21 #include "llvm/IR/Argument.h"
  22 #include "llvm/IR/BasicBlock.h"
  23 #include "llvm/IR/DerivedTypes.h"
  24 #include "llvm/IR/Function.h"
  25 #include "llvm/IR/GlobalAlias.h"
  26 #include "llvm/IR/GlobalVariable.h"
  27 #include "llvm/IR/Instruction.h"
  28 #include "llvm/IR/Module.h"
  29 #include "llvm/IR/PassManager.h"
  30 #include "llvm/IR/Type.h"
  31 #include "llvm/IR/TypeFinder.h"
  32 #include "llvm/InitializePasses.h"
  33 #include "llvm/Pass.h"
  34 #include "llvm/Transforms/Utils.h"
  35
  36 using namespace llvm;
  37
  38 static const char *const metaNames[] = {
  39   // See http://en.wikipedia.org/wiki/Metasyntactic_variable
  40   "foo", "bar", "baz", "quux", "barney", "snork", "zot", "blam", "hoge",
  41   "wibble", "wobble", "widget", "wombat", "ham", "eggs", "pluto", "spam"
  42 };
  43
  44 namespace {
  45 // This PRNG is from the ISO C spec. It is intentionally simple and
  46 // unsuitable for cryptographic use. We're just looking for enough
  47 // variety to surprise and delight users.
  48 struct PRNG {
  49   unsigned long next;
  50
  51   void srand(unsigned int seed) { next = seed; }
  52
  53   int rand() {
  54     next = next * 1103515245 + 12345;
  55     return (unsigned int)(next / 65536) % 32768;
  56   }
  57 };
  58
  59 struct Renamer {
  60   Renamer(unsigned int seed) { prng.srand(seed); }
  61
  62   const char *newName() {
  63     return metaNames[prng.rand() % array_lengthof(metaNames)];
  64   }
  65
  66   PRNG prng;
  67 };
  68
  69 void MetaRename(Function &F) {
  70   for (Argument &Arg : F.args())
  71     if (!Arg.getType()->isVoidTy())
  72       Arg.setName("arg");
  73
  74   for (auto &BB : F) {
  75     BB.setName("bb");
  76
  77     for (auto &I : BB)
  78       if (!I.getType()->isVoidTy())
  79         I.setName("tmp");
  80   }
  81 }
  82
  83 void MetaRename(Module &M,
  84                 function_ref<TargetLibraryInfo &(Function &)> GetTLI) {
  85   // Seed our PRNG with simple additive sum of ModuleID. We're looking to
  86   // simply avoid always having the same function names, and we need to
  87   // remain deterministic.
  88   unsigned int randSeed = 0;
  89   for (auto C : M.getModuleIdentifier())
  90     randSeed += C;
  91
  92   Renamer renamer(randSeed);
  93
  94   // Rename all aliases
  95   for (auto AI = M.alias_begin(), AE = M.alias_end(); AI != AE; ++AI) {
  96     StringRef Name = AI->getName();
  97     if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
  98       continue;
  99
 100     AI->setName("alias");
 101   }
 102
 103   // Rename all global variables
 104   for (GlobalVariable &GV : M.globals()) {
 105     StringRef Name = GV.getName();
 106     if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
 107       continue;
 108
 109     GV.setName("global");
 110   }
 111
 112   // Rename all struct types
 113   TypeFinder StructTypes;
 114   StructTypes.run(M, true);
 115   for (StructType *STy : StructTypes) {
 116     if (STy->isLiteral() || STy->getName().empty())
 117       continue;
 118
 119     SmallString<128> NameStorage;
 120     STy->setName(
 121         (Twine("struct.") + renamer.newName()).toStringRef(NameStorage));
 122   }
 123
 124   // Rename all functions
 125   for (auto &F : M) {
 126     StringRef Name = F.getName();
 127     LibFunc Tmp;
 128     // Leave library functions alone because their presence or absence could
 129     // affect the behavior of other passes.
 130     if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1) ||
 131         GetTLI(F).getLibFunc(F, Tmp))
 132       continue;
 133
 134     // Leave @main alone. The output of -metarenamer might be passed to
 135     // lli for execution and the latter needs a main entry point.
 136     if (Name != "main")
 137       F.setName(renamer.newName());
 138
 139     MetaRename(F);
 140   }
 141 }
 142
 143 struct MetaRenamer : public ModulePass {
 144   // Pass identification, replacement for typeid
 145   static char ID;
 146
 147   MetaRenamer() : ModulePass(ID) {
 148     initializeMetaRenamerPass(*PassRegistry::getPassRegistry());
 149   }
 150
 151   void getAnalysisUsage(AnalysisUsage &AU) const override {
 152     AU.addRequired<TargetLibraryInfoWrapperPass>();
 153     AU.setPreservesAll();
 154   }
 155
 156   bool runOnModule(Module &M) override {
 157     auto GetTLI = [this](Function &F) -> TargetLibraryInfo & {
 158       return this->getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
 159     };
 160     MetaRename(M, GetTLI);
 161     return true;
 162   }
 163 };
 164
 165 } // end anonymous namespace
 166
 167 char MetaRenamer::ID = 0;
 168
 169 INITIALIZE_PASS_BEGIN(MetaRenamer, "metarenamer",
 170                       "Assign new names to everything", false, false)
 171 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 172 INITIALIZE_PASS_END(MetaRenamer, "metarenamer",
 173                     "Assign new names to everything", false, false)
 174
 175 //===----------------------------------------------------------------------===//
 176 //
 177 // MetaRenamer - Rename everything with metasyntactic names.
 178 //
 179 ModulePass *llvm::createMetaRenamerPass() {
 180   return new MetaRenamer();
 181 }
 182
 183 PreservedAnalyses MetaRenamerPass::run(Module &M, ModuleAnalysisManager &AM) {
 184   FunctionAnalysisManager &FAM =
 185       AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
 186   auto GetTLI = [&FAM](Function &F) -> TargetLibraryInfo & {
 187     return FAM.getResult<TargetLibraryAnalysis>(F);
 188   };
 189   MetaRename(M, GetTLI);
 190
 191   return PreservedAnalyses::all();
 192 }