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/ADT/STLExtras.h"
  16 #include "llvm/ADT/SmallString.h"
  17 #include "llvm/ADT/StringRef.h"
  18 #include "llvm/ADT/Twine.h"
  19 #include "llvm/Analysis/TargetLibraryInfo.h"
  20 #include "llvm/IR/Argument.h"
  21 #include "llvm/IR/BasicBlock.h"
  22 #include "llvm/IR/DerivedTypes.h"
  23 #include "llvm/IR/Function.h"
  24 #include "llvm/IR/GlobalAlias.h"
  25 #include "llvm/IR/GlobalVariable.h"
  26 #include "llvm/IR/Instruction.h"
  27 #include "llvm/IR/Module.h"
  28 #include "llvm/IR/Type.h"
  29 #include "llvm/IR/TypeFinder.h"
  30 #include "llvm/Pass.h"
  31 #include "llvm/Transforms/Utils.h"
  32
  33 using namespace llvm;
  34
  35 static const char *const metaNames[] = {
  36   // See http://en.wikipedia.org/wiki/Metasyntactic_variable
  37   "foo", "bar", "baz", "quux", "barney", "snork", "zot", "blam", "hoge",
  38   "wibble", "wobble", "widget", "wombat", "ham", "eggs", "pluto", "spam"
  39 };
  40
  41 namespace {
  42
  43   // This PRNG is from the ISO C spec. It is intentionally simple and
  44   // unsuitable for cryptographic use. We're just looking for enough
  45   // variety to surprise and delight users.
  46   struct PRNG {
  47     unsigned long next;
  48
  49     void srand(unsigned int seed) {
  50       next = seed;
  51     }
  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) {
  61       prng.srand(seed);
  62     }
  63
  64     const char *newName() {
  65       return metaNames[prng.rand() % array_lengthof(metaNames)];
  66     }
  67
  68     PRNG prng;
  69   };
  70
  71   struct MetaRenamer : public ModulePass {
  72     // Pass identification, replacement for typeid
  73     static char ID;
  74
  75     MetaRenamer() : ModulePass(ID) {
  76       initializeMetaRenamerPass(*PassRegistry::getPassRegistry());
  77     }
  78
  79     void getAnalysisUsage(AnalysisUsage &AU) const override {
  80       AU.addRequired<TargetLibraryInfoWrapperPass>();
  81       AU.setPreservesAll();
  82     }
  83
  84     bool runOnModule(Module &M) override {
  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 (auto GI = M.global_begin(), GE = M.global_end(); GI != GE; ++GI) {
 105         StringRef Name = GI->getName();
 106         if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
 107           continue;
 108
 109         GI->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()) continue;
 117
 118         SmallString<128> NameStorage;
 119         STy->setName((Twine("struct.") +
 120           renamer.newName()).toStringRef(NameStorage));
 121       }
 122
 123       // Rename all functions
 124       for (auto &F : M) {
 125         StringRef Name = F.getName();
 126         LibFunc Tmp;
 127         // Leave library functions alone because their presence or absence could
 128         // affect the behavior of other passes.
 129         if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1) ||
 130             getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F).getLibFunc(
 131                 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         runOnFunction(F);
 140       }
 141       return true;
 142     }
 143
 144     bool runOnFunction(Function &F) {
 145       for (auto AI = F.arg_begin(), AE = F.arg_end(); AI != AE; ++AI)
 146         if (!AI->getType()->isVoidTy())
 147           AI->setName("arg");
 148
 149       for (auto &BB : F) {
 150         BB.setName("bb");
 151
 152         for (auto &I : BB)
 153           if (!I.getType()->isVoidTy())
 154             I.setName("tmp");
 155       }
 156       return true;
 157     }
 158   };
 159
 160 } // end anonymous namespace
 161
 162 char MetaRenamer::ID = 0;
 163
 164 INITIALIZE_PASS_BEGIN(MetaRenamer, "metarenamer",
 165                       "Assign new names to everything", false, false)
 166 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 167 INITIALIZE_PASS_END(MetaRenamer, "metarenamer",
 168                     "Assign new names to everything", false, false)
 169
 170 //===----------------------------------------------------------------------===//
 171 //
 172 // MetaRenamer - Rename everything with metasyntactic names.
 173 //
 174 ModulePass *llvm::createMetaRenamerPass() {
 175   return new MetaRenamer();
 176 }