1 //===- MetaRenamer.cpp - Rename everything with metasyntatic names --------===//
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 renames everything with metasyntatic names. The intent is to use
11 // this pass after bugpoint reduction to conceal the nature of the original
12 // program.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/Analysis/TargetLibraryInfo.h"
19 #include "llvm/IR/DerivedTypes.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/IR/Type.h"
23 #include "llvm/IR/TypeFinder.h"
24 #include "llvm/Pass.h"
25 #include "llvm/Transforms/IPO.h"
26 using namespace llvm;
27 
28 namespace {
29 
30   // This PRNG is from the ISO C spec. It is intentionally simple and
31   // unsuitable for cryptographic use. We're just looking for enough
32   // variety to surprise and delight users.
33   struct PRNG {
34     unsigned long next;
35 
36     void srand(unsigned int seed) {
37       next = seed;
38     }
39 
40     int rand() {
41       next = next * 1103515245 + 12345;
42       return (unsigned int)(next / 65536) % 32768;
43     }
44   };
45 
46   static const char *const metaNames[] = {
47     // See http://en.wikipedia.org/wiki/Metasyntactic_variable
48     "foo", "bar", "baz", "quux", "barney", "snork", "zot", "blam", "hoge",
49     "wibble", "wobble", "widget", "wombat", "ham", "eggs", "pluto", "spam"
50   };
51 
52   struct Renamer {
53     Renamer(unsigned int seed) {
54       prng.srand(seed);
55     }
56 
57     const char *newName() {
58       return metaNames[prng.rand() % array_lengthof(metaNames)];
59     }
60 
61     PRNG prng;
62   };
63 
64   struct MetaRenamer : public ModulePass {
65     static char ID; // Pass identification, replacement for typeid
66     MetaRenamer() : ModulePass(ID) {
67       initializeMetaRenamerPass(*PassRegistry::getPassRegistry());
68     }
69 
70     void getAnalysisUsage(AnalysisUsage &AU) const override {
71       AU.addRequired<TargetLibraryInfoWrapperPass>();
72       AU.setPreservesAll();
73     }
74 
75     bool runOnModule(Module &M) override {
76       // Seed our PRNG with simple additive sum of ModuleID. We're looking to
77       // simply avoid always having the same function names, and we need to
78       // remain deterministic.
79       unsigned int randSeed = 0;
80       for (auto C : M.getModuleIdentifier())
81         randSeed += C;
82 
83       Renamer renamer(randSeed);
84 
85       // Rename all aliases
86       for (auto AI = M.alias_begin(), AE = M.alias_end(); AI != AE; ++AI) {
87         StringRef Name = AI->getName();
88         if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
89           continue;
90 
91         AI->setName("alias");
92       }
93 
94       // Rename all global variables
95       for (auto GI = M.global_begin(), GE = M.global_end(); GI != GE; ++GI) {
96         StringRef Name = GI->getName();
97         if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
98           continue;
99 
100         GI->setName("global");
101       }
102 
103       // Rename all struct types
104       TypeFinder StructTypes;
105       StructTypes.run(M, true);
106       for (StructType *STy : StructTypes) {
107         if (STy->isLiteral() || STy->getName().empty()) continue;
108 
109         SmallString<128> NameStorage;
110         STy->setName((Twine("struct.") +
111           renamer.newName()).toStringRef(NameStorage));
112       }
113 
114       // Rename all functions
115       const TargetLibraryInfo &TLI =
116           getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
117       for (auto &F : M) {
118         StringRef Name = F.getName();
119         LibFunc Tmp;
120         // Leave library functions alone because their presence or absence could
121         // affect the behavior of other passes.
122         if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1) ||
123             TLI.getLibFunc(F, Tmp))
124           continue;
125 
126         F.setName(renamer.newName());
127         runOnFunction(F);
128       }
129       return true;
130     }
131 
132     bool runOnFunction(Function &F) {
133       for (auto AI = F.arg_begin(), AE = F.arg_end(); AI != AE; ++AI)
134         if (!AI->getType()->isVoidTy())
135           AI->setName("arg");
136 
137       for (auto &BB : F) {
138         BB.setName("bb");
139 
140         for (auto &I : BB)
141           if (!I.getType()->isVoidTy())
142             I.setName("tmp");
143       }
144       return true;
145     }
146   };
147 }
148 
149 char MetaRenamer::ID = 0;
150 INITIALIZE_PASS_BEGIN(MetaRenamer, "metarenamer",
151                       "Assign new names to everything", false, false)
152 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
153 INITIALIZE_PASS_END(MetaRenamer, "metarenamer",
154                     "Assign new names to everything", false, false)
155 //===----------------------------------------------------------------------===//
156 //
157 // MetaRenamer - Rename everything with metasyntactic names.
158 //
159 ModulePass *llvm::createMetaRenamerPass() {
160   return new MetaRenamer();
161 }
162