StripSymbols.cpp revision 7f8897f22e88271cfa114998a4d6088e7c8e8e11 
1//===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the LLVM research group and is distributed under
6// the University of Illinois Open Source License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements stripping symbols out of symbol tables.
11//
12// Specifically, this allows you to strip all of the symbols out of:
13//   * All functions in a module
14//   * All non-essential symbols in a module (all function symbols + all module
15//     scope symbols)
16//   * Debug information.
17//
18// Notice that:
19//   * This pass makes code much less readable, so it should only be used in
20//     situations where the 'strip' utility would be used (such as reducing
21//     code size, and making it harder to reverse engineer code).
22//
23//===----------------------------------------------------------------------===//
24
25#include "llvm/Transforms/IPO.h"
26#include "llvm/Constants.h"
27#include "llvm/DerivedTypes.h"
28#include "llvm/Instructions.h"
29#include "llvm/Module.h"
30#include "llvm/Pass.h"
31#include "llvm/SymbolTable.h"
32using namespace llvm;
33
34namespace {
35  class StripSymbols : public ModulePass {
36    bool OnlyDebugInfo;
37  public:
38    StripSymbols(bool ODI = false) : OnlyDebugInfo(ODI) {}
39
40    virtual bool runOnModule(Module &M);
41
42    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
43      AU.setPreservesAll();
44    }
45  };
46  RegisterPass<StripSymbols> X("strip", "Strip all symbols from a module");
47}
48
49ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
50  return new StripSymbols(OnlyDebugInfo);
51}
52
53static void RemoveDeadConstant(Constant *C) {
54  assert(C->use_empty() && "Constant is not dead!");
55  std::vector<Constant*> Operands;
56  for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
57    if (isa<DerivedType>(C->getOperand(i)->getType()) &&
58        C->getOperand(i)->hasOneUse())
59      Operands.push_back(C->getOperand(i));
60  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
61    if (!GV->hasInternalLinkage()) return;   // Don't delete non static globals.
62    GV->eraseFromParent();
63  }
64  else if (!isa<Function>(C))
65    C->destroyConstant();
66
67  // If the constant referenced anything, see if we can delete it as well.
68  while (!Operands.empty()) {
69    RemoveDeadConstant(Operands.back());
70    Operands.pop_back();
71  }
72}
73
74bool StripSymbols::runOnModule(Module &M) {
75  // If we're not just stripping debug info, strip all symbols from the
76  // functions and the names from any internal globals.
77  if (!OnlyDebugInfo) {
78    for (Module::global_iterator I = M.global_begin(), E = M.global_end();
79         I != E; ++I)
80      if (I->hasInternalLinkage())
81        I->setName("");     // Internal symbols can't participate in linkage
82
83    for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
84      if (I->hasInternalLinkage())
85        I->setName("");     // Internal symbols can't participate in linkage
86      I->getSymbolTable().strip();
87    }
88
89    // Remove all names from types.
90    SymbolTable &SymTab = M.getSymbolTable();
91    while (SymTab.type_begin() != SymTab.type_end())
92      SymTab.remove(SymTab.type_begin());
93  }
94
95  // Strip debug info in the module if it exists.  To do this, we remove
96  // llvm.dbg.func.start, llvm.dbg.stoppoint, and llvm.dbg.region.end calls, and
97  // any globals they point to if now dead.
98  Function *FuncStart = M.getNamedFunction("llvm.dbg.func.start");
99  Function *StopPoint = M.getNamedFunction("llvm.dbg.stoppoint");
100  Function *RegionStart = M.getNamedFunction("llvm.dbg.region.start");
101  Function *RegionEnd = M.getNamedFunction("llvm.dbg.region.end");
102  Function *Declare = M.getNamedFunction("llvm.dbg.declare");
103  if (!FuncStart && !StopPoint && !RegionStart && !RegionEnd && !Declare)
104    return true;
105
106  std::vector<GlobalVariable*> DeadGlobals;
107
108  // Remove all of the calls to the debugger intrinsics, and remove them from
109  // the module.
110  if (FuncStart) {
111    while (!FuncStart->use_empty()) {
112      CallInst *CI = cast<CallInst>(FuncStart->use_back());
113      Value *Arg = CI->getOperand(1);
114      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
115      CI->eraseFromParent();
116      if (Arg->use_empty())
117        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
118          DeadGlobals.push_back(GV);
119    }
120    FuncStart->eraseFromParent();
121  }
122  if (StopPoint) {
123    while (!StopPoint->use_empty()) {
124      CallInst *CI = cast<CallInst>(StopPoint->use_back());
125      Value *Arg = CI->getOperand(3);
126      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
127      CI->eraseFromParent();
128      if (Arg->use_empty())
129        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
130          DeadGlobals.push_back(GV);
131    }
132    StopPoint->eraseFromParent();
133  }
134  if (RegionStart) {
135    while (!RegionStart->use_empty()) {
136      CallInst *CI = cast<CallInst>(RegionStart->use_back());
137      Value *Arg = CI->getOperand(1);
138      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
139      CI->eraseFromParent();
140      if (Arg->use_empty())
141        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
142          DeadGlobals.push_back(GV);
143    }
144    RegionStart->eraseFromParent();
145  }
146  if (RegionEnd) {
147    while (!RegionEnd->use_empty()) {
148      CallInst *CI = cast<CallInst>(RegionEnd->use_back());
149      Value *Arg = CI->getOperand(1);
150      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
151      CI->eraseFromParent();
152      if (Arg->use_empty())
153        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
154          DeadGlobals.push_back(GV);
155    }
156    RegionEnd->eraseFromParent();
157  }
158  if (Declare) {
159    while (!Declare->use_empty()) {
160      CallInst *CI = cast<CallInst>(Declare->use_back());
161      Value *Arg = CI->getOperand(2);
162      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
163      CI->eraseFromParent();
164      if (Arg->use_empty())
165        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
166          DeadGlobals.push_back(GV);
167    }
168    Declare->eraseFromParent();
169  }
170
171  // Finally, delete any internal globals that were only used by the debugger
172  // intrinsics.
173  while (!DeadGlobals.empty()) {
174    GlobalVariable *GV = DeadGlobals.back();
175    DeadGlobals.pop_back();
176    if (GV->hasInternalLinkage())
177      RemoveDeadConstant(GV);
178  }
179
180  return true;
181}
182