StripSymbols.cpp revision 001dbfebcbbded8c8e74b19e838b50da2b6c6fb5 
1//===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
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// The StripSymbols transformation implements code stripping. Specifically, it
11// can delete:
12//
13//   * names for virtual registers
14//   * symbols for internal globals and functions
15//   * debug information
16//
17// Note that this transformation makes code much less readable, so it should
18// only be used in situations where the 'strip' utility would be used, such as
19// reducing code size or making it harder to reverse engineer code.
20//
21//===----------------------------------------------------------------------===//
22
23#include "llvm/Transforms/IPO.h"
24#include "llvm/Constants.h"
25#include "llvm/DerivedTypes.h"
26#include "llvm/Instructions.h"
27#include "llvm/LLVMContext.h"
28#include "llvm/Module.h"
29#include "llvm/Pass.h"
30#include "llvm/Analysis/DebugInfo.h"
31#include "llvm/ValueSymbolTable.h"
32#include "llvm/TypeSymbolTable.h"
33#include "llvm/Transforms/Utils/Local.h"
34#include "llvm/Support/Compiler.h"
35#include "llvm/ADT/SmallPtrSet.h"
36using namespace llvm;
37
38namespace {
39  class VISIBILITY_HIDDEN StripSymbols : public ModulePass {
40    bool OnlyDebugInfo;
41  public:
42    static char ID; // Pass identification, replacement for typeid
43    explicit StripSymbols(bool ODI = false)
44      : ModulePass(&ID), OnlyDebugInfo(ODI) {}
45
46    virtual bool runOnModule(Module &M);
47
48    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
49      AU.setPreservesAll();
50    }
51  };
52
53  class VISIBILITY_HIDDEN StripNonDebugSymbols : public ModulePass {
54  public:
55    static char ID; // Pass identification, replacement for typeid
56    explicit StripNonDebugSymbols()
57      : ModulePass(&ID) {}
58
59    virtual bool runOnModule(Module &M);
60
61    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
62      AU.setPreservesAll();
63    }
64  };
65
66  class VISIBILITY_HIDDEN StripDebugDeclare : public ModulePass {
67  public:
68    static char ID; // Pass identification, replacement for typeid
69    explicit StripDebugDeclare()
70      : ModulePass(&ID) {}
71
72    virtual bool runOnModule(Module &M);
73
74    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
75      AU.setPreservesAll();
76    }
77  };
78}
79
80char StripSymbols::ID = 0;
81static RegisterPass<StripSymbols>
82X("strip", "Strip all symbols from a module");
83
84ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
85  return new StripSymbols(OnlyDebugInfo);
86}
87
88char StripNonDebugSymbols::ID = 0;
89static RegisterPass<StripNonDebugSymbols>
90Y("strip-nondebug", "Strip all symbols, except dbg symbols, from a module");
91
92ModulePass *llvm::createStripNonDebugSymbolsPass() {
93  return new StripNonDebugSymbols();
94}
95
96char StripDebugDeclare::ID = 0;
97static RegisterPass<StripDebugDeclare>
98Z("strip-debug-declare", "Strip all llvm.dbg.declare intrinsics");
99
100ModulePass *llvm::createStripDebugDeclarePass() {
101  return new StripDebugDeclare();
102}
103
104/// OnlyUsedBy - Return true if V is only used by Usr.
105static bool OnlyUsedBy(Value *V, Value *Usr) {
106  for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
107    User *U = *I;
108    if (U != Usr)
109      return false;
110  }
111  return true;
112}
113
114static void RemoveDeadConstant(Constant *C) {
115  assert(C->use_empty() && "Constant is not dead!");
116  SmallPtrSet<Constant *, 4> Operands;
117  for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
118    if (isa<DerivedType>(C->getOperand(i)->getType()) &&
119        OnlyUsedBy(C->getOperand(i), C))
120      Operands.insert(C->getOperand(i));
121  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
122    if (!GV->hasLocalLinkage()) return;   // Don't delete non static globals.
123    GV->eraseFromParent();
124  }
125  else if (!isa<Function>(C))
126    if (isa<CompositeType>(C->getType()))
127      C->destroyConstant();
128
129  // If the constant referenced anything, see if we can delete it as well.
130  for (SmallPtrSet<Constant *, 4>::iterator OI = Operands.begin(),
131         OE = Operands.end(); OI != OE; ++OI)
132    RemoveDeadConstant(*OI);
133}
134
135// Strip the symbol table of its names.
136//
137static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
138  for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
139    Value *V = VI->getValue();
140    ++VI;
141    if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
142      if (!PreserveDbgInfo || strncmp(V->getNameStart(), "llvm.dbg", 8))
143        // Set name to "", removing from symbol table!
144        V->setName("");
145    }
146  }
147}
148
149// Strip the symbol table of its names.
150static void StripTypeSymtab(TypeSymbolTable &ST, bool PreserveDbgInfo) {
151  for (TypeSymbolTable::iterator TI = ST.begin(), E = ST.end(); TI != E; ) {
152    if (PreserveDbgInfo && strncmp(TI->first.c_str(), "llvm.dbg", 8) == 0)
153      ++TI;
154    else
155      ST.remove(TI++);
156  }
157}
158
159/// Find values that are marked as llvm.used.
160void findUsedValues(Module &M,
161                    SmallPtrSet<const GlobalValue*, 8>& llvmUsedValues) {
162  if (GlobalVariable *LLVMUsed = M.getGlobalVariable("llvm.used")) {
163    llvmUsedValues.insert(LLVMUsed);
164    // Collect values that are preserved as per explicit request.
165    // llvm.used is used to list these values.
166    if (ConstantArray *Inits =
167        dyn_cast<ConstantArray>(LLVMUsed->getInitializer())) {
168      for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) {
169        if (GlobalValue *GV = dyn_cast<GlobalValue>(Inits->getOperand(i)))
170          llvmUsedValues.insert(GV);
171        else if (ConstantExpr *CE =
172                 dyn_cast<ConstantExpr>(Inits->getOperand(i)))
173          if (CE->getOpcode() == Instruction::BitCast)
174            if (GlobalValue *GV = dyn_cast<GlobalValue>(CE->getOperand(0)))
175              llvmUsedValues.insert(GV);
176      }
177    }
178  }
179}
180
181/// StripSymbolNames - Strip symbol names.
182bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
183
184  SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
185  findUsedValues(M, llvmUsedValues);
186
187  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
188       I != E; ++I) {
189    if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
190      if (!PreserveDbgInfo || strncmp(I->getNameStart(), "llvm.dbg", 8))
191        I->setName("");     // Internal symbols can't participate in linkage
192  }
193
194  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
195    if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
196      if (!PreserveDbgInfo || strncmp(I->getNameStart(), "llvm.dbg", 8))
197        I->setName("");     // Internal symbols can't participate in linkage
198    StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
199  }
200
201  // Remove all names from types.
202  StripTypeSymtab(M.getTypeSymbolTable(), PreserveDbgInfo);
203
204  return true;
205}
206
207// StripDebugInfo - Strip debug info in the module if it exists.
208// To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and
209// llvm.dbg.region.end calls, and any globals they point to if now dead.
210bool StripDebugInfo(Module &M) {
211
212  SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
213  findUsedValues(M, llvmUsedValues);
214
215  SmallVector<GlobalVariable *, 2> CUs;
216  SmallVector<GlobalVariable *, 4> GVs;
217  SmallVector<GlobalVariable *, 4> SPs;
218  CollectDebugInfoAnchors(M, CUs, GVs, SPs);
219  // These anchors use LinkOnce linkage so that the optimizer does not
220  // remove them accidently. Set InternalLinkage for all these debug
221  // info anchors.
222  for (SmallVector<GlobalVariable *, 2>::iterator I = CUs.begin(),
223         E = CUs.end(); I != E; ++I)
224    (*I)->setLinkage(GlobalValue::InternalLinkage);
225  for (SmallVector<GlobalVariable *, 4>::iterator I = GVs.begin(),
226         E = GVs.end(); I != E; ++I)
227    (*I)->setLinkage(GlobalValue::InternalLinkage);
228  for (SmallVector<GlobalVariable *, 4>::iterator I = SPs.begin(),
229         E = SPs.end(); I != E; ++I)
230    (*I)->setLinkage(GlobalValue::InternalLinkage);
231
232
233 // Delete all dbg variables.
234  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
235       I != E; ++I) {
236    GlobalVariable *GV = dyn_cast<GlobalVariable>(I);
237    if (!GV) continue;
238    if (!GV->use_empty() && llvmUsedValues.count(I) == 0) {
239      if (strncmp(GV->getNameStart(), "llvm.dbg", 8) == 0) {
240        GV->replaceAllUsesWith(M.getContext().getUndef(GV->getType()));
241      }
242    }
243  }
244
245  Function *FuncStart = M.getFunction("llvm.dbg.func.start");
246  Function *StopPoint = M.getFunction("llvm.dbg.stoppoint");
247  Function *RegionStart = M.getFunction("llvm.dbg.region.start");
248  Function *RegionEnd = M.getFunction("llvm.dbg.region.end");
249  Function *Declare = M.getFunction("llvm.dbg.declare");
250
251  std::vector<Constant*> DeadConstants;
252
253  // Remove all of the calls to the debugger intrinsics, and remove them from
254  // the module.
255  if (FuncStart) {
256    while (!FuncStart->use_empty()) {
257      CallInst *CI = cast<CallInst>(FuncStart->use_back());
258      Value *Arg = CI->getOperand(1);
259      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
260      CI->eraseFromParent();
261      if (Arg->use_empty())
262        if (Constant *C = dyn_cast<Constant>(Arg))
263          DeadConstants.push_back(C);
264    }
265    FuncStart->eraseFromParent();
266  }
267  if (StopPoint) {
268    while (!StopPoint->use_empty()) {
269      CallInst *CI = cast<CallInst>(StopPoint->use_back());
270      Value *Arg = CI->getOperand(3);
271      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
272      CI->eraseFromParent();
273      if (Arg->use_empty())
274        if (Constant *C = dyn_cast<Constant>(Arg))
275          DeadConstants.push_back(C);
276    }
277    StopPoint->eraseFromParent();
278  }
279  if (RegionStart) {
280    while (!RegionStart->use_empty()) {
281      CallInst *CI = cast<CallInst>(RegionStart->use_back());
282      Value *Arg = CI->getOperand(1);
283      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
284      CI->eraseFromParent();
285      if (Arg->use_empty())
286        if (Constant *C = dyn_cast<Constant>(Arg))
287          DeadConstants.push_back(C);
288    }
289    RegionStart->eraseFromParent();
290  }
291  if (RegionEnd) {
292    while (!RegionEnd->use_empty()) {
293      CallInst *CI = cast<CallInst>(RegionEnd->use_back());
294      Value *Arg = CI->getOperand(1);
295      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
296      CI->eraseFromParent();
297      if (Arg->use_empty())
298        if (Constant *C = dyn_cast<Constant>(Arg))
299          DeadConstants.push_back(C);
300    }
301    RegionEnd->eraseFromParent();
302  }
303  if (Declare) {
304    while (!Declare->use_empty()) {
305      CallInst *CI = cast<CallInst>(Declare->use_back());
306      Value *Arg1 = CI->getOperand(1);
307      Value *Arg2 = CI->getOperand(2);
308      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
309      CI->eraseFromParent();
310      if (Arg1->use_empty()) {
311        if (Constant *C = dyn_cast<Constant>(Arg1))
312          DeadConstants.push_back(C);
313        else
314          RecursivelyDeleteTriviallyDeadInstructions(Arg1);
315      }
316      if (Arg2->use_empty())
317        if (Constant *C = dyn_cast<Constant>(Arg2))
318          DeadConstants.push_back(C);
319    }
320    Declare->eraseFromParent();
321  }
322
323  // llvm.dbg.compile_units and llvm.dbg.subprograms are marked as linkonce
324  // but since we are removing all debug information, make them internal now.
325  // FIXME: Use private linkage maybe?
326  if (Constant *C = M.getNamedGlobal("llvm.dbg.compile_units"))
327    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
328      GV->setLinkage(GlobalValue::InternalLinkage);
329
330  if (Constant *C = M.getNamedGlobal("llvm.dbg.subprograms"))
331    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
332      GV->setLinkage(GlobalValue::InternalLinkage);
333
334  if (Constant *C = M.getNamedGlobal("llvm.dbg.global_variables"))
335    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
336      GV->setLinkage(GlobalValue::InternalLinkage);
337
338  // Delete all dbg variables.
339  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
340       I != E; ++I) {
341    GlobalVariable *GV = dyn_cast<GlobalVariable>(I);
342    if (!GV) continue;
343    if (GV->use_empty() && llvmUsedValues.count(I) == 0
344        && (!GV->hasSection()
345            || strcmp(GV->getSection().c_str(), "llvm.metadata") == 0))
346      DeadConstants.push_back(GV);
347  }
348
349  if (DeadConstants.empty())
350    return false;
351
352  // Delete any internal globals that were only used by the debugger intrinsics.
353  while (!DeadConstants.empty()) {
354    Constant *C = DeadConstants.back();
355    DeadConstants.pop_back();
356    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
357      if (GV->hasLocalLinkage())
358        RemoveDeadConstant(GV);
359    }
360    else
361      RemoveDeadConstant(C);
362  }
363
364  // Remove all llvm.dbg types.
365  TypeSymbolTable &ST = M.getTypeSymbolTable();
366  for (TypeSymbolTable::iterator TI = ST.begin(), TE = ST.end(); TI != TE; ) {
367    if (!strncmp(TI->first.c_str(), "llvm.dbg.", 9))
368      ST.remove(TI++);
369    else
370      ++TI;
371  }
372
373  return true;
374}
375
376bool StripSymbols::runOnModule(Module &M) {
377  Context = &M.getContext();
378  bool Changed = false;
379  Changed |= StripDebugInfo(M);
380  if (!OnlyDebugInfo)
381    Changed |= StripSymbolNames(M, false);
382  return Changed;
383}
384
385bool StripNonDebugSymbols::runOnModule(Module &M) {
386  return StripSymbolNames(M, true);
387}
388
389bool StripDebugDeclare::runOnModule(Module &M) {
390
391  Function *Declare = M.getFunction("llvm.dbg.declare");
392  std::vector<Constant*> DeadConstants;
393
394  if (Declare) {
395    while (!Declare->use_empty()) {
396      CallInst *CI = cast<CallInst>(Declare->use_back());
397      Value *Arg1 = CI->getOperand(1);
398      Value *Arg2 = CI->getOperand(2);
399      assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
400      CI->eraseFromParent();
401      if (Arg1->use_empty()) {
402        if (Constant *C = dyn_cast<Constant>(Arg1))
403          DeadConstants.push_back(C);
404        else
405          RecursivelyDeleteTriviallyDeadInstructions(Arg1);
406      }
407      if (Arg2->use_empty())
408        if (Constant *C = dyn_cast<Constant>(Arg2))
409          DeadConstants.push_back(C);
410    }
411    Declare->eraseFromParent();
412  }
413
414  // Delete all llvm.dbg.global_variables.
415  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
416       I != E; ++I) {
417    GlobalVariable *GV = dyn_cast<GlobalVariable>(I);
418    if (!GV) continue;
419    if (GV->use_empty() && GV->hasName()
420        && strncmp(GV->getNameStart(), "llvm.dbg.global_variable", 24) == 0)
421      DeadConstants.push_back(GV);
422  }
423
424  while (!DeadConstants.empty()) {
425    Constant *C = DeadConstants.back();
426    DeadConstants.pop_back();
427    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
428      if (GV->hasLocalLinkage())
429        RemoveDeadConstant(GV);
430    }
431    else
432      RemoveDeadConstant(C);
433  }
434
435  return true;
436}
437