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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/Module.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Analysis/DebugInfo.h"
30 #include "llvm/ValueSymbolTable.h"
31 #include "llvm/Transforms/Utils/Local.h"
32 #include "llvm/ADT/DenseMap.h"
33 #include "llvm/ADT/SmallPtrSet.h"
34 using namespace llvm;
35 
36 namespace {
37   class StripSymbols : public ModulePass {
38     bool OnlyDebugInfo;
39   public:
40     static char ID; // Pass identification, replacement for typeid
StripSymbols(bool ODI=false)41     explicit StripSymbols(bool ODI = false)
42       : ModulePass(ID), OnlyDebugInfo(ODI) {
43         initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
44       }
45 
46     virtual bool runOnModule(Module &M);
47 
getAnalysisUsage(AnalysisUsage & AU) const48     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
49       AU.setPreservesAll();
50     }
51   };
52 
53   class StripNonDebugSymbols : public ModulePass {
54   public:
55     static char ID; // Pass identification, replacement for typeid
StripNonDebugSymbols()56     explicit StripNonDebugSymbols()
57       : ModulePass(ID) {
58         initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
59       }
60 
61     virtual bool runOnModule(Module &M);
62 
getAnalysisUsage(AnalysisUsage & AU) const63     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
64       AU.setPreservesAll();
65     }
66   };
67 
68   class StripDebugDeclare : public ModulePass {
69   public:
70     static char ID; // Pass identification, replacement for typeid
StripDebugDeclare()71     explicit StripDebugDeclare()
72       : ModulePass(ID) {
73         initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
74       }
75 
76     virtual bool runOnModule(Module &M);
77 
getAnalysisUsage(AnalysisUsage & AU) const78     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
79       AU.setPreservesAll();
80     }
81   };
82 
83   class StripDeadDebugInfo : public ModulePass {
84   public:
85     static char ID; // Pass identification, replacement for typeid
StripDeadDebugInfo()86     explicit StripDeadDebugInfo()
87       : ModulePass(ID) {
88         initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
89       }
90 
91     virtual bool runOnModule(Module &M);
92 
getAnalysisUsage(AnalysisUsage & AU) const93     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
94       AU.setPreservesAll();
95     }
96   };
97 }
98 
99 char StripSymbols::ID = 0;
100 INITIALIZE_PASS(StripSymbols, "strip",
101                 "Strip all symbols from a module", false, false)
102 
createStripSymbolsPass(bool OnlyDebugInfo)103 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
104   return new StripSymbols(OnlyDebugInfo);
105 }
106 
107 char StripNonDebugSymbols::ID = 0;
108 INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
109                 "Strip all symbols, except dbg symbols, from a module",
110                 false, false)
111 
createStripNonDebugSymbolsPass()112 ModulePass *llvm::createStripNonDebugSymbolsPass() {
113   return new StripNonDebugSymbols();
114 }
115 
116 char StripDebugDeclare::ID = 0;
117 INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
118                 "Strip all llvm.dbg.declare intrinsics", false, false)
119 
createStripDebugDeclarePass()120 ModulePass *llvm::createStripDebugDeclarePass() {
121   return new StripDebugDeclare();
122 }
123 
124 char StripDeadDebugInfo::ID = 0;
125 INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
126                 "Strip debug info for unused symbols", false, false)
127 
createStripDeadDebugInfoPass()128 ModulePass *llvm::createStripDeadDebugInfoPass() {
129   return new StripDeadDebugInfo();
130 }
131 
132 /// OnlyUsedBy - Return true if V is only used by Usr.
OnlyUsedBy(Value * V,Value * Usr)133 static bool OnlyUsedBy(Value *V, Value *Usr) {
134   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
135     User *U = *I;
136     if (U != Usr)
137       return false;
138   }
139   return true;
140 }
141 
RemoveDeadConstant(Constant * C)142 static void RemoveDeadConstant(Constant *C) {
143   assert(C->use_empty() && "Constant is not dead!");
144   SmallPtrSet<Constant*, 4> Operands;
145   for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
146     if (OnlyUsedBy(C->getOperand(i), C))
147       Operands.insert(cast<Constant>(C->getOperand(i)));
148   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
149     if (!GV->hasLocalLinkage()) return;   // Don't delete non static globals.
150     GV->eraseFromParent();
151   }
152   else if (!isa<Function>(C))
153     if (isa<CompositeType>(C->getType()))
154       C->destroyConstant();
155 
156   // If the constant referenced anything, see if we can delete it as well.
157   for (SmallPtrSet<Constant*, 4>::iterator OI = Operands.begin(),
158          OE = Operands.end(); OI != OE; ++OI)
159     RemoveDeadConstant(*OI);
160 }
161 
162 // Strip the symbol table of its names.
163 //
StripSymtab(ValueSymbolTable & ST,bool PreserveDbgInfo)164 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
165   for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
166     Value *V = VI->getValue();
167     ++VI;
168     if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
169       if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
170         // Set name to "", removing from symbol table!
171         V->setName("");
172     }
173   }
174 }
175 
176 // Strip any named types of their names.
StripTypeNames(Module & M,bool PreserveDbgInfo)177 static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
178   std::vector<StructType*> StructTypes;
179   M.findUsedStructTypes(StructTypes);
180 
181   for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
182     StructType *STy = StructTypes[i];
183     if (STy->isAnonymous() || STy->getName().empty()) continue;
184 
185     if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
186       continue;
187 
188     STy->setName("");
189   }
190 }
191 
192 /// Find values that are marked as llvm.used.
findUsedValues(GlobalVariable * LLVMUsed,SmallPtrSet<const GlobalValue *,8> & UsedValues)193 static void findUsedValues(GlobalVariable *LLVMUsed,
194                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
195   if (LLVMUsed == 0) return;
196   UsedValues.insert(LLVMUsed);
197 
198   ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
199   if (Inits == 0) return;
200 
201   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
202     if (GlobalValue *GV =
203           dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
204       UsedValues.insert(GV);
205 }
206 
207 /// StripSymbolNames - Strip symbol names.
StripSymbolNames(Module & M,bool PreserveDbgInfo)208 static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
209 
210   SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
211   findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
212   findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
213 
214   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
215        I != E; ++I) {
216     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
217       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
218         I->setName("");     // Internal symbols can't participate in linkage
219   }
220 
221   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
222     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
223       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
224         I->setName("");     // Internal symbols can't participate in linkage
225     StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
226   }
227 
228   // Remove all names from types.
229   StripTypeNames(M, PreserveDbgInfo);
230 
231   return true;
232 }
233 
234 // StripDebugInfo - Strip debug info in the module if it exists.
235 // To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and
236 // llvm.dbg.region.end calls, and any globals they point to if now dead.
StripDebugInfo(Module & M)237 static bool StripDebugInfo(Module &M) {
238 
239   bool Changed = false;
240 
241   // Remove all of the calls to the debugger intrinsics, and remove them from
242   // the module.
243   if (Function *Declare = M.getFunction("llvm.dbg.declare")) {
244     while (!Declare->use_empty()) {
245       CallInst *CI = cast<CallInst>(Declare->use_back());
246       CI->eraseFromParent();
247     }
248     Declare->eraseFromParent();
249     Changed = true;
250   }
251 
252   if (Function *DbgVal = M.getFunction("llvm.dbg.value")) {
253     while (!DbgVal->use_empty()) {
254       CallInst *CI = cast<CallInst>(DbgVal->use_back());
255       CI->eraseFromParent();
256     }
257     DbgVal->eraseFromParent();
258     Changed = true;
259   }
260 
261   for (Module::named_metadata_iterator NMI = M.named_metadata_begin(),
262          NME = M.named_metadata_end(); NMI != NME;) {
263     NamedMDNode *NMD = NMI;
264     ++NMI;
265     if (NMD->getName().startswith("llvm.dbg.")) {
266       NMD->eraseFromParent();
267       Changed = true;
268     }
269   }
270 
271   for (Module::iterator MI = M.begin(), ME = M.end(); MI != ME; ++MI)
272     for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE;
273          ++FI)
274       for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE;
275            ++BI) {
276         if (!BI->getDebugLoc().isUnknown()) {
277           Changed = true;
278           BI->setDebugLoc(DebugLoc());
279         }
280       }
281 
282   return Changed;
283 }
284 
runOnModule(Module & M)285 bool StripSymbols::runOnModule(Module &M) {
286   bool Changed = false;
287   Changed |= StripDebugInfo(M);
288   if (!OnlyDebugInfo)
289     Changed |= StripSymbolNames(M, false);
290   return Changed;
291 }
292 
runOnModule(Module & M)293 bool StripNonDebugSymbols::runOnModule(Module &M) {
294   return StripSymbolNames(M, true);
295 }
296 
runOnModule(Module & M)297 bool StripDebugDeclare::runOnModule(Module &M) {
298 
299   Function *Declare = M.getFunction("llvm.dbg.declare");
300   std::vector<Constant*> DeadConstants;
301 
302   if (Declare) {
303     while (!Declare->use_empty()) {
304       CallInst *CI = cast<CallInst>(Declare->use_back());
305       Value *Arg1 = CI->getArgOperand(0);
306       Value *Arg2 = CI->getArgOperand(1);
307       assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
308       CI->eraseFromParent();
309       if (Arg1->use_empty()) {
310         if (Constant *C = dyn_cast<Constant>(Arg1))
311           DeadConstants.push_back(C);
312         else
313           RecursivelyDeleteTriviallyDeadInstructions(Arg1);
314       }
315       if (Arg2->use_empty())
316         if (Constant *C = dyn_cast<Constant>(Arg2))
317           DeadConstants.push_back(C);
318     }
319     Declare->eraseFromParent();
320   }
321 
322   while (!DeadConstants.empty()) {
323     Constant *C = DeadConstants.back();
324     DeadConstants.pop_back();
325     if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
326       if (GV->hasLocalLinkage())
327         RemoveDeadConstant(GV);
328     } else
329       RemoveDeadConstant(C);
330   }
331 
332   return true;
333 }
334 
335 /// getRealLinkageName - If special LLVM prefix that is used to inform the asm
336 /// printer to not emit usual symbol prefix before the symbol name is used then
337 /// return linkage name after skipping this special LLVM prefix.
getRealLinkageName(StringRef LinkageName)338 static StringRef getRealLinkageName(StringRef LinkageName) {
339   char One = '\1';
340   if (LinkageName.startswith(StringRef(&One, 1)))
341     return LinkageName.substr(1);
342   return LinkageName;
343 }
344 
runOnModule(Module & M)345 bool StripDeadDebugInfo::runOnModule(Module &M) {
346   bool Changed = false;
347 
348   // Debugging infomration is encoded in llvm IR using metadata. This is designed
349   // such a way that debug info for symbols preserved even if symbols are
350   // optimized away by the optimizer. This special pass removes debug info for
351   // such symbols.
352 
353   // llvm.dbg.gv keeps track of debug info for global variables.
354   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
355     SmallVector<MDNode *, 8> MDs;
356     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
357       if (DIGlobalVariable(NMD->getOperand(i)).Verify())
358         MDs.push_back(NMD->getOperand(i));
359       else
360         Changed = true;
361     NMD->eraseFromParent();
362     NMD = NULL;
363 
364     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
365            E = MDs.end(); I != E; ++I) {
366       GlobalVariable *GV = DIGlobalVariable(*I).getGlobal();
367       if (GV && M.getGlobalVariable(GV->getName(), true)) {
368         if (!NMD)
369           NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
370         NMD->addOperand(*I);
371       }
372       else
373         Changed = true;
374     }
375   }
376 
377   // llvm.dbg.sp keeps track of debug info for subprograms.
378   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
379     SmallVector<MDNode *, 8> MDs;
380     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
381       if (DISubprogram(NMD->getOperand(i)).Verify())
382         MDs.push_back(NMD->getOperand(i));
383       else
384         Changed = true;
385     NMD->eraseFromParent();
386     NMD = NULL;
387 
388     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
389            E = MDs.end(); I != E; ++I) {
390       bool FnIsLive = false;
391       if (Function *F = DISubprogram(*I).getFunction())
392         if (M.getFunction(F->getName()))
393           FnIsLive = true;
394       if (FnIsLive) {
395           if (!NMD)
396             NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
397           NMD->addOperand(*I);
398       } else {
399         // Remove llvm.dbg.lv.fnname named mdnode which may have been used
400         // to hold debug info for dead function's local variables.
401         StringRef FName = DISubprogram(*I).getLinkageName();
402         if (FName.empty())
403           FName = DISubprogram(*I).getName();
404         if (NamedMDNode *LVNMD =
405             M.getNamedMetadata(Twine("llvm.dbg.lv.",
406                                      getRealLinkageName(FName))))
407           LVNMD->eraseFromParent();
408       }
409     }
410   }
411 
412   return Changed;
413 }
414