//===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The StripSymbols transformation implements code stripping. Specifically, it
// can delete:
//
// * names for virtual registers
// * symbols for internal globals and functions
// * debug information
//
// Note that this transformation makes code much less readable, so it should
// only be used in situations where the 'strip' utility would be used, such as
// reducing code size or making it harder to reverse engineer code.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/TypeFinder.h"
#include "llvm/IR/ValueSymbolTable.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
namespace {
class StripSymbols : public ModulePass {
bool OnlyDebugInfo;
public:
static char ID; // Pass identification, replacement for typeid
explicit StripSymbols(bool ODI = false)
: ModulePass(ID), OnlyDebugInfo(ODI) {
initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesAll();
}
};
class StripNonDebugSymbols : public ModulePass {
public:
static char ID; // Pass identification, replacement for typeid
explicit StripNonDebugSymbols()
: ModulePass(ID) {
initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesAll();
}
};
class StripDebugDeclare : public ModulePass {
public:
static char ID; // Pass identification, replacement for typeid
explicit StripDebugDeclare()
: ModulePass(ID) {
initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesAll();
}
};
class StripDeadDebugInfo : public ModulePass {
public:
static char ID; // Pass identification, replacement for typeid
explicit StripDeadDebugInfo()
: ModulePass(ID) {
initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesAll();
}
};
}
char StripSymbols::ID = 0;
INITIALIZE_PASS(StripSymbols, "strip",
"Strip all symbols from a module", false, false)
ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
return new StripSymbols(OnlyDebugInfo);
}
char StripNonDebugSymbols::ID = 0;
INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
"Strip all symbols, except dbg symbols, from a module",
false, false)
ModulePass *llvm::createStripNonDebugSymbolsPass() {
return new StripNonDebugSymbols();
}
char StripDebugDeclare::ID = 0;
INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
"Strip all llvm.dbg.declare intrinsics", false, false)
ModulePass *llvm::createStripDebugDeclarePass() {
return new StripDebugDeclare();
}
char StripDeadDebugInfo::ID = 0;
INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
"Strip debug info for unused symbols", false, false)
ModulePass *llvm::createStripDeadDebugInfoPass() {
return new StripDeadDebugInfo();
}
/// OnlyUsedBy - Return true if V is only used by Usr.
static bool OnlyUsedBy(Value *V, Value *Usr) {
for (User *U : V->users())
if (U != Usr)
return false;
return true;
}
static void RemoveDeadConstant(Constant *C) {
assert(C->use_empty() && "Constant is not dead!");
SmallPtrSet<Constant*, 4> Operands;
for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
if (OnlyUsedBy(C->getOperand(i), C))
Operands.insert(cast<Constant>(C->getOperand(i)));
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
if (!GV->hasLocalLinkage()) return; // Don't delete non-static globals.
GV->eraseFromParent();
}
else if (!isa<Function>(C))
if (isa<CompositeType>(C->getType()))
C->destroyConstant();
// If the constant referenced anything, see if we can delete it as well.
for (SmallPtrSet<Constant*, 4>::iterator OI = Operands.begin(),
OE = Operands.end(); OI != OE; ++OI)
RemoveDeadConstant(*OI);
}
// Strip the symbol table of its names.
//
static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
Value *V = VI->getValue();
++VI;
if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
// Set name to "", removing from symbol table!
V->setName("");
}
}
}
// Strip any named types of their names.
static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
TypeFinder StructTypes;
StructTypes.run(M, false);
for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
StructType *STy = StructTypes[i];
if (STy->isLiteral() || STy->getName().empty()) continue;
if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
continue;
STy->setName("");
}
}
/// Find values that are marked as llvm.used.
static void findUsedValues(GlobalVariable *LLVMUsed,
SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
if (!LLVMUsed) return;
UsedValues.insert(LLVMUsed);
ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
if (GlobalValue *GV =
dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
UsedValues.insert(GV);
}
/// StripSymbolNames - Strip symbol names.
static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I) {
if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
I->setName(""); // Internal symbols can't participate in linkage
}
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
I->setName(""); // Internal symbols can't participate in linkage
StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
}
// Remove all names from types.
StripTypeNames(M, PreserveDbgInfo);
return true;
}
bool StripSymbols::runOnModule(Module &M) {
bool Changed = false;
Changed |= StripDebugInfo(M);
if (!OnlyDebugInfo)
Changed |= StripSymbolNames(M, false);
return Changed;
}
bool StripNonDebugSymbols::runOnModule(Module &M) {
return StripSymbolNames(M, true);
}
bool StripDebugDeclare::runOnModule(Module &M) {
Function *Declare = M.getFunction("llvm.dbg.declare");
std::vector<Constant*> DeadConstants;
if (Declare) {
while (!Declare->use_empty()) {
CallInst *CI = cast<CallInst>(Declare->user_back());
Value *Arg1 = CI->getArgOperand(0);
Value *Arg2 = CI->getArgOperand(1);
assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
CI->eraseFromParent();
if (Arg1->use_empty()) {
if (Constant *C = dyn_cast<Constant>(Arg1))
DeadConstants.push_back(C);
else
RecursivelyDeleteTriviallyDeadInstructions(Arg1);
}
if (Arg2->use_empty())
if (Constant *C = dyn_cast<Constant>(Arg2))
DeadConstants.push_back(C);
}
Declare->eraseFromParent();
}
while (!DeadConstants.empty()) {
Constant *C = DeadConstants.back();
DeadConstants.pop_back();
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
if (GV->hasLocalLinkage())
RemoveDeadConstant(GV);
} else
RemoveDeadConstant(C);
}
return true;
}
/// Remove any debug info for global variables/functions in the given module for
/// which said global variable/function no longer exists (i.e. is null).
///
/// Debugging information is encoded in llvm IR using metadata. This is designed
/// such a way that debug info for symbols preserved even if symbols are
/// optimized away by the optimizer. This special pass removes debug info for
/// such symbols.
bool StripDeadDebugInfo::runOnModule(Module &M) {
bool Changed = false;
LLVMContext &C = M.getContext();
// Find all debug info in F. This is actually overkill in terms of what we
// want to do, but we want to try and be as resilient as possible in the face
// of potential debug info changes by using the formal interfaces given to us
// as much as possible.
DebugInfoFinder F;
F.processModule(M);
// For each compile unit, find the live set of global variables/functions and
// replace the current list of potentially dead global variables/functions
// with the live list.
SmallVector<Value *, 64> LiveGlobalVariables;
SmallVector<Value *, 64> LiveSubprograms;
DenseSet<const MDNode *> VisitedSet;
for (DICompileUnit DIC : F.compile_units()) {
assert(DIC.Verify() && "DIC must verify as a DICompileUnit.");
// Create our live subprogram list.
DIArray SPs = DIC.getSubprograms();
bool SubprogramChange = false;
for (unsigned i = 0, e = SPs.getNumElements(); i != e; ++i) {
DISubprogram DISP(SPs.getElement(i));
assert(DISP.Verify() && "DISP must verify as a DISubprogram.");
// Make sure we visit each subprogram only once.
if (!VisitedSet.insert(DISP).second)
continue;
// If the function referenced by DISP is not null, the function is live.
if (DISP.getFunction())
LiveSubprograms.push_back(DISP);
else
SubprogramChange = true;
}
// Create our live global variable list.
DIArray GVs = DIC.getGlobalVariables();
bool GlobalVariableChange = false;
for (unsigned i = 0, e = GVs.getNumElements(); i != e; ++i) {
DIGlobalVariable DIG(GVs.getElement(i));
assert(DIG.Verify() && "DIG must verify as DIGlobalVariable.");
// Make sure we only visit each global variable only once.
if (!VisitedSet.insert(DIG).second)
continue;
// If the global variable referenced by DIG is not null, the global
// variable is live.
if (DIG.getGlobal())
LiveGlobalVariables.push_back(DIG);
else
GlobalVariableChange = true;
}
// If we found dead subprograms or global variables, replace the current
// subprogram list/global variable list with our new live subprogram/global
// variable list.
if (SubprogramChange) {
// Make sure that 9 is still the index of the subprograms. This is to make
// sure that an assert is hit if the location of the subprogram array
// changes. This is just to make sure that this is updated if such an
// event occurs.
assert(DIC->getNumOperands() >= 10 &&
SPs == DIC->getOperand(9) &&
"DICompileUnits is expected to store Subprograms in operand "
"9.");
DIC->replaceOperandWith(9, MDNode::get(C, LiveSubprograms));
Changed = true;
}
if (GlobalVariableChange) {
// Make sure that 10 is still the index of global variables. This is to
// make sure that an assert is hit if the location of the subprogram array
// changes. This is just to make sure that this index is updated if such
// an event occurs.
assert(DIC->getNumOperands() >= 11 &&
GVs == DIC->getOperand(10) &&
"DICompileUnits is expected to store Global Variables in operand "
"10.");
DIC->replaceOperandWith(10, MDNode::get(C, LiveGlobalVariables));
Changed = true;
}
// Reset lists for the next iteration.
LiveSubprograms.clear();
LiveGlobalVariables.clear();
}
return Changed;
}