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[msan] Put msan constructor in a comdat.

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MSan adds a constructor to each translation unit that calls
__msan_init, and does nothing else. The idea is to run __msan_init
before any instrumented code. This results in multiple constructors
and multiple .init_array entries in the final binary, one per
translation unit. This is absolutely unnecessary; one would be
enough.

This change moves the constructors to a comdat group in order to drop
the extra ones.

llvm-svn: 260632
This commit is contained in:
Evgeniy Stepanov
2016-02-12 00:37:52 +00:00
parent 0466c7ce23
commit ba6ca87ffb
5 changed files with 51 additions and 18 deletions
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37
llvm/lib/Transforms/Utils/ModuleUtils.cpp
View File

@@ -21,8 +21,8 @@
using namespace llvm;
static void appendToGlobalArray(const char *Array,
Module &M, Function *F, int Priority) {
static void appendToGlobalArray(const char *Array, Module &M, Function *F,
int Priority, Constant *Data) {
IRBuilder<> IRB(M.getContext());
FunctionType *FnTy = FunctionType::get(IRB.getVoidTy(), false);
@@ -31,15 +31,26 @@ static void appendToGlobalArray(const char *Array,
SmallVector<Constant *, 16> CurrentCtors;
StructType *EltTy;
if (GlobalVariable *GVCtor = M.getNamedGlobal(Array)) {
// If there is a global_ctors array, use the existing struct type, which can
// have 2 or 3 fields.
ArrayType *ATy = cast<ArrayType>(GVCtor->getValueType());
EltTy = cast<StructType>(ATy->getElementType());
StructType *OldEltTy = cast<StructType>(ATy->getElementType());
// Upgrade a 2-field global array type to the new 3-field format if needed.
if (Data && OldEltTy->getNumElements() < 3)
EltTy = StructType::get(IRB.getInt32Ty(), PointerType::getUnqual(FnTy),
IRB.getInt8PtrTy(), nullptr);
else
EltTy = OldEltTy;
if (Constant *Init = GVCtor->getInitializer()) {
unsigned n = Init->getNumOperands();
CurrentCtors.reserve(n + 1);
for (unsigned i = 0; i != n; ++i)
CurrentCtors.push_back(cast<Constant>(Init->getOperand(i)));
for (unsigned i = 0; i != n; ++i) {
auto Ctor = cast<Constant>(Init->getOperand(i));
if (EltTy != OldEltTy)
Ctor = ConstantStruct::get(
EltTy, Ctor->getAggregateElement((unsigned)0),
Ctor->getAggregateElement(1),
Constant::getNullValue(IRB.getInt8PtrTy()), nullptr);
CurrentCtors.push_back(Ctor);
}
}
GVCtor->eraseFromParent();
} else {
@@ -54,7 +65,8 @@ static void appendToGlobalArray(const char *Array,
CSVals[1] = F;
// FIXME: Drop support for the two element form in LLVM 4.0.
if (EltTy->getNumElements() >= 3)
CSVals[2] = llvm::Constant::getNullValue(IRB.getInt8PtrTy());
CSVals[2] = Data ? ConstantExpr::getPointerCast(Data, IRB.getInt8PtrTy())
: Constant::getNullValue(IRB.getInt8PtrTy());
Constant *RuntimeCtorInit =
ConstantStruct::get(EltTy, makeArrayRef(CSVals, EltTy->getNumElements()));
@@ -70,12 +82,12 @@ static void appendToGlobalArray(const char *Array,
GlobalValue::AppendingLinkage, NewInit, Array);
}
void llvm::appendToGlobalCtors(Module &M, Function *F, int Priority) {
appendToGlobalArray("llvm.global_ctors", M, F, Priority);
void llvm::appendToGlobalCtors(Module &M, Function *F, int Priority, Constant *Data) {
appendToGlobalArray("llvm.global_ctors", M, F, Priority, Data);
}
void llvm::appendToGlobalDtors(Module &M, Function *F, int Priority) {
appendToGlobalArray("llvm.global_dtors", M, F, Priority);
void llvm::appendToGlobalDtors(Module &M, Function *F, int Priority, Constant *Data) {
appendToGlobalArray("llvm.global_dtors", M, F, Priority, Data);
}
GlobalVariable *
@@ -132,4 +144,3 @@ std::pair<Function *, Function *> llvm::createSanitizerCtorAndInitFunctions(
}
return std::make_pair(Ctor, InitFunction);
}