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Diffstat (limited to 'lib/Transforms/NaCl/ExpandTls.cpp')
| -rw-r--r-- | lib/Transforms/NaCl/ExpandTls.cpp | 351 |
1 files changed, 351 insertions, 0 deletions
diff --git a/lib/Transforms/NaCl/ExpandTls.cpp b/lib/Transforms/NaCl/ExpandTls.cpp new file mode 100644 index 0000000000..8ce439c018 --- /dev/null +++ b/lib/Transforms/NaCl/ExpandTls.cpp @@ -0,0 +1,351 @@ +//===- ExpandTls.cpp - Convert TLS variables to a concrete layout----------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This pass expands out uses of thread-local (TLS) variables into +// more primitive operations. +// +// A reference to the address of a TLS variable is expanded into code +// which gets the current thread's thread pointer using +// @llvm.nacl.read.tp() and adds a fixed offset. +// +// This pass allocates the offsets (relative to the thread pointer) +// that will be used for TLS variables. It sets up the global +// variables __tls_template_start, __tls_template_end etc. to contain +// a template for initializing TLS variables' values for each thread. +// This is a task normally performed by the linker in ELF systems. +// +//===----------------------------------------------------------------------===// + +#include <vector> + +#include "llvm/Constants.h" +#include "llvm/DataLayout.h" +#include "llvm/DerivedTypes.h" +#include "llvm/Instructions.h" +#include "llvm/Module.h" +#include "llvm/Pass.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/NaCl.h" + +using namespace llvm; + +namespace { + struct VarInfo { + GlobalVariable *TlsVar; + bool IsBss; // Whether variable is in zero-intialized part of template + int TemplateIndex; + }; + + class PassState { + public: + PassState(Module *M): M(M), DL(M), Offset(0), Alignment(1) {} + + Module *M; + DataLayout DL; + uint64_t Offset; + // 'Alignment' is the maximum variable alignment seen so far, in + // bytes. After visiting all TLS variables, this is the overall + // alignment required for the TLS template. + uint32_t Alignment; + }; + + class ExpandTls : public ModulePass { + public: + static char ID; // Pass identification, replacement for typeid + ExpandTls() : ModulePass(ID) { + initializeExpandTlsPass(*PassRegistry::getPassRegistry()); + } + + virtual bool runOnModule(Module &M); + }; +} + +char ExpandTls::ID = 0; +INITIALIZE_PASS(ExpandTls, "nacl-expand-tls", + "Expand out TLS variables and fix TLS variable layout", + false, false) + +static void setGlobalVariableValue(Module &M, const char *Name, + Constant *Value) { + GlobalVariable *Var = M.getNamedGlobal(Name); + if (!Var) { + // This warning can happen in a program that does not use a libc + // and does not initialize TLS variables. Such a program might be + // linked with "-nostdlib". + errs() << "Warning: Variable " << Name << " not referenced\n"; + } else { + if (Var->hasInitializer()) { + report_fatal_error(std::string("Variable ") + Name + + " already has an initializer"); + } + Var->replaceAllUsesWith(ConstantExpr::getBitCast(Value, Var->getType())); + Var->eraseFromParent(); + } +} + +// Insert alignment padding into the TLS template. +static void padToAlignment(PassState *State, + std::vector<Type*> *FieldTypes, + std::vector<Constant*> *FieldValues, + unsigned Alignment) { + if ((State->Offset & (Alignment - 1)) != 0) { + unsigned PadSize = Alignment - (State->Offset & (Alignment - 1)); + Type *i8 = Type::getInt8Ty(State->M->getContext()); + Type *PadType = ArrayType::get(i8, PadSize); + FieldTypes->push_back(PadType); + if (FieldValues) + FieldValues->push_back(Constant::getNullValue(PadType)); + State->Offset += PadSize; + } + if (State->Alignment < Alignment) { + State->Alignment = Alignment; + } +} + +static void addVarToTlsTemplate(PassState *State, + std::vector<Type*> *FieldTypes, + std::vector<Constant*> *FieldValues, + GlobalVariable *TlsVar) { + unsigned Alignment = State->DL.getPreferredAlignment(TlsVar); + padToAlignment(State, FieldTypes, FieldValues, Alignment); + + FieldTypes->push_back(TlsVar->getType()->getElementType()); + if (FieldValues) + FieldValues->push_back(TlsVar->getInitializer()); + State->Offset += + State->DL.getTypeAllocSize(TlsVar->getType()->getElementType()); +} + +static PointerType *buildTlsTemplate(Module &M, std::vector<VarInfo> *TlsVars) { + std::vector<Type*> FieldBssTypes; + std::vector<Type*> FieldInitTypes; + std::vector<Constant*> FieldInitValues; + PassState State(&M); + + for (Module::global_iterator GV = M.global_begin(); + GV != M.global_end(); + ++GV) { + if (GV->isThreadLocal()) { + if (!GV->hasInitializer()) { + // Since this is a whole-program transformation, "extern" TLS + // variables are not allowed at this point. + report_fatal_error(std::string("TLS variable without an initializer: ") + + GV->getName()); + } + if (!GV->getInitializer()->isNullValue()) { + addVarToTlsTemplate(&State, &FieldInitTypes, + &FieldInitValues, GV); + VarInfo Info; + Info.TlsVar = GV; + Info.IsBss = false; + Info.TemplateIndex = FieldInitTypes.size() - 1; + TlsVars->push_back(Info); + } + } + } + // Handle zero-initialized TLS variables in a second pass, because + // these should follow non-zero-initialized TLS variables. + for (Module::global_iterator GV = M.global_begin(); + GV != M.global_end(); + ++GV) { + if (GV->isThreadLocal() && GV->getInitializer()->isNullValue()) { + addVarToTlsTemplate(&State, &FieldBssTypes, NULL, GV); + VarInfo Info; + Info.TlsVar = GV; + Info.IsBss = true; + Info.TemplateIndex = FieldBssTypes.size() - 1; + TlsVars->push_back(Info); + } + } + // Add final alignment padding so that + // (struct tls_struct *) __nacl_read_tp() - 1 + // gives the correct, aligned start of the TLS variables given the + // x86-style layout we are using. This requires some more bytes to + // be memset() to zero at runtime. This wastage doesn't seem + // important gives that we're not trying to optimize packing by + // reordering to put similarly-aligned variables together. + padToAlignment(&State, &FieldBssTypes, NULL, State.Alignment); + + // We create the TLS template structs as "packed" because we insert + // alignment padding ourselves, and LLVM's implicit insertion of + // padding would interfere with ours. tls_bss_template can start at + // a non-aligned address immediately following the last field in + // tls_init_template. + StructType *InitTemplateType = + StructType::create(M.getContext(), "tls_init_template"); + InitTemplateType->setBody(FieldInitTypes, /*isPacked=*/true); + StructType *BssTemplateType = + StructType::create(M.getContext(), "tls_bss_template"); + BssTemplateType->setBody(FieldBssTypes, /*isPacked=*/true); + + StructType *TemplateType = StructType::create(M.getContext(), "tls_struct"); + SmallVector<Type*, 2> TemplateTopFields; + TemplateTopFields.push_back(InitTemplateType); + TemplateTopFields.push_back(BssTemplateType); + TemplateType->setBody(TemplateTopFields, /*isPacked=*/true); + PointerType *TemplatePtrType = PointerType::get(TemplateType, 0); + + // We define the following symbols, which are the same as those + // defined by NaCl's original customized binutils linker scripts: + // __tls_template_start + // __tls_template_tdata_end + // __tls_template_end + // We also define __tls_template_alignment, which was not defined by + // the original linker scripts. + + const char *StartSymbol = "__tls_template_start"; + Constant *TemplateData = ConstantStruct::get(InitTemplateType, + FieldInitValues); + GlobalVariable *TemplateDataVar = + new GlobalVariable(M, InitTemplateType, /*isConstant=*/true, + GlobalValue::InternalLinkage, TemplateData); + setGlobalVariableValue(M, StartSymbol, TemplateDataVar); + TemplateDataVar->setName(StartSymbol); + + Constant *TdataEnd = ConstantExpr::getGetElementPtr( + TemplateDataVar, + ConstantInt::get(M.getContext(), APInt(32, 1))); + setGlobalVariableValue(M, "__tls_template_tdata_end", TdataEnd); + + Constant *TotalEnd = ConstantExpr::getGetElementPtr( + ConstantExpr::getBitCast(TemplateDataVar, TemplatePtrType), + ConstantInt::get(M.getContext(), APInt(32, 1))); + setGlobalVariableValue(M, "__tls_template_end", TotalEnd); + + const char *AlignmentSymbol = "__tls_template_alignment"; + Type *i32 = Type::getInt32Ty(M.getContext()); + GlobalVariable *AlignmentVar = new GlobalVariable( + M, i32, /*isConstant=*/true, + GlobalValue::InternalLinkage, + ConstantInt::get(M.getContext(), APInt(32, State.Alignment))); + setGlobalVariableValue(M, AlignmentSymbol, AlignmentVar); + AlignmentVar->setName(AlignmentSymbol); + + return TemplatePtrType; +} + +static void rewriteTlsVars(Module &M, std::vector<VarInfo> *TlsVars, + PointerType *TemplatePtrType) { + // Set up the intrinsic that reads the thread pointer. + Type *i8 = Type::getInt8Ty(M.getContext()); + FunctionType *ReadTpType = FunctionType::get(PointerType::get(i8, 0), + /*isVarArg=*/false); + AttrBuilder B; + B.addAttribute(Attributes::ReadOnly); + B.addAttribute(Attributes::NoUnwind); + AttrListPtr ReadTpAttrs = AttrListPtr().addAttr( + M.getContext(), AttrListPtr::FunctionIndex, + Attributes::get(M.getContext(), B)); + Constant *ReadTpFunc = M.getOrInsertTargetIntrinsic("llvm.nacl.read.tp", + ReadTpType, + ReadTpAttrs); + + for (std::vector<VarInfo>::iterator VarInfo = TlsVars->begin(); + VarInfo != TlsVars->end(); + ++VarInfo) { + GlobalVariable *Var = VarInfo->TlsVar; + while (!Var->use_empty()) { + Instruction *U = cast<Instruction>(*Var->use_begin()); + Instruction *InsertPt = U; + if (PHINode *PN = dyn_cast<PHINode>(InsertPt)) { + // We cannot insert instructions before a PHI node, so insert + // before the incoming block's terminator. Note that if the + // terminator is conditional, this could be suboptimal, + // because we might be calling ReadTpFunc unnecessarily. + InsertPt = PN->getIncomingBlock(Var->use_begin())->getTerminator(); + } + Value *RawThreadPtr = CallInst::Create(ReadTpFunc, "tls_raw", InsertPt); + Value *TypedThreadPtr = new BitCastInst(RawThreadPtr, TemplatePtrType, + "tls_struct", InsertPt); + SmallVector<Value*, 3> Indexes; + // We use -1 because we use the x86-style TLS layout in which + // the TLS data is stored at addresses below the thread pointer. + // This is largely because a check in nacl_irt_thread_create() + // in irt/irt_thread.c requires the thread pointer to be a + // self-pointer on x86-32. + // TODO(mseaborn): I intend to remove that check because it is + // non-portable. In the mean time, we want PNaCl pexes to work + // in older Chromium releases when translated to nexes. + Indexes.push_back(ConstantInt::get( + M.getContext(), APInt(32, -1))); + Indexes.push_back(ConstantInt::get( + M.getContext(), APInt(32, VarInfo->IsBss ? 1 : 0))); + Indexes.push_back(ConstantInt::get( + M.getContext(), APInt(32, VarInfo->TemplateIndex))); + Value *TlsField = GetElementPtrInst::Create(TypedThreadPtr, Indexes, + "field", InsertPt); + U->replaceUsesOfWith(Var, TlsField); + } + VarInfo->TlsVar->eraseFromParent(); + } +} + +// Provide fixed definitions for PNaCl's TLS layout intrinsics. We +// adopt the x86-style layout: ExpandTls will output a program that +// uses the x86-style layout wherever it runs. This overrides any +// architecture-specific definitions of the intrinsics that the LLVM +// backend might provide. +static void defineTlsLayoutIntrinsics(Module &M) { + Type *i32 = Type::getInt32Ty(M.getContext()); + SmallVector<Type*, 1> ArgTypes; + ArgTypes.push_back(i32); + FunctionType *FuncType = FunctionType::get(i32, ArgTypes, /*isVarArg=*/false); + Function *NewFunc; + BasicBlock *BB; + + // Define the intrinsic as follows: + // uint32_t __nacl_tp_tdb_offset(uint32_t tdb_size) { + // return 0; + // } + // This means the thread pointer points to the TDB. + NewFunc = Function::Create(FuncType, GlobalValue::InternalLinkage, + "nacl_tp_tdb_offset", &M); + BB = BasicBlock::Create(M.getContext(), "entry", NewFunc); + ReturnInst::Create(M.getContext(), + ConstantInt::get(M.getContext(), APInt(32, 0)), BB); + if (Function *Intrinsic = M.getFunction("llvm.nacl.tp.tdb.offset")) { + Intrinsic->replaceAllUsesWith(NewFunc); + Intrinsic->eraseFromParent(); + } + + // Define the intrinsic as follows: + // uint32_t __nacl_tp_tls_offset(uint32_t tls_size) { + // return -tls_size; + // } + // This means the TLS variables are stored below the thread pointer. + NewFunc = Function::Create(FuncType, GlobalValue::InternalLinkage, + "nacl_tp_tls_offset", &M); + BB = BasicBlock::Create(M.getContext(), "entry", NewFunc); + Value *Arg = NewFunc->arg_begin(); + Arg->setName("size"); + Value *Result = BinaryOperator::CreateNeg(Arg, "result", BB); + ReturnInst::Create(M.getContext(), Result, BB); + if (Function *Intrinsic = M.getFunction("llvm.nacl.tp.tls.offset")) { + Intrinsic->replaceAllUsesWith(NewFunc); + Intrinsic->eraseFromParent(); + } +} + +bool ExpandTls::runOnModule(Module &M) { + ModulePass *Pass = createExpandTlsConstantExprPass(); + Pass->runOnModule(M); + delete Pass; + + std::vector<VarInfo> TlsVars; + PointerType *TemplatePtrType = buildTlsTemplate(M, &TlsVars); + rewriteTlsVars(M, &TlsVars, TemplatePtrType); + + defineTlsLayoutIntrinsics(M); + + return true; +} + +ModulePass *llvm::createExpandTlsPass() { + return new ExpandTls(); +} |