llvm-project/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp

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//===-- AArch64TargetMachine.cpp - Define TargetMachine for AArch64 -------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//
//===----------------------------------------------------------------------===//
#include "AArch64TargetMachine.h"
#include "AArch64.h"
#include "AArch64MacroFusion.h"
#include "AArch64Subtarget.h"
#include "AArch64TargetObjectFile.h"
#include "AArch64TargetTransformInfo.h"
#include "MCTargetDesc/AArch64MCTargetDesc.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/CodeGen/CSEConfigBase.h"
#include "llvm/CodeGen/GlobalISel/IRTranslator.h"
#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
#include "llvm/CodeGen/GlobalISel/Legalizer.h"
#include "llvm/CodeGen/GlobalISel/Localizer.h"
#include "llvm/CodeGen/GlobalISel/RegBankSelect.h"
#include "llvm/CodeGen/MachineScheduler.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Pass.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Transforms/Scalar.h"
#include <memory>
#include <string>
using namespace llvm;
static cl::opt<bool> EnableCCMP("aarch64-enable-ccmp",
cl::desc("Enable the CCMP formation pass"),
cl::init(true), cl::Hidden);
static cl::opt<bool>
EnableCondBrTuning("aarch64-enable-cond-br-tune",
cl::desc("Enable the conditional branch tuning pass"),
cl::init(true), cl::Hidden);
static cl::opt<bool> EnableMCR("aarch64-enable-mcr",
cl::desc("Enable the machine combiner pass"),
cl::init(true), cl::Hidden);
static cl::opt<bool> EnableStPairSuppress("aarch64-enable-stp-suppress",
cl::desc("Suppress STP for AArch64"),
cl::init(true), cl::Hidden);
static cl::opt<bool> EnableAdvSIMDScalar(
"aarch64-enable-simd-scalar",
cl::desc("Enable use of AdvSIMD scalar integer instructions"),
cl::init(false), cl::Hidden);
static cl::opt<bool>
EnablePromoteConstant("aarch64-enable-promote-const",
cl::desc("Enable the promote constant pass"),
cl::init(true), cl::Hidden);
static cl::opt<bool> EnableCollectLOH(
"aarch64-enable-collect-loh",
cl::desc("Enable the pass that emits the linker optimization hints (LOH)"),
cl::init(true), cl::Hidden);
static cl::opt<bool>
EnableDeadRegisterElimination("aarch64-enable-dead-defs", cl::Hidden,
cl::desc("Enable the pass that removes dead"
" definitons and replaces stores to"
" them with stores to the zero"
" register"),
cl::init(true));
static cl::opt<bool> EnableRedundantCopyElimination(
"aarch64-enable-copyelim",
cl::desc("Enable the redundant copy elimination pass"), cl::init(true),
cl::Hidden);
static cl::opt<bool> EnableLoadStoreOpt("aarch64-enable-ldst-opt",
cl::desc("Enable the load/store pair"
" optimization pass"),
cl::init(true), cl::Hidden);
static cl::opt<bool> EnableAtomicTidy(
"aarch64-enable-atomic-cfg-tidy", cl::Hidden,
cl::desc("Run SimplifyCFG after expanding atomic operations"
" to make use of cmpxchg flow-based information"),
cl::init(true));
static cl::opt<bool>
EnableEarlyIfConversion("aarch64-enable-early-ifcvt", cl::Hidden,
cl::desc("Run early if-conversion"),
cl::init(true));
static cl::opt<bool>
EnableCondOpt("aarch64-enable-condopt",
cl::desc("Enable the condition optimizer pass"),
cl::init(true), cl::Hidden);
static cl::opt<bool>
EnableA53Fix835769("aarch64-fix-cortex-a53-835769", cl::Hidden,
cl::desc("Work around Cortex-A53 erratum 835769"),
cl::init(false));
static cl::opt<bool>
EnableGEPOpt("aarch64-enable-gep-opt", cl::Hidden,
cl::desc("Enable optimizations on complex GEPs"),
cl::init(false));
static cl::opt<bool>
BranchRelaxation("aarch64-enable-branch-relax", cl::Hidden, cl::init(true),
cl::desc("Relax out of range conditional branches"));
static cl::opt<bool> EnableCompressJumpTables(
"aarch64-enable-compress-jump-tables", cl::Hidden, cl::init(true),
cl::desc("Use smallest entry possible for jump tables"));
// FIXME: Unify control over GlobalMerge.
static cl::opt<cl::boolOrDefault>
EnableGlobalMerge("aarch64-enable-global-merge", cl::Hidden,
cl::desc("Enable the global merge pass"));
static cl::opt<bool>
EnableLoopDataPrefetch("aarch64-enable-loop-data-prefetch", cl::Hidden,
cl::desc("Enable the loop data prefetch pass"),
cl::init(true));
static cl::opt<int> EnableGlobalISelAtO(
"aarch64-enable-global-isel-at-O", cl::Hidden,
cl::desc("Enable GlobalISel at or below an opt level (-1 to disable)"),
cl::init(0));
static cl::opt<bool> EnableFalkorHWPFFix("aarch64-enable-falkor-hwpf-fix",
cl::init(true), cl::Hidden);
[AArch64][v8.5A] Branch Target Identification code-generation pass The Branch Target Identification extension, introduced to AArch64 in Armv8.5-A, adds the BTI instruction, which is used to mark valid targets of indirect branches. When enabled, the processor will trap if an instruction in a protected page tries to perform an indirect branch to any instruction other than a BTI. The BTI instruction uses encodings which were NOPs in earlier versions of the architecture, so BTI-enabled code will still run on earlier hardware, just without the extra protection. There are 3 variants of the BTI instruction, which are valid targets for different kinds or branches: - BTI C can be targeted by call instructions, and is inteneded to be used at function entry points. These are the BLR instruction, as well as BR with x16 or x17. These BR instructions are allowed for use in PLT entries, and we can also use them to allow indirect tail-calls. - BTI J can be targeted by BR only, and is intended to be used by jump tables. - BTI JC acts ab both a BTI C and a BTI J instruction, and can be targeted by any BLR or BR instruction. Note that RET instructions are not restricted by branch target identification, the reason for this is that return addresses can be protected more effectively using return address signing. Direct branches and calls are also unaffected, as it is assumed that an attacker cannot modify executable pages (if they could, they wouldn't need to do a ROP/JOP attack). This patch adds a MachineFunctionPass which: - Adds a BTI C at the start of every function which could be indirectly called (either because it is address-taken, or externally visible so could be address-taken in another translation unit). - Adds a BTI J at the start of every basic block which could be indirectly branched to. This could be either done by a jump table, or by taking the address of the block (e.g. the using GCC label values extension). We only need to use BTI JC when a function is indirectly-callable, and takes the address of the entry block. I've not been able to trigger this from C or IR, but I've included a MIR test just in case. Using BTI C at function entries relies on the fact that no other code in BTI-protected pages uses indirect tail-calls, unless they use x16 or x17 to hold the address. I'll add that code-generation restriction as a separate patch. Differential revision: https://reviews.llvm.org/D52867 llvm-svn: 343967
2018-10-08 22:04:24 +08:00
static cl::opt<bool>
EnableBranchTargets("aarch64-enable-branch-targets", cl::Hidden,
cl::desc("Enable the AAcrh64 branch target pass"),
cl::init(true));
extern "C" void LLVMInitializeAArch64Target() {
// Register the target.
RegisterTargetMachine<AArch64leTargetMachine> X(getTheAArch64leTarget());
RegisterTargetMachine<AArch64beTargetMachine> Y(getTheAArch64beTarget());
RegisterTargetMachine<AArch64leTargetMachine> Z(getTheARM64Target());
auto PR = PassRegistry::getPassRegistry();
initializeGlobalISel(*PR);
initializeAArch64A53Fix835769Pass(*PR);
initializeAArch64A57FPLoadBalancingPass(*PR);
initializeAArch64AdvSIMDScalarPass(*PR);
[AArch64][v8.5A] Branch Target Identification code-generation pass The Branch Target Identification extension, introduced to AArch64 in Armv8.5-A, adds the BTI instruction, which is used to mark valid targets of indirect branches. When enabled, the processor will trap if an instruction in a protected page tries to perform an indirect branch to any instruction other than a BTI. The BTI instruction uses encodings which were NOPs in earlier versions of the architecture, so BTI-enabled code will still run on earlier hardware, just without the extra protection. There are 3 variants of the BTI instruction, which are valid targets for different kinds or branches: - BTI C can be targeted by call instructions, and is inteneded to be used at function entry points. These are the BLR instruction, as well as BR with x16 or x17. These BR instructions are allowed for use in PLT entries, and we can also use them to allow indirect tail-calls. - BTI J can be targeted by BR only, and is intended to be used by jump tables. - BTI JC acts ab both a BTI C and a BTI J instruction, and can be targeted by any BLR or BR instruction. Note that RET instructions are not restricted by branch target identification, the reason for this is that return addresses can be protected more effectively using return address signing. Direct branches and calls are also unaffected, as it is assumed that an attacker cannot modify executable pages (if they could, they wouldn't need to do a ROP/JOP attack). This patch adds a MachineFunctionPass which: - Adds a BTI C at the start of every function which could be indirectly called (either because it is address-taken, or externally visible so could be address-taken in another translation unit). - Adds a BTI J at the start of every basic block which could be indirectly branched to. This could be either done by a jump table, or by taking the address of the block (e.g. the using GCC label values extension). We only need to use BTI JC when a function is indirectly-callable, and takes the address of the entry block. I've not been able to trigger this from C or IR, but I've included a MIR test just in case. Using BTI C at function entries relies on the fact that no other code in BTI-protected pages uses indirect tail-calls, unless they use x16 or x17 to hold the address. I'll add that code-generation restriction as a separate patch. Differential revision: https://reviews.llvm.org/D52867 llvm-svn: 343967
2018-10-08 22:04:24 +08:00
initializeAArch64BranchTargetsPass(*PR);
initializeAArch64CollectLOHPass(*PR);
initializeAArch64CompressJumpTablesPass(*PR);
initializeAArch64ConditionalComparesPass(*PR);
initializeAArch64ConditionOptimizerPass(*PR);
initializeAArch64DeadRegisterDefinitionsPass(*PR);
initializeAArch64ExpandPseudoPass(*PR);
initializeAArch64LoadStoreOptPass(*PR);
initializeAArch64SIMDInstrOptPass(*PR);
initializeAArch64PreLegalizerCombinerPass(*PR);
initializeAArch64PromoteConstantPass(*PR);
initializeAArch64RedundantCopyEliminationPass(*PR);
initializeAArch64StorePairSuppressPass(*PR);
initializeFalkorHWPFFixPass(*PR);
initializeFalkorMarkStridedAccessesLegacyPass(*PR);
initializeLDTLSCleanupPass(*PR);
Introduce control flow speculation tracking pass for AArch64 The pass implements tracking of control flow miss-speculation into a "taint" register. That taint register can then be used to mask off registers with sensitive data when executing under miss-speculation, a.k.a. "transient execution". This pass is aimed at mitigating against SpectreV1-style vulnarabilities. At the moment, it implements the tracking of miss-speculation of control flow into a taint register, but doesn't implement a mechanism yet to then use that taint register to mask off vulnerable data in registers (something for a follow-on improvement). Possible strategies to mask out vulnerable data that can be implemented on top of this are: - speculative load hardening to automatically mask of data loaded in registers. - using intrinsics to mask of data in registers as indicated by the programmer (see https://lwn.net/Articles/759423/). For AArch64, the following implementation choices are made. Some of these are different than the implementation choices made in the similar pass implemented in X86SpeculativeLoadHardening.cpp, as the instruction set characteristics result in different trade-offs. - The speculation hardening is done after register allocation. With a relative abundance of registers, one register is reserved (X16) to be the taint register. X16 is expected to not clash with other register reservation mechanisms with very high probability because: . The AArch64 ABI doesn't guarantee X16 to be retained across any call. . The only way to request X16 to be used as a programmer is through inline assembly. In the rare case a function explicitly demands to use X16/W16, this pass falls back to hardening against speculation by inserting a DSB SYS/ISB barrier pair which will prevent control flow speculation. - It is easy to insert mask operations at this late stage as we have mask operations available that don't set flags. - The taint variable contains all-ones when no miss-speculation is detected, and contains all-zeros when miss-speculation is detected. Therefore, when masking, an AND instruction (which only changes the register to be masked, no other side effects) can easily be inserted anywhere that's needed. - The tracking of miss-speculation is done by using a data-flow conditional select instruction (CSEL) to evaluate the flags that were also used to make conditional branch direction decisions. Speculation of the CSEL instruction can be limited with a CSDB instruction - so the combination of CSEL + a later CSDB gives the guarantee that the flags as used in the CSEL aren't speculated. When conditional branch direction gets miss-speculated, the semantics of the inserted CSEL instruction is such that the taint register will contain all zero bits. One key requirement for this to work is that the conditional branch is followed by an execution of the CSEL instruction, where the CSEL instruction needs to use the same flags status as the conditional branch. This means that the conditional branches must not be implemented as one of the AArch64 conditional branches that do not use the flags as input (CB(N)Z and TB(N)Z). This is implemented by ensuring in the instruction selectors to not produce these instructions when speculation hardening is enabled. This pass will assert if it does encounter such an instruction. - On function call boundaries, the miss-speculation state is transferred from the taint register X16 to be encoded in the SP register as value 0. Future extensions/improvements could be: - Implement this functionality using full speculation barriers, akin to the x86-slh-lfence option. This may be more useful for the intrinsics-based approach than for the SLH approach to masking. Note that this pass already inserts the full speculation barriers if the function for some niche reason makes use of X16/W16. - no indirect branch misprediction gets protected/instrumented; but this could be done for some indirect branches, such as switch jump tables. Differential Revision: https://reviews.llvm.org/D54896 llvm-svn: 349456
2018-12-18 16:50:02 +08:00
initializeAArch64SpeculationHardeningPass(*PR);
}
//===----------------------------------------------------------------------===//
// AArch64 Lowering public interface.
//===----------------------------------------------------------------------===//
static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
if (TT.isOSBinFormatMachO())
return llvm::make_unique<AArch64_MachoTargetObjectFile>();
if (TT.isOSBinFormatCOFF())
return llvm::make_unique<AArch64_COFFTargetObjectFile>();
return llvm::make_unique<AArch64_ELFTargetObjectFile>();
}
// Helper function to build a DataLayout string
static std::string computeDataLayout(const Triple &TT,
const MCTargetOptions &Options,
bool LittleEndian) {
if (Options.getABIName() == "ilp32")
return "e-m:e-p:32:32-i8:8-i16:16-i64:64-S128";
if (TT.isOSBinFormatMachO())
return "e-m:o-i64:64-i128:128-n32:64-S128";
if (TT.isOSBinFormatCOFF())
return "e-m:w-p:64:64-i32:32-i64:64-i128:128-n32:64-S128";
if (LittleEndian)
return "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128";
return "E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128";
}
static Reloc::Model getEffectiveRelocModel(const Triple &TT,
Optional<Reloc::Model> RM) {
// AArch64 Darwin and Windows are always PIC.
if (TT.isOSDarwin() || TT.isOSWindows())
return Reloc::PIC_;
// On ELF platforms the default static relocation model has a smart enough
// linker to cope with referencing external symbols defined in a shared
// library. Hence DynamicNoPIC doesn't need to be promoted to PIC.
if (!RM.hasValue() || *RM == Reloc::DynamicNoPIC)
return Reloc::Static;
return *RM;
}
static CodeModel::Model
getEffectiveAArch64CodeModel(const Triple &TT, Optional<CodeModel::Model> CM,
bool JIT) {
if (CM) {
if (*CM != CodeModel::Small && *CM != CodeModel::Tiny &&
*CM != CodeModel::Large) {
if (!TT.isOSFuchsia())
report_fatal_error(
"Only small, tiny and large code models are allowed on AArch64");
else if (*CM != CodeModel::Kernel)
report_fatal_error("Only small, tiny, kernel, and large code models "
"are allowed on AArch64");
} else if (*CM == CodeModel::Tiny && !TT.isOSBinFormatELF())
report_fatal_error("tiny code model is only supported on ELF");
return *CM;
}
// The default MCJIT memory managers make no guarantees about where they can
// find an executable page; JITed code needs to be able to refer to globals
// no matter how far away they are.
if (JIT)
return CodeModel::Large;
return CodeModel::Small;
}
/// Create an AArch64 architecture model.
///
AArch64TargetMachine::AArch64TargetMachine(const Target &T, const Triple &TT,
StringRef CPU, StringRef FS,
const TargetOptions &Options,
Optional<Reloc::Model> RM,
Optional<CodeModel::Model> CM,
CodeGenOpt::Level OL, bool JIT,
bool LittleEndian)
: LLVMTargetMachine(T,
computeDataLayout(TT, Options.MCOptions, LittleEndian),
TT, CPU, FS, Options, getEffectiveRelocModel(TT, RM),
getEffectiveAArch64CodeModel(TT, CM, JIT), OL),
TLOF(createTLOF(getTargetTriple())), isLittle(LittleEndian) {
initAsmInfo();
if (TT.isOSBinFormatMachO()) {
this->Options.TrapUnreachable = true;
this->Options.NoTrapAfterNoreturn = true;
}
if (getMCAsmInfo()->usesWindowsCFI()) {
// Unwinding can get confused if the last instruction in an
// exception-handling region (function, funclet, try block, etc.)
// is a call.
//
// FIXME: We could elide the trap if the next instruction would be in
// the same region anyway.
this->Options.TrapUnreachable = true;
}
// Enable GlobalISel at or below EnableGlobalISelAt0.
if (getOptLevel() <= EnableGlobalISelAtO) {
setGlobalISel(true);
setGlobalISelAbort(GlobalISelAbortMode::Disable);
}
// AArch64 supports the MachineOutliner.
setMachineOutliner(true);
// AArch64 supports default outlining behaviour.
setSupportsDefaultOutlining(true);
}
AArch64TargetMachine::~AArch64TargetMachine() = default;
const AArch64Subtarget *
AArch64TargetMachine::getSubtargetImpl(const Function &F) const {
Attribute CPUAttr = F.getFnAttribute("target-cpu");
Attribute FSAttr = F.getFnAttribute("target-features");
std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
? CPUAttr.getValueAsString().str()
: TargetCPU;
std::string FS = !FSAttr.hasAttribute(Attribute::None)
? FSAttr.getValueAsString().str()
: TargetFS;
auto &I = SubtargetMap[CPU + FS];
if (!I) {
// This needs to be done before we create a new subtarget since any
// creation will depend on the TM and the code generation flags on the
// function that reside in TargetOptions.
resetTargetOptions(F);
I = llvm::make_unique<AArch64Subtarget>(TargetTriple, CPU, FS, *this,
isLittle);
}
return I.get();
}
void AArch64leTargetMachine::anchor() { }
AArch64leTargetMachine::AArch64leTargetMachine(
const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
const TargetOptions &Options, Optional<Reloc::Model> RM,
Optional<CodeModel::Model> CM, CodeGenOpt::Level OL, bool JIT)
: AArch64TargetMachine(T, TT, CPU, FS, Options, RM, CM, OL, JIT, true) {}
void AArch64beTargetMachine::anchor() { }
AArch64beTargetMachine::AArch64beTargetMachine(
const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
const TargetOptions &Options, Optional<Reloc::Model> RM,
Optional<CodeModel::Model> CM, CodeGenOpt::Level OL, bool JIT)
: AArch64TargetMachine(T, TT, CPU, FS, Options, RM, CM, OL, JIT, false) {}
namespace {
/// AArch64 Code Generator Pass Configuration Options.
class AArch64PassConfig : public TargetPassConfig {
public:
AArch64PassConfig(AArch64TargetMachine &TM, PassManagerBase &PM)
: TargetPassConfig(TM, PM) {
if (TM.getOptLevel() != CodeGenOpt::None)
substitutePass(&PostRASchedulerID, &PostMachineSchedulerID);
}
AArch64TargetMachine &getAArch64TargetMachine() const {
return getTM<AArch64TargetMachine>();
}
ScheduleDAGInstrs *
createMachineScheduler(MachineSchedContext *C) const override {
const AArch64Subtarget &ST = C->MF->getSubtarget<AArch64Subtarget>();
ScheduleDAGMILive *DAG = createGenericSchedLive(C);
DAG->addMutation(createLoadClusterDAGMutation(DAG->TII, DAG->TRI));
DAG->addMutation(createStoreClusterDAGMutation(DAG->TII, DAG->TRI));
if (ST.hasFusion())
DAG->addMutation(createAArch64MacroFusionDAGMutation());
return DAG;
}
ScheduleDAGInstrs *
createPostMachineScheduler(MachineSchedContext *C) const override {
const AArch64Subtarget &ST = C->MF->getSubtarget<AArch64Subtarget>();
if (ST.hasFusion()) {
// Run the Macro Fusion after RA again since literals are expanded from
// pseudos then (v. addPreSched2()).
ScheduleDAGMI *DAG = createGenericSchedPostRA(C);
DAG->addMutation(createAArch64MacroFusionDAGMutation());
return DAG;
}
return nullptr;
}
void addIRPasses() override;
bool addPreISel() override;
bool addInstSelector() override;
bool addIRTranslator() override;
void addPreLegalizeMachineIR() override;
bool addLegalizeMachineIR() override;
bool addRegBankSelect() override;
void addPreGlobalInstructionSelect() override;
bool addGlobalInstructionSelect() override;
bool addILPOpts() override;
void addPreRegAlloc() override;
void addPostRegAlloc() override;
void addPreSched2() override;
void addPreEmitPass() override;
std::unique_ptr<CSEConfigBase> getCSEConfig() const override;
};
} // end anonymous namespace
TargetTransformInfo
AArch64TargetMachine::getTargetTransformInfo(const Function &F) {
return TargetTransformInfo(AArch64TTIImpl(this, F));
}
TargetPassConfig *AArch64TargetMachine::createPassConfig(PassManagerBase &PM) {
return new AArch64PassConfig(*this, PM);
}
std::unique_ptr<CSEConfigBase> AArch64PassConfig::getCSEConfig() const {
return getStandardCSEConfigForOpt(TM->getOptLevel());
}
void AArch64PassConfig::addIRPasses() {
// Always expand atomic operations, we don't deal with atomicrmw or cmpxchg
// ourselves.
addPass(createAtomicExpandPass());
// Cmpxchg instructions are often used with a subsequent comparison to
// determine whether it succeeded. We can exploit existing control-flow in
// ldrex/strex loops to simplify this, but it needs tidying up.
if (TM->getOptLevel() != CodeGenOpt::None && EnableAtomicTidy)
addPass(createCFGSimplificationPass(1, true, true, false, true));
// Run LoopDataPrefetch
//
// Run this before LSR to remove the multiplies involved in computing the
// pointer values N iterations ahead.
if (TM->getOptLevel() != CodeGenOpt::None) {
if (EnableLoopDataPrefetch)
addPass(createLoopDataPrefetchPass());
if (EnableFalkorHWPFFix)
addPass(createFalkorMarkStridedAccessesPass());
}
TargetPassConfig::addIRPasses();
// Match interleaved memory accesses to ldN/stN intrinsics.
if (TM->getOptLevel() != CodeGenOpt::None) {
addPass(createInterleavedLoadCombinePass());
addPass(createInterleavedAccessPass());
}
if (TM->getOptLevel() == CodeGenOpt::Aggressive && EnableGEPOpt) {
// Call SeparateConstOffsetFromGEP pass to extract constants within indices
// and lower a GEP with multiple indices to either arithmetic operations or
// multiple GEPs with single index.
addPass(createSeparateConstOffsetFromGEPPass(true));
// Call EarlyCSE pass to find and remove subexpressions in the lowered
// result.
addPass(createEarlyCSEPass());
// Do loop invariant code motion in case part of the lowered result is
// invariant.
addPass(createLICMPass());
}
}
// Pass Pipeline Configuration
bool AArch64PassConfig::addPreISel() {
// Run promote constant before global merge, so that the promoted constants
// get a chance to be merged
if (TM->getOptLevel() != CodeGenOpt::None && EnablePromoteConstant)
addPass(createAArch64PromoteConstantPass());
// FIXME: On AArch64, this depends on the type.
// Basically, the addressable offsets are up to 4095 * Ty.getSizeInBytes().
// and the offset has to be a multiple of the related size in bytes.
if ((TM->getOptLevel() != CodeGenOpt::None &&
EnableGlobalMerge == cl::BOU_UNSET) ||
EnableGlobalMerge == cl::BOU_TRUE) {
bool OnlyOptimizeForSize = (TM->getOptLevel() < CodeGenOpt::Aggressive) &&
(EnableGlobalMerge == cl::BOU_UNSET);
addPass(createGlobalMergePass(TM, 4095, OnlyOptimizeForSize));
}
return false;
}
bool AArch64PassConfig::addInstSelector() {
addPass(createAArch64ISelDag(getAArch64TargetMachine(), getOptLevel()));
// For ELF, cleanup any local-dynamic TLS accesses (i.e. combine as many
// references to _TLS_MODULE_BASE_ as possible.
if (TM->getTargetTriple().isOSBinFormatELF() &&
getOptLevel() != CodeGenOpt::None)
addPass(createAArch64CleanupLocalDynamicTLSPass());
return false;
}
bool AArch64PassConfig::addIRTranslator() {
addPass(new IRTranslator());
return false;
}
void AArch64PassConfig::addPreLegalizeMachineIR() {
addPass(createAArch64PreLegalizeCombiner());
}
bool AArch64PassConfig::addLegalizeMachineIR() {
addPass(new Legalizer());
return false;
}
bool AArch64PassConfig::addRegBankSelect() {
addPass(new RegBankSelect());
return false;
}
void AArch64PassConfig::addPreGlobalInstructionSelect() {
// Workaround the deficiency of the fast register allocator.
if (TM->getOptLevel() == CodeGenOpt::None)
addPass(new Localizer());
}
bool AArch64PassConfig::addGlobalInstructionSelect() {
addPass(new InstructionSelect());
return false;
}
bool AArch64PassConfig::addILPOpts() {
if (EnableCondOpt)
addPass(createAArch64ConditionOptimizerPass());
if (EnableCCMP)
addPass(createAArch64ConditionalCompares());
if (EnableMCR)
addPass(&MachineCombinerID);
if (EnableCondBrTuning)
addPass(createAArch64CondBrTuning());
if (EnableEarlyIfConversion)
addPass(&EarlyIfConverterID);
if (EnableStPairSuppress)
addPass(createAArch64StorePairSuppressPass());
addPass(createAArch64SIMDInstrOptPass());
return true;
}
void AArch64PassConfig::addPreRegAlloc() {
// Change dead register definitions to refer to the zero register.
if (TM->getOptLevel() != CodeGenOpt::None && EnableDeadRegisterElimination)
addPass(createAArch64DeadRegisterDefinitions());
// Use AdvSIMD scalar instructions whenever profitable.
if (TM->getOptLevel() != CodeGenOpt::None && EnableAdvSIMDScalar) {
addPass(createAArch64AdvSIMDScalar());
// The AdvSIMD pass may produce copies that can be rewritten to
// be register coaleascer friendly.
addPass(&PeepholeOptimizerID);
}
}
void AArch64PassConfig::addPostRegAlloc() {
// Remove redundant copy instructions.
if (TM->getOptLevel() != CodeGenOpt::None && EnableRedundantCopyElimination)
addPass(createAArch64RedundantCopyEliminationPass());
if (TM->getOptLevel() != CodeGenOpt::None && usingDefaultRegAlloc())
// Improve performance for some FP/SIMD code for A57.
addPass(createAArch64A57FPLoadBalancing());
}
void AArch64PassConfig::addPreSched2() {
// Expand some pseudo instructions to allow proper scheduling.
addPass(createAArch64ExpandPseudoPass());
// Use load/store pair instructions when possible.
if (TM->getOptLevel() != CodeGenOpt::None) {
if (EnableLoadStoreOpt)
addPass(createAArch64LoadStoreOptimizationPass());
Introduce control flow speculation tracking pass for AArch64 The pass implements tracking of control flow miss-speculation into a "taint" register. That taint register can then be used to mask off registers with sensitive data when executing under miss-speculation, a.k.a. "transient execution". This pass is aimed at mitigating against SpectreV1-style vulnarabilities. At the moment, it implements the tracking of miss-speculation of control flow into a taint register, but doesn't implement a mechanism yet to then use that taint register to mask off vulnerable data in registers (something for a follow-on improvement). Possible strategies to mask out vulnerable data that can be implemented on top of this are: - speculative load hardening to automatically mask of data loaded in registers. - using intrinsics to mask of data in registers as indicated by the programmer (see https://lwn.net/Articles/759423/). For AArch64, the following implementation choices are made. Some of these are different than the implementation choices made in the similar pass implemented in X86SpeculativeLoadHardening.cpp, as the instruction set characteristics result in different trade-offs. - The speculation hardening is done after register allocation. With a relative abundance of registers, one register is reserved (X16) to be the taint register. X16 is expected to not clash with other register reservation mechanisms with very high probability because: . The AArch64 ABI doesn't guarantee X16 to be retained across any call. . The only way to request X16 to be used as a programmer is through inline assembly. In the rare case a function explicitly demands to use X16/W16, this pass falls back to hardening against speculation by inserting a DSB SYS/ISB barrier pair which will prevent control flow speculation. - It is easy to insert mask operations at this late stage as we have mask operations available that don't set flags. - The taint variable contains all-ones when no miss-speculation is detected, and contains all-zeros when miss-speculation is detected. Therefore, when masking, an AND instruction (which only changes the register to be masked, no other side effects) can easily be inserted anywhere that's needed. - The tracking of miss-speculation is done by using a data-flow conditional select instruction (CSEL) to evaluate the flags that were also used to make conditional branch direction decisions. Speculation of the CSEL instruction can be limited with a CSDB instruction - so the combination of CSEL + a later CSDB gives the guarantee that the flags as used in the CSEL aren't speculated. When conditional branch direction gets miss-speculated, the semantics of the inserted CSEL instruction is such that the taint register will contain all zero bits. One key requirement for this to work is that the conditional branch is followed by an execution of the CSEL instruction, where the CSEL instruction needs to use the same flags status as the conditional branch. This means that the conditional branches must not be implemented as one of the AArch64 conditional branches that do not use the flags as input (CB(N)Z and TB(N)Z). This is implemented by ensuring in the instruction selectors to not produce these instructions when speculation hardening is enabled. This pass will assert if it does encounter such an instruction. - On function call boundaries, the miss-speculation state is transferred from the taint register X16 to be encoded in the SP register as value 0. Future extensions/improvements could be: - Implement this functionality using full speculation barriers, akin to the x86-slh-lfence option. This may be more useful for the intrinsics-based approach than for the SLH approach to masking. Note that this pass already inserts the full speculation barriers if the function for some niche reason makes use of X16/W16. - no indirect branch misprediction gets protected/instrumented; but this could be done for some indirect branches, such as switch jump tables. Differential Revision: https://reviews.llvm.org/D54896 llvm-svn: 349456
2018-12-18 16:50:02 +08:00
}
// The AArch64SpeculationHardeningPass destroys dominator tree and natural
// loop info, which is needed for the FalkorHWPFFixPass and also later on.
// Therefore, run the AArch64SpeculationHardeningPass before the
// FalkorHWPFFixPass to avoid recomputing dominator tree and natural loop
// info.
addPass(createAArch64SpeculationHardeningPass());
if (TM->getOptLevel() != CodeGenOpt::None) {
if (EnableFalkorHWPFFix)
addPass(createFalkorHWPFFixPass());
}
}
void AArch64PassConfig::addPreEmitPass() {
// Machine Block Placement might have created new opportunities when run
// at O3, where the Tail Duplication Threshold is set to 4 instructions.
// Run the load/store optimizer once more.
if (TM->getOptLevel() >= CodeGenOpt::Aggressive && EnableLoadStoreOpt)
addPass(createAArch64LoadStoreOptimizationPass());
if (EnableA53Fix835769)
addPass(createAArch64A53Fix835769());
// Relax conditional branch instructions if they're otherwise out of
// range of their destination.
if (BranchRelaxation)
addPass(&BranchRelaxationPassID);
[AArch64][v8.5A] Branch Target Identification code-generation pass The Branch Target Identification extension, introduced to AArch64 in Armv8.5-A, adds the BTI instruction, which is used to mark valid targets of indirect branches. When enabled, the processor will trap if an instruction in a protected page tries to perform an indirect branch to any instruction other than a BTI. The BTI instruction uses encodings which were NOPs in earlier versions of the architecture, so BTI-enabled code will still run on earlier hardware, just without the extra protection. There are 3 variants of the BTI instruction, which are valid targets for different kinds or branches: - BTI C can be targeted by call instructions, and is inteneded to be used at function entry points. These are the BLR instruction, as well as BR with x16 or x17. These BR instructions are allowed for use in PLT entries, and we can also use them to allow indirect tail-calls. - BTI J can be targeted by BR only, and is intended to be used by jump tables. - BTI JC acts ab both a BTI C and a BTI J instruction, and can be targeted by any BLR or BR instruction. Note that RET instructions are not restricted by branch target identification, the reason for this is that return addresses can be protected more effectively using return address signing. Direct branches and calls are also unaffected, as it is assumed that an attacker cannot modify executable pages (if they could, they wouldn't need to do a ROP/JOP attack). This patch adds a MachineFunctionPass which: - Adds a BTI C at the start of every function which could be indirectly called (either because it is address-taken, or externally visible so could be address-taken in another translation unit). - Adds a BTI J at the start of every basic block which could be indirectly branched to. This could be either done by a jump table, or by taking the address of the block (e.g. the using GCC label values extension). We only need to use BTI JC when a function is indirectly-callable, and takes the address of the entry block. I've not been able to trigger this from C or IR, but I've included a MIR test just in case. Using BTI C at function entries relies on the fact that no other code in BTI-protected pages uses indirect tail-calls, unless they use x16 or x17 to hold the address. I'll add that code-generation restriction as a separate patch. Differential revision: https://reviews.llvm.org/D52867 llvm-svn: 343967
2018-10-08 22:04:24 +08:00
if (EnableBranchTargets)
addPass(createAArch64BranchTargetsPass());
if (TM->getOptLevel() != CodeGenOpt::None && EnableCompressJumpTables)
addPass(createAArch64CompressJumpTablesPass());
if (TM->getOptLevel() != CodeGenOpt::None && EnableCollectLOH &&
TM->getTargetTriple().isOSBinFormatMachO())
addPass(createAArch64CollectLOHPass());
}