Google Git
Sign in
llvm / llvm-project / 37d72991c136244fe53be02f5af0ad643247a1e6 / . / llvm / lib / Target / X86 / MCTargetDesc / X86AsmBackend.cpp
blob: 3df48b466d075d199da07e51a1f6fa7c7c3a0313 [file] [log] [blame]
//===-- X86AsmBackend.cpp - X86 Assembler Backend -------------------------===//
//
// 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 "MCTargetDesc/X86BaseInfo.h"
#include "MCTargetDesc/X86FixupKinds.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
namespace {
/// A wrapper for holding a mask of the values from X86::AlignBranchBoundaryKind
class X86AlignBranchKind {
private:
uint8_t AlignBranchKind = 0;
public:
void operator=(const std::string &Val) {
if (Val.empty())
return;
SmallVector<StringRef, 6> BranchTypes;
StringRef(Val).split(BranchTypes, '+', -1, false);
for (auto BranchType : BranchTypes) {
if (BranchType == "fused")
addKind(X86::AlignBranchFused);
else if (BranchType == "jcc")
addKind(X86::AlignBranchJcc);
else if (BranchType == "jmp")
addKind(X86::AlignBranchJmp);
else if (BranchType == "call")
addKind(X86::AlignBranchCall);
else if (BranchType == "ret")
addKind(X86::AlignBranchRet);
else if (BranchType == "indirect")
addKind(X86::AlignBranchIndirect);
else {
errs() << "invalid argument " << BranchType.str()
<< " to -x86-align-branch=; each element must be one of: fused, "
"jcc, jmp, call, ret, indirect.(plus separated)\n";
}
}
}
operator uint8_t() const { return AlignBranchKind; }
void addKind(X86::AlignBranchBoundaryKind Value) { AlignBranchKind |= Value; }
};
X86AlignBranchKind X86AlignBranchKindLoc;
cl::opt<unsigned> X86AlignBranchBoundary(
"x86-align-branch-boundary", cl::init(0),
cl::desc(
"Control how the assembler should align branches with NOP. If the "
"boundary's size is not 0, it should be a power of 2 and no less "
"than 32. Branches will be aligned to prevent from being across or "
"against the boundary of specified size. The default value 0 does not "
"align branches."));
cl::opt<X86AlignBranchKind, true, cl::parser<std::string>> X86AlignBranch(
"x86-align-branch",
cl::desc(
"Specify types of branches to align (plus separated list of types):"
"\njcc indicates conditional jumps"
"\nfused indicates fused conditional jumps"
"\njmp indicates direct unconditional jumps"
"\ncall indicates direct and indirect calls"
"\nret indicates rets"
"\nindirect indicates indirect unconditional jumps"),
cl::location(X86AlignBranchKindLoc));
cl::opt<bool> X86AlignBranchWithin32BBoundaries(
"x86-branches-within-32B-boundaries", cl::init(false),
cl::desc(
"Align selected instructions to mitigate negative performance impact "
"of Intel's micro code update for errata skx102. May break "
"assumptions about labels corresponding to particular instructions, "
"and should be used with caution."));
cl::opt<unsigned> X86PadMaxPrefixSize(
"x86-pad-max-prefix-size", cl::init(0),
cl::desc("Maximum number of prefixes to use for padding"));
cl::opt<bool> X86PadForAlign(
"x86-pad-for-align", cl::init(false), cl::Hidden,
cl::desc("Pad previous instructions to implement align directives"));
cl::opt<bool> X86PadForBranchAlign(
"x86-pad-for-branch-align", cl::init(true), cl::Hidden,
cl::desc("Pad previous instructions to implement branch alignment"));
class X86AsmBackend : public MCAsmBackend {
const MCSubtargetInfo &STI;
std::unique_ptr<const MCInstrInfo> MCII;
X86AlignBranchKind AlignBranchType;
Align AlignBoundary;
unsigned TargetPrefixMax = 0;
MCInst PrevInst;
MCBoundaryAlignFragment *PendingBA = nullptr;
std::pair<MCFragment *, size_t> PrevInstPosition;
bool CanPadInst;
uint8_t determinePaddingPrefix(const MCInst &Inst) const;
bool isMacroFused(const MCInst &Cmp, const MCInst &Jcc) const;
bool needAlign(const MCInst &Inst) const;
bool canPadBranches(MCObjectStreamer &OS) const;
bool canPadInst(const MCInst &Inst, MCObjectStreamer &OS) const;
public:
X86AsmBackend(const Target &T, const MCSubtargetInfo &STI)
: MCAsmBackend(support::little), STI(STI),
MCII(T.createMCInstrInfo()) {
if (X86AlignBranchWithin32BBoundaries) {
// At the moment, this defaults to aligning fused branches, unconditional
// jumps, and (unfused) conditional jumps with nops. Both the
// instructions aligned and the alignment method (nop vs prefix) may
// change in the future.
AlignBoundary = assumeAligned(32);;
AlignBranchType.addKind(X86::AlignBranchFused);
AlignBranchType.addKind(X86::AlignBranchJcc);
AlignBranchType.addKind(X86::AlignBranchJmp);
}
// Allow overriding defaults set by main flag
if (X86AlignBranchBoundary.getNumOccurrences())
AlignBoundary = assumeAligned(X86AlignBranchBoundary);
if (X86AlignBranch.getNumOccurrences())
AlignBranchType = X86AlignBranchKindLoc;
if (X86PadMaxPrefixSize.getNumOccurrences())
TargetPrefixMax = X86PadMaxPrefixSize;
}
bool allowAutoPadding() const override;
bool allowEnhancedRelaxation() const override;
void emitInstructionBegin(MCObjectStreamer &OS, const MCInst &Inst,
const MCSubtargetInfo &STI) override;
void emitInstructionEnd(MCObjectStreamer &OS, const MCInst &Inst) override;
unsigned getNumFixupKinds() const override {
return X86::NumTargetFixupKinds;
}
Optional<MCFixupKind> getFixupKind(StringRef Name) const override;
const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
const MCValue &Target) override;
void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
const MCValue &Target, MutableArrayRef<char> Data,
uint64_t Value, bool IsResolved,
const MCSubtargetInfo *STI) const override;
bool mayNeedRelaxation(const MCInst &Inst,
const MCSubtargetInfo &STI) const override;
bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const override;
void relaxInstruction(MCInst &Inst,
const MCSubtargetInfo &STI) const override;
bool padInstructionViaRelaxation(MCRelaxableFragment &RF,
MCCodeEmitter &Emitter,
unsigned &RemainingSize) const;
bool padInstructionViaPrefix(MCRelaxableFragment &RF, MCCodeEmitter &Emitter,
unsigned &RemainingSize) const;
bool padInstructionEncoding(MCRelaxableFragment &RF, MCCodeEmitter &Emitter,
unsigned &RemainingSize) const;
void finishLayout(MCAssembler const &Asm, MCAsmLayout &Layout) const override;
unsigned getMaximumNopSize(const MCSubtargetInfo &STI) const override;
bool writeNopData(raw_ostream &OS, uint64_t Count,
const MCSubtargetInfo *STI) const override;
};
} // end anonymous namespace
static unsigned getRelaxedOpcodeBranch(const MCInst &Inst, bool Is16BitMode) {
unsigned Op = Inst.getOpcode();
switch (Op) {
default:
return Op;
case X86::JCC_1:
return (Is16BitMode) ? X86::JCC_2 : X86::JCC_4;
case X86::JMP_1:
return (Is16BitMode) ? X86::JMP_2 : X86::JMP_4;
}
}
static unsigned getRelaxedOpcodeArith(const MCInst &Inst) {
unsigned Op = Inst.getOpcode();
switch (Op) {
default:
return Op;
// IMUL
case X86::IMUL16rri8: return X86::IMUL16rri;
case X86::IMUL16rmi8: return X86::IMUL16rmi;
case X86::IMUL32rri8: return X86::IMUL32rri;
case X86::IMUL32rmi8: return X86::IMUL32rmi;
case X86::IMUL64rri8: return X86::IMUL64rri32;
case X86::IMUL64rmi8: return X86::IMUL64rmi32;
// AND
case X86::AND16ri8: return X86::AND16ri;
case X86::AND16mi8: return X86::AND16mi;
case X86::AND32ri8: return X86::AND32ri;
case X86::AND32mi8: return X86::AND32mi;
case X86::AND64ri8: return X86::AND64ri32;
case X86::AND64mi8: return X86::AND64mi32;
// OR
case X86::OR16ri8: return X86::OR16ri;
case X86::OR16mi8: return X86::OR16mi;
case X86::OR32ri8: return X86::OR32ri;
case X86::OR32mi8: return X86::OR32mi;
case X86::OR64ri8: return X86::OR64ri32;
case X86::OR64mi8: return X86::OR64mi32;
// XOR
case X86::XOR16ri8: return X86::XOR16ri;
case X86::XOR16mi8: return X86::XOR16mi;
case X86::XOR32ri8: return X86::XOR32ri;
case X86::XOR32mi8: return X86::XOR32mi;
case X86::XOR64ri8: return X86::XOR64ri32;
case X86::XOR64mi8: return X86::XOR64mi32;
// ADD
case X86::ADD16ri8: return X86::ADD16ri;
case X86::ADD16mi8: return X86::ADD16mi;
case X86::ADD32ri8: return X86::ADD32ri;
case X86::ADD32mi8: return X86::ADD32mi;
case X86::ADD64ri8: return X86::ADD64ri32;
case X86::ADD64mi8: return X86::ADD64mi32;
// ADC
case X86::ADC16ri8: return X86::ADC16ri;
case X86::ADC16mi8: return X86::ADC16mi;
case X86::ADC32ri8: return X86::ADC32ri;
case X86::ADC32mi8: return X86::ADC32mi;
case X86::ADC64ri8: return X86::ADC64ri32;
case X86::ADC64mi8: return X86::ADC64mi32;
// SUB
case X86::SUB16ri8: return X86::SUB16ri;
case X86::SUB16mi8: return X86::SUB16mi;
case X86::SUB32ri8: return X86::SUB32ri;
case X86::SUB32mi8: return X86::SUB32mi;
case X86::SUB64ri8: return X86::SUB64ri32;
case X86::SUB64mi8: return X86::SUB64mi32;
// SBB
case X86::SBB16ri8: return X86::SBB16ri;
case X86::SBB16mi8: return X86::SBB16mi;
case X86::SBB32ri8: return X86::SBB32ri;
case X86::SBB32mi8: return X86::SBB32mi;
case X86::SBB64ri8: return X86::SBB64ri32;
case X86::SBB64mi8: return X86::SBB64mi32;
// CMP
case X86::CMP16ri8: return X86::CMP16ri;
case X86::CMP16mi8: return X86::CMP16mi;
case X86::CMP32ri8: return X86::CMP32ri;
case X86::CMP32mi8: return X86::CMP32mi;
case X86::CMP64ri8: return X86::CMP64ri32;
case X86::CMP64mi8: return X86::CMP64mi32;
// PUSH
case X86::PUSH32i8: return X86::PUSHi32;
case X86::PUSH16i8: return X86::PUSHi16;
case X86::PUSH64i8: return X86::PUSH64i32;
}
}
static unsigned getRelaxedOpcode(const MCInst &Inst, bool Is16BitMode) {
unsigned R = getRelaxedOpcodeArith(Inst);
if (R != Inst.getOpcode())
return R;
return getRelaxedOpcodeBranch(Inst, Is16BitMode);
}
static X86::CondCode getCondFromBranch(const MCInst &MI,
const MCInstrInfo &MCII) {
unsigned Opcode = MI.getOpcode();
switch (Opcode) {
default:
return X86::COND_INVALID;
case X86::JCC_1: {
const MCInstrDesc &Desc = MCII.get(Opcode);
return static_cast<X86::CondCode>(
MI.getOperand(Desc.getNumOperands() - 1).getImm());
}
}
}
static X86::SecondMacroFusionInstKind
classifySecondInstInMacroFusion(const MCInst &MI, const MCInstrInfo &MCII) {
X86::CondCode CC = getCondFromBranch(MI, MCII);
return classifySecondCondCodeInMacroFusion(CC);
}
/// Check if the instruction uses RIP relative addressing.
static bool isRIPRelative(const MCInst &MI, const MCInstrInfo &MCII) {
unsigned Opcode = MI.getOpcode();
const MCInstrDesc &Desc = MCII.get(Opcode);
uint64_t TSFlags = Desc.TSFlags;
unsigned CurOp = X86II::getOperandBias(Desc);
int MemoryOperand = X86II::getMemoryOperandNo(TSFlags);
if (MemoryOperand < 0)
return false;
unsigned BaseRegNum = MemoryOperand + CurOp + X86::AddrBaseReg;
unsigned BaseReg = MI.getOperand(BaseRegNum).getReg();
return (BaseReg == X86::RIP);
}
/// Check if the instruction is a prefix.
static bool isPrefix(const MCInst &MI, const MCInstrInfo &MCII) {
return X86II::isPrefix(MCII.get(MI.getOpcode()).TSFlags);
}
/// Check if the instruction is valid as the first instruction in macro fusion.
static bool isFirstMacroFusibleInst(const MCInst &Inst,
const MCInstrInfo &MCII) {
// An Intel instruction with RIP relative addressing is not macro fusible.
if (isRIPRelative(Inst, MCII))
return false;
X86::FirstMacroFusionInstKind FIK =
X86::classifyFirstOpcodeInMacroFusion(Inst.getOpcode());
return FIK != X86::FirstMacroFusionInstKind::Invalid;
}
/// X86 can reduce the bytes of NOP by padding instructions with prefixes to
/// get a better peformance in some cases. Here, we determine which prefix is
/// the most suitable.
///
/// If the instruction has a segment override prefix, use the existing one.
/// If the target is 64-bit, use the CS.
/// If the target is 32-bit,
/// - If the instruction has a ESP/EBP base register, use SS.
/// - Otherwise use DS.
uint8_t X86AsmBackend::determinePaddingPrefix(const MCInst &Inst) const {
assert((STI.hasFeature(X86::Mode32Bit) || STI.hasFeature(X86::Mode64Bit)) &&
"Prefixes can be added only in 32-bit or 64-bit mode.");
const MCInstrDesc &Desc = MCII->get(Inst.getOpcode());
uint64_t TSFlags = Desc.TSFlags;
// Determine where the memory operand starts, if present.
int MemoryOperand = X86II::getMemoryOperandNo(TSFlags);
if (MemoryOperand != -1)
MemoryOperand += X86II::getOperandBias(Desc);
unsigned SegmentReg = 0;
if (MemoryOperand >= 0) {
// Check for explicit segment override on memory operand.
SegmentReg = Inst.getOperand(MemoryOperand + X86::AddrSegmentReg).getReg();
}
switch (TSFlags & X86II::FormMask) {
default:
break;
case X86II::RawFrmDstSrc: {
// Check segment override opcode prefix as needed (not for %ds).
if (Inst.getOperand(2).getReg() != X86::DS)
SegmentReg = Inst.getOperand(2).getReg();
break;
}
case X86II::RawFrmSrc: {
// Check segment override opcode prefix as needed (not for %ds).
if (Inst.getOperand(1).getReg() != X86::DS)
SegmentReg = Inst.getOperand(1).getReg();
break;
}
case X86II::RawFrmMemOffs: {
// Check segment override opcode prefix as needed.
SegmentReg = Inst.getOperand(1).getReg();
break;
}
}
if (SegmentReg != 0)
return X86::getSegmentOverridePrefixForReg(SegmentReg);
if (STI.hasFeature(X86::Mode64Bit))
return X86::CS_Encoding;
if (MemoryOperand >= 0) {
unsigned BaseRegNum = MemoryOperand + X86::AddrBaseReg;
unsigned BaseReg = Inst.getOperand(BaseRegNum).getReg();
if (BaseReg == X86::ESP || BaseReg == X86::EBP)
return X86::SS_Encoding;
}
return X86::DS_Encoding;
}
/// Check if the two instructions will be macro-fused on the target cpu.
bool X86AsmBackend::isMacroFused(const MCInst &Cmp, const MCInst &Jcc) const {
const MCInstrDesc &InstDesc = MCII->get(Jcc.getOpcode());
if (!InstDesc.isConditionalBranch())
return false;
if (!isFirstMacroFusibleInst(Cmp, *MCII))
return false;
const X86::FirstMacroFusionInstKind CmpKind =
X86::classifyFirstOpcodeInMacroFusion(Cmp.getOpcode());
const X86::SecondMacroFusionInstKind BranchKind =
classifySecondInstInMacroFusion(Jcc, *MCII);
return X86::isMacroFused(CmpKind, BranchKind);
}
/// Check if the instruction has a variant symbol operand.
static bool hasVariantSymbol(const MCInst &MI) {
for (auto &Operand : MI) {
if (!Operand.isExpr())
continue;
const MCExpr &Expr = *Operand.getExpr();
if (Expr.getKind() == MCExpr::SymbolRef &&
cast<MCSymbolRefExpr>(Expr).getKind() != MCSymbolRefExpr::VK_None)
return true;
}
return false;
}
bool X86AsmBackend::allowAutoPadding() const {
return (AlignBoundary != Align(1) && AlignBranchType != X86::AlignBranchNone);
}
bool X86AsmBackend::allowEnhancedRelaxation() const {
return allowAutoPadding() && TargetPrefixMax != 0 && X86PadForBranchAlign;
}
/// X86 has certain instructions which enable interrupts exactly one
/// instruction *after* the instruction which stores to SS. Return true if the
/// given instruction has such an interrupt delay slot.
static bool hasInterruptDelaySlot(const MCInst &Inst) {
switch (Inst.getOpcode()) {
case X86::POPSS16:
case X86::POPSS32:
case X86::STI:
return true;
case X86::MOV16sr:
case X86::MOV32sr:
case X86::MOV64sr:
case X86::MOV16sm:
if (Inst.getOperand(0).getReg() == X86::SS)
return true;
break;
}
return false;
}
/// Check if the instruction to be emitted is right after any data.
static bool
isRightAfterData(MCFragment *CurrentFragment,
const std::pair<MCFragment *, size_t> &PrevInstPosition) {
MCFragment *F = CurrentFragment;
// Empty data fragments may be created to prevent further data being
// added into the previous fragment, we need to skip them since they
// have no contents.
for (; isa_and_nonnull<MCDataFragment>(F); F = F->getPrevNode())
if (cast<MCDataFragment>(F)->getContents().size() != 0)
break;
// Since data is always emitted into a DataFragment, our check strategy is
// simple here.
// - If the fragment is a DataFragment
// - If it's not the fragment where the previous instruction is,
// returns true.
// - If it's the fragment holding the previous instruction but its
// size changed since the the previous instruction was emitted into
// it, returns true.
// - Otherwise returns false.
// - If the fragment is not a DataFragment, returns false.
if (auto *DF = dyn_cast_or_null<MCDataFragment>(F))
return DF != PrevInstPosition.first ||
DF->getContents().size() != PrevInstPosition.second;
return false;
}
/// \returns the fragment size if it has instructions, otherwise returns 0.
static size_t getSizeForInstFragment(const MCFragment *F) {
if (!F || !F->hasInstructions())
return 0;
// MCEncodedFragmentWithContents being templated makes this tricky.
switch (F->getKind()) {
default:
llvm_unreachable("Unknown fragment with instructions!");
case MCFragment::FT_Data:
return cast<MCDataFragment>(*F).getContents().size();
case MCFragment::FT_Relaxable:
return cast<MCRelaxableFragment>(*F).getContents().size();
case MCFragment::FT_CompactEncodedInst:
return cast<MCCompactEncodedInstFragment>(*F).getContents().size();
}
}
/// Return true if we can insert NOP or prefixes automatically before the
/// the instruction to be emitted.
bool X86AsmBackend::canPadInst(const MCInst &Inst, MCObjectStreamer &OS) const {
if (hasVariantSymbol(Inst))
// Linker may rewrite the instruction with variant symbol operand(e.g.
// TLSCALL).
return false;
if (hasInterruptDelaySlot(PrevInst))
// If this instruction follows an interrupt enabling instruction with a one
// instruction delay, inserting a nop would change behavior.
return false;
if (isPrefix(PrevInst, *MCII))
// If this instruction follows a prefix, inserting a nop/prefix would change
// semantic.
return false;
if (isPrefix(Inst, *MCII))
// If this instruction is a prefix, inserting a prefix would change
// semantic.
return false;
if (isRightAfterData(OS.getCurrentFragment(), PrevInstPosition))
// If this instruction follows any data, there is no clear
// instruction boundary, inserting a nop/prefix would change semantic.
return false;
return true;
}
bool X86AsmBackend::canPadBranches(MCObjectStreamer &OS) const {
if (!OS.getAllowAutoPadding())
return false;
assert(allowAutoPadding() && "incorrect initialization!");
// We only pad in text section.
if (!OS.getCurrentSectionOnly()->getKind().isText())
return false;
// To be Done: Currently don't deal with Bundle cases.
if (OS.getAssembler().isBundlingEnabled())
return false;
// Branches only need to be aligned in 32-bit or 64-bit mode.
if (!(STI.hasFeature(X86::Mode64Bit) || STI.hasFeature(X86::Mode32Bit)))
return false;
return true;
}
/// Check if the instruction operand needs to be aligned.
bool X86AsmBackend::needAlign(const MCInst &Inst) const {
const MCInstrDesc &Desc = MCII->get(Inst.getOpcode());
return (Desc.isConditionalBranch() &&
(AlignBranchType & X86::AlignBranchJcc)) ||
(Desc.isUnconditionalBranch() &&
(AlignBranchType & X86::AlignBranchJmp)) ||
(Desc.isCall() && (AlignBranchType & X86::AlignBranchCall)) ||
(Desc.isReturn() && (AlignBranchType & X86::AlignBranchRet)) ||
(Desc.isIndirectBranch() &&
(AlignBranchType & X86::AlignBranchIndirect));
}
/// Insert BoundaryAlignFragment before instructions to align branches.
void X86AsmBackend::emitInstructionBegin(MCObjectStreamer &OS,
const MCInst &Inst, const MCSubtargetInfo &STI) {
CanPadInst = canPadInst(Inst, OS);
if (!canPadBranches(OS))
return;
if (!isMacroFused(PrevInst, Inst))
// Macro fusion doesn't happen indeed, clear the pending.
PendingBA = nullptr;
if (!CanPadInst)
return;
if (PendingBA && OS.getCurrentFragment()->getPrevNode() == PendingBA) {
// Macro fusion actually happens and there is no other fragment inserted
// after the previous instruction.
//
// Do nothing here since we already inserted a BoudaryAlign fragment when
// we met the first instruction in the fused pair and we'll tie them
// together in emitInstructionEnd.
//
// Note: When there is at least one fragment, such as MCAlignFragment,
// inserted after the previous instruction, e.g.
//
// \code
// cmp %rax %rcx
// .align 16
// je .Label0
// \ endcode
//
// We will treat the JCC as a unfused branch although it may be fused
// with the CMP.
return;
}
if (needAlign(Inst) || ((AlignBranchType & X86::AlignBranchFused) &&
isFirstMacroFusibleInst(Inst, *MCII))) {
// If we meet a unfused branch or the first instuction in a fusiable pair,
// insert a BoundaryAlign fragment.
OS.insert(PendingBA = new MCBoundaryAlignFragment(AlignBoundary, STI));
}
}
/// Set the last fragment to be aligned for the BoundaryAlignFragment.
void X86AsmBackend::emitInstructionEnd(MCObjectStreamer &OS, const MCInst &Inst) {
PrevInst = Inst;
MCFragment *CF = OS.getCurrentFragment();
PrevInstPosition = std::make_pair(CF, getSizeForInstFragment(CF));
if (auto *F = dyn_cast_or_null<MCRelaxableFragment>(CF))
F->setAllowAutoPadding(CanPadInst);
if (!canPadBranches(OS))
return;
if (!needAlign(Inst) || !PendingBA)
return;
// Tie the aligned instructions into a a pending BoundaryAlign.
PendingBA->setLastFragment(CF);
PendingBA = nullptr;
// We need to ensure that further data isn't added to the current
// DataFragment, so that we can get the size of instructions later in
// MCAssembler::relaxBoundaryAlign. The easiest way is to insert a new empty
// DataFragment.
if (isa_and_nonnull<MCDataFragment>(CF))
OS.insert(new MCDataFragment());
// Update the maximum alignment on the current section if necessary.
MCSection *Sec = OS.getCurrentSectionOnly();
if (AlignBoundary.value() > Sec->getAlignment())
Sec->setAlignment(AlignBoundary);
}
Optional<MCFixupKind> X86AsmBackend::getFixupKind(StringRef Name) const {
if (STI.getTargetTriple().isOSBinFormatELF()) {
unsigned Type;
if (STI.getTargetTriple().getArch() == Triple::x86_64) {
Type = llvm::StringSwitch<unsigned>(Name)
#define ELF_RELOC(X, Y) .Case(#X, Y)
#include "llvm/BinaryFormat/ELFRelocs/x86_64.def"
#undef ELF_RELOC
.Case("BFD_RELOC_NONE", ELF::R_X86_64_NONE)
.Case("BFD_RELOC_8", ELF::R_X86_64_8)
.Case("BFD_RELOC_16", ELF::R_X86_64_16)
.Case("BFD_RELOC_32", ELF::R_X86_64_32)
.Case("BFD_RELOC_64", ELF::R_X86_64_64)
.Default(-1u);
} else {
Type = llvm::StringSwitch<unsigned>(Name)
#define ELF_RELOC(X, Y) .Case(#X, Y)
#include "llvm/BinaryFormat/ELFRelocs/i386.def"
#undef ELF_RELOC
.Case("BFD_RELOC_NONE", ELF::R_386_NONE)
.Case("BFD_RELOC_8", ELF::R_386_8)
.Case("BFD_RELOC_16", ELF::R_386_16)
.Case("BFD_RELOC_32", ELF::R_386_32)
.Default(-1u);
}
if (Type == -1u)
return None;
return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
}
return MCAsmBackend::getFixupKind(Name);
}
const MCFixupKindInfo &X86AsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
const static MCFixupKindInfo Infos[X86::NumTargetFixupKinds] = {
{"reloc_riprel_4byte", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
{"reloc_riprel_4byte_movq_load", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
{"reloc_riprel_4byte_relax", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
{"reloc_riprel_4byte_relax_rex", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
{"reloc_signed_4byte", 0, 32, 0},
{"reloc_signed_4byte_relax", 0, 32, 0},
{"reloc_global_offset_table", 0, 32, 0},
{"reloc_global_offset_table8", 0, 64, 0},
{"reloc_branch_4byte_pcrel", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
};
// Fixup kinds from .reloc directive are like R_386_NONE/R_X86_64_NONE. They
// do not require any extra processing.
if (Kind >= FirstLiteralRelocationKind)
return MCAsmBackend::getFixupKindInfo(FK_NONE);
if (Kind < FirstTargetFixupKind)
return MCAsmBackend::getFixupKindInfo(Kind);
assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
"Invalid kind!");
assert(Infos[Kind - FirstTargetFixupKind].Name && "Empty fixup name!");
return Infos[Kind - FirstTargetFixupKind];
}
bool X86AsmBackend::shouldForceRelocation(const MCAssembler &,
const MCFixup &Fixup,
const MCValue &) {
return Fixup.getKind() >= FirstLiteralRelocationKind;
}
static unsigned getFixupKindSize(unsigned Kind) {
switch (Kind) {
default:
llvm_unreachable("invalid fixup kind!");
case FK_NONE:
return 0;
case FK_PCRel_1:
case FK_SecRel_1:
case FK_Data_1:
return 1;
case FK_PCRel_2:
case FK_SecRel_2:
case FK_Data_2:
return 2;
case FK_PCRel_4:
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_relax:
case X86::reloc_riprel_4byte_relax_rex:
case X86::reloc_riprel_4byte_movq_load:
case X86::reloc_signed_4byte:
case X86::reloc_signed_4byte_relax:
case X86::reloc_global_offset_table:
case X86::reloc_branch_4byte_pcrel:
case FK_SecRel_4:
case FK_Data_4:
return 4;
case FK_PCRel_8:
case FK_SecRel_8:
case FK_Data_8:
case X86::reloc_global_offset_table8:
return 8;
}
}
void X86AsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
const MCValue &Target,
MutableArrayRef<char> Data,
uint64_t Value, bool IsResolved,
const MCSubtargetInfo *STI) const {
unsigned Kind = Fixup.getKind();
if (Kind >= FirstLiteralRelocationKind)
return;
unsigned Size = getFixupKindSize(Kind);
assert(Fixup.getOffset() + Size <= Data.size() && "Invalid fixup offset!");
int64_t SignedValue = static_cast<int64_t>(Value);
if ((Target.isAbsolute() || IsResolved) &&
getFixupKindInfo(Fixup.getKind()).Flags &
MCFixupKindInfo::FKF_IsPCRel) {
// check that PC relative fixup fits into the fixup size.
if (Size > 0 && !isIntN(Size * 8, SignedValue))
Asm.getContext().reportError(
Fixup.getLoc(), "value of " + Twine(SignedValue) +
" is too large for field of " + Twine(Size) +
((Size == 1) ? " byte." : " bytes."));
} else {
// Check that uppper bits are either all zeros or all ones.
// Specifically ignore overflow/underflow as long as the leakage is
// limited to the lower bits. This is to remain compatible with
// other assemblers.
assert((Size == 0 || isIntN(Size * 8 + 1, SignedValue)) &&
"Value does not fit in the Fixup field");
}
for (unsigned i = 0; i != Size; ++i)
Data[Fixup.getOffset() + i] = uint8_t(Value >> (i * 8));
}
bool X86AsmBackend::mayNeedRelaxation(const MCInst &Inst,
const MCSubtargetInfo &STI) const {
// Branches can always be relaxed in either mode.
if (getRelaxedOpcodeBranch(Inst, false) != Inst.getOpcode())
return true;
// Check if this instruction is ever relaxable.
if (getRelaxedOpcodeArith(Inst) == Inst.getOpcode())
return false;
// Check if the relaxable operand has an expression. For the current set of
// relaxable instructions, the relaxable operand is always the last operand.
unsigned RelaxableOp = Inst.getNumOperands() - 1;
if (Inst.getOperand(RelaxableOp).isExpr())
return true;
return false;
}
bool X86AsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup,
uint64_t Value,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const {
// Relax if the value is too big for a (signed) i8.
return !isInt<8>(Value);
}
// FIXME: Can tblgen help at all here to verify there aren't other instructions
// we can relax?
void X86AsmBackend::relaxInstruction(MCInst &Inst,
const MCSubtargetInfo &STI) const {
// The only relaxations X86 does is from a 1byte pcrel to a 4byte pcrel.
bool Is16BitMode = STI.getFeatureBits()[X86::Mode16Bit];
unsigned RelaxedOp = getRelaxedOpcode(Inst, Is16BitMode);
if (RelaxedOp == Inst.getOpcode()) {
SmallString<256> Tmp;
raw_svector_ostream OS(Tmp);
Inst.dump_pretty(OS);
OS << "\n";
report_fatal_error("unexpected instruction to relax: " + OS.str());
}
Inst.setOpcode(RelaxedOp);
}
/// Return true if this instruction has been fully relaxed into it's most
/// general available form.
static bool isFullyRelaxed(const MCRelaxableFragment &RF) {
auto &Inst = RF.getInst();
auto &STI = *RF.getSubtargetInfo();
bool Is16BitMode = STI.getFeatureBits()[X86::Mode16Bit];
return getRelaxedOpcode(Inst, Is16BitMode) == Inst.getOpcode();
}
bool X86AsmBackend::padInstructionViaPrefix(MCRelaxableFragment &RF,
MCCodeEmitter &Emitter,
unsigned &RemainingSize) const {
if (!RF.getAllowAutoPadding())
return false;
// If the instruction isn't fully relaxed, shifting it around might require a
// larger value for one of the fixups then can be encoded. The outer loop
// will also catch this before moving to the next instruction, but we need to
// prevent padding this single instruction as well.
if (!isFullyRelaxed(RF))
return false;
const unsigned OldSize = RF.getContents().size();
if (OldSize == 15)
return false;
const unsigned MaxPossiblePad = std::min(15 - OldSize, RemainingSize);
const unsigned RemainingPrefixSize = [&]() -> unsigned {
SmallString<15> Code;
raw_svector_ostream VecOS(Code);
Emitter.emitPrefix(RF.getInst(), VecOS, STI);
assert(Code.size() < 15 && "The number of prefixes must be less than 15.");
// TODO: It turns out we need a decent amount of plumbing for the target
// specific bits to determine number of prefixes its safe to add. Various
// targets (older chips mostly, but also Atom family) encounter decoder
// stalls with too many prefixes. For testing purposes, we set the value
// externally for the moment.
unsigned ExistingPrefixSize = Code.size();
if (TargetPrefixMax <= ExistingPrefixSize)
return 0;
return TargetPrefixMax - ExistingPrefixSize;
}();
const unsigned PrefixBytesToAdd =
std::min(MaxPossiblePad, RemainingPrefixSize);
if (PrefixBytesToAdd == 0)
return false;
const uint8_t Prefix = determinePaddingPrefix(RF.getInst());
SmallString<256> Code;
Code.append(PrefixBytesToAdd, Prefix);
Code.append(RF.getContents().begin(), RF.getContents().end());
RF.getContents() = Code;
// Adjust the fixups for the change in offsets
for (auto &F : RF.getFixups()) {
F.setOffset(F.getOffset() + PrefixBytesToAdd);
}
RemainingSize -= PrefixBytesToAdd;
return true;
}
bool X86AsmBackend::padInstructionViaRelaxation(MCRelaxableFragment &RF,
MCCodeEmitter &Emitter,
unsigned &RemainingSize) const {
if (isFullyRelaxed(RF))
// TODO: There are lots of other tricks we could apply for increasing
// encoding size without impacting performance.
return false;
MCInst Relaxed = RF.getInst();
relaxInstruction(Relaxed, *RF.getSubtargetInfo());
SmallVector<MCFixup, 4> Fixups;
SmallString<15> Code;
raw_svector_ostream VecOS(Code);
Emitter.encodeInstruction(Relaxed, VecOS, Fixups, *RF.getSubtargetInfo());
const unsigned OldSize = RF.getContents().size();
const unsigned NewSize = Code.size();
assert(NewSize >= OldSize && "size decrease during relaxation?");
unsigned Delta = NewSize - OldSize;
if (Delta > RemainingSize)
return false;
RF.setInst(Relaxed);
RF.getContents() = Code;
RF.getFixups() = Fixups;
RemainingSize -= Delta;
return true;
}
bool X86AsmBackend::padInstructionEncoding(MCRelaxableFragment &RF,
MCCodeEmitter &Emitter,
unsigned &RemainingSize) const {
bool Changed = false;
if (RemainingSize != 0)
Changed |= padInstructionViaRelaxation(RF, Emitter, RemainingSize);
if (RemainingSize != 0)
Changed |= padInstructionViaPrefix(RF, Emitter, RemainingSize);
return Changed;
}
void X86AsmBackend::finishLayout(MCAssembler const &Asm,
MCAsmLayout &Layout) const {
// See if we can further relax some instructions to cut down on the number of
// nop bytes required for code alignment. The actual win is in reducing
// instruction count, not number of bytes. Modern X86-64 can easily end up
// decode limited. It is often better to reduce the number of instructions
// (i.e. eliminate nops) even at the cost of increasing the size and
// complexity of others.
if (!X86PadForAlign && !X86PadForBranchAlign)
return;
// The processed regions are delimitered by LabeledFragments. -g may have more
// MCSymbols and therefore different relaxation results. X86PadForAlign is
// disabled by default to eliminate the -g vs non -g difference.
DenseSet<MCFragment *> LabeledFragments;
for (const MCSymbol &S : Asm.symbols())
LabeledFragments.insert(S.getFragment(false));
for (MCSection &Sec : Asm) {
if (!Sec.getKind().isText())
continue;
SmallVector<MCRelaxableFragment *, 4> Relaxable;
for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
MCFragment &F = *I;
if (LabeledFragments.count(&F))
Relaxable.clear();
if (F.getKind() == MCFragment::FT_Data ||
F.getKind() == MCFragment::FT_CompactEncodedInst)
// Skip and ignore
continue;
if (F.getKind() == MCFragment::FT_Relaxable) {
auto &RF = cast<MCRelaxableFragment>(*I);
Relaxable.push_back(&RF);
continue;
}
auto canHandle = [](MCFragment &F) -> bool {
switch (F.getKind()) {
default:
return false;
case MCFragment::FT_Align:
return X86PadForAlign;
case MCFragment::FT_BoundaryAlign:
return X86PadForBranchAlign;
}
};
// For any unhandled kind, assume we can't change layout.
if (!canHandle(F)) {
Relaxable.clear();
continue;
}
#ifndef NDEBUG
const uint64_t OrigOffset = Layout.getFragmentOffset(&F);
#endif
const uint64_t OrigSize = Asm.computeFragmentSize(Layout, F);
// To keep the effects local, prefer to relax instructions closest to
// the align directive. This is purely about human understandability
// of the resulting code. If we later find a reason to expand
// particular instructions over others, we can adjust.
MCFragment *FirstChangedFragment = nullptr;
unsigned RemainingSize = OrigSize;
while (!Relaxable.empty() && RemainingSize != 0) {
auto &RF = *Relaxable.pop_back_val();
// Give the backend a chance to play any tricks it wishes to increase
// the encoding size of the given instruction. Target independent code
// will try further relaxation, but target's may play further tricks.
if (padInstructionEncoding(RF, Asm.getEmitter(), RemainingSize))
FirstChangedFragment = &RF;
// If we have an instruction which hasn't been fully relaxed, we can't
// skip past it and insert bytes before it. Changing its starting
// offset might require a larger negative offset than it can encode.
// We don't need to worry about larger positive offsets as none of the
// possible offsets between this and our align are visible, and the
// ones afterwards aren't changing.
if (!isFullyRelaxed(RF))
break;
}
Relaxable.clear();
if (FirstChangedFragment) {
// Make sure the offsets for any fragments in the effected range get
// updated. Note that this (conservatively) invalidates the offsets of
// those following, but this is not required.
Layout.invalidateFragmentsFrom(FirstChangedFragment);
}
// BoundaryAlign explicitly tracks it's size (unlike align)
if (F.getKind() == MCFragment::FT_BoundaryAlign)
cast<MCBoundaryAlignFragment>(F).setSize(RemainingSize);
#ifndef NDEBUG
const uint64_t FinalOffset = Layout.getFragmentOffset(&F);
const uint64_t FinalSize = Asm.computeFragmentSize(Layout, F);
assert(OrigOffset + OrigSize == FinalOffset + FinalSize &&
"can't move start of next fragment!");
assert(FinalSize == RemainingSize && "inconsistent size computation?");
#endif
// If we're looking at a boundary align, make sure we don't try to pad
// its target instructions for some following directive. Doing so would
// break the alignment of the current boundary align.
if (auto *BF = dyn_cast<MCBoundaryAlignFragment>(&F)) {
const MCFragment *LastFragment = BF->getLastFragment();
if (!LastFragment)
continue;
while (&*I != LastFragment)
++I;
}
}
}
// The layout is done. Mark every fragment as valid.
for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
MCSection &Section = *Layout.getSectionOrder()[i];
Layout.getFragmentOffset(&*Section.getFragmentList().rbegin());
Asm.computeFragmentSize(Layout, *Section.getFragmentList().rbegin());
}
}
unsigned X86AsmBackend::getMaximumNopSize(const MCSubtargetInfo &STI) const {
if (STI.hasFeature(X86::Mode16Bit))
return 4;
if (!STI.hasFeature(X86::FeatureNOPL) && !STI.hasFeature(X86::Mode64Bit))
return 1;
if (STI.getFeatureBits()[X86::TuningFast7ByteNOP])
return 7;
if (STI.getFeatureBits()[X86::TuningFast15ByteNOP])
return 15;
if (STI.getFeatureBits()[X86::TuningFast11ByteNOP])
return 11;
// FIXME: handle 32-bit mode
// 15-bytes is the longest single NOP instruction, but 10-bytes is
// commonly the longest that can be efficiently decoded.
return 10;
}
/// Write a sequence of optimal nops to the output, covering \p Count
/// bytes.
/// \return - true on success, false on failure
bool X86AsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
const MCSubtargetInfo *STI) const {
static const char Nops32Bit[10][11] = {
// nop
"\x90",
// xchg %ax,%ax
"\x66\x90",
// nopl (%[re]ax)
"\x0f\x1f\x00",
// nopl 0(%[re]ax)
"\x0f\x1f\x40\x00",
// nopl 0(%[re]ax,%[re]ax,1)
"\x0f\x1f\x44\x00\x00",
// nopw 0(%[re]ax,%[re]ax,1)
"\x66\x0f\x1f\x44\x00\x00",
// nopl 0L(%[re]ax)
"\x0f\x1f\x80\x00\x00\x00\x00",
// nopl 0L(%[re]ax,%[re]ax,1)
"\x0f\x1f\x84\x00\x00\x00\x00\x00",
// nopw 0L(%[re]ax,%[re]ax,1)
"\x66\x0f\x1f\x84\x00\x00\x00\x00\x00",
// nopw %cs:0L(%[re]ax,%[re]ax,1)
"\x66\x2e\x0f\x1f\x84\x00\x00\x00\x00\x00",
};
// 16-bit mode uses different nop patterns than 32-bit.
static const char Nops16Bit[4][11] = {
// nop
"\x90",
// xchg %eax,%eax
"\x66\x90",
// lea 0(%si),%si
"\x8d\x74\x00",
// lea 0w(%si),%si
"\x8d\xb4\x00\x00",
};
const char(*Nops)[11] =
STI->getFeatureBits()[X86::Mode16Bit] ? Nops16Bit : Nops32Bit;
uint64_t MaxNopLength = (uint64_t)getMaximumNopSize(*STI);
// Emit as many MaxNopLength NOPs as needed, then emit a NOP of the remaining
// length.
do {
const uint8_t ThisNopLength = (uint8_t) std::min(Count, MaxNopLength);
const uint8_t Prefixes = ThisNopLength <= 10 ? 0 : ThisNopLength - 10;
for (uint8_t i = 0; i < Prefixes; i++)
OS << '\x66';
const uint8_t Rest = ThisNopLength - Prefixes;
if (Rest != 0)
OS.write(Nops[Rest - 1], Rest);
Count -= ThisNopLength;
} while (Count != 0);
return true;
}
/* *** */
namespace {
class ELFX86AsmBackend : public X86AsmBackend {
public:
uint8_t OSABI;
ELFX86AsmBackend(const Target &T, uint8_t OSABI, const MCSubtargetInfo &STI)
: X86AsmBackend(T, STI), OSABI(OSABI) {}
};
class ELFX86_32AsmBackend : public ELFX86AsmBackend {
public:
ELFX86_32AsmBackend(const Target &T, uint8_t OSABI,
const MCSubtargetInfo &STI)
: ELFX86AsmBackend(T, OSABI, STI) {}
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override {
return createX86ELFObjectWriter(/*IsELF64*/ false, OSABI, ELF::EM_386);
}
};
class ELFX86_X32AsmBackend : public ELFX86AsmBackend {
public:
ELFX86_X32AsmBackend(const Target &T, uint8_t OSABI,
const MCSubtargetInfo &STI)
: ELFX86AsmBackend(T, OSABI, STI) {}
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override {
return createX86ELFObjectWriter(/*IsELF64*/ false, OSABI,
ELF::EM_X86_64);
}
};
class ELFX86_IAMCUAsmBackend : public ELFX86AsmBackend {
public:
ELFX86_IAMCUAsmBackend(const Target &T, uint8_t OSABI,
const MCSubtargetInfo &STI)
: ELFX86AsmBackend(T, OSABI, STI) {}
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override {
return createX86ELFObjectWriter(/*IsELF64*/ false, OSABI,
ELF::EM_IAMCU);
}
};
class ELFX86_64AsmBackend : public ELFX86AsmBackend {
public:
ELFX86_64AsmBackend(const Target &T, uint8_t OSABI,
const MCSubtargetInfo &STI)
: ELFX86AsmBackend(T, OSABI, STI) {}
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override {
return createX86ELFObjectWriter(/*IsELF64*/ true, OSABI, ELF::EM_X86_64);
}
};
class WindowsX86AsmBackend : public X86AsmBackend {
bool Is64Bit;
public:
WindowsX86AsmBackend(const Target &T, bool is64Bit,
const MCSubtargetInfo &STI)
: X86AsmBackend(T, STI)
, Is64Bit(is64Bit) {
}
Optional<MCFixupKind> getFixupKind(StringRef Name) const override {
return StringSwitch<Optional<MCFixupKind>>(Name)
.Case("dir32", FK_Data_4)
.Case("secrel32", FK_SecRel_4)
.Case("secidx", FK_SecRel_2)
.Default(MCAsmBackend::getFixupKind(Name));
}
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override {
return createX86WinCOFFObjectWriter(Is64Bit);
}
};
namespace CU {
/// Compact unwind encoding values.
enum CompactUnwindEncodings {
/// [RE]BP based frame where [RE]BP is pused on the stack immediately after
/// the return address, then [RE]SP is moved to [RE]BP.
UNWIND_MODE_BP_FRAME = 0x01000000,
/// A frameless function with a small constant stack size.
UNWIND_MODE_STACK_IMMD = 0x02000000,
/// A frameless function with a large constant stack size.
UNWIND_MODE_STACK_IND = 0x03000000,
/// No compact unwind encoding is available.
UNWIND_MODE_DWARF = 0x04000000,
/// Mask for encoding the frame registers.
UNWIND_BP_FRAME_REGISTERS = 0x00007FFF,
/// Mask for encoding the frameless registers.
UNWIND_FRAMELESS_STACK_REG_PERMUTATION = 0x000003FF
};
} // namespace CU
class DarwinX86AsmBackend : public X86AsmBackend {
const MCRegisterInfo &MRI;
/// Number of registers that can be saved in a compact unwind encoding.
enum { CU_NUM_SAVED_REGS = 6 };
mutable unsigned SavedRegs[CU_NUM_SAVED_REGS];
Triple TT;
bool Is64Bit;
unsigned OffsetSize; ///< Offset of a "push" instruction.
unsigned MoveInstrSize; ///< Size of a "move" instruction.
unsigned StackDivide; ///< Amount to adjust stack size by.
protected:
/// Size of a "push" instruction for the given register.
unsigned PushInstrSize(unsigned Reg) const {
switch (Reg) {
case X86::EBX:
case X86::ECX:
case X86::EDX:
case X86::EDI:
case X86::ESI:
case X86::EBP:
case X86::RBX:
case X86::RBP:
return 1;
case X86::R12:
case X86::R13:
case X86::R14:
case X86::R15:
return 2;
}
return 1;
}
private:
/// Get the compact unwind number for a given register. The number
/// corresponds to the enum lists in compact_unwind_encoding.h.
int getCompactUnwindRegNum(unsigned Reg) const {
static const MCPhysReg CU32BitRegs[7] = {
X86::EBX, X86::ECX, X86::EDX, X86::EDI, X86::ESI, X86::EBP, 0
};
static const MCPhysReg CU64BitRegs[] = {
X86::RBX, X86::R12, X86::R13, X86::R14, X86::R15, X86::RBP, 0
};
const MCPhysReg *CURegs = Is64Bit ? CU64BitRegs : CU32BitRegs;
for (int Idx = 1; *CURegs; ++CURegs, ++Idx)
if (*CURegs == Reg)
return Idx;
return -1;
}
/// Return the registers encoded for a compact encoding with a frame
/// pointer.
uint32_t encodeCompactUnwindRegistersWithFrame() const {
// Encode the registers in the order they were saved --- 3-bits per
// register. The list of saved registers is assumed to be in reverse
// order. The registers are numbered from 1 to CU_NUM_SAVED_REGS.
uint32_t RegEnc = 0;
for (int i = 0, Idx = 0; i != CU_NUM_SAVED_REGS; ++i) {
unsigned Reg = SavedRegs[i];
if (Reg == 0) break;
int CURegNum = getCompactUnwindRegNum(Reg);
if (CURegNum == -1) return ~0U;
// Encode the 3-bit register number in order, skipping over 3-bits for
// each register.
RegEnc |= (CURegNum & 0x7) << (Idx++ * 3);
}
assert((RegEnc & 0x3FFFF) == RegEnc &&
"Invalid compact register encoding!");
return RegEnc;
}
/// Create the permutation encoding used with frameless stacks. It is
/// passed the number of registers to be saved and an array of the registers
/// saved.
uint32_t encodeCompactUnwindRegistersWithoutFrame(unsigned RegCount) const {
// The saved registers are numbered from 1 to 6. In order to encode the
// order in which they were saved, we re-number them according to their
// place in the register order. The re-numbering is relative to the last
// re-numbered register. E.g., if we have registers {6, 2, 4, 5} saved in
// that order:
//
// Orig Re-Num
// ---- ------
// 6 6
// 2 2
// 4 3
// 5 3
//
for (unsigned i = 0; i < RegCount; ++i) {
int CUReg = getCompactUnwindRegNum(SavedRegs[i]);
if (CUReg == -1) return ~0U;
SavedRegs[i] = CUReg;
}
// Reverse the list.
std::reverse(&SavedRegs[0], &SavedRegs[CU_NUM_SAVED_REGS]);
uint32_t RenumRegs[CU_NUM_SAVED_REGS];
for (unsigned i = CU_NUM_SAVED_REGS - RegCount; i < CU_NUM_SAVED_REGS; ++i){
unsigned Countless = 0;
for (unsigned j = CU_NUM_SAVED_REGS - RegCount; j < i; ++j)
if (SavedRegs[j] < SavedRegs[i])
++Countless;
RenumRegs[i] = SavedRegs[i] - Countless - 1;
}
// Take the renumbered values and encode them into a 10-bit number.
uint32_t permutationEncoding = 0;
switch (RegCount) {
case 6:
permutationEncoding |= 120 * RenumRegs[0] + 24 * RenumRegs[1]
+ 6 * RenumRegs[2] + 2 * RenumRegs[3]
+ RenumRegs[4];
break;
case 5:
permutationEncoding |= 120 * RenumRegs[1] + 24 * RenumRegs[2]
+ 6 * RenumRegs[3] + 2 * RenumRegs[4]
+ RenumRegs[5];
break;
case 4:
permutationEncoding |= 60 * RenumRegs[2] + 12 * RenumRegs[3]
+ 3 * RenumRegs[4] + RenumRegs[5];
break;
case 3:
permutationEncoding |= 20 * RenumRegs[3] + 4 * RenumRegs[4]
+ RenumRegs[5];
break;
case 2:
permutationEncoding |= 5 * RenumRegs[4] + RenumRegs[5];
break;
case 1:
permutationEncoding |= RenumRegs[5];
break;
}
assert((permutationEncoding & 0x3FF) == permutationEncoding &&
"Invalid compact register encoding!");
return permutationEncoding;
}
public:
DarwinX86AsmBackend(const Target &T, const MCRegisterInfo &MRI,
const MCSubtargetInfo &STI)
: X86AsmBackend(T, STI), MRI(MRI), TT(STI.getTargetTriple()),
Is64Bit(TT.isArch64Bit()) {
memset(SavedRegs, 0, sizeof(SavedRegs));
OffsetSize = Is64Bit ? 8 : 4;
MoveInstrSize = Is64Bit ? 3 : 2;
StackDivide = Is64Bit ? 8 : 4;
}
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override {
uint32_t CPUType = cantFail(MachO::getCPUType(TT));
uint32_t CPUSubType = cantFail(MachO::getCPUSubType(TT));
return createX86MachObjectWriter(Is64Bit, CPUType, CPUSubType);
}
/// Implementation of algorithm to generate the compact unwind encoding
/// for the CFI instructions.
uint32_t
generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction> Instrs) const override {
if (Instrs.empty()) return 0;
// Reset the saved registers.
unsigned SavedRegIdx = 0;
memset(SavedRegs, 0, sizeof(SavedRegs));
bool HasFP = false;
// Encode that we are using EBP/RBP as the frame pointer.
uint32_t CompactUnwindEncoding = 0;
unsigned SubtractInstrIdx = Is64Bit ? 3 : 2;
unsigned InstrOffset = 0;
unsigned StackAdjust = 0;
unsigned StackSize = 0;
unsigned NumDefCFAOffsets = 0;
int MinAbsOffset = std::numeric_limits<int>::max();
for (const MCCFIInstruction &Inst : Instrs) {
switch (Inst.getOperation()) {
default:
// Any other CFI directives indicate a frame that we aren't prepared
// to represent via compact unwind, so just bail out.
return 0;
case MCCFIInstruction::OpDefCfaRegister: {
// Defines a frame pointer. E.g.
//
// movq %rsp, %rbp
// L0:
// .cfi_def_cfa_register %rbp
//
HasFP = true;
// If the frame pointer is other than esp/rsp, we do not have a way to
// generate a compact unwinding representation, so bail out.
if (*MRI.getLLVMRegNum(Inst.getRegister(), true) !=
(Is64Bit ? X86::RBP : X86::EBP))
return 0;
// Reset the counts.
memset(SavedRegs, 0, sizeof(SavedRegs));
StackAdjust = 0;
SavedRegIdx = 0;
MinAbsOffset = std::numeric_limits<int>::max();
InstrOffset += MoveInstrSize;
break;
}
case MCCFIInstruction::OpDefCfaOffset: {
// Defines a new offset for the CFA. E.g.
//
// With frame:
//
// pushq %rbp
// L0:
// .cfi_def_cfa_offset 16
//
// Without frame:
//
// subq $72, %rsp
// L0:
// .cfi_def_cfa_offset 80
//
StackSize = Inst.getOffset() / StackDivide;
++NumDefCFAOffsets;
break;
}
case MCCFIInstruction::OpOffset: {
// Defines a "push" of a callee-saved register. E.g.
//
// pushq %r15
// pushq %r14
// pushq %rbx
// L0:
// subq $120, %rsp
// L1:
// .cfi_offset %rbx, -40
// .cfi_offset %r14, -32
// .cfi_offset %r15, -24
//
if (SavedRegIdx == CU_NUM_SAVED_REGS)
// If there are too many saved registers, we cannot use a compact
// unwind encoding.
return CU::UNWIND_MODE_DWARF;
unsigned Reg = *MRI.getLLVMRegNum(Inst.getRegister(), true);
SavedRegs[SavedRegIdx++] = Reg;
StackAdjust += OffsetSize;
MinAbsOffset = std::min(MinAbsOffset, abs(Inst.getOffset()));
InstrOffset += PushInstrSize(Reg);
break;
}
}
}
StackAdjust /= StackDivide;
if (HasFP) {
if ((StackAdjust & 0xFF) != StackAdjust)
// Offset was too big for a compact unwind encoding.
return CU::UNWIND_MODE_DWARF;
// We don't attempt to track a real StackAdjust, so if the saved registers
// aren't adjacent to rbp we can't cope.
if (SavedRegIdx != 0 && MinAbsOffset != 3 * (int)OffsetSize)
return CU::UNWIND_MODE_DWARF;
// Get the encoding of the saved registers when we have a frame pointer.
uint32_t RegEnc = encodeCompactUnwindRegistersWithFrame();
if (RegEnc == ~0U) return CU::UNWIND_MODE_DWARF;
CompactUnwindEncoding |= CU::UNWIND_MODE_BP_FRAME;
CompactUnwindEncoding |= (StackAdjust & 0xFF) << 16;
CompactUnwindEncoding |= RegEnc & CU::UNWIND_BP_FRAME_REGISTERS;
} else {
SubtractInstrIdx += InstrOffset;
++StackAdjust;
if ((StackSize & 0xFF) == StackSize) {
// Frameless stack with a small stack size.
CompactUnwindEncoding |= CU::UNWIND_MODE_STACK_IMMD;
// Encode the stack size.
CompactUnwindEncoding |= (StackSize & 0xFF) << 16;
} else {
if ((StackAdjust & 0x7) != StackAdjust)
// The extra stack adjustments are too big for us to handle.
return CU::UNWIND_MODE_DWARF;
// Frameless stack with an offset too large for us to encode compactly.
CompactUnwindEncoding |= CU::UNWIND_MODE_STACK_IND;
// Encode the offset to the nnnnnn value in the 'subl $nnnnnn, ESP'
// instruction.
CompactUnwindEncoding |= (SubtractInstrIdx & 0xFF) << 16;
// Encode any extra stack adjustments (done via push instructions).
CompactUnwindEncoding |= (StackAdjust & 0x7) << 13;
}
// Encode the number of registers saved. (Reverse the list first.)
std::reverse(&SavedRegs[0], &SavedRegs[SavedRegIdx]);
CompactUnwindEncoding |= (SavedRegIdx & 0x7) << 10;
// Get the encoding of the saved registers when we don't have a frame
// pointer.
uint32_t RegEnc = encodeCompactUnwindRegistersWithoutFrame(SavedRegIdx);
if (RegEnc == ~0U) return CU::UNWIND_MODE_DWARF;
// Encode the register encoding.
CompactUnwindEncoding |=
RegEnc & CU::UNWIND_FRAMELESS_STACK_REG_PERMUTATION;
}
return CompactUnwindEncoding;
}
};
} // end anonymous namespace
MCAsmBackend *llvm::createX86_32AsmBackend(const Target &T,
const MCSubtargetInfo &STI,
const MCRegisterInfo &MRI,
const MCTargetOptions &Options) {
const Triple &TheTriple = STI.getTargetTriple();
if (TheTriple.isOSBinFormatMachO())
return new DarwinX86AsmBackend(T, MRI, STI);
if (TheTriple.isOSWindows() && TheTriple.isOSBinFormatCOFF())
return new WindowsX86AsmBackend(T, false, STI);
uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
if (TheTriple.isOSIAMCU())
return new ELFX86_IAMCUAsmBackend(T, OSABI, STI);
return new ELFX86_32AsmBackend(T, OSABI, STI);
}
MCAsmBackend *llvm::createX86_64AsmBackend(const Target &T,
const MCSubtargetInfo &STI,
const MCRegisterInfo &MRI,
const MCTargetOptions &Options) {
const Triple &TheTriple = STI.getTargetTriple();
if (TheTriple.isOSBinFormatMachO())
return new DarwinX86AsmBackend(T, MRI, STI);
if (TheTriple.isOSWindows() && TheTriple.isOSBinFormatCOFF())
return new WindowsX86AsmBackend(T, true, STI);
uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
if (TheTriple.isX32())
return new ELFX86_X32AsmBackend(T, OSABI, STI);
return new ELFX86_64AsmBackend(T, OSABI, STI);
}