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llvm-project/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp

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//===-- AArch64AsmBackend.cpp - AArch64 Assembler Backend -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "AArch64.h"
#include "AArch64RegisterInfo.h"
#include "MCTargetDesc/AArch64FixupKinds.h"
#include "llvm/ADT/Triple.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCDirectives.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MachO.h"
using namespace llvm;
namespace {
class AArch64AsmBackend : public MCAsmBackend {
static const unsigned PCRelFlagVal =
MCFixupKindInfo::FKF_IsAlignedDownTo32Bits | MCFixupKindInfo::FKF_IsPCRel;
public:
AArch64AsmBackend(const Target &T) : MCAsmBackend() {}
unsigned getNumFixupKinds() const override {
return AArch64::NumTargetFixupKinds;
}
const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
const static MCFixupKindInfo Infos[AArch64::NumTargetFixupKinds] = {
// This table *must* be in the order that the fixup_* kinds are defined in
// AArch64FixupKinds.h.
//
// Name Offset (bits) Size (bits) Flags
{ "fixup_aarch64_pcrel_adr_imm21", 0, 32, PCRelFlagVal },
{ "fixup_aarch64_pcrel_adrp_imm21", 0, 32, PCRelFlagVal },
{ "fixup_aarch64_add_imm12", 10, 12, 0 },
{ "fixup_aarch64_ldst_imm12_scale1", 10, 12, 0 },
{ "fixup_aarch64_ldst_imm12_scale2", 10, 12, 0 },
{ "fixup_aarch64_ldst_imm12_scale4", 10, 12, 0 },
{ "fixup_aarch64_ldst_imm12_scale8", 10, 12, 0 },
{ "fixup_aarch64_ldst_imm12_scale16", 10, 12, 0 },
{ "fixup_aarch64_ldr_pcrel_imm19", 5, 19, PCRelFlagVal },
{ "fixup_aarch64_movw", 5, 16, 0 },
{ "fixup_aarch64_pcrel_branch14", 5, 14, PCRelFlagVal },
{ "fixup_aarch64_pcrel_branch19", 5, 19, PCRelFlagVal },
{ "fixup_aarch64_pcrel_branch26", 0, 26, PCRelFlagVal },
{ "fixup_aarch64_pcrel_call26", 0, 26, PCRelFlagVal },
{ "fixup_aarch64_tlsdesc_call", 0, 0, 0 }
};
if (Kind < FirstTargetFixupKind)
return MCAsmBackend::getFixupKindInfo(Kind);
assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
"Invalid kind!");
return Infos[Kind - FirstTargetFixupKind];
}
void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
uint64_t Value, bool IsPCRel) const override;
bool mayNeedRelaxation(const MCInst &Inst) const override;
bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const override;
void relaxInstruction(const MCInst &Inst, MCInst &Res) const override;
bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override;
void HandleAssemblerFlag(MCAssemblerFlag Flag) {}
unsigned getPointerSize() const { return 8; }
};
} // end anonymous namespace
/// \brief The number of bytes the fixup may change.
static unsigned getFixupKindNumBytes(unsigned Kind) {
switch (Kind) {
default:
llvm_unreachable("Unknown fixup kind!");
case AArch64::fixup_aarch64_tlsdesc_call:
return 0;
case FK_Data_1:
return 1;
case FK_Data_2:
case AArch64::fixup_aarch64_movw:
return 2;
case AArch64::fixup_aarch64_pcrel_branch14:
case AArch64::fixup_aarch64_add_imm12:
case AArch64::fixup_aarch64_ldst_imm12_scale1:
case AArch64::fixup_aarch64_ldst_imm12_scale2:
case AArch64::fixup_aarch64_ldst_imm12_scale4:
case AArch64::fixup_aarch64_ldst_imm12_scale8:
case AArch64::fixup_aarch64_ldst_imm12_scale16:
case AArch64::fixup_aarch64_ldr_pcrel_imm19:
case AArch64::fixup_aarch64_pcrel_branch19:
return 3;
case AArch64::fixup_aarch64_pcrel_adr_imm21:
case AArch64::fixup_aarch64_pcrel_adrp_imm21:
case AArch64::fixup_aarch64_pcrel_branch26:
case AArch64::fixup_aarch64_pcrel_call26:
case FK_Data_4:
return 4;
case FK_Data_8:
return 8;
}
}
static unsigned AdrImmBits(unsigned Value) {
unsigned lo2 = Value & 0x3;
unsigned hi19 = (Value & 0x1ffffc) >> 2;
return (hi19 << 5) | (lo2 << 29);
}
static uint64_t adjustFixupValue(unsigned Kind, uint64_t Value) {
int64_t SignedValue = static_cast<int64_t>(Value);
switch (Kind) {
default:
llvm_unreachable("Unknown fixup kind!");
case AArch64::fixup_aarch64_pcrel_adr_imm21:
if (SignedValue > 2097151 || SignedValue < -2097152)
report_fatal_error("fixup value out of range");
return AdrImmBits(Value & 0x1fffffULL);
case AArch64::fixup_aarch64_pcrel_adrp_imm21:
return AdrImmBits((Value & 0x1fffff000ULL) >> 12);
case AArch64::fixup_aarch64_ldr_pcrel_imm19:
case AArch64::fixup_aarch64_pcrel_branch19:
// Signed 21-bit immediate
if (SignedValue > 2097151 || SignedValue < -2097152)
report_fatal_error("fixup value out of range");
// Low two bits are not encoded.
return (Value >> 2) & 0x7ffff;
case AArch64::fixup_aarch64_add_imm12:
case AArch64::fixup_aarch64_ldst_imm12_scale1:
// Unsigned 12-bit immediate
if (Value >= 0x1000)
report_fatal_error("invalid imm12 fixup value");
return Value;
case AArch64::fixup_aarch64_ldst_imm12_scale2:
// Unsigned 12-bit immediate which gets multiplied by 2
if (Value & 1 || Value >= 0x2000)
report_fatal_error("invalid imm12 fixup value");
return Value >> 1;
case AArch64::fixup_aarch64_ldst_imm12_scale4:
// Unsigned 12-bit immediate which gets multiplied by 4
if (Value & 3 || Value >= 0x4000)
report_fatal_error("invalid imm12 fixup value");
return Value >> 2;
case AArch64::fixup_aarch64_ldst_imm12_scale8:
// Unsigned 12-bit immediate which gets multiplied by 8
if (Value & 7 || Value >= 0x8000)
report_fatal_error("invalid imm12 fixup value");
return Value >> 3;
case AArch64::fixup_aarch64_ldst_imm12_scale16:
// Unsigned 12-bit immediate which gets multiplied by 16
if (Value & 15 || Value >= 0x10000)
report_fatal_error("invalid imm12 fixup value");
return Value >> 4;
case AArch64::fixup_aarch64_movw:
report_fatal_error("no resolvable MOVZ/MOVK fixups supported yet");
return Value;
case AArch64::fixup_aarch64_pcrel_branch14:
// Signed 16-bit immediate
if (SignedValue > 32767 || SignedValue < -32768)
report_fatal_error("fixup value out of range");
// Low two bits are not encoded (4-byte alignment assumed).
if (Value & 0x3)
report_fatal_error("fixup not sufficiently aligned");
return (Value >> 2) & 0x3fff;
case AArch64::fixup_aarch64_pcrel_branch26:
case AArch64::fixup_aarch64_pcrel_call26:
// Signed 28-bit immediate
if (SignedValue > 134217727 || SignedValue < -134217728)
report_fatal_error("fixup value out of range");
// Low two bits are not encoded (4-byte alignment assumed).
if (Value & 0x3)
report_fatal_error("fixup not sufficiently aligned");
return (Value >> 2) & 0x3ffffff;
case FK_Data_1:
case FK_Data_2:
case FK_Data_4:
case FK_Data_8:
return Value;
}
}
void AArch64AsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
unsigned DataSize, uint64_t Value,
bool IsPCRel) const {
unsigned NumBytes = getFixupKindNumBytes(Fixup.getKind());
if (!Value)
return; // Doesn't change encoding.
MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind());
// Apply any target-specific value adjustments.
Value = adjustFixupValue(Fixup.getKind(), Value);
// Shift the value into position.
Value <<= Info.TargetOffset;
unsigned Offset = Fixup.getOffset();
assert(Offset + NumBytes <= DataSize && "Invalid fixup offset!");
// For each byte of the fragment that the fixup touches, mask in the
// bits from the fixup value.
for (unsigned i = 0; i != NumBytes; ++i)
Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
}
bool AArch64AsmBackend::mayNeedRelaxation(const MCInst &Inst) const {
return false;
}
bool AArch64AsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup,
uint64_t Value,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const {
// FIXME: This isn't correct for AArch64. Just moving the "generic" logic
// into the targets for now.
//
// Relax if the value is too big for a (signed) i8.
return int64_t(Value) != int64_t(int8_t(Value));
}
void AArch64AsmBackend::relaxInstruction(const MCInst &Inst,
MCInst &Res) const {
llvm_unreachable("AArch64AsmBackend::relaxInstruction() unimplemented");
}
bool AArch64AsmBackend::writeNopData(uint64_t Count, MCObjectWriter *OW) const {
// If the count is not 4-byte aligned, we must be writing data into the text
// section (otherwise we have unaligned instructions, and thus have far
// bigger problems), so just write zeros instead.
OW->WriteZeros(Count % 4);
// We are properly aligned, so write NOPs as requested.
Count /= 4;
for (uint64_t i = 0; i != Count; ++i)
OW->write32(0xd503201f);
return true;
}
namespace {
namespace CU {
/// \brief Compact unwind encoding values.
enum CompactUnwindEncodings {
/// \brief A "frameless" leaf function, where no non-volatile registers are
/// saved. The return remains in LR throughout the function.
UNWIND_AArch64_MODE_FRAMELESS = 0x02000000,
/// \brief No compact unwind encoding available. Instead the low 23-bits of
/// the compact unwind encoding is the offset of the DWARF FDE in the
/// __eh_frame section. This mode is never used in object files. It is only
/// generated by the linker in final linked images, which have only DWARF info
/// for a function.
UNWIND_AArch64_MODE_DWARF = 0x03000000,
/// \brief This is a standard arm64 prologue where FP/LR are immediately
/// pushed on the stack, then SP is copied to FP. If there are any
/// non-volatile register saved, they are copied into the stack fame in pairs
/// in a contiguous ranger right below the saved FP/LR pair. Any subset of the
/// five X pairs and four D pairs can be saved, but the memory layout must be
/// in register number order.
UNWIND_AArch64_MODE_FRAME = 0x04000000,
/// \brief Frame register pair encodings.
UNWIND_AArch64_FRAME_X19_X20_PAIR = 0x00000001,
UNWIND_AArch64_FRAME_X21_X22_PAIR = 0x00000002,
UNWIND_AArch64_FRAME_X23_X24_PAIR = 0x00000004,
UNWIND_AArch64_FRAME_X25_X26_PAIR = 0x00000008,
UNWIND_AArch64_FRAME_X27_X28_PAIR = 0x00000010,
UNWIND_AArch64_FRAME_D8_D9_PAIR = 0x00000100,
UNWIND_AArch64_FRAME_D10_D11_PAIR = 0x00000200,
UNWIND_AArch64_FRAME_D12_D13_PAIR = 0x00000400,
UNWIND_AArch64_FRAME_D14_D15_PAIR = 0x00000800
};
} // end CU namespace
// FIXME: This should be in a separate file.
class DarwinAArch64AsmBackend : public AArch64AsmBackend {
const MCRegisterInfo &MRI;
/// \brief Encode compact unwind stack adjustment for frameless functions.
/// See UNWIND_AArch64_FRAMELESS_STACK_SIZE_MASK in compact_unwind_encoding.h.
/// The stack size always needs to be 16 byte aligned.
uint32_t encodeStackAdjustment(uint32_t StackSize) const {
return (StackSize / 16) << 12;
}
public:
DarwinAArch64AsmBackend(const Target &T, const MCRegisterInfo &MRI)
: AArch64AsmBackend(T), MRI(MRI) {}
MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override {
return createAArch64MachObjectWriter(OS, MachO::CPU_TYPE_ARM64,
MachO::CPU_SUBTYPE_ARM64_ALL);
}
/// \brief Generate the compact unwind encoding from the CFI directives.
uint32_t generateCompactUnwindEncoding(
ArrayRef<MCCFIInstruction> Instrs) const override {
if (Instrs.empty())
return CU::UNWIND_AArch64_MODE_FRAMELESS;
bool HasFP = false;
unsigned StackSize = 0;
uint32_t CompactUnwindEncoding = 0;
for (size_t i = 0, e = Instrs.size(); i != e; ++i) {
const MCCFIInstruction &Inst = Instrs[i];
switch (Inst.getOperation()) {
default:
// Cannot handle this directive: bail out.
return CU::UNWIND_AArch64_MODE_DWARF;
case MCCFIInstruction::OpDefCfa: {
// Defines a frame pointer.
assert(getXRegFromWReg(MRI.getLLVMRegNum(Inst.getRegister(), true)) ==
AArch64::FP &&
"Invalid frame pointer!");
assert(i + 2 < e && "Insufficient CFI instructions to define a frame!");
const MCCFIInstruction &LRPush = Instrs[++i];
assert(LRPush.getOperation() == MCCFIInstruction::OpOffset &&
"Link register not pushed!");
const MCCFIInstruction &FPPush = Instrs[++i];
assert(FPPush.getOperation() == MCCFIInstruction::OpOffset &&
"Frame pointer not pushed!");
unsigned LRReg = MRI.getLLVMRegNum(LRPush.getRegister(), true);
unsigned FPReg = MRI.getLLVMRegNum(FPPush.getRegister(), true);
LRReg = getXRegFromWReg(LRReg);
FPReg = getXRegFromWReg(FPReg);
assert(LRReg == AArch64::LR && FPReg == AArch64::FP &&
"Pushing invalid registers for frame!");
// Indicate that the function has a frame.
CompactUnwindEncoding |= CU::UNWIND_AArch64_MODE_FRAME;
HasFP = true;
break;
}
case MCCFIInstruction::OpDefCfaOffset: {
assert(StackSize == 0 && "We already have the CFA offset!");
StackSize = std::abs(Inst.getOffset());
break;
}
case MCCFIInstruction::OpOffset: {
// Registers are saved in pairs. We expect there to be two consecutive
// `.cfi_offset' instructions with the appropriate registers specified.
unsigned Reg1 = MRI.getLLVMRegNum(Inst.getRegister(), true);
if (i + 1 == e)
return CU::UNWIND_AArch64_MODE_DWARF;
const MCCFIInstruction &Inst2 = Instrs[++i];
if (Inst2.getOperation() != MCCFIInstruction::OpOffset)
return CU::UNWIND_AArch64_MODE_DWARF;
unsigned Reg2 = MRI.getLLVMRegNum(Inst2.getRegister(), true);
// N.B. The encodings must be in register number order, and the X
// registers before the D registers.
// X19/X20 pair = 0x00000001,
// X21/X22 pair = 0x00000002,
// X23/X24 pair = 0x00000004,
// X25/X26 pair = 0x00000008,
// X27/X28 pair = 0x00000010
Reg1 = getXRegFromWReg(Reg1);
Reg2 = getXRegFromWReg(Reg2);
if (Reg1 == AArch64::X19 && Reg2 == AArch64::X20 &&
(CompactUnwindEncoding & 0xF1E) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_X19_X20_PAIR;
else if (Reg1 == AArch64::X21 && Reg2 == AArch64::X22 &&
(CompactUnwindEncoding & 0xF1C) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_X21_X22_PAIR;
else if (Reg1 == AArch64::X23 && Reg2 == AArch64::X24 &&
(CompactUnwindEncoding & 0xF18) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_X23_X24_PAIR;
else if (Reg1 == AArch64::X25 && Reg2 == AArch64::X26 &&
(CompactUnwindEncoding & 0xF10) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_X25_X26_PAIR;
else if (Reg1 == AArch64::X27 && Reg2 == AArch64::X28 &&
(CompactUnwindEncoding & 0xF00) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_X27_X28_PAIR;
else {
Reg1 = getDRegFromBReg(Reg1);
Reg2 = getDRegFromBReg(Reg2);
// D8/D9 pair = 0x00000100,
// D10/D11 pair = 0x00000200,
// D12/D13 pair = 0x00000400,
// D14/D15 pair = 0x00000800
if (Reg1 == AArch64::D8 && Reg2 == AArch64::D9 &&
(CompactUnwindEncoding & 0xE00) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_D8_D9_PAIR;
else if (Reg1 == AArch64::D10 && Reg2 == AArch64::D11 &&
(CompactUnwindEncoding & 0xC00) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_D10_D11_PAIR;
else if (Reg1 == AArch64::D12 && Reg2 == AArch64::D13 &&
(CompactUnwindEncoding & 0x800) == 0)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_D12_D13_PAIR;
else if (Reg1 == AArch64::D14 && Reg2 == AArch64::D15)
CompactUnwindEncoding |= CU::UNWIND_AArch64_FRAME_D14_D15_PAIR;
else
// A pair was pushed which we cannot handle.
return CU::UNWIND_AArch64_MODE_DWARF;
}
break;
}
}
}
if (!HasFP) {
// With compact unwind info we can only represent stack adjustments of up
// to 65520 bytes.
if (StackSize > 65520)
return CU::UNWIND_AArch64_MODE_DWARF;
CompactUnwindEncoding |= CU::UNWIND_AArch64_MODE_FRAMELESS;
CompactUnwindEncoding |= encodeStackAdjustment(StackSize);
}
return CompactUnwindEncoding;
}
};
} // end anonymous namespace
namespace {
class ELFAArch64AsmBackend : public AArch64AsmBackend {
public:
uint8_t OSABI;
bool IsLittleEndian;
ELFAArch64AsmBackend(const Target &T, uint8_t OSABI, bool IsLittleEndian)
: AArch64AsmBackend(T), OSABI(OSABI), IsLittleEndian(IsLittleEndian) {}
MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override {
return createAArch64ELFObjectWriter(OS, OSABI, IsLittleEndian);
}
void processFixupValue(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFixup &Fixup, const MCFragment *DF,
const MCValue &Target, uint64_t &Value,
bool &IsResolved) override;
void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
uint64_t Value, bool IsPCRel) const override;
};
void ELFAArch64AsmBackend::processFixupValue(
const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFixup &Fixup,
const MCFragment *DF, const MCValue &Target, uint64_t &Value,
bool &IsResolved) {
// The ADRP instruction adds some multiple of 0x1000 to the current PC &
// ~0xfff. This means that the required offset to reach a symbol can vary by
// up to one step depending on where the ADRP is in memory. For example:
//
// ADRP x0, there
// there:
//
// If the ADRP occurs at address 0xffc then "there" will be at 0x1000 and
// we'll need that as an offset. At any other address "there" will be in the
// same page as the ADRP and the instruction should encode 0x0. Assuming the
// section isn't 0x1000-aligned, we therefore need to delegate this decision
// to the linker -- a relocation!
if ((uint32_t)Fixup.getKind() == AArch64::fixup_aarch64_pcrel_adrp_imm21)
IsResolved = false;
}
// Returns whether this fixup is based on an address in the .eh_frame section,
// and therefore should be byte swapped.
// FIXME: Should be replaced with something more principled.
static bool isByteSwappedFixup(const MCExpr *E) {
MCValue Val;
if (!E->evaluateAsRelocatable(Val, nullptr, nullptr))
return false;
if (!Val.getSymA() || Val.getSymA()->getSymbol().isUndefined())
return false;
const MCSectionELF *SecELF =
dyn_cast<MCSectionELF>(&Val.getSymA()->getSymbol().getSection());
return SecELF->getSectionName() == ".eh_frame";
}
void ELFAArch64AsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
unsigned DataSize, uint64_t Value,
bool IsPCRel) const {
// store fixups in .eh_frame section in big endian order
if (!IsLittleEndian && Fixup.getKind() == FK_Data_4) {
if (isByteSwappedFixup(Fixup.getValue()))
Value = ByteSwap_32(unsigned(Value));
}
AArch64AsmBackend::applyFixup (Fixup, Data, DataSize, Value, IsPCRel);
}
}
MCAsmBackend *llvm::createAArch64leAsmBackend(const Target &T,
const MCRegisterInfo &MRI,
const Triple &TheTriple,
StringRef CPU) {
if (TheTriple.isOSBinFormatMachO())
return new DarwinAArch64AsmBackend(T, MRI);
assert(TheTriple.isOSBinFormatELF() && "Expect either MachO or ELF target");
uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
return new ELFAArch64AsmBackend(T, OSABI, /*IsLittleEndian=*/true);
}
MCAsmBackend *llvm::createAArch64beAsmBackend(const Target &T,
const MCRegisterInfo &MRI,
const Triple &TheTriple,
StringRef CPU) {
assert(TheTriple.isOSBinFormatELF() &&
"Big endian is only supported for ELF targets!");
uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
return new ELFAArch64AsmBackend(T, OSABI,
/*IsLittleEndian=*/false);
}
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