BPFMCCodeEmitter.cpp
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//===-- BPFMCCodeEmitter.cpp - Convert BPF code to machine code -----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements the BPFMCCodeEmitter class.
//
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/BPFMCTargetDesc.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/EndianStream.h"
#include <cassert>
#include <cstdint>
using namespace llvm;
#define DEBUG_TYPE "mccodeemitter"
namespace {
class BPFMCCodeEmitter : public MCCodeEmitter {
const MCInstrInfo &MCII;
const MCRegisterInfo &MRI;
bool IsLittleEndian;
public:
BPFMCCodeEmitter(const MCInstrInfo &mcii, const MCRegisterInfo &mri,
bool IsLittleEndian)
: MCII(mcii), MRI(mri), IsLittleEndian(IsLittleEndian) {}
BPFMCCodeEmitter(const BPFMCCodeEmitter &) = delete;
void operator=(const BPFMCCodeEmitter &) = delete;
~BPFMCCodeEmitter() override = default;
// getBinaryCodeForInstr - TableGen'erated function for getting the
// binary encoding for an instruction.
uint64_t getBinaryCodeForInstr(const MCInst &MI,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const;
// getMachineOpValue - Return binary encoding of operand. If the machin
// operand requires relocation, record the relocation and return zero.
unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const;
uint64_t getMemoryOpValue(const MCInst &MI, unsigned Op,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const;
void encodeInstruction(const MCInst &MI, raw_ostream &OS,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const override;
private:
FeatureBitset computeAvailableFeatures(const FeatureBitset &FB) const;
void
verifyInstructionPredicates(const MCInst &MI,
const FeatureBitset &AvailableFeatures) const;
};
} // end anonymous namespace
MCCodeEmitter *llvm::createBPFMCCodeEmitter(const MCInstrInfo &MCII,
const MCRegisterInfo &MRI,
MCContext &Ctx) {
return new BPFMCCodeEmitter(MCII, MRI, true);
}
MCCodeEmitter *llvm::createBPFbeMCCodeEmitter(const MCInstrInfo &MCII,
const MCRegisterInfo &MRI,
MCContext &Ctx) {
return new BPFMCCodeEmitter(MCII, MRI, false);
}
unsigned BPFMCCodeEmitter::getMachineOpValue(const MCInst &MI,
const MCOperand &MO,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const {
if (MO.isReg())
return MRI.getEncodingValue(MO.getReg());
if (MO.isImm())
return static_cast<unsigned>(MO.getImm());
assert(MO.isExpr());
const MCExpr *Expr = MO.getExpr();
assert(Expr->getKind() == MCExpr::SymbolRef);
if (MI.getOpcode() == BPF::JAL)
// func call name
Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_4));
else if (MI.getOpcode() == BPF::LD_imm64)
Fixups.push_back(MCFixup::create(0, Expr, FK_SecRel_8));
else
// bb label
Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_2));
return 0;
}
static uint8_t SwapBits(uint8_t Val)
{
return (Val & 0x0F) << 4 | (Val & 0xF0) >> 4;
}
void BPFMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const {
verifyInstructionPredicates(MI,
computeAvailableFeatures(STI.getFeatureBits()));
unsigned Opcode = MI.getOpcode();
support::endian::Writer OSE(OS,
IsLittleEndian ? support::little : support::big);
if (Opcode == BPF::LD_imm64 || Opcode == BPF::LD_pseudo) {
uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
OS << char(Value >> 56);
if (IsLittleEndian)
OS << char((Value >> 48) & 0xff);
else
OS << char(SwapBits((Value >> 48) & 0xff));
OSE.write<uint16_t>(0);
OSE.write<uint32_t>(Value & 0xffffFFFF);
const MCOperand &MO = MI.getOperand(1);
uint64_t Imm = MO.isImm() ? MO.getImm() : 0;
OSE.write<uint8_t>(0);
OSE.write<uint8_t>(0);
OSE.write<uint16_t>(0);
OSE.write<uint32_t>(Imm >> 32);
} else {
// Get instruction encoding and emit it
uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
OS << char(Value >> 56);
if (IsLittleEndian)
OS << char((Value >> 48) & 0xff);
else
OS << char(SwapBits((Value >> 48) & 0xff));
OSE.write<uint16_t>((Value >> 32) & 0xffff);
OSE.write<uint32_t>(Value & 0xffffFFFF);
}
}
// Encode BPF Memory Operand
uint64_t BPFMCCodeEmitter::getMemoryOpValue(const MCInst &MI, unsigned Op,
SmallVectorImpl<MCFixup> &Fixups,
const MCSubtargetInfo &STI) const {
uint64_t Encoding;
const MCOperand Op1 = MI.getOperand(1);
assert(Op1.isReg() && "First operand is not register.");
Encoding = MRI.getEncodingValue(Op1.getReg());
Encoding <<= 16;
MCOperand Op2 = MI.getOperand(2);
assert(Op2.isImm() && "Second operand is not immediate.");
Encoding |= Op2.getImm() & 0xffff;
return Encoding;
}
#define ENABLE_INSTR_PREDICATE_VERIFIER
#include "BPFGenMCCodeEmitter.inc"