lib/Target/BPF/MCTargetDesc/BPFMCCodeEmitter.cpp

//===-- BPFMCCodeEmitter.cpp - Convert BPF code to machine code -----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the BPFMCCodeEmitter class.
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/BPFMCTargetDesc.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/MC/MCSymbol.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

#define DEBUG_TYPE "mccodeemitter"

namespace {
class BPFMCCodeEmitter : public MCCodeEmitter {
  BPFMCCodeEmitter(const BPFMCCodeEmitter &) = delete;
  void operator=(const BPFMCCodeEmitter &) = delete;
  const MCRegisterInfo &MRI;

public:
  BPFMCCodeEmitter(const MCRegisterInfo &mri) : MRI(mri) {}

  ~BPFMCCodeEmitter() {}

  // 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;
};
}

MCCodeEmitter *llvm::createBPFMCCodeEmitter(const MCInstrInfo &MCII,
                                            const MCRegisterInfo &MRI,
                                            MCContext &Ctx) {
  return new BPFMCCodeEmitter(MRI);
}

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_SecRel_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;
}

// Emit one byte through output stream
void EmitByte(unsigned char C, unsigned &CurByte, raw_ostream &OS) {
  OS << (char)C;
  ++CurByte;
}

// Emit a series of bytes (little endian)
void EmitLEConstant(uint64_t Val, unsigned Size, unsigned &CurByte,
                    raw_ostream &OS) {
  assert(Size <= 8 && "size too big in emit constant");

  for (unsigned i = 0; i != Size; ++i) {
    EmitByte(Val & 255, CurByte, OS);
    Val >>= 8;
  }
}

// Emit a series of bytes (big endian)
void EmitBEConstant(uint64_t Val, unsigned Size, unsigned &CurByte,
                    raw_ostream &OS) {
  assert(Size <= 8 && "size too big in emit constant");

  for (int i = (Size - 1) * 8; i >= 0; i -= 8)
    EmitByte((Val >> i) & 255, CurByte, OS);
}

void BPFMCCodeEmitter::EncodeInstruction(const MCInst &MI, raw_ostream &OS,
                                         SmallVectorImpl<MCFixup> &Fixups,
                                         const MCSubtargetInfo &STI) const {
  unsigned Opcode = MI.getOpcode();
  // Keep track of the current byte being emitted
  unsigned CurByte = 0;

  if (Opcode == BPF::LD_imm64 || Opcode == BPF::LD_pseudo) {
    uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
    EmitByte(Value >> 56, CurByte, OS);
    EmitByte(((Value >> 48) & 0xff), CurByte, OS);
    EmitLEConstant(0, 2, CurByte, OS);
    EmitLEConstant(Value & 0xffffFFFF, 4, CurByte, OS);

    const MCOperand &MO = MI.getOperand(1);
    uint64_t Imm = MO.isImm() ? MO.getImm() : 0;
    EmitByte(0, CurByte, OS);
    EmitByte(0, CurByte, OS);
    EmitLEConstant(0, 2, CurByte, OS);
    EmitLEConstant(Imm >> 32, 4, CurByte, OS);
  } else {
    // Get instruction encoding and emit it
    uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
    EmitByte(Value >> 56, CurByte, OS);
    EmitByte((Value >> 48) & 0xff, CurByte, OS);
    EmitLEConstant((Value >> 32) & 0xffff, 2, CurByte, OS);
    EmitLEConstant(Value & 0xffffFFFF, 4, CurByte, OS);
  }
}

// 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;
}

#include "BPFGenMCCodeEmitter.inc"