lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp

//===-- RISCVAsmBackend.cpp - RISCV Assembler Backend ---------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/RISCVFixupKinds.h"
#include "MCTargetDesc/RISCVMCTargetDesc.h"
#include "llvm/ADT/APInt.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDirectives.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;

namespace {
class RISCVAsmBackend : public MCAsmBackend {
  uint8_t OSABI;
  bool Is64Bit;

public:
  RISCVAsmBackend(uint8_t OSABI, bool Is64Bit)
      : MCAsmBackend(), OSABI(OSABI), Is64Bit(Is64Bit) {}
  ~RISCVAsmBackend() override {}

  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                  const MCValue &Target, MutableArrayRef<char> Data,
                  uint64_t Value, bool IsResolved) const override;

  std::unique_ptr<MCObjectWriter>
  createObjectWriter(raw_pwrite_stream &OS) const override;

  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
                            const MCRelaxableFragment *DF,
                            const MCAsmLayout &Layout) const override {
    return false;
  }

  unsigned getNumFixupKinds() const override {
    return RISCV::NumTargetFixupKinds;
  }

  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
    const static MCFixupKindInfo Infos[RISCV::NumTargetFixupKinds] = {
      // This table *must* be in the order that the fixup_* kinds are defined in
      // RISCVFixupKinds.h.
      //
      // name                    offset bits  flags
      { "fixup_riscv_hi20",       12,     20,  0 },
      { "fixup_riscv_lo12_i",     20,     12,  0 },
      { "fixup_riscv_lo12_s",      0,     32,  0 },
      { "fixup_riscv_pcrel_hi20", 12,     20,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_jal",        12,     20,  MCFixupKindInfo::FKF_IsPCRel },
      { "fixup_riscv_branch",      0,     32,  MCFixupKindInfo::FKF_IsPCRel }
    };

    if (Kind < FirstTargetFixupKind)
      return MCAsmBackend::getFixupKindInfo(Kind);

    assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
           "Invalid kind!");
    return Infos[Kind - FirstTargetFixupKind];
  }

  bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }

  void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                        MCInst &Res) const override {

    report_fatal_error("RISCVAsmBackend::relaxInstruction() unimplemented");
  }

  bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override;
};

bool RISCVAsmBackend::writeNopData(uint64_t Count, MCObjectWriter *OW) const {
  // Once support for the compressed instruction set is added, we will be able
  // to conditionally support 16-bit NOPs
  if ((Count % 4) != 0)
    return false;

  // The canonical nop on RISC-V is addi x0, x0, 0
  for (uint64_t i = 0; i < Count; i += 4)
    OW->write32(0x13);

  return true;
}

static uint64_t adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
                                 MCContext &Ctx) {
  unsigned Kind = Fixup.getKind();
  switch (Kind) {
  default:
    llvm_unreachable("Unknown fixup kind!");
  case FK_Data_1:
  case FK_Data_2:
  case FK_Data_4:
  case FK_Data_8:
    return Value;
  case RISCV::fixup_riscv_lo12_i:
    return Value & 0xfff;
  case RISCV::fixup_riscv_lo12_s:
    return (((Value >> 5) & 0x7f) << 25) | ((Value & 0x1f) << 7);
  case RISCV::fixup_riscv_hi20:
  case RISCV::fixup_riscv_pcrel_hi20:
    // Add 1 if bit 11 is 1, to compensate for low 12 bits being negative.
    return ((Value + 0x800) >> 12) & 0xfffff;
  case RISCV::fixup_riscv_jal: {
    if (!isInt<21>(Value))
      Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
    if (Value & 0x1)
      Ctx.reportError(Fixup.getLoc(), "fixup value must be 2-byte aligned");
    // Need to produce imm[19|10:1|11|19:12] from the 21-bit Value.
    unsigned Sbit = (Value >> 20) & 0x1;
    unsigned Hi8 = (Value >> 12) & 0xff;
    unsigned Mid1 = (Value >> 11) & 0x1;
    unsigned Lo10 = (Value >> 1) & 0x3ff;
    // Inst{31} = Sbit;
    // Inst{30-21} = Lo10;
    // Inst{20} = Mid1;
    // Inst{19-12} = Hi8;
    Value = (Sbit << 19) | (Lo10 << 9) | (Mid1 << 8) | Hi8;
    return Value;
  }
  case RISCV::fixup_riscv_branch: {
    if (!isInt<13>(Value))
      Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
    if (Value & 0x1)
      Ctx.reportError(Fixup.getLoc(), "fixup value must be 2-byte aligned");
    // Need to extract imm[12], imm[10:5], imm[4:1], imm[11] from the 13-bit
    // Value.
    unsigned Sbit = (Value >> 12) & 0x1;
    unsigned Hi1 = (Value >> 11) & 0x1;
    unsigned Mid6 = (Value >> 5) & 0x3f;
    unsigned Lo4 = (Value >> 1) & 0xf;
    // Inst{31} = Sbit;
    // Inst{30-25} = Mid6;
    // Inst{11-8} = Lo4;
    // Inst{7} = Hi1;
    Value = (Sbit << 31) | (Mid6 << 25) | (Lo4 << 8) | (Hi1 << 7);
    return Value;
  }

  }
}

void RISCVAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                                 const MCValue &Target,
                                 MutableArrayRef<char> Data, uint64_t Value,
                                 bool IsResolved) const {
  MCContext &Ctx = Asm.getContext();
  MCFixupKind Kind = Fixup.getKind();
  unsigned NumBytes = (getFixupKindInfo(Kind).TargetSize + 7) / 8;
  if (!Value)
    return; // Doesn't change encoding.
  MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind());
  // Apply any target-specific value adjustments.
  Value = adjustFixupValue(Fixup, Value, Ctx);

  // Shift the value into position.
  Value <<= Info.TargetOffset;

  unsigned Offset = Fixup.getOffset();
  assert(Offset + NumBytes <= Data.size() && "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 != 4; ++i) {
    Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
  }
  return;
}

std::unique_ptr<MCObjectWriter>
RISCVAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const {
  return createRISCVELFObjectWriter(OS, OSABI, Is64Bit);
}

} // end anonymous namespace

MCAsmBackend *llvm::createRISCVAsmBackend(const Target &T,
                                          const MCRegisterInfo &MRI,
                                          const Triple &TT, StringRef CPU,
                                          const MCTargetOptions &Options) {
  uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS());
  return new RISCVAsmBackend(OSABI, TT.isArch64Bit());
}