AVRAsmBackend.cpp

//===-- AVRAsmBackend.cpp - AVR Asm 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
//
//===----------------------------------------------------------------------===//
//
// This file implements the AVRAsmBackend class.
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/AVRAsmBackend.h"
#include "MCTargetDesc/AVRFixupKinds.h"
#include "MCTargetDesc/AVRMCTargetDesc.h"
#include "llvm/ADT/StringSwitch.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/MCValue.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"

// FIXME: we should be doing checks to make sure asm operands
// are not out of bounds.

namespace adjust {

using namespace llvm;

static void signed_width(unsigned Width, uint64_t Value,
                         std::string Description, const MCFixup &Fixup,
                         MCContext *Ctx = nullptr) {
  if (!isIntN(Width, Value)) {
    std::string Diagnostic = "out of range " + Description;

    int64_t Min = minIntN(Width);
    int64_t Max = maxIntN(Width);

    Diagnostic += " (expected an integer in the range " + std::to_string(Min) +
                  " to " + std::to_string(Max) + ")";

    if (Ctx) {
      Ctx->reportError(Fixup.getLoc(), Diagnostic);
    } else {
      llvm_unreachable(Diagnostic.c_str());
    }
  }
}

static void unsigned_width(unsigned Width, uint64_t Value,
                           std::string Description, const MCFixup &Fixup,
                           MCContext *Ctx = nullptr) {
  if (!isUIntN(Width, Value)) {
    std::string Diagnostic = "out of range " + Description;

    int64_t Max = maxUIntN(Width);

    Diagnostic +=
        " (expected an integer in the range 0 to " + std::to_string(Max) + ")";

    if (Ctx) {
      Ctx->reportError(Fixup.getLoc(), Diagnostic);
    } else {
      llvm_unreachable(Diagnostic.c_str());
    }
  }
}

/// Adjusts the value of a branch target before fixup application.
static void adjustBranch(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                         MCContext *Ctx = nullptr) {
  // We have one extra bit of precision because the value is rightshifted by
  // one.
  unsigned_width(Size + 1, Value, std::string("branch target"), Fixup, Ctx);

  // Rightshifts the value by one.
  AVR::fixups::adjustBranchTarget(Value);
}

/// Adjusts the value of a relative branch target before fixup application.
static void adjustRelativeBranch(unsigned Size, const MCFixup &Fixup,
                                 uint64_t &Value, MCContext *Ctx = nullptr) {
  // Jumps are relative to the current instruction.
  Value -= 2;

  // We have one extra bit of precision because the value is rightshifted by
  // one.
  signed_width(Size + 1, Value, std::string("branch target"), Fixup, Ctx);

  // Rightshifts the value by one.
  AVR::fixups::adjustBranchTarget(Value);
}

/// 22-bit absolute fixup.
///
/// Resolves to:
/// 1001 kkkk 010k kkkk kkkk kkkk 111k kkkk
///
/// Offset of 0 (so the result is left shifted by 3 bits before application).
static void fixup_call(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                       MCContext *Ctx = nullptr) {
  adjustBranch(Size, Fixup, Value, Ctx);

  auto top = Value & (0xf00000 << 6);   // the top four bits
  auto middle = Value & (0x1ffff << 5); // the middle 13 bits
  auto bottom = Value & 0x1f;           // end bottom 5 bits

  Value = (top << 6) | (middle << 3) | (bottom << 0);
}

/// 7-bit PC-relative fixup.
///
/// Resolves to:
/// 0000 00kk kkkk k000
/// Offset of 0 (so the result is left shifted by 3 bits before application).
static void fixup_7_pcrel(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                          MCContext *Ctx = nullptr) {
  adjustRelativeBranch(Size, Fixup, Value, Ctx);

  // Because the value may be negative, we must mask out the sign bits
  Value &= 0x7f;
}

/// 12-bit PC-relative fixup.
/// Yes, the fixup is 12 bits even though the name says otherwise.
///
/// Resolves to:
/// 0000 kkkk kkkk kkkk
/// Offset of 0 (so the result isn't left-shifted before application).
static void fixup_13_pcrel(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                           MCContext *Ctx = nullptr) {
  adjustRelativeBranch(Size, Fixup, Value, Ctx);

  // Because the value may be negative, we must mask out the sign bits
  Value &= 0xfff;
}

/// 6-bit fixup for the immediate operand of the STD/LDD family of
/// instructions.
///
/// Resolves to:
/// 10q0 qq10 0000 1qqq
static void fixup_6(const MCFixup &Fixup, uint64_t &Value,
                    MCContext *Ctx = nullptr) {
  unsigned_width(6, Value, std::string("immediate"), Fixup, Ctx);

  Value = ((Value & 0x20) << 8) | ((Value & 0x18) << 7) | (Value & 0x07);
}

/// 6-bit fixup for the immediate operand of the ADIW family of
/// instructions.
///
/// Resolves to:
/// 0000 0000 kk00 kkkk
static void fixup_6_adiw(const MCFixup &Fixup, uint64_t &Value,
                         MCContext *Ctx = nullptr) {
  unsigned_width(6, Value, std::string("immediate"), Fixup, Ctx);

  Value = ((Value & 0x30) << 2) | (Value & 0x0f);
}

/// 5-bit port number fixup on the SBIC family of instructions.
///
/// Resolves to:
/// 0000 0000 AAAA A000
static void fixup_port5(const MCFixup &Fixup, uint64_t &Value,
                        MCContext *Ctx = nullptr) {
  unsigned_width(5, Value, std::string("port number"), Fixup, Ctx);

  Value &= 0x1f;

  Value <<= 3;
}

/// 6-bit port number fixup on the `IN` family of instructions.
///
/// Resolves to:
/// 1011 0AAd dddd AAAA
static void fixup_port6(const MCFixup &Fixup, uint64_t &Value,
                        MCContext *Ctx = nullptr) {
  unsigned_width(6, Value, std::string("port number"), Fixup, Ctx);

  Value = ((Value & 0x30) << 5) | (Value & 0x0f);
}

/// 7-bit data space address fixup for the LDS/STS instructions on AVRTiny.
///
/// Resolves to:
/// 1010 ikkk dddd kkkk
static void fixup_lds_sts_16(const MCFixup &Fixup, uint64_t &Value,
                             MCContext *Ctx = nullptr) {
  unsigned_width(7, Value, std::string("immediate"), Fixup, Ctx);
  Value = ((Value & 0x70) << 8) | (Value & 0x0f);
}

/// Adjusts a program memory address.
/// This is a simple right-shift.
static void pm(uint64_t &Value) { Value >>= 1; }

/// Fixups relating to the LDI instruction.
namespace ldi {

/// Adjusts a value to fix up the immediate of an `LDI Rd, K` instruction.
///
/// Resolves to:
/// 0000 KKKK 0000 KKKK
/// Offset of 0 (so the result isn't left-shifted before application).
static void fixup(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                  MCContext *Ctx = nullptr) {
  uint64_t upper = Value & 0xf0;
  uint64_t lower = Value & 0x0f;

  Value = (upper << 4) | lower;
}

static void neg(uint64_t &Value) { Value *= -1; }

static void lo8(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                MCContext *Ctx = nullptr) {
  Value &= 0xff;
  ldi::fixup(Size, Fixup, Value, Ctx);
}

static void hi8(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                MCContext *Ctx = nullptr) {
  Value = (Value & 0xff00) >> 8;
  ldi::fixup(Size, Fixup, Value, Ctx);
}

static void hh8(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                MCContext *Ctx = nullptr) {
  Value = (Value & 0xff0000) >> 16;
  ldi::fixup(Size, Fixup, Value, Ctx);
}

static void ms8(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
                MCContext *Ctx = nullptr) {
  Value = (Value & 0xff000000) >> 24;
  ldi::fixup(Size, Fixup, Value, Ctx);
}

} // namespace ldi
} // namespace adjust

namespace llvm {

// Prepare value for the target space for it
void AVRAsmBackend::adjustFixupValue(const MCFixup &Fixup,
                                     const MCValue &Target, uint64_t &Value,
                                     MCContext *Ctx) const {
  // The size of the fixup in bits.
  uint64_t Size = AVRAsmBackend::getFixupKindInfo(Fixup.getKind()).TargetSize;

  unsigned Kind = Fixup.getKind();
  switch (Kind) {
  default:
    llvm_unreachable("unhandled fixup");
  case AVR::fixup_7_pcrel:
    adjust::fixup_7_pcrel(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_13_pcrel:
    adjust::fixup_13_pcrel(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_call:
    adjust::fixup_call(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_ldi:
    adjust::ldi::fixup(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_lo8_ldi:
    adjust::ldi::lo8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_lo8_ldi_pm:
  case AVR::fixup_lo8_ldi_gs:
    adjust::pm(Value);
    adjust::ldi::lo8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_hi8_ldi:
    adjust::ldi::hi8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_hi8_ldi_pm:
  case AVR::fixup_hi8_ldi_gs:
    adjust::pm(Value);
    adjust::ldi::hi8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_hh8_ldi:
  case AVR::fixup_hh8_ldi_pm:
    if (Kind == AVR::fixup_hh8_ldi_pm)
      adjust::pm(Value);

    adjust::ldi::hh8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_ms8_ldi:
    adjust::ldi::ms8(Size, Fixup, Value, Ctx);
    break;

  case AVR::fixup_lo8_ldi_neg:
  case AVR::fixup_lo8_ldi_pm_neg:
    if (Kind == AVR::fixup_lo8_ldi_pm_neg)
      adjust::pm(Value);

    adjust::ldi::neg(Value);
    adjust::ldi::lo8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_hi8_ldi_neg:
  case AVR::fixup_hi8_ldi_pm_neg:
    if (Kind == AVR::fixup_hi8_ldi_pm_neg)
      adjust::pm(Value);

    adjust::ldi::neg(Value);
    adjust::ldi::hi8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_hh8_ldi_neg:
  case AVR::fixup_hh8_ldi_pm_neg:
    if (Kind == AVR::fixup_hh8_ldi_pm_neg)
      adjust::pm(Value);

    adjust::ldi::neg(Value);
    adjust::ldi::hh8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_ms8_ldi_neg:
    adjust::ldi::neg(Value);
    adjust::ldi::ms8(Size, Fixup, Value, Ctx);
    break;
  case AVR::fixup_16:
    adjust::unsigned_width(16, Value, std::string("port number"), Fixup, Ctx);

    Value &= 0xffff;
    break;
  case AVR::fixup_16_pm:
    Value >>= 1; // Flash addresses are always shifted.
    adjust::unsigned_width(16, Value, std::string("port number"), Fixup, Ctx);

    Value &= 0xffff;
    break;

  case AVR::fixup_6:
    adjust::fixup_6(Fixup, Value, Ctx);
    break;
  case AVR::fixup_6_adiw:
    adjust::fixup_6_adiw(Fixup, Value, Ctx);
    break;

  case AVR::fixup_port5:
    adjust::fixup_port5(Fixup, Value, Ctx);
    break;

  case AVR::fixup_port6:
    adjust::fixup_port6(Fixup, Value, Ctx);
    break;

  case AVR::fixup_lds_sts_16:
    adjust::fixup_lds_sts_16(Fixup, Value, Ctx);
    break;

  // Fixups which do not require adjustments.
  case FK_Data_1:
  case FK_Data_2:
  case FK_Data_4:
  case FK_Data_8:
    break;

  case FK_GPRel_4:
    llvm_unreachable("don't know how to adjust this fixup");
    break;
  }
}

std::unique_ptr<MCObjectTargetWriter>
AVRAsmBackend::createObjectTargetWriter() const {
  return createAVRELFObjectWriter(MCELFObjectTargetWriter::getOSABI(OSType));
}

void AVRAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                               const MCValue &Target,
                               MutableArrayRef<char> Data, uint64_t Value,
                               bool IsResolved,
                               const MCSubtargetInfo *STI) const {
  if (Fixup.getKind() >= FirstLiteralRelocationKind)
    return;
  adjustFixupValue(Fixup, Target, Value, &Asm.getContext());
  if (Value == 0)
    return; // Doesn't change encoding.

  MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind());

  // The number of bits in the fixup mask
  auto NumBits = Info.TargetSize + Info.TargetOffset;
  auto NumBytes = (NumBits / 8) + ((NumBits % 8) == 0 ? 0 : 1);

  // 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 < NumBytes; ++i) {
    uint8_t mask = (((Value >> (i * 8)) & 0xff));
    Data[Offset + i] |= mask;
  }
}

std::optional<MCFixupKind> AVRAsmBackend::getFixupKind(StringRef Name) const {
  unsigned Type;
  Type = llvm::StringSwitch<unsigned>(Name)
#define ELF_RELOC(X, Y) .Case(#X, Y)
#include "llvm/BinaryFormat/ELFRelocs/AVR.def"
#undef ELF_RELOC
             .Case("BFD_RELOC_NONE", ELF::R_AVR_NONE)
             .Case("BFD_RELOC_16", ELF::R_AVR_16)
             .Case("BFD_RELOC_32", ELF::R_AVR_32)
             .Default(-1u);
  if (Type != -1u)
    return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
  return std::nullopt;
}

MCFixupKindInfo const &AVRAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
  // NOTE: Many AVR fixups work on sets of non-contignous bits. We work around
  // this by saying that the fixup is the size of the entire instruction.
  const static MCFixupKindInfo Infos[AVR::NumTargetFixupKinds] = {
      // This table *must* be in same the order of fixup_* kinds in
      // AVRFixupKinds.h.
      //
      // name                    offset  bits  flags
      {"fixup_32", 0, 32, 0},

      {"fixup_7_pcrel", 3, 7, MCFixupKindInfo::FKF_IsPCRel},
      {"fixup_13_pcrel", 0, 12, MCFixupKindInfo::FKF_IsPCRel},

      {"fixup_16", 0, 16, 0},
      {"fixup_16_pm", 0, 16, 0},

      {"fixup_ldi", 0, 8, 0},

      {"fixup_lo8_ldi", 0, 8, 0},
      {"fixup_hi8_ldi", 0, 8, 0},
      {"fixup_hh8_ldi", 0, 8, 0},
      {"fixup_ms8_ldi", 0, 8, 0},

      {"fixup_lo8_ldi_neg", 0, 8, 0},
      {"fixup_hi8_ldi_neg", 0, 8, 0},
      {"fixup_hh8_ldi_neg", 0, 8, 0},
      {"fixup_ms8_ldi_neg", 0, 8, 0},

      {"fixup_lo8_ldi_pm", 0, 8, 0},
      {"fixup_hi8_ldi_pm", 0, 8, 0},
      {"fixup_hh8_ldi_pm", 0, 8, 0},

      {"fixup_lo8_ldi_pm_neg", 0, 8, 0},
      {"fixup_hi8_ldi_pm_neg", 0, 8, 0},
      {"fixup_hh8_ldi_pm_neg", 0, 8, 0},

      {"fixup_call", 0, 22, 0},

      {"fixup_6", 0, 16, 0}, // non-contiguous
      {"fixup_6_adiw", 0, 6, 0},

      {"fixup_lo8_ldi_gs", 0, 8, 0},
      {"fixup_hi8_ldi_gs", 0, 8, 0},

      {"fixup_8", 0, 8, 0},
      {"fixup_8_lo8", 0, 8, 0},
      {"fixup_8_hi8", 0, 8, 0},
      {"fixup_8_hlo8", 0, 8, 0},

      {"fixup_diff8", 0, 8, 0},
      {"fixup_diff16", 0, 16, 0},
      {"fixup_diff32", 0, 32, 0},

      {"fixup_lds_sts_16", 0, 16, 0},

      {"fixup_port6", 0, 16, 0}, // non-contiguous
      {"fixup_port5", 3, 5, 0},
  };

  // Fixup kinds from .reloc directive are like R_AVR_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!");

  return Infos[Kind - FirstTargetFixupKind];
}

bool AVRAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
                                 const MCSubtargetInfo *STI) const {
  // If the count is not 2-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.
  assert((Count % 2) == 0 && "NOP instructions must be 2 bytes");

  OS.write_zeros(Count);
  return true;
}

bool AVRAsmBackend::shouldForceRelocation(const MCAssembler &Asm,
                                          const MCFixup &Fixup,
                                          const MCValue &Target,
                                          const MCSubtargetInfo *STI) {
  switch ((unsigned)Fixup.getKind()) {
  default:
    return Fixup.getKind() >= FirstLiteralRelocationKind;
  case AVR::fixup_7_pcrel:
  case AVR::fixup_13_pcrel:
    // Always resolve relocations for PC-relative branches
    return false;
  case AVR::fixup_call:
    return true;
  }
}

MCAsmBackend *createAVRAsmBackend(const Target &T, const MCSubtargetInfo &STI,
                                  const MCRegisterInfo &MRI,
                                  const llvm::MCTargetOptions &TO) {
  return new AVRAsmBackend(STI.getTargetTriple().getOS());
}

} // end of namespace llvm