Method GetSegment

FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp:3977–4023

}

Ref OpDispatchBuilder::GetSegment(uint32_t Flags, uint32_t DefaultPrefix, bool Override) {
  const auto GPRSize = GetGPROpSize();
  uint32_t Prefix = Flags & FEXCore::X86Tables::DecodeFlags::FLAG_SEGMENTS;

  if (Is64BitMode) {
    if (Prefix == FEXCore::X86Tables::DecodeFlags::FLAG_FS_PREFIX) {
      return _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, fs_cached));
    } else if (Prefix == FEXCore::X86Tables::DecodeFlags::FLAG_GS_PREFIX) {
      return _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, gs_cached));
    }
    // If there was any other segment in 64bit then it is ignored
  } else {
    if (Prefix == FEXCore::X86Tables::DecodeFlags::FLAG_NO_PREFIX || Override) {
      // If there was no prefix then use the default one if available
      // Or the argument only uses a specific prefix (with override set)
      Prefix = DefaultPrefix;
    }
    // With the segment register optimization we store the GDT bases directly in the segment register to remove indexed loads
    Ref SegmentResult {};
    switch (Prefix) {
    [[likely]] case FEXCore::X86Tables::DecodeFlags::FLAG_NO_PREFIX: return nullptr;
    case FEXCore::X86Tables::DecodeFlags::FLAG_ES_PREFIX:
      SegmentResult = _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, es_cached));
      break;
    case FEXCore::X86Tables::DecodeFlags::FLAG_CS_PREFIX:
      SegmentResult = _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, cs_cached));
      break;
    case FEXCore::X86Tables::DecodeFlags::FLAG_SS_PREFIX:
      SegmentResult = _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, ss_cached));
      break;
    case FEXCore::X86Tables::DecodeFlags::FLAG_DS_PREFIX:
      SegmentResult = _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, ds_cached));
      break;
    case FEXCore::X86Tables::DecodeFlags::FLAG_FS_PREFIX:
      SegmentResult = _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, fs_cached));
      break;
    case FEXCore::X86Tables::DecodeFlags::FLAG_GS_PREFIX:
      SegmentResult = _LoadContext(GPRSize, GPRClass, offsetof(FEXCore::Core::CPUState, gs_cached));
      break;
    default: FEX_UNREACHABLE;
    }

    CheckLegacySegmentRead(SegmentResult, Prefix);
    return SegmentResult;
  }
  return nullptr;
}

Ref OpDispatchBuilder::AppendSegmentOffset(Ref Value, uint32_t Flags, uint32_t DefaultPrefix, bool Override) {
  auto Segment = GetSegment(Flags, DefaultPrefix, Override);