GCMemcard: Rework construction logic to better match our knowledge of the format, while providing better error reporting facilities.

2025-07-23 06:09:50 -06:00 · 2019-04-21 15:18:01 +02:00
parent 24718c1a38
commit b54a49eaaf
5 changed files with 369 additions and 223 deletions
--- a/Source/Core/Core/HW/GCMemcard/GCMemcard.cpp
+++ b/Source/Core/Core/HW/GCMemcard/GCMemcard.cpp
@ -27,196 +27,249 @@ static void ByteSwap(u8* valueA, u8* valueB)
  *valueB = tmp;
 }

-GCMemcard::GCMemcard(const std::string& filename, bool forceCreation, bool shift_jis)
-    : m_valid(false), m_filename(filename)
+static constexpr std::optional<u64> BytesToMegabits(u64 bytes)
 {
-  // Currently there is a string freeze. instead of adding a new message about needing r/w
-  // open file read only, if write is denied the error will be reported at that point
-  File::IOFile mcdFile(m_filename, "rb");
-  if (!mcdFile.IsOpen())
-  {
-    if (!forceCreation)
-    {
-      if (!AskYesNoT("\"%s\" does not exist.\n Create a new 16MB Memory Card?", filename.c_str()))
-        return;
-      shift_jis =
-          AskYesNoT("Format as Shift JIS (Japanese)?\nChoose no for Windows-1252 (Western)");
-    }
-    Format(shift_jis);
-    return;
-  }
-  else
-  {
-    // This function can be removed once more about hdr is known and we can check for a valid header
-    std::string fileType;
-    SplitPath(filename, nullptr, nullptr, &fileType);
-    if (strcasecmp(fileType.c_str(), ".raw") && strcasecmp(fileType.c_str(), ".gcp"))
-    {
-      PanicAlertT("File has the extension \"%s\".\nValid extensions are (.raw/.gcp)",
-                  fileType.c_str());
-      return;
-    }
-    auto size = mcdFile.GetSize();
-    if (size < MC_FST_BLOCKS * BLOCK_SIZE)
-    {
-      PanicAlertT("%s failed to load as a memory card.\nFile is not large enough to be a valid "
-                  "memory card file (0x%x bytes)",
-                  filename.c_str(), (unsigned)size);
-      return;
-    }
-    if (size % BLOCK_SIZE)
-    {
-      PanicAlertT("%s failed to load as a memory card.\nCard file size is invalid (0x%x bytes)",
-                  filename.c_str(), (unsigned)size);
-      return;
-    }
-
-    m_size_mb = (u16)((size / BLOCK_SIZE) / MBIT_TO_BLOCKS);
-    switch (m_size_mb)
-    {
-    case MemCard59Mb:
-    case MemCard123Mb:
-    case MemCard251Mb:
-    case Memcard507Mb:
-    case MemCard1019Mb:
-    case MemCard2043Mb:
-      break;
-    default:
-      PanicAlertT("%s failed to load as a memory card.\nCard size is invalid (0x%x bytes)",
-                  filename.c_str(), (unsigned)size);
-      return;
-    }
-  }
-
-  mcdFile.Seek(0, SEEK_SET);
-  if (!mcdFile.ReadBytes(&m_header_block, BLOCK_SIZE))
-  {
-    PanicAlertT("Failed to read header correctly\n(0x0000-0x1FFF)");
-    return;
-  }
-  if (m_size_mb != m_header_block.m_size_mb)
-  {
-    PanicAlertT("Memory card file size does not match the header size");
-    return;
-  }
-
-  if (!mcdFile.ReadBytes(&m_directory_blocks[0], BLOCK_SIZE))
-  {
-    PanicAlertT("Failed to read 1st directory block correctly\n(0x2000-0x3FFF)");
-    return;
-  }
-
-  if (!mcdFile.ReadBytes(&m_directory_blocks[1], BLOCK_SIZE))
-  {
-    PanicAlertT("Failed to read 2nd directory block correctly\n(0x4000-0x5FFF)");
-    return;
-  }
-
-  if (!mcdFile.ReadBytes(&m_bat_blocks[0], BLOCK_SIZE))
-  {
-    PanicAlertT("Failed to read 1st block allocation table block correctly\n(0x6000-0x7FFF)");
-    return;
-  }
-
-  if (!mcdFile.ReadBytes(&m_bat_blocks[1], BLOCK_SIZE))
-  {
-    PanicAlertT("Failed to read 2nd block allocation table block correctly\n(0x8000-0x9FFF)");
-    return;
-  }
-
-  u32 csums = TestChecksums();
-
-  if (csums & 0x1)
-  {
-    // header checksum error!
-    // invalid files do not always get here
-    PanicAlertT("Header checksum failed");
-    return;
-  }
-
-  if (csums & 0x2)  // 1st directory block checksum error!
-  {
-    if (csums & 0x4)
-    {
-      // 2nd block is also wrong!
-      PanicAlertT("Both directory block checksums are invalid");
-      return;
-    }
-    else
-    {
-      // FIXME: This is probably incorrect behavior, confirm what actually happens on hardware here.
-      // The currently active directory block and currently active BAT block don't necessarily have
-      // to correlate.
-
-      // 2nd block is correct, restore
-      m_directory_blocks[0] = m_directory_blocks[1];
-      m_bat_blocks[0] = m_bat_blocks[1];
-
-      // update checksums
-      csums = TestChecksums();
-    }
-  }
-
-  if (csums & 0x8)  // 1st BAT checksum error!
-  {
-    if (csums & 0x10)
-    {
-      // 2nd BAT is also wrong!
-      PanicAlertT("Both Block Allocation Table block checksums are invalid");
-      return;
-    }
-    else
-    {
-      // FIXME: Same as above, this feels incorrect.
-
-      // 2nd block is correct, restore
-      m_directory_blocks[0] = m_directory_blocks[1];
-      m_bat_blocks[0] = m_bat_blocks[1];
-
-      // update checksums
-      csums = TestChecksums();
-    }
-  }
-
-  mcdFile.Seek(0xa000, SEEK_SET);
-
-  m_size_blocks = (u32)m_size_mb * MBIT_TO_BLOCKS;
-  m_data_blocks.reserve(m_size_blocks - MC_FST_BLOCKS);
-
-  m_valid = true;
-  for (u32 i = MC_FST_BLOCKS; i < m_size_blocks; ++i)
-  {
-    GCMBlock b;
-    if (mcdFile.ReadBytes(b.m_block.data(), b.m_block.size()))
-    {
-      m_data_blocks.push_back(b);
-    }
-    else
-    {
-      PanicAlertT("Failed to read block %u of the save data\nMemory card may be truncated\nFile "
-                  "position: 0x%" PRIx64,
-                  i, mcdFile.Tell());
-      m_valid = false;
-      break;
-    }
-  }
-
-  mcdFile.Close();
-
-  InitActiveDirBat();
+  const u64 factor = ((1024 * 1024) / 8);
+  const u64 megabits = bytes / factor;
+  const u64 remainder = bytes % factor;
+  if (remainder != 0)
+    return std::nullopt;
+  return megabits;
 }

-void GCMemcard::InitActiveDirBat()
+bool GCMemcardErrorCode::HasCriticalErrors() const
 {
-  if (m_directory_blocks[0].m_update_counter > m_directory_blocks[1].m_update_counter)
-    m_active_directory = 0;
-  else
-    m_active_directory = 1;
+  return Test(GCMemcardValidityIssues::FAILED_TO_OPEN) || Test(GCMemcardValidityIssues::IO_ERROR) ||
+         Test(GCMemcardValidityIssues::INVALID_CARD_SIZE) ||
+         Test(GCMemcardValidityIssues::INVALID_CHECKSUM) ||
+         Test(GCMemcardValidityIssues::MISMATCHED_CARD_SIZE) ||
+         Test(GCMemcardValidityIssues::FREE_BLOCK_MISMATCH);
+}

-  if (m_bat_blocks[0].m_update_counter > m_bat_blocks[1].m_update_counter)
-    m_active_bat = 0;
+bool GCMemcardErrorCode::Test(GCMemcardValidityIssues code) const
+{
+  return m_errors.test(static_cast<size_t>(code));
+}
+
+void GCMemcardErrorCode::Set(GCMemcardValidityIssues code)
+{
+  m_errors.set(static_cast<size_t>(code));
+}
+
+GCMemcardErrorCode& GCMemcardErrorCode::operator|=(const GCMemcardErrorCode& other)
+{
+  this->m_errors |= other.m_errors;
+  return *this;
+}
+
+GCMemcard::GCMemcard()
+    : m_valid(false), m_size_blocks(0), m_size_mb(0), m_active_directory(0), m_active_bat(0)
+{
+}
+
+std::optional<GCMemcard> GCMemcard::Create(std::string filename, u16 size_mbits, bool shift_jis)
+{
+  GCMemcard card;
+  card.m_filename = std::move(filename);
+
+  // TODO: Format() not only formats the card but also writes it to disk at m_filename.
+  // Those tasks should probably be separated.
+  if (!card.Format(shift_jis, size_mbits))
+    return std::nullopt;
+
+  return std::move(card);
+}
+
+std::pair<GCMemcardErrorCode, std::optional<GCMemcard>> GCMemcard::Open(std::string filename)
+{
+  GCMemcardErrorCode error_code;
+  File::IOFile file(filename, "rb");
+  if (!file.IsOpen())
+  {
+    error_code.Set(GCMemcardValidityIssues::FAILED_TO_OPEN);
+    return std::make_pair(error_code, std::nullopt);
+  }
+
+  // check if the filesize is a valid memory card size
+  const u64 filesize = file.GetSize();
+  const u64 filesize_megabits = BytesToMegabits(filesize).value_or(0);
+  const std::array<u16, 6> valid_megabits = {{
+      MemCard59Mb,
+      MemCard123Mb,
+      MemCard251Mb,
+      Memcard507Mb,
+      MemCard1019Mb,
+      MemCard2043Mb,
+  }};
+
+  if (!std::any_of(valid_megabits.begin(), valid_megabits.end(),
+                   [filesize_megabits](u64 mbits) { return mbits == filesize_megabits; }))
+  {
+    error_code.Set(GCMemcardValidityIssues::INVALID_CARD_SIZE);
+    return std::make_pair(error_code, std::nullopt);
+  }
+
+  const u16 card_size_mbits = static_cast<u16>(filesize_megabits);
+
+  // read the entire card into memory
+  GCMemcard card;
+  file.Seek(0, SEEK_SET);
+  if (!file.ReadBytes(&card.m_header_block, BLOCK_SIZE) ||
+      !file.ReadBytes(&card.m_directory_blocks[0], BLOCK_SIZE) ||
+      !file.ReadBytes(&card.m_directory_blocks[1], BLOCK_SIZE) ||
+      !file.ReadBytes(&card.m_bat_blocks[0], BLOCK_SIZE) ||
+      !file.ReadBytes(&card.m_bat_blocks[1], BLOCK_SIZE))
+  {
+    error_code.Set(GCMemcardValidityIssues::IO_ERROR);
+    return std::make_pair(error_code, std::nullopt);
+  }
+
+  const u16 card_size_blocks = card_size_mbits * MBIT_TO_BLOCKS;
+  const u16 user_data_blocks = card_size_blocks - MC_FST_BLOCKS;
+  card.m_data_blocks.reserve(user_data_blocks);
+  for (u16 i = 0; i < user_data_blocks; ++i)
+  {
+    GCMBlock& block = card.m_data_blocks.emplace_back();
+    if (!file.ReadArray(block.m_block.data(), BLOCK_SIZE))
+    {
+      error_code.Set(GCMemcardValidityIssues::IO_ERROR);
+      return std::make_pair(error_code, std::nullopt);
+    }
+  }
+
+  file.Close();
+
+  card.m_filename = std::move(filename);
+  card.m_size_blocks = card_size_blocks;
+  card.m_size_mb = card_size_mbits;
+
+  // can return invalid card size, invalid checksum, data in unused area
+  // data in unused area is okay, otherwise fail
+  const GCMemcardErrorCode header_error_code = card.m_header_block.CheckForErrors(card_size_mbits);
+  error_code |= header_error_code;
+  if (header_error_code.HasCriticalErrors())
+    return std::make_pair(error_code, std::nullopt);
+
+  // The GC BIOS counts any card as corrupted as long as at least any two of [dir0, dir1, bat0,
+  // bat1] are corrupted. Yes, even if we have one valid dir and one valid bat, and even if those
+  // are both supposedly the newer ones.
+  //
+  // If both blocks of a single category are non-corrupted the used block depends on the update
+  // counter. If both blocks have the same update counter, it prefers block 0. Otherwise it prefers
+  // whichever block has the higher value. Essentially, if (0.update_ctr >= 1.update_ctr) { use 0 }
+  // else { use 1 }.
+  //
+  // If a single block of the four is corrupted, the non-corrupted one of the same category is
+  // immediately copied over the corrupted block with an incremented update counter. At this point
+  // both blocks contain the same data, so it's hard to tell which one is used, but presumably it
+  // uses the one with the now-higher update counter, same as it would have otherwise.
+  //
+  // This rule only applies for errors within a single block! That is, invalid checksums for both
+  // types, and free block mismatch for the BATs. Once two valid blocks have been selected but it
+  // later turns out they do not match eachother (eg. claimed block count of a file in the directory
+  // does not match the actual block count arrived at by following BAT), the card will be treated as
+  // corrupted, even if perhaps a different combination of the two blocks would result in a valid
+  // memory card.
+
+  // can return invalid checksum, data in unused area
+  GCMemcardErrorCode dir_block_0_error_code = card.m_directory_blocks[0].CheckForErrors();
+  GCMemcardErrorCode dir_block_1_error_code = card.m_directory_blocks[1].CheckForErrors();
+
+  // can return invalid card size, invalid checksum, data in unused area, free block mismatch
+  GCMemcardErrorCode bat_block_0_error_code = card.m_bat_blocks[0].CheckForErrors(card_size_mbits);
+  GCMemcardErrorCode bat_block_1_error_code = card.m_bat_blocks[1].CheckForErrors(card_size_mbits);
+
+  const bool dir_block_0_valid = !dir_block_0_error_code.HasCriticalErrors();
+  const bool dir_block_1_valid = !dir_block_1_error_code.HasCriticalErrors();
+  const bool bat_block_0_valid = !bat_block_0_error_code.HasCriticalErrors();
+  const bool bat_block_1_valid = !bat_block_1_error_code.HasCriticalErrors();
+
+  // if any two (at least) blocks are corrupted return failure
+  // TODO: Consider allowing a recovery option when there's still a valid one of each type.
+  int number_of_corrupted_dir_bat_blocks = 0;
+  if (!dir_block_0_valid)
+    ++number_of_corrupted_dir_bat_blocks;
+  if (!dir_block_1_valid)
+    ++number_of_corrupted_dir_bat_blocks;
+  if (!bat_block_0_valid)
+    ++number_of_corrupted_dir_bat_blocks;
+  if (!bat_block_1_valid)
+    ++number_of_corrupted_dir_bat_blocks;
+
+  if (number_of_corrupted_dir_bat_blocks > 1)
+  {
+    error_code |= dir_block_0_error_code;
+    error_code |= dir_block_1_error_code;
+    error_code |= bat_block_0_error_code;
+    error_code |= bat_block_1_error_code;
+    return std::make_pair(error_code, std::nullopt);
+  }
+
+  // if exactly one block is corrupted copy and update it over the non-corrupted block
+  if (number_of_corrupted_dir_bat_blocks == 1)
+  {
+    if (!dir_block_0_valid)
+    {
+      card.m_directory_blocks[0] = card.m_directory_blocks[1];
+      card.m_directory_blocks[0].m_update_counter = card.m_directory_blocks[0].m_update_counter + 1;
+      card.m_directory_blocks[0].FixChecksums();
+      dir_block_0_error_code = card.m_directory_blocks[0].CheckForErrors();
+    }
+    else if (!dir_block_1_valid)
+    {
+      card.m_directory_blocks[1] = card.m_directory_blocks[0];
+      card.m_directory_blocks[1].m_update_counter = card.m_directory_blocks[1].m_update_counter + 1;
+      card.m_directory_blocks[1].FixChecksums();
+      dir_block_1_error_code = card.m_directory_blocks[1].CheckForErrors();
+    }
+    else if (!bat_block_0_valid)
+    {
+      card.m_bat_blocks[0] = card.m_bat_blocks[1];
+      card.m_bat_blocks[0].m_update_counter = card.m_bat_blocks[0].m_update_counter + 1;
+      card.m_bat_blocks[0].FixChecksums();
+      bat_block_0_error_code = card.m_bat_blocks[0].CheckForErrors(card_size_mbits);
+    }
+    else if (!bat_block_1_valid)
+    {
+      card.m_bat_blocks[1] = card.m_bat_blocks[0];
+      card.m_bat_blocks[1].m_update_counter = card.m_bat_blocks[1].m_update_counter + 1;
+      card.m_bat_blocks[1].FixChecksums();
+      bat_block_1_error_code = card.m_bat_blocks[1].CheckForErrors(card_size_mbits);
+    }
+    else
+    {
+      // should never reach here
+      assert(0);
+    }
+  }
+
+  error_code |= dir_block_0_error_code;
+  error_code |= dir_block_1_error_code;
+  error_code |= bat_block_0_error_code;
+  error_code |= bat_block_1_error_code;
+
+  // select the in-use Dir and BAT blocks based on update counter
+  // TODO: Is there a special case for wraparound after 65535 block updates, or is it assumed that
+  // the hardware fails long before that anyway?
+
+  if (card.m_directory_blocks[0].m_update_counter >= card.m_directory_blocks[1].m_update_counter)
+    card.m_active_directory = 0;
  else
-    m_active_bat = 1;
+    card.m_active_directory = 1;
+
+  if (card.m_bat_blocks[0].m_update_counter >= card.m_bat_blocks[1].m_update_counter)
+    card.m_active_bat = 0;
+  else
+    card.m_active_bat = 1;
+
+  // TODO: Do a card-wide corruption check here, such as cross-checking the active Dir's files with
+  // the active BAT's allocated sectors. The GC BIOS does at the very least recognize if a file's
+  // number of used blocks is inconsistent between the two, and will count a card as corrupted if
+  // that is the case.
+
+  card.m_valid = true;
+
+  return std::make_pair(error_code, std::move(card));
 }

 const Directory& GCMemcard::GetActiveDirectory() const
@ -292,31 +345,6 @@ std::pair<u16, u16> CalculateMemcardChecksums(const u8* data, size_t size)
  return std::make_pair(csum, inv_csum);
 }

-u32 GCMemcard::TestChecksums() const
-{
-  const auto [csum_hdr, cinv_hdr] = m_header_block.CalculateChecksums();
-  const auto [csum_dir0, cinv_dir0] = m_directory_blocks[0].CalculateChecksums();
-  const auto [csum_dir1, cinv_dir1] = m_directory_blocks[1].CalculateChecksums();
-  const auto [csum_bat0, cinv_bat0] = m_bat_blocks[0].CalculateChecksums();
-  const auto [csum_bat1, cinv_bat1] = m_bat_blocks[1].CalculateChecksums();
-
-  u32 results = 0;
-  if ((m_header_block.m_checksum != csum_hdr) || (m_header_block.m_checksum_inv != cinv_hdr))
-    results |= 1;
-  if ((m_directory_blocks[0].m_checksum != csum_dir0) ||
-      (m_directory_blocks[0].m_checksum_inv != cinv_dir0))
-    results |= 2;
-  if ((m_directory_blocks[1].m_checksum != csum_dir1) ||
-      (m_directory_blocks[1].m_checksum_inv != cinv_dir1))
-    results |= 4;
-  if ((m_bat_blocks[0].m_checksum != csum_bat0) || (m_bat_blocks[0].m_checksum_inv != cinv_bat0))
-    results |= 8;
-  if ((m_bat_blocks[1].m_checksum != csum_bat1) || (m_bat_blocks[1].m_checksum_inv != cinv_bat1))
-    results |= 16;
-
-  return results;
-}
-
 bool GCMemcard::FixChecksums()
 {
  if (!m_valid)
@ -679,6 +707,50 @@ std::pair<u16, u16> BlockAlloc::CalculateChecksums() const
  return CalculateMemcardChecksums(&raw[checksum_area_start], checksum_area_size);
 }

+GCMemcardErrorCode BlockAlloc::CheckForErrors(u16 size_mbits) const
+{
+  GCMemcardErrorCode error_code;
+
+  // verify checksums
+  const auto [checksum_sum, checksum_inv] = CalculateChecksums();
+  if (checksum_sum != m_checksum || checksum_inv != m_checksum_inv)
+    error_code.Set(GCMemcardValidityIssues::INVALID_CHECKSUM);
+
+  if (size_mbits > 0 && size_mbits <= 256)
+  {
+    // check if free block count matches the actual amount of free blocks in m_map
+    const u16 total_available_blocks = (size_mbits * MBIT_TO_BLOCKS) - MC_FST_BLOCKS;
+    assert(total_available_blocks <= m_map.size());
+    u16 blocks_in_use = 0;
+    for (size_t i = 0; i < total_available_blocks; ++i)
+    {
+      if (m_map[i] != 0)
+        ++blocks_in_use;
+    }
+    const u16 free_blocks = total_available_blocks - blocks_in_use;
+
+    if (free_blocks != m_free_blocks)
+      error_code.Set(GCMemcardValidityIssues::FREE_BLOCK_MISMATCH);
+
+    // remaining blocks map to nothing on hardware and must be empty
+    for (size_t i = total_available_blocks; i < m_map.size(); ++i)
+    {
+      if (m_map[i] != 0)
+      {
+        error_code.Set(GCMemcardValidityIssues::DATA_IN_UNUSED_AREA);
+        break;
+      }
+    }
+  }
+  else
+  {
+    // card size is outside the range of blocks that can be addressed
+    error_code.Set(GCMemcardValidityIssues::INVALID_CARD_SIZE);
+  }
+
+  return error_code;
+}
+
 GCMemcardGetSaveDataRetVal GCMemcard::GetSaveData(u8 index, std::vector<GCMBlock>& Blocks) const
 {
  if (!m_valid)
@ -1253,7 +1325,8 @@ bool GCMemcard::Format(bool shift_jis, u16 SizeMb)
  m_data_blocks.clear();
  m_data_blocks.resize(m_size_blocks - MC_FST_BLOCKS);

-  InitActiveDirBat();
+  m_active_directory = 0;
+  m_active_bat = 0;
  m_valid = true;

  return Save();
@ -1473,6 +1546,29 @@ std::pair<u16, u16> Header::CalculateChecksums() const
  return CalculateMemcardChecksums(&raw[checksum_area_start], checksum_area_size);
 }

+GCMemcardErrorCode Header::CheckForErrors(u16 card_size_mbits) const
+{
+  GCMemcardErrorCode error_code;
+
+  // total card size should match card size in header
+  if (m_size_mb != card_size_mbits)
+    error_code.Set(GCMemcardValidityIssues::MISMATCHED_CARD_SIZE);
+
+  // unused areas, should always be filled with 0xFF
+  if (std::any_of(m_unused_1.begin(), m_unused_1.end(), [](u8 val) { return val != 0xFF; }) ||
+      std::any_of(m_unused_2.begin(), m_unused_2.end(), [](u8 val) { return val != 0xFF; }))
+  {
+    error_code.Set(GCMemcardValidityIssues::DATA_IN_UNUSED_AREA);
+  }
+
+  // verify checksums
+  const auto [checksum_sum, checksum_inv] = CalculateChecksums();
+  if (checksum_sum != m_checksum || checksum_inv != m_checksum_inv)
+    error_code.Set(GCMemcardValidityIssues::INVALID_CHECKSUM);
+
+  return error_code;
+}
+
 Directory::Directory()
 {
  memset(this, 0xFF, BLOCK_SIZE);
@ -1508,3 +1604,19 @@ std::pair<u16, u16> Directory::CalculateChecksums() const
  constexpr size_t checksum_area_size = checksum_area_end - checksum_area_start;
  return CalculateMemcardChecksums(&raw[checksum_area_start], checksum_area_size);
 }
+
+GCMemcardErrorCode Directory::CheckForErrors() const
+{
+  GCMemcardErrorCode error_code;
+
+  // verify checksums
+  const auto [checksum_sum, checksum_inv] = CalculateChecksums();
+  if (checksum_sum != m_checksum || checksum_inv != m_checksum_inv)
+    error_code.Set(GCMemcardValidityIssues::INVALID_CHECKSUM);
+
+  // unused area, should always be filled with 0xFF
+  if (std::any_of(m_padding.begin(), m_padding.end(), [](u8 val) { return val != 0xFF; }))
+    error_code.Set(GCMemcardValidityIssues::DATA_IN_UNUSED_AREA);
+
+  return error_code;
+}
--- a/Source/Core/Core/HW/GCMemcard/GCMemcard.h
+++ b/Source/Core/Core/HW/GCMemcard/GCMemcard.h
@ -6,6 +6,7 @@

 #include <algorithm>
 #include <array>
+#include <bitset>
 #include <string>
 #include <vector>

@ -79,6 +80,30 @@ enum class GCMemcardRemoveFileRetVal
  DELETE_FAIL,
 };

+enum class GCMemcardValidityIssues
+{
+  FAILED_TO_OPEN,
+  IO_ERROR,
+  INVALID_CARD_SIZE,
+  INVALID_CHECKSUM,
+  MISMATCHED_CARD_SIZE,
+  FREE_BLOCK_MISMATCH,
+  DATA_IN_UNUSED_AREA,
+  COUNT
+};
+
+class GCMemcardErrorCode
+{
+public:
+  bool HasCriticalErrors() const;
+  bool Test(GCMemcardValidityIssues code) const;
+  void Set(GCMemcardValidityIssues code);
+  GCMemcardErrorCode& operator|=(const GCMemcardErrorCode& other);
+
+private:
+  std::bitset<static_cast<size_t>(GCMemcardValidityIssues::COUNT)> m_errors;
+};
+
 // size of a single memory card block in bytes
 constexpr u32 BLOCK_SIZE = 0x2000;

@ -106,7 +131,7 @@ constexpr u16 BAT_SIZE = 0xFFB;
 constexpr u16 MemCard59Mb = 0x04;
 constexpr u16 MemCard123Mb = 0x08;
 constexpr u16 MemCard251Mb = 0x10;
-constexpr u16 Memcard507Mb = 0x20;
+constexpr u16 Memcard507Mb = 0x20;  // FIXME: case
 constexpr u16 MemCard1019Mb = 0x40;
 constexpr u16 MemCard2043Mb = 0x80;

@ -192,6 +217,8 @@ struct Header

  void FixChecksums();
  std::pair<u16, u16> CalculateChecksums() const;
+
+  GCMemcardErrorCode CheckForErrors(u16 card_size_mbits) const;
 };
 static_assert(sizeof(Header) == BLOCK_SIZE);

@ -301,6 +328,8 @@ struct Directory

  void FixChecksums();
  std::pair<u16, u16> CalculateChecksums() const;
+
+  GCMemcardErrorCode CheckForErrors() const;
 };
 static_assert(sizeof(Directory) == BLOCK_SIZE);

@ -333,6 +362,8 @@ struct BlockAlloc

  void FixChecksums();
  std::pair<u16, u16> CalculateChecksums() const;
+
+  GCMemcardErrorCode CheckForErrors(u16 size_mbits) const;
 };
 static_assert(sizeof(BlockAlloc) == BLOCK_SIZE);
 #pragma pack(pop)
@ -354,8 +385,9 @@ private:
  int m_active_directory;
  int m_active_bat;

+  GCMemcard();
+
  GCMemcardImportFileRetVal ImportGciInternal(File::IOFile&& gci, const std::string& inputFile);
-  void InitActiveDirBat();

  const Directory& GetActiveDirectory() const;
  const BlockAlloc& GetActiveBat() const;
@ -364,8 +396,9 @@ private:
  void UpdateBat(const BlockAlloc& bat);

 public:
-  explicit GCMemcard(const std::string& fileName, bool forceCreation = false,
-                     bool shift_jis = false);
+  static std::optional<GCMemcard> Create(std::string filename, u16 size_mbits, bool shift_jis);
+
+  static std::pair<GCMemcardErrorCode, std::optional<GCMemcard>> Open(std::string filename);

  GCMemcard(const GCMemcard&) = delete;
  GCMemcard& operator=(const GCMemcard&) = delete;
@ -382,7 +415,6 @@ public:
  static s32 PSO_MakeSaveGameValid(const Header& cardheader, const DEntry& direntry,
                                   std::vector<GCMBlock>& FileBuffer);

-  u32 TestChecksums() const;
  bool FixChecksums();

  // get number of file entries in the directory
--- a/Source/Core/Core/HW/GCMemcard/GCMemcardDirectory.cpp
+++ b/Source/Core/Core/HW/GCMemcard/GCMemcardDirectory.cpp
@ -703,12 +703,12 @@ void MigrateFromMemcardFile(const std::string& directory_name, int card_index)
                                                Config::Get(Config::MAIN_MEMCARD_B_PATH);
  if (File::Exists(ini_memcard))
  {
-    GCMemcard memcard(ini_memcard.c_str());
-    if (memcard.IsValid())
+    auto [error_code, memcard] = GCMemcard::Open(ini_memcard.c_str());
+    if (!error_code.HasCriticalErrors() && memcard && memcard->IsValid())
    {
      for (u8 i = 0; i < DIRLEN; i++)
      {
-        memcard.ExportGci(i, "", directory_name);
+        memcard->ExportGci(i, "", directory_name);
      }
    }
  }
--- a/Source/Core/DolphinQt/GCMemcardManager.cpp
+++ b/Source/Core/DolphinQt/GCMemcardManager.cpp
@ -241,13 +241,14 @@ void GCMemcardManager::UpdateActions()

 void GCMemcardManager::SetSlotFile(int slot, QString path)
 {
-  auto memcard = std::make_unique<GCMemcard>(path.toStdString());
+  // TODO: Check error codes and give reasonable error messages.
+  auto [error_code, memcard] = GCMemcard::Open(path.toStdString());

-  if (!memcard->IsValid())
+  if (error_code.HasCriticalErrors() || !memcard || !memcard->IsValid())
    return;

  m_slot_file_edit[slot]->setText(path);
-  m_slot_memcard[slot] = std::move(memcard);
+  m_slot_memcard[slot] = std::make_unique<GCMemcard>(std::move(*memcard));

  UpdateSlotTable(slot);
  UpdateActions();
--- a/Source/Core/DolphinQt/Settings/GameCubePane.cpp
+++ b/Source/Core/DolphinQt/Settings/GameCubePane.cpp
@ -212,9 +212,10 @@ void GameCubePane::OnConfigPressed(int slot)
  {
    if (File::Exists(filename.toStdString()))
    {
-      GCMemcard mc(filename.toStdString());
+      // TODO: check error codes and give reasonable error messages
+      auto [error_code, mc] = GCMemcard::Open(filename.toStdString());

-      if (!mc.IsValid())
+      if (error_code.HasCriticalErrors() || !mc || !mc->IsValid())
      {
        ModalMessageBox::critical(this, tr("Error"),
                                  tr("Cannot use that file as a memory card.\n%1\n"