Update Logger to use NDK Logger APIs + Improve Backing API + Fix FDSAN issues

app/src/main/cpp/emu_jni.cpp

@@ -4,6 +4,7 @@
 #include <csignal>
 #include <unistd.h>
 #include <sys/resource.h>
+#include <android/log.h>
 #include "skyline/loader/loader.h"
 #include "skyline/common.h"
 #include "skyline/os.h"
@@ -12,24 +13,18 @@
 
 bool Halt;
 jobject Surface;
-uint FaultCount;
 skyline::GroupMutex JniMtx;
 skyline::u16 fps;
 skyline::u32 frametime;
 std::weak_ptr<skyline::input::Input> inputWeak;
 
 void signalHandler(int signal) {
-    syslog(LOG_ERR, "Halting program due to signal: %s", strsignal(signal));
+    __android_log_print(ANDROID_LOG_FATAL, "emu-cpp", "Halting program due to signal: %s", strsignal(signal));
-    if (FaultCount > 2)
+    exit(signal);
-        exit(SIGKILL);
-    else
-        Halt = true;
-    FaultCount++;
 }
 
 extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_executeApplication(JNIEnv *env, jobject instance, jstring romUriJstring, jint romType, jint romFd, jint preferenceFd, jstring appFilesPathJstring) {
     Halt = false;
-    FaultCount = 0;
     fps = 0;
     frametime = 0;
 
@@ -44,6 +39,7 @@ extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_executeApplication(
 
     auto jvmManager{std::make_shared<skyline::JvmManager>(env, instance)};
     auto settings{std::make_shared<skyline::Settings>(preferenceFd)};
+    close(preferenceFd);
 
     auto appFilesPath{env->GetStringUTFChars(appFilesPathJstring, nullptr)};
     auto logger{std::make_shared<skyline::Logger>(std::string(appFilesPath) + "skyline.log", static_cast<skyline::Logger::LogLevel>(std::stoi(settings->GetString("log_level"))))};
@@ -74,6 +70,8 @@ extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_executeApplication(
 
     auto end{std::chrono::steady_clock::now()};
     logger->Info("Done in: {} ms", (std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()));
+
+    close(romFd);
 }
 
 extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_setHalt(JNIEnv *, jobject, jboolean halt) {

app/src/main/cpp/skyline/common.cpp

@@ -2,6 +2,7 @@
 // Copyright © 2020 Skyline Team and Contributors (https://github.com/skyline-emu/)
 
 #include <tinyxml2.h>
+#include <android/log.h>
 #include "common.h"
 #include "nce.h"
 #include "gpu.h"
@@ -68,11 +69,12 @@ namespace skyline {
     Settings::Settings(int fd) {
         tinyxml2::XMLDocument pref;
 
-        if (pref.LoadFile(fdopen(fd, "r")))
+        auto fileDeleter = [](FILE *file) { fclose(file); };
+        std::unique_ptr<FILE, decltype(fileDeleter)> file{fdopen(fd, "r"), fileDeleter};
+        if (pref.LoadFile(file.get()))
             throw exception("TinyXML2 Error: " + std::string(pref.ErrorStr()));
 
         tinyxml2::XMLElement *elem{pref.LastChild()->FirstChild()->ToElement()};
-
         while (elem) {
             switch (elem->Value()[0]) {
                 case 's':
@@ -88,7 +90,7 @@ namespace skyline {
                     break;
 
                 default:
-                    syslog(LOG_ALERT, "Settings type is missing: %s for %s", elem->Value(), elem->FindAttribute("name")->Value());
+                    __android_log_print(ANDROID_LOG_WARN, "emu-cpp", "Settings type is missing: %s for %s", elem->Value(), elem->FindAttribute("name")->Value());
                     break;
             };
 
@@ -122,7 +124,7 @@ namespace skyline {
     }
 
     Logger::Logger(const std::string &path, LogLevel configLevel) : configLevel(configLevel) {
-        logFile.open(path, std::ios::app);
+        logFile.open(path, std::ios::trunc);
         WriteHeader("Logging started");
     }
 
@@ -132,14 +134,17 @@ namespace skyline {
     }
 
     void Logger::WriteHeader(const std::string &str) {
-        syslog(LOG_ALERT, "%s", str.c_str());
+        __android_log_write(ANDROID_LOG_INFO, "emu-cpp", str.c_str());
 
         std::lock_guard guard(mtx);
         logFile << "0|" << str << "\n";
     }
 
     void Logger::Write(LogLevel level, std::string str) {
-        syslog(levelSyslog[static_cast<u8>(level)], "%s", str.c_str());
+        constexpr std::array<char, 4> levelCharacter{'0', '1', '2', '3'}; // The LogLevel as written out to a file
+        constexpr std::array<int, 4> levelAlog{ANDROID_LOG_ERROR, ANDROID_LOG_WARN, ANDROID_LOG_INFO, ANDROID_LOG_DEBUG}; // This corresponds to LogLevel and provides it's equivalent for NDK Logging
+
+        __android_log_write(levelAlog[static_cast<u8>(level)], "emu-cpp", str.c_str());
 
         for (auto &character : str)
             if (character == '\n')

app/src/main/cpp/skyline/common.h

@@ -17,7 +17,6 @@
 #include <string>
 #include <sstream>
 #include <memory>
-#include <syslog.h>
 #include <sys/mman.h>
 #include <fmt/format.h>
 #include <frozen/unordered_map.h>
@@ -366,8 +365,6 @@ namespace skyline {
     class Logger {
       private:
         std::ofstream logFile; //!< An output stream to the log file
-        std::array<char, 4> levelCharacter{'0', '1', '2', '3'}; //!< The LogLevel as written out to a file
-        static constexpr std::array<int, 4> levelSyslog{LOG_ERR, LOG_WARNING, LOG_INFO, LOG_DEBUG}; //!< This corresponds to LogLevel and provides it's equivalent for syslog
         Mutex mtx; //!< A mutex to lock before logging anything
 
       public:
@@ -377,6 +374,7 @@ namespace skyline {
             Info,
             Debug,
         };
+
         LogLevel configLevel; //!< The minimum level of logs to write
 
         /**
@@ -457,9 +455,9 @@ namespace skyline {
      */
     class Settings {
       private:
-        std::map<std::string, std::string> stringMap; //!< A mapping from all keys to their corresponding string value
+        std::unordered_map<std::string, std::string> stringMap; //!< A mapping from all keys to their corresponding string value
-        std::map<std::string, bool> boolMap; //!< A mapping from all keys to their corresponding boolean value
+        std::unordered_map<std::string, bool> boolMap; //!< A mapping from all keys to their corresponding boolean value
-        std::map<std::string, int> intMap; //!< A mapping from all keys to their corresponding integer value
+        std::unordered_map<std::string, int> intMap; //!< A mapping from all keys to their corresponding integer value
 
       public:
         /**

app/src/main/cpp/skyline/crypto/key_store.cpp

@@ -15,7 +15,7 @@ namespace skyline::crypto {
 
     void KeyStore::ReadPairs(const std::shared_ptr<vfs::Backing> &backing, ReadPairsCallback callback) {
         std::vector<char> fileContent(backing->size);
-        backing->Read(fileContent.data(), 0, fileContent.size());
+        backing->Read(span(fileContent).cast<u8>());
 
         auto lineStart{fileContent.begin()};
         std::vector<char>::iterator lineEnd;

app/src/main/cpp/skyline/crypto/key_store.h

@@ -28,14 +28,14 @@ namespace skyline::crypto {
         std::map<Key128, Key128> titleKeys;
 
         std::unordered_map<std::string_view, std::optional<Key256> &> key256Names{
-            {"header_key", headerKey}
+            {"header_key", headerKey},
         };
 
         std::unordered_map<std::string_view, IndexedKeys128 &> indexedKey128Names{
             {"titlekek_", titleKek},
             {"key_area_key_application_", areaKeyApplication},
             {"key_area_key_ocean_", areaKeyOcean},
-            {"key_area_key_system_", areaKeySystem}
+            {"key_area_key_system_", areaKeySystem},
         };
 
         using ReadPairsCallback = void (skyline::crypto::KeyStore::*)(std::string_view, std::string_view);

app/src/main/cpp/skyline/kernel/types/KSession.h

@@ -16,8 +16,8 @@ namespace skyline::kernel::type {
     class KSession : public KSyncObject {
       public:
         std::shared_ptr<service::BaseService> serviceObject;
-        std::unordered_map<KHandle, std::shared_ptr<service::BaseService>> domainTable; //!< A map from a virtual handle to it's service
+        std::vector<std::shared_ptr<service::BaseService>> domains; //!< A vector of services that correspond to virtual handles
-        KHandle handleIndex{0x1}; //!< The currently allocated handle index
+        KHandle handleIndex{}; //!< The currently allocated handle index
         bool isOpen{true}; //!< If the session is open or not
         bool isDomain{}; //!< If this is a domain session or not
 
@@ -33,7 +33,7 @@ namespace skyline::kernel::type {
          */
         KHandle ConvertDomain() {
             isDomain = true;
-            domainTable[handleIndex] = serviceObject;
+            domains.push_back(serviceObject);
             return handleIndex++;
         }
     };

app/src/main/cpp/skyline/loader/nro.cpp

@@ -10,14 +10,14 @@
 
 namespace skyline::loader {
     NroLoader::NroLoader(const std::shared_ptr<vfs::Backing> &backing) : backing(backing) {
-        backing->Read(&header);
+        header = backing->Read<NroHeader>();
 
         if (header.magic != util::MakeMagic<u32>("NRO0"))
             throw exception("Invalid NRO magic! 0x{0:X}", header.magic);
 
         // The homebrew asset section is appended to the end of an NRO file
         if (backing->size > header.size) {
-            backing->Read(&assetHeader, header.size);
+            assetHeader = backing->Read<NroAssetHeader>(header.size);
 
             if (assetHeader.magic != util::MakeMagic<u32>("ASET"))
                 throw exception("Invalid ASET magic! 0x{0:X}", assetHeader.magic);
@@ -34,14 +34,14 @@ namespace skyline::loader {
         NroAssetSection &segmentHeader{assetHeader.icon};
         std::vector<u8> buffer(segmentHeader.size);
 
-        backing->Read(buffer.data(), header.size + segmentHeader.offset, segmentHeader.size);
+        backing->Read(buffer, header.size + segmentHeader.offset);
         return buffer;
     }
 
     std::vector<u8> NroLoader::GetSegment(const NroSegmentHeader &segment) {
         std::vector<u8> buffer(segment.size);
 
-        backing->Read(buffer.data(), segment.offset, segment.size);
+        backing->Read(buffer, segment.offset);
         return buffer;
     }
 

app/src/main/cpp/skyline/loader/nso.cpp

@@ -9,8 +9,7 @@
 
 namespace skyline::loader {
     NsoLoader::NsoLoader(const std::shared_ptr<vfs::Backing> &backing) : backing(backing) {
-        u32 magic{};
+        u32 magic{backing->Read<u32>()};
-        backing->Read(&magic);
 
         if (magic != util::MakeMagic<u32>("NSO0"))
             throw exception("Invalid NSO magic! 0x{0:X}", magic);
@@ -21,19 +20,18 @@ namespace skyline::loader {
 
         if (compressedSize) {
             std::vector<u8> compressedBuffer(compressedSize);
-            backing->Read(compressedBuffer.data(), segment.fileOffset, compressedSize);
+            backing->Read(compressedBuffer, segment.fileOffset);
 
             LZ4_decompress_safe(reinterpret_cast<char *>(compressedBuffer.data()), reinterpret_cast<char *>(outputBuffer.data()), compressedSize, segment.decompressedSize);
         } else {
-            backing->Read(outputBuffer.data(), segment.fileOffset, segment.decompressedSize);
+            backing->Read(outputBuffer, segment.fileOffset);
         }
 
         return outputBuffer;
     }
 
     Loader::ExecutableLoadInfo NsoLoader::LoadNso(const std::shared_ptr<vfs::Backing> &backing, const std::shared_ptr<kernel::type::KProcess> process, const DeviceState &state, size_t offset) {
-        NsoHeader header{};
+        auto header{backing->Read<NsoHeader>()};
-        backing->Read(&header);
 
         if (header.magic != util::MakeMagic<u32>("NSO0"))
             throw exception("Invalid NSO magic! 0x{0:X}", header.magic);

app/src/main/cpp/skyline/loader/nsp.cpp

@@ -57,8 +57,7 @@ namespace skyline::loader {
             return std::vector<u8>();
 
         std::vector<u8> buffer(icon->size);
-
+        icon->Read(buffer);
-        icon->Read(buffer.data(), 0, icon->size);
         return buffer;
     }
 }

app/src/main/cpp/skyline/services/fssrv/IFile.cpp

@@ -23,7 +23,7 @@ namespace skyline::service::fssrv {
             return result::InvalidSize;
         }
 
-        response.Push<u32>(static_cast<u32>(backing->Read(request.outputBuf.at(0).data(), offset, size)));
+        response.Push<u32>(static_cast<u32>(backing->Read(request.outputBuf.at(0), offset)));
         return {};
     }
 
@@ -48,7 +48,7 @@ namespace skyline::service::fssrv {
             return result::InvalidSize;
         }
 
-        if (backing->Write(request.inputBuf.at(0).data(), offset, request.inputBuf.at(0).size()) != size) {
+        if (backing->Write(request.inputBuf.at(0), offset) != size) {
             state.logger->Warn("Failed to write all data to the backing");
             return result::UnexpectedFailure;
         }

app/src/main/cpp/skyline/services/fssrv/IStorage.cpp

@@ -21,7 +21,7 @@ namespace skyline::service::fssrv {
             return result::InvalidSize;
         }
 
-        backing->Read(request.outputBuf.at(0).data(), offset, size);
+        backing->Read(request.outputBuf.at(0), offset);
         return {};
     }
 

app/src/main/cpp/skyline/services/nvdrv/devices/nvhost_syncpoint.cpp

@@ -10,7 +10,9 @@ namespace skyline::service::nvdrv {
         constexpr u32 VBlank0SyncpointId{26};
         constexpr u32 VBlank1SyncpointId{27};
 
-        // Reserve both vblank syncpoints as client managed since the userspace driver has direct access to them
+        // Reserve both vblank syncpoints as client managed as they use Continuous Mode
+        // Refer to section 14.3.5.3 of the TRM for more information on Continuous Mode
+        // https://github.com/Jetson-TX1-AndroidTV/android_kernel_jetson_tx1_hdmi_primary/blob/8f74a72394efb871cb3f886a3de2998cd7ff2990/drivers/gpu/host1x/drm/dc.c#L660
         ReserveSyncpoint(VBlank0SyncpointId, true);
         ReserveSyncpoint(VBlank1SyncpointId, true);
     }
@@ -20,7 +22,7 @@ namespace skyline::service::nvdrv {
             throw exception("Requested syncpoint is in use");
 
         syncpoints.at(id).reserved = true;
-        syncpoints.at(id).clientManaged = clientManaged;
+        syncpoints.at(id).interfaceManaged = clientManaged;
 
         return id;
     }
@@ -44,7 +46,8 @@ namespace skyline::service::nvdrv {
         if (!syncpoint.reserved)
             throw exception("Cannot check the expiry status of an unreserved syncpoint!");
 
-        if (syncpoint.clientManaged)
+        // If the interface manages counters then we don't keep track of the maximum value as it handles sanity checking the values then
+        if (syncpoint.interfaceManaged)
             return static_cast<i32>(syncpoint.counterMin - threshold) >= 0;
         else
             return (syncpoint.counterMax - threshold) >= (syncpoint.counterMin - threshold);

app/src/main/cpp/skyline/services/nvdrv/devices/nvhost_syncpoint.h

@@ -7,16 +7,17 @@
 
 namespace skyline::service::nvdrv {
     /**
-     * @brief NvHostSyncpoint handles allocating and accessing host1x syncpoints
+     * @brief NvHostSyncpoint handles allocating and accessing host1x syncpoints, these are cached versions of the HW syncpoints which are intermittently synced
+     * @note Refer to Chapter 14 of the Tegra X1 TRM for an exhaustive overview of them
      * @url https://http.download.nvidia.com/tegra-public-appnotes/host1x.html
      * @url https://github.com/Jetson-TX1-AndroidTV/android_kernel_jetson_tx1_hdmi_primary/blob/jetson-tx1/drivers/video/tegra/host/nvhost_syncpt.c
      */
     class NvHostSyncpoint {
       private:
         struct SyncpointInfo {
-            std::atomic<u32> counterMin; //!< The least value the syncpoint can be (The value it was when it was last synchronized with the GPU for host managed syncpoints)
+            std::atomic<u32> counterMin; //!< The least value the syncpoint can be (The value it was when it was last synchronized with host1x)
             std::atomic<u32> counterMax; //!< The maximum value the syncpoint can reach according to the current usage
-            bool clientManaged;          //!< If the syncpoint is managed by the client (CPU) or host (GPU), it determines if the value is absolute or not
+            bool interfaceManaged;       //!< If the syncpoint is managed by a host1x client interface, a client interface is a HW block that can handle host1x transactions on behalf of a host1x client (Which would otherwise need to be manually synced using PIO which is synchronous and requires direct cooperation of the CPU)
             bool reserved;
         };
 

app/src/main/cpp/skyline/services/serviceman.cpp

@@ -89,9 +89,9 @@ namespace skyline::service {
         auto serviceObject{CreateService(name)};
         KHandle handle{};
         if (session.isDomain) {
-            session.domainTable[++session.handleIndex] = serviceObject;
+            session.domains.push_back(serviceObject);
             response.domainObjects.push_back(session.handleIndex);
-            handle = session.handleIndex;
+            handle = session.handleIndex++;
         } else {
             handle = state.process->NewHandle<type::KSession>(serviceObject).handle;
             response.moveHandles.push_back(handle);
@@ -105,7 +105,7 @@ namespace skyline::service {
         KHandle handle{};
 
         if (session.isDomain) {
-            session.domainTable[session.handleIndex] = serviceObject;
+            session.domains.push_back(serviceObject);
             response.domainObjects.push_back(session.handleIndex);
             handle = session.handleIndex++;
         } else {
@@ -121,9 +121,9 @@ namespace skyline::service {
         auto session{state.process->GetHandle<type::KSession>(handle)};
         if (session->isOpen) {
             if (session->isDomain) {
-                for (const auto &domainEntry : session->domainTable)
+                for (const auto &domainService : session->domains)
-                    std::erase_if(serviceMap, [domainEntry](const auto &entry) {
+                    std::erase_if(serviceMap, [domainService](const auto &entry) {
-                        return entry.second == domainEntry.second;
+                        return entry.second == domainService;
                     });
             } else {
                 std::erase_if(serviceMap, [session](const auto &entry) {
@@ -148,7 +148,9 @@ namespace skyline::service {
                 case ipc::CommandType::RequestWithContext:
                     if (session->isDomain) {
                         try {
-                            auto service{session->domainTable.at(request.domain->objectId)};
+                            auto service{session->domains.at(request.domain->objectId)};
+                            if (service == nullptr)
+                                throw exception("Domain request used an expired handle");
                             switch (request.domain->command) {
                                 case ipc::DomainCommand::SendMessage:
                                     response.errorCode = service->HandleRequest(*session, request, response);
@@ -158,7 +160,7 @@ namespace skyline::service {
                                     std::erase_if(serviceMap, [service](const auto &entry) {
                                         return entry.second == service;
                                     });
-                                    session->domainTable.erase(request.domain->objectId);
+                                    session->domains.at(request.domain->objectId).reset();
                                     break;
                             }
                         } catch (std::out_of_range &) {

app/src/main/cpp/skyline/vfs/backing.h

@@ -11,9 +11,6 @@ namespace skyline::vfs {
      */
     class Backing {
       public:
-        /**
-         * @brief The capabilities of the Backing
-         */
         union Mode {
             struct {
                 bool read : 1; //!< The backing is readable
@@ -41,47 +38,44 @@ namespace skyline::vfs {
 
         /**
          * @brief Read bytes from the backing at a particular offset to a buffer
-         * @param output The object to write to
+         * @param output The object to write the data read to
          * @param offset The offset to start reading from
-         * @param size The amount to read in bytes
          * @return The amount of bytes read
          */
-        virtual size_t Read(u8 *output, size_t offset, size_t size) = 0;
+        virtual size_t Read(span<u8> output, size_t offset = 0) = 0;
 
         /**
-         * @brief Read bytes from the backing at a particular offset to a buffer (template version)
+         * @brief Read bytes from the backing at a particular offset into an object
-         * @param output The object to write to
          * @param offset The offset to start reading from
-         * @param size The amount to read in bytes
+         * @return The object that was read
-         * @return The amount of bytes read
          */
         template<typename T>
-        inline size_t Read(T *output, size_t offset = 0, size_t size = 0) {
+        inline T Read(size_t offset = 0) {
-            return Read(reinterpret_cast<u8 *>(output), offset, size ? size : sizeof(T));
+            T object;
+            Read(span(reinterpret_cast<u8 *>(&object), sizeof(T)), offset);
+            return object;
         }
 
         /**
          * @brief Writes from a buffer to a particular offset in the backing
-         * @param input The object to write to the backing
+         * @param input The data to write to the backing
          * @param offset The offset where the input buffer should be written
-         * @param size The amount to write
          * @return The amount of bytes written
          */
-        virtual size_t Write(u8 *input, size_t offset, size_t size) {
+        virtual size_t Write(span<u8> input, size_t offset = 0) {
             throw exception("This backing does not support being written to");
         }
 
         /**
-         * @brief Writes from a buffer to a particular offset in the backing (template version)
+         * @brief Writes from an object into a particular offset in the backing
-         * @tparam T The type of object to write
+         * @param object The object to write to the backing
-         * @param input The object to write to the backing
+         * @param offset The offset where the input should be written
-         * @param offset The offset where the input buffer should be written
-         * @param size The amount to write
-         * @return The amount of bytes written
          */
         template<typename T>
-        inline size_t Write(T *output, size_t offset = 0, size_t size = 0) {
+        inline void WriteObject(const T& object, size_t offset = 0) {
-            return Write(reinterpret_cast<u8 *>(output), offset, size ? size : sizeof(T));
+            size_t size;
+            if((size = Write(span(reinterpret_cast<u8 *>(&object), sizeof(T)), offset)) != sizeof(T))
+                throw exception("Object wasn't written fully into output backing: {}/{}", size, sizeof(T));
         }
 
         /**

app/src/main/cpp/skyline/vfs/ctr_encrypted_backing.cpp

@@ -15,34 +15,34 @@ namespace skyline::vfs {
         cipher.SetIV(ctr);
     }
 
-    size_t CtrEncryptedBacking::Read(u8 *output, size_t offset, size_t size) {
+    size_t CtrEncryptedBacking::Read(span<u8> output, size_t offset) {
         if (size == 0)
             return 0;
 
         size_t sectorOffset{offset % SectorSize};
         if (sectorOffset == 0) {
             UpdateCtr(baseOffset + offset);
-            size_t read{backing->Read(output, offset, size)};
+            size_t read{backing->Read(output, offset)};
             if (read != size)
                 return 0;
-            cipher.Decrypt({output, size});
+            cipher.Decrypt(output);
             return size;
         }
 
         size_t sectorStart{offset - sectorOffset};
         std::vector<u8> blockBuf(SectorSize);
-        size_t read{backing->Read(blockBuf.data(), sectorStart, SectorSize)};
+        size_t read{backing->Read(blockBuf, sectorStart)};
         if (read != SectorSize)
             return 0;
         UpdateCtr(baseOffset + sectorStart);
         cipher.Decrypt(blockBuf);
         if (size + sectorOffset < SectorSize) {
-            std::memcpy(output, blockBuf.data() + sectorOffset, size);
+            std::memcpy(output.data(), blockBuf.data() + sectorOffset, size);
             return size;
         }
 
         size_t readInBlock{SectorSize - sectorOffset};
-        std::memcpy(output, blockBuf.data() + sectorOffset, readInBlock);
+        std::memcpy(output.data(), blockBuf.data() + sectorOffset, readInBlock);
-        return readInBlock + Read(output + readInBlock, offset + readInBlock, size - readInBlock);
+        return readInBlock + Read(output.subspan(readInBlock), offset + readInBlock);
     }
 }

app/src/main/cpp/skyline/vfs/ctr_encrypted_backing.h

@@ -26,6 +26,6 @@ namespace skyline::vfs {
       public:
         CtrEncryptedBacking(crypto::KeyStore::Key128 &ctr, crypto::KeyStore::Key128 &key, const std::shared_ptr<Backing> &backing, size_t baseOffset);
 
-        size_t Read(u8 *output, size_t offset, size_t size) override;
+        size_t Read(span<u8> output, size_t offset = 0) override;
     };
 }

app/src/main/cpp/skyline/vfs/nacp.cpp

@@ -5,7 +5,7 @@
 
 namespace skyline::vfs {
     NACP::NACP(const std::shared_ptr<vfs::Backing> &backing) {
-        backing->Read(&nacpContents);
+        nacpContents = backing->Read<NacpData>();
 
         // TODO: Select based on language settings, complete struct, yada yada
 

app/src/main/cpp/skyline/vfs/nca.cpp

@@ -14,7 +14,7 @@ namespace skyline::vfs {
     using namespace loader;
 
     NCA::NCA(const std::shared_ptr<vfs::Backing> &backing, const std::shared_ptr<crypto::KeyStore> &keyStore) : backing(backing), keyStore(keyStore) {
-        backing->Read(&header);
+        header = backing->Read<NcaHeader>();
 
         if (header.magic != util::MakeMagic<u32>("NCA3")) {
             if (!keyStore->headerKey)

app/src/main/cpp/skyline/vfs/os_backing.cpp

@@ -20,22 +20,22 @@ namespace skyline::vfs {
             close(fd);
     }
 
-    size_t OsBacking::Read(u8 *output, size_t offset, size_t size) {
+    size_t OsBacking::Read(span<u8> output, size_t offset) {
         if (!mode.read)
             throw exception("Attempting to read a backing that is not readable");
 
-        auto ret{pread64(fd, output, size, offset)};
+        auto ret{pread64(fd, output.data(), output.size(), offset)};
         if (ret < 0)
             throw exception("Failed to read from fd: {}", strerror(errno));
 
         return static_cast<size_t>(ret);
     }
 
-    size_t OsBacking::Write(u8 *output, size_t offset, size_t size) {
+    size_t OsBacking::Write(span<u8> input, size_t offset) {
         if (!mode.write)
             throw exception("Attempting to write to a backing that is not writable");
 
-        auto ret{pwrite64(fd, output, size, offset)};
+        auto ret{pwrite64(fd, input.data(), input.size(), offset)};
         if (ret < 0)
             throw exception("Failed to write to fd: {}", strerror(errno));
 

app/src/main/cpp/skyline/vfs/os_backing.h

@@ -22,9 +22,9 @@ namespace skyline::vfs {
 
         ~OsBacking();
 
-        size_t Read(u8 *output, size_t offset, size_t size);
+        size_t Read(span<u8> output, size_t offset = 0);
 
-        size_t Write(u8 *output, size_t offset, size_t size);
+        size_t Write(span<u8> input, size_t offset = 0);
 
         void Resize(size_t size);
     };

app/src/main/cpp/skyline/vfs/partition_filesystem.cpp

@@ -6,7 +6,7 @@
 
 namespace skyline::vfs {
     PartitionFileSystem::PartitionFileSystem(std::shared_ptr<Backing> backing) : FileSystem(), backing(backing) {
-        backing->Read(&header);
+        header = backing->Read<FsHeader>();
 
         if (header.magic == util::MakeMagic<u32>("PFS0"))
             hashed = false;
@@ -20,12 +20,11 @@ namespace skyline::vfs {
         fileDataOffset = stringTableOffset + header.stringTableSize;
 
         std::vector<char> stringTable(header.stringTableSize + 1);
-        backing->Read(stringTable.data(), stringTableOffset, header.stringTableSize);
+        backing->Read(span(stringTable).first(header.stringTableSize).cast<u8>(), stringTableOffset);
         stringTable[header.stringTableSize] = 0;
 
         for (u32 entryOffset{sizeof(FsHeader)}; entryOffset < header.numFiles * entrySize; entryOffset += entrySize) {
-            PartitionFileEntry entry;
+            auto entry{backing->Read<PartitionFileEntry>(entryOffset)};
-            backing->Read(&entry, entryOffset);
 
             std::string name(&stringTable[entry.stringTableOffset]);
             fileMap.emplace(name, std::move(entry));

app/src/main/cpp/skyline/vfs/partition_filesystem.h

@@ -16,7 +16,7 @@ namespace skyline::vfs {
             u32 numFiles; //!< The number of files in the filesystem
             u32 stringTableSize; //!< The size of the filesystem's string table
             u32 _pad_;
-        } header{};
+        } header;
         static_assert(sizeof(FsHeader) == 0x10);
 
         struct PartitionFileEntry {

app/src/main/cpp/skyline/vfs/region_backing.h

@@ -22,13 +22,12 @@ namespace skyline::vfs {
          */
         RegionBacking(const std::shared_ptr<vfs::Backing> &backing, size_t offset, size_t size, Mode mode = {true, false, false}) : Backing(mode, size), backing(backing), baseOffset(offset) {};
 
-        inline size_t Read(u8 *output, size_t offset, size_t size) {
+        virtual size_t Read(span<u8> output, size_t offset = 0) {
             if (!mode.read)
                 throw exception("Attempting to read a backing that is not readable");
-
+            if (size - offset < output.size())
-            size = std::min(offset + size, this->size) - offset;
+                throw exception("Trying to read past the end of a region backing: 0x{:X}/0x{:X} (Offset: 0x{:X})", output.size(), size, offset);
-
+            return backing->Read(output, baseOffset + offset);
-            return backing->Read(output, baseOffset + offset, size);
         }
     };
 }

app/src/main/cpp/skyline/vfs/rom_filesystem.cpp

@@ -6,20 +6,18 @@
 
 namespace skyline::vfs {
     RomFileSystem::RomFileSystem(std::shared_ptr<Backing> backing) : FileSystem(), backing(backing) {
-        backing->Read(&header);
+        header = backing->Read<RomFsHeader>();
-
         TraverseDirectory(0, "");
     }
 
     void RomFileSystem::TraverseFiles(u32 offset, const std::string &path) {
-        RomFsFileEntry entry{};
+        RomFsFileEntry entry;
-
         do {
-            backing->Read(&entry, header.fileMetaTableOffset + offset);
+            entry = backing->Read<RomFsFileEntry>(header.fileMetaTableOffset + offset);
 
             if (entry.nameSize) {
                 std::vector<char> name(entry.nameSize);
-                backing->Read(name.data(), header.fileMetaTableOffset + offset + sizeof(RomFsFileEntry), entry.nameSize);
+                backing->Read(span(name).cast<u8>(), header.fileMetaTableOffset + offset + sizeof(RomFsFileEntry));
 
                 std::string fullPath{path + (path.empty() ? "" : "/") + std::string(name.data(), entry.nameSize)};
                 fileMap.emplace(fullPath, entry);
@@ -30,13 +28,12 @@ namespace skyline::vfs {
     }
 
     void RomFileSystem::TraverseDirectory(u32 offset, const std::string &path) {
-        RomFsDirectoryEntry entry{};
+        auto entry{backing->Read<RomFsDirectoryEntry>(header.dirMetaTableOffset + offset)};
-        backing->Read(&entry, header.dirMetaTableOffset + offset);
 
         std::string childPath{path};
         if (entry.nameSize) {
             std::vector<char> name(entry.nameSize);
-            backing->Read(name.data(), header.dirMetaTableOffset + offset + sizeof(RomFsDirectoryEntry), entry.nameSize);
+            backing->Read(span(name).cast<u8>(), header.dirMetaTableOffset + offset + sizeof(RomFsDirectoryEntry));
             childPath = path + (path.empty() ? "" : "/") + std::string(name.data(), entry.nameSize);
         }
 
@@ -89,11 +86,11 @@ namespace skyline::vfs {
             u32 offset{ownEntry.fileOffset};
 
             do {
-                backing->Read(&romFsFileEntry, header.fileMetaTableOffset + offset);
+                romFsFileEntry = backing->Read<RomFileSystem::RomFsFileEntry>(header.fileMetaTableOffset + offset);
 
                 if (romFsFileEntry.nameSize) {
                     std::vector<char> name(romFsFileEntry.nameSize);
-                    backing->Read(name.data(), header.fileMetaTableOffset + offset + sizeof(RomFileSystem::RomFsFileEntry), romFsFileEntry.nameSize);
+                    backing->Read(span(name).cast<u8>(), header.fileMetaTableOffset + offset + sizeof(RomFileSystem::RomFsFileEntry));
 
                     contents.emplace_back(Entry{std::string(name.data(), romFsFileEntry.nameSize), EntryType::File});
                 }
@@ -107,11 +104,11 @@ namespace skyline::vfs {
             u32 offset{ownEntry.childOffset};
 
             do {
-                backing->Read(&romFsDirectoryEntry, header.dirMetaTableOffset + offset);
+                romFsDirectoryEntry = backing->Read<RomFileSystem::RomFsDirectoryEntry>(header.dirMetaTableOffset + offset);
 
                 if (romFsDirectoryEntry.nameSize) {
                     std::vector<char> name(romFsDirectoryEntry.nameSize);
-                    backing->Read(name.data(), header.dirMetaTableOffset + offset + sizeof(RomFileSystem::RomFsDirectoryEntry), romFsDirectoryEntry.nameSize);
+                    backing->Read(span(name).cast<u8>(), header.dirMetaTableOffset + offset + sizeof(RomFileSystem::RomFsDirectoryEntry));
 
                     contents.emplace_back(Entry{std::string(name.data(), romFsDirectoryEntry.nameSize), EntryType::Directory});
                 }

app/src/main/java/emu/skyline/EmulationActivity.kt

@@ -29,16 +29,6 @@ class EmulationActivity : AppCompatActivity(), SurfaceHolder.Callback, View.OnTo
         System.loadLibrary("skyline") // libskyline.so
     }
 
-    /**
-     * The file descriptor of the ROM
-     */
-    private lateinit var romFd : ParcelFileDescriptor
-
-    /**
-     * The file descriptor of the application Preference XML
-     */
-    private lateinit var preferenceFd : ParcelFileDescriptor
-
     /**
      * The [InputManager] class handles loading/saving the input data
      */
@@ -187,12 +177,13 @@ class EmulationActivity : AppCompatActivity(), SurfaceHolder.Callback, View.OnTo
      */
     private fun executeApplication(rom : Uri) {
         val romType = getRomFormat(rom, contentResolver).ordinal
-        romFd = contentResolver.openFileDescriptor(rom, "r")!!
+        val romFd = contentResolver.openFileDescriptor(rom, "r")!!
+        val preferenceFd = ParcelFileDescriptor.open(File("${applicationInfo.dataDir}/shared_prefs/${applicationInfo.packageName}_preferences.xml"), ParcelFileDescriptor.MODE_READ_WRITE)
 
         emulationThread = Thread {
             surfaceReady.block()
 
-            executeApplication(rom.toString(), romType, romFd.fd, preferenceFd.fd, applicationContext.filesDir.canonicalPath + "/")
+            executeApplication(rom.toString(), romType, romFd.detachFd(), preferenceFd.detachFd(), applicationContext.filesDir.canonicalPath + "/")
 
             if (shouldFinish)
                 runOnUiThread { finish() }
@@ -225,9 +216,6 @@ class EmulationActivity : AppCompatActivity(), SurfaceHolder.Callback, View.OnTo
 
         input = InputManager(this)
 
-        val preference = File("${applicationInfo.dataDir}/shared_prefs/${applicationInfo.packageName}_preferences.xml")
-        preferenceFd = ParcelFileDescriptor.open(preference, ParcelFileDescriptor.MODE_READ_WRITE)
-
         game_view.holder.addCallback(this)
 
         val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this)
@@ -262,8 +250,6 @@ class EmulationActivity : AppCompatActivity(), SurfaceHolder.Callback, View.OnTo
 
         shouldFinish = true
 
-        romFd.close()
-
         executeApplication(intent?.data!!)
 
         super.onNewIntent(intent)
@@ -281,9 +267,6 @@ class EmulationActivity : AppCompatActivity(), SurfaceHolder.Callback, View.OnTo
         vibrators.forEach { (_, vibrator) -> vibrator.cancel() }
         vibrators.clear()
 
-        romFd.close()
-        preferenceFd.close()
-
         super.onDestroy()
     }