common: Rewrite logging based on cut down citra logger (#86)

* common: Rewrite logging based on cut down Citra logger

* code: Misc fixes

* core: Bring back tls handler

* linker: Cleanup

* config: Remove log level

* logging: Enable console output by default

* core: Fix windows build

src/common/logging/backend.cpp

@@ -0,0 +1,277 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <chrono>
+#include <filesystem>
+#include <thread>
+
+#include <fmt/format.h>
+#include "Util/config.h"
+
+#ifdef _WIN32
+#include <windows.h> // For OutputDebugStringW
+#endif
+
+#include "common/bounded_threadsafe_queue.h"
+#include "common/io_file.h"
+#include "common/logging/backend.h"
+#include "common/logging/log.h"
+#include "common/logging/log_entry.h"
+#include "common/logging/text_formatter.h"
+#include "common/path_util.h"
+#include "common/string_util.h"
+#include "common/thread.h"
+
+namespace Common::Log {
+
+using namespace Common::FS;
+
+namespace {
+
+/**
+ * Backend that writes to stderr and with color
+ */
+class ColorConsoleBackend {
+public:
+    explicit ColorConsoleBackend() = default;
+
+    ~ColorConsoleBackend() = default;
+
+    void Write(const Entry& entry) {
+        if (enabled.load(std::memory_order_relaxed)) {
+            PrintColoredMessage(entry);
+        }
+    }
+
+    void Flush() {
+        // stderr shouldn't be buffered
+    }
+
+    void SetEnabled(bool enabled_) {
+        enabled = enabled_;
+    }
+
+private:
+    std::atomic_bool enabled{true};
+};
+
+/**
+ * Backend that writes to a file passed into the constructor
+ */
+class FileBackend {
+public:
+    explicit FileBackend(const std::filesystem::path& filename)
+        : file{filename, FS::FileAccessMode::Write, FS::FileType::TextFile} {}
+
+    ~FileBackend() = default;
+
+    void Write(const Entry& entry) {
+        if (!enabled) {
+            return;
+        }
+
+        bytes_written += file.WriteString(FormatLogMessage(entry).append(1, '\n'));
+
+        // Prevent logs from exceeding a set maximum size in the event that log entries are spammed.
+        const auto write_limit = 100_MB;
+        const bool write_limit_exceeded = bytes_written > write_limit;
+        if (entry.log_level >= Level::Error || write_limit_exceeded) {
+            if (write_limit_exceeded) {
+                // Stop writing after the write limit is exceeded.
+                // Don't close the file so we can print a stacktrace if necessary
+                enabled = false;
+            }
+            file.Flush();
+        }
+    }
+
+    void Flush() {
+        file.Flush();
+    }
+
+private:
+    Common::FS::IOFile file;
+    bool enabled = true;
+    std::size_t bytes_written = 0;
+};
+
+/**
+ * Backend that writes to Visual Studio's output window
+ */
+class DebuggerBackend {
+public:
+    explicit DebuggerBackend() = default;
+
+    ~DebuggerBackend() = default;
+
+    void Write(const Entry& entry) {
+#ifdef _WIN32
+        ::OutputDebugStringW(UTF8ToUTF16W(FormatLogMessage(entry).append(1, '\n')).c_str());
+#endif
+    }
+
+    void Flush() {}
+
+    void EnableForStacktrace() {}
+};
+
+bool initialization_in_progress_suppress_logging = true;
+
+/**
+ * Static state as a singleton.
+ */
+class Impl {
+public:
+    static Impl& Instance() {
+        if (!instance) {
+            throw std::runtime_error("Using Logging instance before its initialization");
+        }
+        return *instance;
+    }
+
+    static void Initialize(std::string_view log_file) {
+        if (instance) {
+            LOG_WARNING(Log, "Reinitializing logging backend");
+            return;
+        }
+        const auto& log_dir = GetUserPath(PathType::LogDir);
+        std::filesystem::create_directory(log_dir);
+        Filter filter;
+        filter.ParseFilterString(Config::getLogFilter());
+        instance = std::unique_ptr<Impl, decltype(&Deleter)>(new Impl(log_dir / LOG_FILE, filter),
+                                                             Deleter);
+        initialization_in_progress_suppress_logging = false;
+    }
+
+    static void Start() {
+        instance->StartBackendThread();
+    }
+
+    static void Stop() {
+        instance->StopBackendThread();
+    }
+
+    Impl(const Impl&) = delete;
+    Impl& operator=(const Impl&) = delete;
+
+    Impl(Impl&&) = delete;
+    Impl& operator=(Impl&&) = delete;
+
+    void SetGlobalFilter(const Filter& f) {
+        filter = f;
+    }
+
+    void SetColorConsoleBackendEnabled(bool enabled) {
+        color_console_backend.SetEnabled(enabled);
+    }
+
+    void PushEntry(Class log_class, Level log_level, const char* filename, unsigned int line_num,
+                   const char* function, std::string message) {
+        if (!filter.CheckMessage(log_class, log_level)) {
+            return;
+        }
+
+        using std::chrono::duration_cast;
+        using std::chrono::microseconds;
+        using std::chrono::steady_clock;
+
+        message_queue.EmplaceWait(Entry{
+            .timestamp = duration_cast<microseconds>(steady_clock::now() - time_origin),
+            .log_class = log_class,
+            .log_level = log_level,
+            .filename = filename,
+            .line_num = line_num,
+            .function = function,
+            .message = std::move(message),
+        });
+    }
+
+private:
+    Impl(const std::filesystem::path& file_backend_filename, const Filter& filter_)
+        : filter{filter_}, file_backend{file_backend_filename} {}
+
+    ~Impl() = default;
+
+    void StartBackendThread() {
+        backend_thread = std::jthread([this](std::stop_token stop_token) {
+            Common::SetCurrentThreadName("shadPS4:Log");
+            Entry entry;
+            const auto write_logs = [this, &entry]() {
+                ForEachBackend([&entry](auto& backend) { backend.Write(entry); });
+            };
+            while (!stop_token.stop_requested()) {
+                message_queue.PopWait(entry, stop_token);
+                if (entry.filename != nullptr) {
+                    write_logs();
+                }
+            }
+            // Drain the logging queue. Only writes out up to MAX_LOGS_TO_WRITE to prevent a
+            // case where a system is repeatedly spamming logs even on close.
+            int max_logs_to_write = filter.IsDebug() ? std::numeric_limits<s32>::max() : 100;
+            while (max_logs_to_write-- && message_queue.TryPop(entry)) {
+                write_logs();
+            }
+        });
+    }
+
+    void StopBackendThread() {
+        backend_thread.request_stop();
+        if (backend_thread.joinable()) {
+            backend_thread.join();
+        }
+
+        ForEachBackend([](auto& backend) { backend.Flush(); });
+    }
+
+    void ForEachBackend(auto lambda) {
+        lambda(debugger_backend);
+        lambda(color_console_backend);
+        lambda(file_backend);
+    }
+
+    static void Deleter(Impl* ptr) {
+        delete ptr;
+    }
+
+    static inline std::unique_ptr<Impl, decltype(&Deleter)> instance{nullptr, Deleter};
+
+    Filter filter;
+    DebuggerBackend debugger_backend{};
+    ColorConsoleBackend color_console_backend{};
+    FileBackend file_backend;
+
+    MPSCQueue<Entry> message_queue{};
+    std::chrono::steady_clock::time_point time_origin{std::chrono::steady_clock::now()};
+    std::jthread backend_thread;
+};
+} // namespace
+
+void Initialize(std::string_view log_file) {
+    Impl::Initialize(log_file.empty() ? LOG_FILE : log_file);
+}
+
+void Start() {
+    Impl::Start();
+}
+
+void Stop() {
+    Impl::Stop();
+}
+
+void SetGlobalFilter(const Filter& filter) {
+    Impl::Instance().SetGlobalFilter(filter);
+}
+
+void SetColorConsoleBackendEnabled(bool enabled) {
+    Impl::Instance().SetColorConsoleBackendEnabled(enabled);
+}
+
+void FmtLogMessageImpl(Class log_class, Level log_level, const char* filename,
+                       unsigned int line_num, const char* function, const char* format,
+                       const fmt::format_args& args) {
+    if (!initialization_in_progress_suppress_logging) [[likely]] {
+        Impl::Instance().PushEntry(log_class, log_level, filename, line_num, function,
+                                   fmt::vformat(format, args));
+    }
+}
+} // namespace Common::Log

src/common/logging/backend.h

@@ -0,0 +1,27 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <string_view>
+#include "common/logging/filter.h"
+
+namespace Common::Log {
+
+class Filter;
+
+/// Initializes the logging system. This should be the first thing called in main.
+void Initialize(std::string_view log_file = "");
+
+/// Starts the logging threads.
+void Start();
+
+/// Explictily stops the logger thread and flushes the buffers
+void Stop();
+
+/// The global filter will prevent any messages from even being processed if they are filtered.
+void SetGlobalFilter(const Filter& filter);
+
+void SetColorConsoleBackendEnabled(bool enabled);
+
+} // namespace Common::Log

src/common/logging/filter.cpp

@@ -0,0 +1,173 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <algorithm>
+
+#include "common/assert.h"
+#include "common/logging/filter.h"
+
+namespace Common::Log {
+namespace {
+template <typename It>
+Level GetLevelByName(const It begin, const It end) {
+    for (u8 i = 0; i < static_cast<u8>(Level::Count); ++i) {
+        const char* level_name = GetLevelName(static_cast<Level>(i));
+        if (std::string_view(begin, end).compare(level_name) == 0) {
+            return static_cast<Level>(i);
+        }
+    }
+    return Level::Count;
+}
+
+template <typename It>
+Class GetClassByName(const It begin, const It end) {
+    for (u8 i = 0; i < static_cast<u8>(Class::Count); ++i) {
+        const char* level_name = GetLogClassName(static_cast<Class>(i));
+        if (std::string_view(begin, end).compare(level_name) == 0) {
+            return static_cast<Class>(i);
+        }
+    }
+    return Class::Count;
+}
+
+template <typename Iterator>
+bool ParseFilterRule(Filter& instance, Iterator begin, Iterator end) {
+    auto level_separator = std::find(begin, end, ':');
+    if (level_separator == end) {
+        LOG_ERROR(Log, "Invalid log filter. Must specify a log level after `:`: {}",
+                  std::string_view(begin, end));
+        return false;
+    }
+
+    const Level level = GetLevelByName(level_separator + 1, end);
+    if (level == Level::Count) {
+        LOG_ERROR(Log, "Unknown log level in filter: {}", std::string_view(begin, end));
+        return false;
+    }
+
+    if (std::string_view(begin, level_separator).compare("*") == 0) {
+        instance.ResetAll(level);
+        return true;
+    }
+
+    const Class log_class = GetClassByName(begin, level_separator);
+    if (log_class == Class::Count) {
+        LOG_ERROR(Log, "Unknown log class in filter: {}", std::string(begin, end));
+        return false;
+    }
+
+    instance.SetClassLevel(log_class, level);
+    return true;
+}
+} // Anonymous namespace
+
+/// Macro listing all log classes. Code should define CLS and SUB as desired before invoking this.
+#define ALL_LOG_CLASSES()                                                                          \
+    CLS(Log)                                                                                       \
+    CLS(Common)                                                                                    \
+    SUB(Common, Filesystem)                                                                        \
+    SUB(Common, Memory)                                                                            \
+    CLS(Core)                                                                                      \
+    SUB(Core, Linker)                                                                              \
+    CLS(Config)                                                                                    \
+    CLS(Debug)                                                                                     \
+    CLS(Kernel)                                                                                    \
+    SUB(Kernel, Pthread)                                                                           \
+    SUB(Kernel, Vmm)                                                                               \
+    SUB(Kernel, Fs)                                                                                \
+    SUB(Kernel, Event)                                                                             \
+    SUB(Kernel, Sce)                                                                               \
+    CLS(Lib)                                                                                       \
+    SUB(Lib, LibC)                                                                                 \
+    SUB(Lib, Kernel)                                                                               \
+    SUB(Lib, Pad)                                                                                  \
+    SUB(Lib, GnmDriver)                                                                            \
+    SUB(Lib, SystemService)                                                                        \
+    SUB(Lib, UserService)                                                                          \
+    SUB(Lib, VideoOut)                                                                             \
+    CLS(Frontend)                                                                                  \
+    CLS(Render)                                                                                    \
+    SUB(Render, Vulkan)                                                                            \
+    CLS(Input)                                                                                     \
+    CLS(Loader)
+
+// GetClassName is a macro defined by Windows.h, grrr...
+const char* GetLogClassName(Class log_class) {
+    switch (log_class) {
+#define CLS(x)                                                                                     \
+    case Class::x:                                                                                 \
+        return #x;
+#define SUB(x, y)                                                                                  \
+    case Class::x##_##y:                                                                           \
+        return #x "." #y;
+        ALL_LOG_CLASSES()
+#undef CLS
+#undef SUB
+    case Class::Count:
+    default:
+        break;
+    }
+    UNREACHABLE();
+}
+
+const char* GetLevelName(Level log_level) {
+#define LVL(x)                                                                                     \
+    case Level::x:                                                                                 \
+        return #x
+    switch (log_level) {
+        LVL(Trace);
+        LVL(Debug);
+        LVL(Info);
+        LVL(Warning);
+        LVL(Error);
+        LVL(Critical);
+    case Level::Count:
+    default:
+        break;
+    }
+#undef LVL
+    UNREACHABLE();
+}
+
+Filter::Filter(Level default_level) {
+    ResetAll(default_level);
+}
+
+void Filter::ResetAll(Level level) {
+    class_levels.fill(level);
+}
+
+void Filter::SetClassLevel(Class log_class, Level level) {
+    class_levels[static_cast<std::size_t>(log_class)] = level;
+}
+
+void Filter::ParseFilterString(std::string_view filter_view) {
+    auto clause_begin = filter_view.cbegin();
+    while (clause_begin != filter_view.cend()) {
+        auto clause_end = std::find(clause_begin, filter_view.cend(), ' ');
+
+        // If clause isn't empty
+        if (clause_end != clause_begin) {
+            ParseFilterRule(*this, clause_begin, clause_end);
+        }
+
+        if (clause_end != filter_view.cend()) {
+            // Skip over the whitespace
+            ++clause_end;
+        }
+        clause_begin = clause_end;
+    }
+}
+
+bool Filter::CheckMessage(Class log_class, Level level) const {
+    return static_cast<u8>(level) >=
+           static_cast<u8>(class_levels[static_cast<std::size_t>(log_class)]);
+}
+
+bool Filter::IsDebug() const {
+    return std::any_of(class_levels.begin(), class_levels.end(), [](const Level& l) {
+        return static_cast<u8>(l) <= static_cast<u8>(Level::Debug);
+    });
+}
+
+} // namespace Common::Log

src/common/logging/filter.h

@@ -0,0 +1,66 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <array>
+#include <cstddef>
+#include <string_view>
+#include "common/logging/types.h"
+
+namespace Common::Log {
+
+/**
+ * Returns the name of the passed log class as a C-string. Subclasses are separated by periods
+ * instead of underscores as in the enumeration.
+ */
+const char* GetLogClassName(Class log_class);
+
+/**
+ * Returns the name of the passed log level as a C-string.
+ */
+const char* GetLevelName(Level log_level);
+
+/**
+ * Implements a log message filter which allows different log classes to have different minimum
+ * severity levels. The filter can be changed at runtime and can be parsed from a string to allow
+ * editing via the interface or loading from a configuration file.
+ */
+class Filter {
+public:
+    /// Initializes the filter with all classes having `default_level` as the minimum level.
+    explicit Filter(Level default_level = Level::Info);
+
+    /// Resets the filter so that all classes have `level` as the minimum displayed level.
+    void ResetAll(Level level);
+
+    /// Sets the minimum level of `log_class` (and not of its subclasses) to `level`.
+    void SetClassLevel(Class log_class, Level level);
+
+    /**
+     * Parses a filter string and applies it to this filter.
+     *
+     * A filter string consists of a space-separated list of filter rules, each of the format
+     * `<class>:<level>`. `<class>` is a log class name, with subclasses separated using periods.
+     * `*` is allowed as a class name and will reset all filters to the specified level. `<level>`
+     * a severity level name which will be set as the minimum logging level of the matched classes.
+     * Rules are applied left to right, with each rule overriding previous ones in the sequence.
+     *
+     * A few examples of filter rules:
+     *  - `*:Info` -- Resets the level of all classes to Info.
+     *  - `Service:Info` -- Sets the level of Service to Info.
+     *  - `Service.FS:Trace` -- Sets the level of the Service.FS class to Trace.
+     */
+    void ParseFilterString(std::string_view filter_view);
+
+    /// Matches class/level combination against the filter, returning true if it passed.
+    bool CheckMessage(Class log_class, Level level) const;
+
+    /// Returns true if any logging classes are set to debug
+    bool IsDebug() const;
+
+private:
+    std::array<Level, static_cast<std::size_t>(Class::Count)> class_levels;
+};
+
+} // namespace Common::Log

src/common/logging/formatter.h

@@ -0,0 +1,21 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <type_traits>
+#include <fmt/format.h>
+
+// Adapted from https://github.com/fmtlib/fmt/issues/2704
+// a generic formatter for enum classes
+#if FMT_VERSION >= 80100
+template <typename T>
+struct fmt::formatter<T, std::enable_if_t<std::is_enum_v<T>, char>>
+    : formatter<std::underlying_type_t<T>> {
+    template <typename FormatContext>
+    auto format(const T& value, FormatContext& ctx) -> decltype(ctx.out()) {
+        return fmt::formatter<std::underlying_type_t<T>>::format(
+            static_cast<std::underlying_type_t<T>>(value), ctx);
+    }
+};
+#endif

src/common/logging/log.h

@@ -0,0 +1,70 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <string_view>
+
+#include "common/logging/formatter.h"
+#include "common/logging/types.h"
+
+namespace Common::Log {
+
+constexpr const char* TrimSourcePath(std::string_view source) {
+    const auto rfind = [source](const std::string_view match) {
+        return source.rfind(match) == source.npos ? 0 : (source.rfind(match) + match.size());
+    };
+    auto idx = std::max({rfind("/"), rfind("\\")});
+    return source.data() + idx;
+}
+
+/// Logs a message to the global logger, using fmt
+void FmtLogMessageImpl(Class log_class, Level log_level, const char* filename,
+                       unsigned int line_num, const char* function, const char* format,
+                       const fmt::format_args& args);
+
+template <typename... Args>
+void FmtLogMessage(Class log_class, Level log_level, const char* filename, unsigned int line_num,
+                   const char* function, const char* format, const Args&... args) {
+    FmtLogMessageImpl(log_class, log_level, filename, line_num, function, format,
+                      fmt::make_format_args(args...));
+}
+
+} // namespace Common::Log
+
+// Define the fmt lib macros
+#define LOG_GENERIC(log_class, log_level, ...)                                                     \
+    Common::Log::FmtLogMessage(log_class, log_level, Common::Log::TrimSourcePath(__FILE__),        \
+                               __LINE__, __func__, __VA_ARGS__)
+
+#ifdef _DEBUG
+#define LOG_TRACE(log_class, ...)                                                                  \
+    Common::Log::FmtLogMessage(Common::Log::Class::log_class, Common::Log::Level::Trace,           \
+                               Common::Log::TrimSourcePath(__FILE__), __LINE__, __func__,          \
+                               __VA_ARGS__)
+#else
+#define LOG_TRACE(log_class, fmt, ...) (void(0))
+#endif
+
+#define LOG_DEBUG(log_class, ...)                                                                  \
+    Common::Log::FmtLogMessage(Common::Log::Class::log_class, Common::Log::Level::Debug,           \
+                               Common::Log::TrimSourcePath(__FILE__), __LINE__, __func__,          \
+                               __VA_ARGS__)
+#define LOG_INFO(log_class, ...)                                                                   \
+    Common::Log::FmtLogMessage(Common::Log::Class::log_class, Common::Log::Level::Info,            \
+                               Common::Log::TrimSourcePath(__FILE__), __LINE__, __func__,          \
+                               __VA_ARGS__)
+#define LOG_WARNING(log_class, ...)                                                                \
+    Common::Log::FmtLogMessage(Common::Log::Class::log_class, Common::Log::Level::Warning,         \
+                               Common::Log::TrimSourcePath(__FILE__), __LINE__, __func__,          \
+                               __VA_ARGS__)
+#define LOG_ERROR(log_class, ...)                                                                  \
+    Common::Log::FmtLogMessage(Common::Log::Class::log_class, Common::Log::Level::Error,           \
+                               Common::Log::TrimSourcePath(__FILE__), __LINE__, __func__,          \
+                               __VA_ARGS__)
+#define LOG_CRITICAL(log_class, ...)                                                               \
+    Common::Log::FmtLogMessage(Common::Log::Class::log_class, Common::Log::Level::Critical,        \
+                               Common::Log::TrimSourcePath(__FILE__), __LINE__, __func__,          \
+                               __VA_ARGS__)

src/common/logging/log_entry.h

@@ -0,0 +1,26 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <chrono>
+
+#include "common/logging/types.h"
+
+namespace Common::Log {
+
+/**
+ * A log entry. Log entries are store in a structured format to permit more varied output
+ * formatting on different frontends, as well as facilitating filtering and aggregation.
+ */
+struct Entry {
+    std::chrono::microseconds timestamp;
+    Class log_class{};
+    Level log_level{};
+    const char* filename = nullptr;
+    u32 line_num = 0;
+    std::string function;
+    std::string message;
+};
+
+} // namespace Common::Log

src/common/logging/text_formatter.cpp

@@ -0,0 +1,109 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <array>
+#include <cstdio>
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+#include "common/assert.h"
+#include "common/logging/filter.h"
+#include "common/logging/log.h"
+#include "common/logging/log_entry.h"
+#include "common/logging/text_formatter.h"
+
+namespace Common::Log {
+
+std::string FormatLogMessage(const Entry& entry) {
+    const u32 time_seconds = static_cast<u32>(entry.timestamp.count() / 1000000);
+    const u32 time_fractional = static_cast<u32>(entry.timestamp.count() % 1000000);
+
+    const char* class_name = GetLogClassName(entry.log_class);
+    const char* level_name = GetLevelName(entry.log_level);
+
+    return fmt::format("[{}] <{}> {}:{}:{}: {}", class_name, level_name, entry.filename,
+                       entry.function, entry.line_num, entry.message);
+}
+
+void PrintMessage(const Entry& entry) {
+    const auto str = FormatLogMessage(entry).append(1, '\n');
+    fputs(str.c_str(), stdout);
+}
+
+void PrintColoredMessage(const Entry& entry) {
+#ifdef _WIN32
+    HANDLE console_handle = GetStdHandle(STD_ERROR_HANDLE);
+    if (console_handle == INVALID_HANDLE_VALUE) {
+        return;
+    }
+
+    CONSOLE_SCREEN_BUFFER_INFO original_info{};
+    GetConsoleScreenBufferInfo(console_handle, &original_info);
+
+    WORD color = 0;
+    switch (entry.log_level) {
+    case Level::Trace: // Grey
+        color = FOREGROUND_INTENSITY;
+        break;
+    case Level::Debug: // Cyan
+        color = FOREGROUND_GREEN | FOREGROUND_BLUE;
+        break;
+    case Level::Info: // Bright gray
+        color = FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE;
+        break;
+    case Level::Warning: // Bright yellow
+        color = FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_INTENSITY;
+        break;
+    case Level::Error: // Bright red
+        color = FOREGROUND_RED | FOREGROUND_INTENSITY;
+        break;
+    case Level::Critical: // Bright magenta
+        color = FOREGROUND_RED | FOREGROUND_BLUE | FOREGROUND_INTENSITY;
+        break;
+    case Level::Count:
+        UNREACHABLE();
+    }
+
+    SetConsoleTextAttribute(console_handle, color);
+#else
+#define ESC "\x1b"
+    const char* color = "";
+    switch (entry.log_level) {
+    case Level::Trace: // Grey
+        color = ESC "[1;30m";
+        break;
+    case Level::Debug: // Cyan
+        color = ESC "[0;36m";
+        break;
+    case Level::Info: // Bright gray
+        color = ESC "[0;37m";
+        break;
+    case Level::Warning: // Bright yellow
+        color = ESC "[1;33m";
+        break;
+    case Level::Error: // Bright red
+        color = ESC "[1;31m";
+        break;
+    case Level::Critical: // Bright magenta
+        color = ESC "[1;35m";
+        break;
+    case Level::Count:
+        UNREACHABLE();
+    }
+
+    fputs(color, stdout);
+#endif
+
+    PrintMessage(entry);
+
+#ifdef _WIN32
+    SetConsoleTextAttribute(console_handle, original_info.wAttributes);
+#else
+    fputs(ESC "[0m", stdout);
+#undef ESC
+#endif
+}
+
+} // namespace Common::Log

src/common/logging/text_formatter.h

@@ -0,0 +1,21 @@
+// SPDX-FileCopyrightText: Copyright 2014 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <string>
+
+namespace Common::Log {
+
+struct Entry;
+
+/// Formats a log entry into the provided text buffer.
+std::string FormatLogMessage(const Entry& entry);
+
+/// Formats and prints a log entry to stderr.
+void PrintMessage(const Entry& entry);
+
+/// Prints the same message as `PrintMessage`, but colored according to the severity level.
+void PrintColoredMessage(const Entry& entry);
+
+} // namespace Common::Log

src/common/logging/types.h

@@ -0,0 +1,63 @@
+// SPDX-FileCopyrightText: Copyright 2023 Citra Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "common/types.h"
+
+namespace Common::Log {
+
+/// Specifies the severity or level of detail of the log message.
+enum class Level : u8 {
+    Trace, ///< Extremely detailed and repetitive debugging information that is likely to
+    ///< pollute logs.
+    Debug,   ///< Less detailed debugging information.
+    Info,    ///< Status information from important points during execution.
+    Warning, ///< Minor or potential problems found during execution of a task.
+    Error,   ///< Major problems found during execution of a task that prevent it from being
+    ///< completed.
+    Critical, ///< Major problems during execution that threaten the stability of the entire
+    ///< application.
+
+    Count, ///< Total number of logging levels
+};
+
+/**
+ * Specifies the sub-system that generated the log message.
+ *
+ * @note If you add a new entry here, also add a corresponding one to `ALL_LOG_CLASSES` in
+ * backend.cpp.
+ */
+enum class Class : u8 {
+    Log,               ///< Messages about the log system itself
+    Common,            ///< Library routines
+    Common_Filesystem, ///< Filesystem interface library
+    Common_Memory,     ///< Memory mapping and management functions
+    Core,              ///< LLE emulation core
+    Core_Linker,       ///< The module linker
+    Config,            ///< Emulator configuration (including commandline)
+    Debug,             ///< Debugging tools
+    Kernel,            ///< The HLE implementation of the PS4 kernel.
+    Kernel_Pthread,    ///< The pthread implementation of the kernel.
+    Kernel_Fs,         ///< The filesystem implementation of the kernel.
+    Kernel_Vmm,        ///< The virtual memory implementation of the kernel.
+    Kernel_Event,      ///< The event management implementation of the kernel.
+    Kernel_Sce,        ///< The sony specific interfaces provided by the kernel.
+    Lib,               ///< HLE implementation of system library. Each major library
+                       ///< should have its own subclass.
+    Lib_LibC,          ///< The LibC implementation.
+    Lib_Kernel,        ///< The LibKernel implementation.
+    Lib_Pad,           ///< The LibScePad implementation.
+    Lib_GnmDriver,     ///< The LibSceGnmDriver implementation.
+    Lib_SystemService, ///< The LibSceSystemService implementation.
+    Lib_UserService,   ///< The LibSceUserService implementation.
+    Lib_VideoOut,      ///< The LibSceVideoOut implementation.
+    Frontend,          ///< Emulator UI
+    Render,            ///< Video Core
+    Render_Vulkan,     ///< Vulkan backend
+    Loader,            ///< ROM loader
+    Input,             ///< Input emulation
+    Count              ///< Total number of logging classes
+};
+
+} // namespace Common::Log