Moves GDB server to GUI thread (#1022)

gui/CMakeLists.txt

@@ -1,5 +1,5 @@
 # External dependencies.
-find_package(Qt6 REQUIRED COMPONENTS Svg Widgets)
+find_package(Qt6 REQUIRED COMPONENTS Network Svg Widgets)
 find_package(Threads REQUIRED)
 
 if(WIN32 OR (UNIX AND NOT APPLE))
@@ -64,7 +64,7 @@ endif()
 
 target_compile_features(obliteration PRIVATE cxx_std_17)
 
-target_link_libraries(obliteration PRIVATE Qt6::Svg Qt6::Widgets)
+target_link_libraries(obliteration PRIVATE Qt6::Network Qt6::Svg Qt6::Widgets)
 target_link_libraries(obliteration PRIVATE Threads::Threads)
 target_link_libraries(obliteration PRIVATE ${LIBGUI})
 

gui/core.h

@@ -44,6 +44,11 @@ enum VmmLog {
     VmmLog_Error,
 };
 
+/**
+ * Reason for [`VmmEvent::Breakpoint`].
+ */
+struct KernelStop;
+
 /**
  * Contains settings to launch the kernel.
  */
@@ -86,21 +91,15 @@ struct VmmScreen {
  */
 enum VmmEvent_Tag {
     VmmEvent_Error,
-    VmmEvent_WaitingDebugger,
-    VmmEvent_DebuggerDisconnected,
     VmmEvent_Exiting,
     VmmEvent_Log,
+    VmmEvent_Breakpoint,
 };
 
 struct VmmEvent_Error_Body {
     const struct RustError *reason;
 };
 
-struct VmmEvent_WaitingDebugger_Body {
-    const char *addr;
-    size_t len;
-};
-
 struct VmmEvent_Exiting_Body {
     bool success;
 };
@@ -111,13 +110,38 @@ struct VmmEvent_Log_Body {
     size_t len;
 };
 
+struct VmmEvent_Breakpoint_Body {
+    struct KernelStop *stop;
+};
+
 struct VmmEvent {
     enum VmmEvent_Tag tag;
     union {
         struct VmmEvent_Error_Body error;
-        struct VmmEvent_WaitingDebugger_Body waiting_debugger;
         struct VmmEvent_Exiting_Body exiting;
         struct VmmEvent_Log_Body log;
+        struct VmmEvent_Breakpoint_Body breakpoint;
+    };
+};
+
+/**
+ * Result of [`vmm_dispatch_debug()`].
+ */
+enum DebugResult_Tag {
+    DebugResult_Ok,
+    DebugResult_Disconnected,
+    DebugResult_ReadFailed,
+    DebugResult_Error,
+};
+
+struct DebugResult_Error_Body {
+    struct RustError *reason;
+};
+
+struct DebugResult {
+    enum DebugResult_Tag tag;
+    union {
+        struct DebugResult_Error_Body error;
     };
 };
 
@@ -183,18 +207,26 @@ struct RustError *update_firmware(const char *root,
                                   void *cx,
                                   void (*status)(const char*, uint64_t, uint64_t, void*));
 
-void vmm_free(struct Vmm *vmm);
-
-struct Vmm *vmm_run(const char *kernel,
+struct Vmm *vmm_start(const char *kernel,
                       const struct VmmScreen *screen,
                       const struct Profile *profile,
-                    const char *debug,
+                      bool (*debug)(void*, const uint8_t*, size_t, int*),
                       void (*event)(const struct VmmEvent*, void*),
                       void *cx,
                       struct RustError **err);
 
+void vmm_free(struct Vmm *vmm);
+
 struct RustError *vmm_draw(struct Vmm *vmm);
 
+struct DebugResult vmm_dispatch_debug(struct Vmm *vmm,
+                                      struct KernelStop *stop,
+                                      bool (*read)(uint8_t*, void*));
+
+void vmm_shutdown(struct Vmm *vmm);
+
+bool vmm_shutting_down(struct Vmm *vmm);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif // __cplusplus

gui/main.cpp

@@ -222,10 +222,8 @@ int main(int argc, char *argv[])
     win.restoreGeometry();
 
     // Run main window.
-    auto debug = args.value(Args::debug);
-
-    if (!debug.isEmpty()) {
-        win.startVmm(debug);
+    if (args.isSet(Args::debug)) {
+        win.startDebug(args.value(Args::debug));
     }
 
     return QApplication::exec();

gui/main_window.cpp

@@ -20,6 +20,7 @@
 #include <QDir>
 #include <QFile>
 #include <QFileDialog>
+#include <QHostAddress>
 #include <QIcon>
 #include <QMenuBar>
 #include <QMessageBox>
@@ -28,6 +29,8 @@
 #include <QScrollBar>
 #include <QSettings>
 #include <QStackedWidget>
+#include <QTcpServer>
+#include <QTcpSocket>
 #include <QToolBar>
 #include <QUrl>
 
@@ -54,7 +57,8 @@ MainWindow::MainWindow(
     m_profiles(nullptr),
     m_games(nullptr),
     m_launch(nullptr),
-    m_screen(nullptr)
+    m_screen(nullptr),
+    m_debug(nullptr)
 {
     setWindowTitle("Obliteration");
 
@@ -111,7 +115,13 @@ MainWindow::MainWindow(
 #endif
 
     connect(m_launch, &LaunchSettings::saveClicked, this, &MainWindow::saveProfile);
-    connect(m_launch, &LaunchSettings::startClicked, this, &MainWindow::startVmm);
+    connect(m_launch, &LaunchSettings::startClicked, [this](const QString &debug) {
+        if (debug.isEmpty()) {
+            startVmm();
+        } else {
+            startDebug(debug);
+        }
+    });
 
     m_main->addWidget(m_launch);
 
@@ -224,6 +234,8 @@ void MainWindow::closeEvent(QCloseEvent *event)
 
     // Ask user to confirm.
     if (m_vmm) {
+        // Ask user to confirm only if we did not shutdown the VMM programmatically.
+        if (!vmm_shutting_down(m_vmm)) {
             QMessageBox confirm(this);
 
             confirm.setText("Do you want to exit?");
@@ -235,8 +247,9 @@ void MainWindow::closeEvent(QCloseEvent *event)
             if (confirm.exec() != QMessageBox::Yes) {
                 return;
             }
+        }
 
-        m_vmm.free();
+        killVmm();
     }
 
     // Close child windows.
@@ -364,7 +377,7 @@ void MainWindow::updateScreen()
     error = vmm_draw(m_vmm);
 
     if (error) {
-        m_vmm.free();
+        killVmm();
 
         QMessageBox::critical(
             this,
@@ -379,7 +392,7 @@ void MainWindow::updateScreen()
 
 void MainWindow::vmmError(const QString &msg)
 {
-    m_vmm.free();
+    killVmm();
 
     QMessageBox::critical(this, "Error", msg);
 
@@ -390,26 +403,9 @@ void MainWindow::vmmError(const QString &msg)
     }
 }
 
-void MainWindow::waitingDebugger(const QString &addr)
-{
-    if (!m_args.isSet(Args::debug)) {
-        QMessageBox::information(
-            this,
-            "Debug",
-            QString("The VMM are waiting for a debugger at %1.").arg(addr));
-    }
-}
-
-void MainWindow::debuggerDisconnected()
-{
-    if (m_args.isSet(Args::debug)) {
-        close();
-    }
-}
-
 void MainWindow::waitKernelExit(bool success)
 {
-    m_vmm.free();
+    killVmm();
 
     if (!success) {
         QMessageBox::critical(
@@ -438,6 +434,92 @@ void MainWindow::log(VmmLog type, const QString &msg)
     }
 }
 
+void MainWindow::breakpoint(KernelStop *stop)
+{
+    // Do nothing if the previous thread already trigger the shutdown.
+    if (vmm_shutting_down(m_vmm)) {
+        return;
+    }
+
+    // Dispatch debug events.
+    auto r = vmm_dispatch_debug(m_vmm, stop, [](uint8_t *buf, void *cx) -> bool {
+        auto w = reinterpret_cast<MainWindow *>(cx);
+
+        while (w->m_debug->bytesAvailable() == 0) {
+            QCoreApplication::processEvents();
+        }
+
+        return w->m_debug->getChar(reinterpret_cast<char *>(buf));
+    });
+
+    switch (r.tag) {
+    case DebugResult_Ok:
+        break;
+    case DebugResult_Disconnected:
+        // It is not safe to let the kernel running since it is assume there are a debugger.
+        vmm_shutdown(m_vmm);
+        break;
+    case DebugResult_ReadFailed:
+        QMessageBox::critical(
+            this,
+            "Error",
+            QString("Failed to read data from the debugger: %1").arg(m_debug->errorString()));
+        vmm_shutdown(m_vmm);
+        break;
+    case DebugResult_Error:
+        {
+            Rust<RustError> e(r.error.reason);
+
+            QMessageBox::critical(
+                this,
+                "Error",
+                QString("Failed to dispatch debug events: %1").arg(error_message(e)));
+        }
+
+        vmm_shutdown(m_vmm);
+        break;
+    }
+
+    if (!vmm_shutting_down(m_vmm)) {
+        return;
+    }
+
+    // We can't free the VMM here because the thread that trigger this method are waiting
+    // for us to return.
+    if (m_args.isSet(Args::debug)) {
+        QMetaObject::invokeMethod(
+            this,
+            &MainWindow::close,
+            Qt::QueuedConnection);
+    } else {
+        QMetaObject::invokeMethod(
+            this,
+            &MainWindow::waitKernelExit,
+            Qt::QueuedConnection,
+            true);
+    }
+}
+
+std::optional<QAbstractSocket::SocketError> MainWindow::sendDebug(const uint8_t *data, size_t len)
+{
+    while (len) {
+        auto r = m_debug->write(reinterpret_cast<const char *>(data), len);
+
+        if (r < 0) {
+            return m_debug->error();
+        }
+
+        data += r;
+        len -= r;
+
+        while (m_debug->bytesToWrite() != 0) {
+            QCoreApplication::processEvents();
+        }
+    }
+
+    return {};
+}
+
 bool MainWindow::loadGame(const QString &gameId)
 {
     auto gamesDirectory = readGamesDirectorySetting();
@@ -498,7 +580,103 @@ void MainWindow::restoreGeometry()
     }
 }
 
-void MainWindow::startVmm(const QString &debugAddr)
+void MainWindow::startDebug(const QString &addr)
+{
+    // Check address format.
+    auto parts = addr.split(':');
+
+    if (parts.size() > 2) {
+        QMessageBox::critical(
+            this,
+            "Error",
+            QString("%1 is not a valid debug server address").arg(addr));
+        return;
+    }
+
+    // Parse IP address.
+    QHostAddress ip(parts[0]);
+
+    if (ip.isNull()) {
+        QMessageBox::critical(
+            this,
+            "Error",
+            QString("%1 is not a valid debug server address").arg(addr));
+        return;
+    }
+
+    // Parse port.
+    unsigned short port = 0;
+
+    if (parts.size() == 2) {
+        bool ok;
+
+        port = parts[1].toUShort(&ok);
+
+        if (!ok) {
+            QMessageBox::critical(
+                this,
+                "Error",
+                QString("%1 is not a valid debug server address").arg(addr));
+            return;
+        }
+    }
+
+    // Start server.
+    auto server = new QTcpServer(this);
+
+    server->setListenBacklogSize(1);
+    server->setMaxPendingConnections(1);
+
+    connect(
+        server,
+        &QTcpServer::acceptError,
+        [this](QAbstractSocket::SocketError e) {
+            QMessageBox::critical(
+                this,
+                "Error",
+                QString("Failed to accept a debugger connection (%1).").arg(e));
+        });
+
+    connect(
+        server,
+        &QTcpServer::pendingConnectionAvailable,
+        this, [this, server]() {
+            m_debug = server->nextPendingConnection();
+            m_debug->setParent(this);
+            m_debug->setSocketOption(QAbstractSocket::LowDelayOption, 1);
+
+            startVmm();
+
+            server->deleteLater();
+        },
+        Qt::SingleShotConnection);
+
+    if (!server->listen(ip, port)) {
+        auto msg = QString("Failed to start a debug server on %1: %2")
+            .arg(addr)
+            .arg(server->errorString());
+
+        QMessageBox::critical(this, "Error", msg);
+        delete server;
+        return;
+    }
+
+    // Swap launch settings with the screen now to prevent user update settings.
+    m_main->setCurrentIndex(1);
+
+    // Tell the user to connect a debugger.
+    if (!m_args.isSet(Args::debug)) {
+        auto addr = server->serverAddress();
+        auto port = server->serverPort();
+
+        QMessageBox::information(
+            this,
+            "Debug",
+            QString("Waiting for a debugger at %1:%2.").arg(addr.toString()).arg(port));
+    }
+}
+
+void MainWindow::startVmm()
 {
     // Get full path to kernel binary.
     std::string kernel;
@@ -543,8 +721,7 @@ void MainWindow::startVmm(const QString &debugAddr)
     // Swap launch settings with the screen before getting a Vulkan surface otherwise it will fail.
     m_main->setCurrentIndex(1);
 
-    // Run.
-    auto debug = debugAddr.toStdString();
+    // Setup the screen.
     VmmScreen screen;
     Rust<RustError> error;
     Rust<Vmm> vmm;
@@ -559,27 +736,38 @@ void MainWindow::startVmm(const QString &debugAddr)
     screen.vk_surface = reinterpret_cast<size_t>(QVulkanInstance::surfaceForWindow(m_screen));
 
     if (!screen.vk_surface) {
-        m_main->setCurrentIndex(0);
         QMessageBox::critical(this, "Error", "Couldn't create VkSurfaceKHR.");
+
+        m_main->setCurrentIndex(0);
+
+        delete m_debug;
+        m_debug = nullptr;
         return;
     }
 #endif
 
-    vmm = vmm_run(
+    // Run.
+    vmm = vmm_start(
         kernel.c_str(),
         &screen,
         m_launch->currentProfile(),
-        debug.empty() ? nullptr : debug.c_str(),
+        m_debug
+            ? qOverload<void *, const uint8_t *, size_t, int *>(MainWindow::sendDebug)
+            : nullptr,
         MainWindow::vmmHandler,
         this,
         &error);
 
     if (!vmm) {
-        m_main->setCurrentIndex(0);
         QMessageBox::critical(
             this,
             "Error",
             QString("Couldn't run %1: %2").arg(kernel.c_str()).arg(error_message(error)));
+
+        m_main->setCurrentIndex(0);
+
+        delete m_debug;
+        m_debug = nullptr;
         return;
     }
 
@@ -602,12 +790,20 @@ bool MainWindow::requireVmmStopped()
             return false;
         }
 
-        m_vmm.free();
+        killVmm();
     }
 
     return true;
 }
 
+void MainWindow::killVmm()
+{
+    m_vmm.free();
+
+    delete m_debug;
+    m_debug = nullptr;
+}
+
 void MainWindow::vmmHandler(const VmmEvent *ev, void *cx)
 {
     // This method will be called from non-main thread.
@@ -621,19 +817,6 @@ void MainWindow::vmmHandler(const VmmEvent *ev, void *cx)
             Qt::QueuedConnection,
             QString(error_message(ev->error.reason)));
         break;
-    case VmmEvent_WaitingDebugger:
-        QMetaObject::invokeMethod(
-            w,
-            &MainWindow::waitingDebugger,
-            Qt::QueuedConnection,
-            QString::fromUtf8(ev->waiting_debugger.addr, ev->waiting_debugger.len));
-        break;
-    case VmmEvent_DebuggerDisconnected:
-        QMetaObject::invokeMethod(
-            w,
-            &MainWindow::debuggerDisconnected,
-            Qt::QueuedConnection);
-        break;
     case VmmEvent_Exiting:
         QMetaObject::invokeMethod(
             w,
@@ -649,5 +832,26 @@ void MainWindow::vmmHandler(const VmmEvent *ev, void *cx)
             ev->log.ty,
             QString::fromUtf8(ev->log.data, ev->log.len));
         break;
+    case VmmEvent_Breakpoint:
+        QMetaObject::invokeMethod(
+            w,
+            &MainWindow::breakpoint,
+            Qt::BlockingQueuedConnection,
+            ev->breakpoint.stop);
+        break;
+    }
+}
+
+bool MainWindow::sendDebug(void *cx, const uint8_t *data, size_t len, int *err)
+{
+    // This method always be called from a main thread.
+    auto w = reinterpret_cast<MainWindow *>(cx);
+    auto r = w->sendDebug(data, len);
+
+    if (r) {
+        *err = *r;
+        return false;
+    } else {
+        return true;
     }
 }

gui/main_window.hpp

@@ -2,6 +2,7 @@
 
 #include "core.hpp"
 
+#include <QAbstractSocket>
 #include <QList>
 #include <QMainWindow>
 #include <QPointer>
@@ -9,6 +10,8 @@
 #include <QVulkanInstance>
 #endif
 
+#include <optional>
+
 class GameListModel;
 class LaunchSettings;
 class LogsViewer;
@@ -16,6 +19,7 @@ class ProfileList;
 class QCommandLineOption;
 class QCommandLineParser;
 class QStackedWidget;
+class QTcpSocket;
 class Screen;
 
 class MainWindow final : public QMainWindow {
@@ -33,10 +37,10 @@ public:
     bool loadProfiles();
     bool loadGames();
     void restoreGeometry();
-    void startVmm(const QString &debugAddr);
+    void startDebug(const QString &addr);
+    void startVmm();
 protected:
     void closeEvent(QCloseEvent *event) override;
-
 private slots:
     void installPkg();
     void openSystemFolder();
@@ -47,14 +51,16 @@ private slots:
     void updateScreen();
 private:
     void vmmError(const QString &msg);
-    void waitingDebugger(const QString &addr);
-    void debuggerDisconnected();
     void waitKernelExit(bool success);
     void log(VmmLog type, const QString &msg);
+    void breakpoint(KernelStop *stop);
+    std::optional<QAbstractSocket::SocketError> sendDebug(const uint8_t *data, size_t len);
     bool loadGame(const QString &gameId);
     bool requireVmmStopped();
+    void killVmm();
 
     static void vmmHandler(const VmmEvent *ev, void *cx);
+    static bool sendDebug(void *cx, const uint8_t *data, size_t len, int *err);
 
     const QCommandLineParser &m_args;
     QStackedWidget *m_main;
@@ -63,6 +69,7 @@ private:
     LaunchSettings *m_launch;
     Screen *m_screen;
     QPointer<LogsViewer> m_logs;
+    QTcpSocket *m_debug;
     Rust<Vmm> m_vmm; // Destroy first.
 };
 

gui/src/vmm/debug/mod.rs

@@ -2,78 +2,49 @@
 pub use self::arch::*;
 
 use gdbstub::conn::Connection;
-use std::io::{Read, Write};
-use std::net::TcpStream;
+use std::ffi::{c_int, c_void};
 
 #[cfg_attr(target_arch = "aarch64", path = "aarch64.rs")]
 #[cfg_attr(target_arch = "x86_64", path = "x86_64.rs")]
 mod arch;
 
-/// Implementation of [`Connection`] using `select` system call to check if data available.
+/// Encapsulates a C++ function on Qt side to provide [`Connection`] implementation.
 pub struct Client {
-    sock: TcpStream,
-    buf: Vec<u8>,
-    next: usize,
+    fp: unsafe extern "C" fn(*mut c_void, *const u8, usize, *mut c_int) -> bool,
+    cx: *mut c_void,
 }
 
 impl Client {
-    pub fn new(sock: TcpStream) -> Self {
-        Self {
-            sock,
-            buf: Vec::new(),
-            next: 0,
-        }
-    }
-
-    pub fn read(&mut self) -> Result<u8, std::io::Error> {
-        // Fill the buffer if needed.
-        while self.next == self.buf.len() {
-            use std::io::ErrorKind;
-
-            // Clear previous data.
-            self.buf.clear();
-            self.next = 0;
-
-            // Read.
-            let mut buf = [0; 1024];
-            let len = match self.sock.read(&mut buf) {
-                Ok(v) => v,
-                Err(e) if e.kind() == ErrorKind::Interrupted => continue,
-                Err(e) => return Err(e),
-            };
-
-            if len == 0 {
-                return Err(std::io::Error::from(ErrorKind::UnexpectedEof));
-            }
-
-            self.buf.extend_from_slice(&buf[..len]);
-        }
-
-        // Get byte.
-        let b = self.buf[self.next];
-
-        self.next += 1;
-
-        Ok(b)
+    pub fn new(
+        fp: unsafe extern "C" fn(*mut c_void, *const u8, usize, *mut c_int) -> bool,
+        cx: *mut c_void,
+    ) -> Self {
+        Self { fp, cx }
     }
 }
 
 impl Connection for Client {
-    type Error = std::io::Error;
+    type Error = c_int;
 
     fn write(&mut self, byte: u8) -> Result<(), Self::Error> {
-        Write::write_all(&mut self.sock, std::slice::from_ref(&byte))
+        self.write_all(std::slice::from_ref(&byte))
     }
 
     fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
-        Write::write_all(&mut self.sock, buf)
+        let mut e = 0;
+
+        if unsafe { (self.fp)(self.cx, buf.as_ptr(), buf.len(), &mut e) } {
+            Ok(())
+        } else {
+            Err(e)
+        }
     }
 
     fn flush(&mut self) -> Result<(), Self::Error> {
-        Write::flush(&mut self.sock)
+        Ok(())
     }
 
     fn on_session_start(&mut self) -> Result<(), Self::Error> {
-        self.sock.set_nodelay(true)
+        Ok(())
     }
 }

gui/src/vmm/hw/debugger/context.rs

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+use super::Debugger;
+use crate::vmm::hv::CpuIo;
+use crate::vmm::hw::{read_u8, DeviceContext, MmioError};
+use crate::vmm::VmmEvent;
+use obconf::{DebuggerMemory, StopReason};
+use std::error::Error;
+use std::mem::offset_of;
+use std::ptr::null_mut;
+use thiserror::Error;
+
+/// Implementation of [`DeviceContext`].
+pub struct Context<'a> {
+    dev: &'a Debugger,
+}
+
+impl<'a> Context<'a> {
+    pub fn new(dev: &'a Debugger) -> Self {
+        Self { dev }
+    }
+}
+
+impl<'a> DeviceContext for Context<'a> {
+    fn exec(&mut self, exit: &mut dyn CpuIo) -> Result<bool, Box<dyn Error>> {
+        // Check field.
+        let off = exit.addr() - self.dev.addr;
+
+        if off == offset_of!(DebuggerMemory, stop) {
+            let stop = read_u8(exit).map_err(|e| ExecError::ReadFailed(off, e))?;
+            let stop: StopReason = stop
+                .try_into()
+                .map_err(|_| Box::new(ExecError::InvalidStop(stop)))?;
+            let stop = match stop {
+                StopReason::WaitForDebugger => null_mut(),
+            };
+
+            unsafe { self.dev.event.invoke(VmmEvent::Breakpoint { stop }) };
+        } else {
+            return Err(Box::new(ExecError::UnknownField(off)));
+        }
+
+        return Ok(true);
+    }
+}
+
+/// Represents an error when [`Context::exec()`] fails.
+#[derive(Debug, Error)]
+enum ExecError {
+    #[error("unknown field at offset {0:#}")]
+    UnknownField(usize),
+
+    #[error("couldn't read data for offset {0:#}")]
+    ReadFailed(usize, #[source] MmioError),
+
+    #[error("{0:#} is not a valid stop reason")]
+    InvalidStop(u8),
+}

gui/src/vmm/hw/debugger/mod.rs

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+use self::context::Context;
+use super::{Device, DeviceContext};
+use crate::vmm::hv::Hypervisor;
+use crate::vmm::VmmEventHandler;
+use obconf::DebuggerMemory;
+use std::num::NonZero;
+
+mod context;
+
+/// Virtual device for the kernel to communicate with the debugger.
+pub struct Debugger {
+    addr: usize,
+    len: NonZero<usize>,
+    event: VmmEventHandler,
+}
+
+impl Debugger {
+    pub fn new(addr: usize, block_size: NonZero<usize>, event: VmmEventHandler) -> Self {
+        let len = size_of::<DebuggerMemory>()
+            .checked_next_multiple_of(block_size.get())
+            .and_then(NonZero::new)
+            .unwrap();
+
+        Self { addr, len, event }
+    }
+}
+
+impl<H: Hypervisor> Device<H> for Debugger {
+    fn addr(&self) -> usize {
+        self.addr
+    }
+
+    fn len(&self) -> NonZero<usize> {
+        self.len
+    }
+
+    fn create_context<'a>(&'a self, _: &'a H) -> Box<dyn DeviceContext + 'a> {
+        Box::new(Context::new(self))
+    }
+}

gui/src/vmm/hw/mod.rs

@@ -8,9 +8,11 @@ use std::sync::Arc;
 use thiserror::Error;
 
 pub use self::console::*;
+pub use self::debugger::*;
 pub use self::vmm::*;
 
 mod console;
+mod debugger;
 mod vmm;
 
 pub fn setup_devices<H: Hypervisor>(
@@ -25,10 +27,12 @@ pub fn setup_devices<H: Hypervisor>(
 
     let vmm = b.push(|addr| Vmm::new(addr, block_size, event));
     let console = b.push(|addr| Console::new(addr, block_size, event));
+    let debugger = b.push(|addr| Debugger::new(addr, block_size, event));
 
     DeviceTree {
         vmm,
         console,
+        debugger,
         map: b.map,
     }
 }
@@ -91,6 +95,7 @@ fn read_bin<'b>(
 pub struct DeviceTree<H: Hypervisor> {
     vmm: Arc<Vmm>,
     console: Arc<Console>,
+    debugger: Arc<Debugger>,
     map: BTreeMap<usize, Arc<dyn Device<H>>>,
 }
 
@@ -103,6 +108,10 @@ impl<H: Hypervisor> DeviceTree<H> {
         self.console.as_ref()
     }
 
+    pub fn debugger(&self) -> &impl Device<H> {
+        self.debugger.as_ref()
+    }
+
     /// Returns iterator ordered by physical address.
     pub fn map(&self) -> impl Iterator<Item = (usize, &dyn Device<H>)> + '_ {
         self.map.iter().map(|(addr, dev)| (*addr, dev.as_ref()))

gui/src/vmm/mod.rs

@@ -8,22 +8,19 @@ use self::ram::{Ram, RamMap};
 use self::screen::Screen;
 use crate::error::RustError;
 use crate::profile::Profile;
-use gdbstub::stub::state_machine::state::Running;
-use gdbstub::stub::state_machine::{GdbStubStateMachine, GdbStubStateMachineInner};
+use gdbstub::stub::state_machine::GdbStubStateMachine;
 use gdbstub::stub::{GdbStub, MultiThreadStopReason};
 use obconf::{BootEnv, ConsoleType, Vm};
 use std::cmp::max;
 use std::collections::BTreeMap;
 use std::error::Error;
-use std::ffi::{c_char, c_void, CStr};
+use std::ffi::{c_char, c_int, c_void, CStr};
 use std::io::Read;
-use std::net::TcpListener;
 use std::num::NonZero;
 use std::ptr::null_mut;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
-use std::thread::{sleep, JoinHandle};
-use std::time::Duration;
+use std::thread::JoinHandle;
 use thiserror::Error;
 
 #[cfg_attr(target_arch = "aarch64", path = "aarch64.rs")]
@@ -37,29 +34,15 @@ mod ram;
 mod screen;
 
 #[no_mangle]
-pub unsafe extern "C" fn vmm_free(vmm: *mut Vmm) {
-    drop(Box::from_raw(vmm));
-}
-
-#[no_mangle]
-pub unsafe extern "C" fn vmm_run(
+pub unsafe extern "C" fn vmm_start(
     kernel: *const c_char,
     screen: *const VmmScreen,
     profile: *const Profile,
-    debug: *const c_char,
+    debug: Option<unsafe extern "C" fn(*mut c_void, *const u8, usize, *mut c_int) -> bool>,
     event: unsafe extern "C" fn(*const VmmEvent, *mut c_void),
     cx: *mut c_void,
     err: *mut *mut RustError,
 ) -> *mut Vmm {
-    // Setup debug server.
-    let debug = match setup_debug_server(debug) {
-        Ok(v) => v,
-        Err(e) => {
-            *err = e.into_c();
-            return null_mut();
-        }
-    };
-
     // Check if path UTF-8.
     let path = match CStr::from_ptr(kernel).to_str() {
         Ok(v) => v,
@@ -424,6 +407,11 @@ pub unsafe extern "C" fn vmm_run(
     let env = BootEnv::Vm(Vm {
         vmm: devices.vmm().addr(),
         console: devices.console().addr(),
+        debugger: if debug.is_some() {
+            devices.debugger().addr()
+        } else {
+            0
+        },
         host_page_size,
     });
 
@@ -450,6 +438,29 @@ pub unsafe extern "C" fn vmm_run(
         }
     };
 
+    // Setup GDB stub.
+    let debugger = match debug
+        .map(move |fp| -> Result<Debugger, RustError> {
+            let mut target = self::debug::Target::new();
+            let client = self::debug::Client::new(fp, cx);
+            let state = GdbStub::new(client)
+                .run_state_machine(&mut target)
+                .map_err(|e| RustError::with_source("couldn't setup a GDB stub", e))?;
+
+            Ok(Debugger {
+                target,
+                state: Some(state),
+            })
+        })
+        .transpose()
+    {
+        Ok(v) => v,
+        Err(e) => {
+            *err = e.into_c();
+            return null_mut();
+        }
+    };
+
     // Setup arguments for main CPU.
     let shutdown = Arc::new(AtomicBool::new(false));
     let args = CpuArgs {
@@ -463,7 +474,7 @@ pub unsafe extern "C" fn vmm_run(
 
     // Spawn a thread to drive main CPU.
     let e_entry = file.entry();
-    let main = move || main_cpu(&args, e_entry, map, debug);
+    let main = move || main_cpu(&args, e_entry, map);
     let main = match std::thread::Builder::new().spawn(main) {
         Ok(v) => v,
         Err(e) => {
@@ -476,12 +487,19 @@ pub unsafe extern "C" fn vmm_run(
     let vmm = Vmm {
         cpus: vec![main],
         screen,
+        debugger,
         shutdown,
+        cx,
     };
 
     Box::into_raw(vmm.into())
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn vmm_free(vmm: *mut Vmm) {
+    drop(Box::from_raw(vmm));
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn vmm_draw(vmm: *mut Vmm) -> *mut RustError {
     match (*vmm).screen.update() {
@@ -490,33 +508,68 @@ pub unsafe extern "C" fn vmm_draw(vmm: *mut Vmm) -> *mut RustError {
     }
 }
 
-/// # Safety
-/// `addr` cannot be null and must point to a null-terminated string.
-unsafe fn setup_debug_server(addr: *const c_char) -> Result<Option<TcpListener>, RustError> {
-    // Get listen address.
-    let addr = match addr.is_null() {
-        true => return Ok(None),
-        false => CStr::from_ptr(addr)
-            .to_str()
-            .map_err(|_| RustError::new("address to listen for a debugger is not UTF-8"))?,
+#[no_mangle]
+pub unsafe extern "C" fn vmm_dispatch_debug(
+    vmm: *mut Vmm,
+    stop: *mut KernelStop,
+    read: unsafe extern "C" fn(*mut u8, *mut c_void) -> bool,
+) -> DebugResult {
+    let vmm = &mut *vmm;
+    let debug = vmm.debugger.as_mut().unwrap();
+    let stop = match stop.is_null() {
+        true => None,
+        false => Some(Box::from_raw(stop)),
     };
 
-    // Setup server.
-    let sock = TcpListener::bind(addr)
-        .map_err(|e| RustError::with_source("couldn't listen for a debugger", e))?;
+    loop {
+        // Check current state.
+        let s = match debug.state.take().unwrap() {
+            GdbStubStateMachine::Idle(s) => s,
+            GdbStubStateMachine::Running(s) => {
+                debug.state = Some(s.into());
+                return DebugResult::Ok;
+            }
+            GdbStubStateMachine::CtrlCInterrupt(s) => {
+                match s.interrupt_handled(&mut debug.target, None::<MultiThreadStopReason<u64>>) {
+                    Ok(v) => debug.state = Some(v),
+                    Err(e) => {
+                        let r = RustError::with_source("couldn't handle CTRL+C from a debugger", e);
+                        return DebugResult::Error { reason: r.into_c() };
+                    }
+                }
+                continue;
+            }
+            GdbStubStateMachine::Disconnected(_) => return DebugResult::Disconnected,
+        };
 
-    sock.set_nonblocking(true)
-        .map(|_| Some(sock))
-        .map_err(|e| RustError::with_source("couldn't enable non-blocking on a debug server", e))
+        // Read data from the client.
+        let mut b = 0;
+
+        if !read(&mut b, vmm.cx) {
+            return DebugResult::ReadFailed;
+        }
+
+        match s.incoming_data(&mut debug.target, b) {
+            Ok(v) => debug.state = Some(v),
+            Err(e) => {
+                let r = RustError::with_source("couldn't process data from a debugger", e);
+                return DebugResult::Error { reason: r.into_c() };
+            }
+        }
+    }
 }
 
-fn main_cpu<H: Hypervisor>(
-    args: &CpuArgs<H>,
-    entry: usize,
-    map: RamMap,
-    debug: Option<TcpListener>,
-) {
-    // Create vCPU.
+#[no_mangle]
+pub unsafe extern "C" fn vmm_shutdown(vmm: *mut Vmm) {
+    (*vmm).shutdown.store(true, Ordering::Relaxed);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn vmm_shutting_down(vmm: *mut Vmm) -> bool {
+    (*vmm).shutdown.load(Ordering::Relaxed)
+}
+
+fn main_cpu<H: Hypervisor>(args: &CpuArgs<H>, entry: usize, map: RamMap) {
     let mut cpu = match args.hv.create_cpu(0) {
         Ok(v) => v,
         Err(e) => {
@@ -532,81 +585,10 @@ fn main_cpu<H: Hypervisor>(
         return;
     }
 
-    // Check if debug.
-    let debug = match debug {
-        Some(v) => v,
-        None => {
-            run_cpu(cpu, args, None);
-            return;
-        }
-    };
-
-    // Get server address.
-    let addr = match debug.local_addr() {
-        Ok(v) => v.to_string(),
-        Err(e) => {
-            let e = RustError::with_source("couldn't get debug server address", e);
-            unsafe { args.event.invoke(VmmEvent::Error { reason: &e }) };
-            return;
-        }
-    };
-
-    // Tell the user to connect a debugger.
-    let len = addr.len();
-    let addr = addr.as_ptr().cast();
-
-    unsafe { args.event.invoke(VmmEvent::WaitingDebugger { addr, len }) };
-
-    // Wait for a debugger.
-    let client = loop {
-        use std::io::ErrorKind;
-
-        if args.shutdown.load(Ordering::Relaxed) {
-            return;
-        }
-
-        // Try accept a connection.
-        let e = match debug.accept() {
-            Ok(v) => break self::debug::Client::new(v.0),
-            Err(e) => e,
-        };
-
-        match e.kind() {
-            ErrorKind::WouldBlock => sleep(Duration::from_millis(500)),
-            ErrorKind::Interrupted => {}
-            _ => {
-                let e = RustError::with_source("couldn't accept a debugger connection", e);
-                unsafe { args.event.invoke(VmmEvent::Error { reason: &e }) };
-                return;
-            }
-        }
-    };
-
-    // Setup GDB stub.
-    let mut target = self::debug::Target::new();
-    let gdb = match GdbStub::new(client).run_state_machine(&mut target) {
-        Ok(v) => v,
-        Err(e) => {
-            let e = RustError::with_source("couldn't setup a GDB stub", e);
-            unsafe { args.event.invoke(VmmEvent::Error { reason: &e }) };
-            return;
-        }
-    };
-
-    // Run GDB until the client is waiting for the target to report a stop reason.
-    let gdb = match run_gdb(args, &mut target, gdb) {
-        Some(v) => v,
-        None => return,
-    };
-
-    run_cpu(cpu, args, Some(gdb));
+    run_cpu(cpu, args);
 }
 
-fn run_cpu<H: Hypervisor>(
-    mut cpu: H::Cpu<'_>,
-    args: &CpuArgs<H>,
-    gdb: Option<GdbStubStateMachineInner<Running, self::debug::Target, self::debug::Client>>,
-) {
+fn run_cpu<H: Hypervisor>(mut cpu: H::Cpu<'_>, args: &CpuArgs<H>) {
     // Build device contexts for this CPU.
     let mut devices = args
         .devices
@@ -667,55 +649,6 @@ fn exec_io<'a>(
     dev.exec(&mut io)
 }
 
-fn run_gdb<'a, H: Hypervisor>(
-    args: &CpuArgs<H>,
-    target: &mut self::debug::Target,
-    mut state: GdbStubStateMachine<'a, self::debug::Target, self::debug::Client>,
-) -> Option<GdbStubStateMachineInner<'a, Running, self::debug::Target, self::debug::Client>> {
-    loop {
-        // Check current state.
-        let mut s = match state {
-            GdbStubStateMachine::Idle(s) => s,
-            GdbStubStateMachine::Running(s) => return Some(s),
-            GdbStubStateMachine::CtrlCInterrupt(s) => {
-                state = match s.interrupt_handled(target, None::<MultiThreadStopReason<u64>>) {
-                    Ok(v) => v,
-                    Err(e) => {
-                        let e = RustError::with_source("couldn't handle CTRL+C from a debugger", e);
-                        unsafe { args.event.invoke(VmmEvent::Error { reason: &e }) };
-                        return None;
-                    }
-                };
-
-                continue;
-            }
-            GdbStubStateMachine::Disconnected(_) => {
-                unsafe { args.event.invoke(VmmEvent::DebuggerDisconnected) };
-                return None;
-            }
-        };
-
-        // Read data from the client.
-        let b = match s.borrow_conn().read() {
-            Ok(v) => v,
-            Err(e) => {
-                let e = RustError::with_source("couldn't read data from a debugger", e);
-                unsafe { args.event.invoke(VmmEvent::Error { reason: &e }) };
-                return None;
-            }
-        };
-
-        state = match s.incoming_data(target, b) {
-            Ok(v) => v,
-            Err(e) => {
-                let e = RustError::with_source("couldn't process data from a debugger", e);
-                unsafe { args.event.invoke(VmmEvent::Error { reason: &e }) };
-                return None;
-            }
-        };
-    }
-}
-
 #[cfg(unix)]
 fn get_page_size() -> Result<NonZero<usize>, std::io::Error> {
     let v = unsafe { libc::sysconf(libc::_SC_PAGE_SIZE) };
@@ -742,7 +675,9 @@ fn get_page_size() -> Result<NonZero<usize>, std::io::Error> {
 pub struct Vmm {
     cpus: Vec<JoinHandle<()>>,
     screen: self::screen::Default,
+    debugger: Option<Debugger>,
     shutdown: Arc<AtomicBool>,
+    cx: *mut c_void,
 }
 
 impl Drop for Vmm {
@@ -792,11 +727,6 @@ pub enum VmmEvent {
     Error {
         reason: *const RustError,
     },
-    WaitingDebugger {
-        addr: *const c_char,
-        len: usize,
-    },
-    DebuggerDisconnected,
     Exiting {
         success: bool,
     },
@@ -805,6 +735,9 @@ pub enum VmmEvent {
         data: *const c_char,
         len: usize,
     },
+    Breakpoint {
+        stop: *mut KernelStop,
+    },
 }
 
 /// Log category.
@@ -830,6 +763,20 @@ impl From<ConsoleType> for VmmLog {
     }
 }
 
+/// Reason for [`VmmEvent::Breakpoint`].
+#[allow(dead_code)]
+pub struct KernelStop(MultiThreadStopReason<u64>);
+
+/// Result of [`vmm_dispatch_debug()`].
+#[allow(dead_code)]
+#[repr(C)]
+pub enum DebugResult {
+    Ok,
+    Disconnected,
+    ReadFailed,
+    Error { reason: *mut RustError },
+}
+
 /// Encapsulates arguments for a function to run a CPU.
 struct CpuArgs<H: Hypervisor> {
     hv: H,
@@ -840,6 +787,12 @@ struct CpuArgs<H: Hypervisor> {
     shutdown: Arc<AtomicBool>,
 }
 
+/// Contains data for a debugger.
+struct Debugger {
+    target: self::debug::Target,
+    state: Option<GdbStubStateMachine<'static, self::debug::Target, self::debug::Client>>,
+}
+
 /// Represents an error when [`vmm_new()`] fails.
 #[derive(Debug, Error)]
 enum VmmError {

kernel/src/debug/mod.rs

@@ -0,0 +1,12 @@
+use core::ptr::{addr_of_mut, write_volatile};
+use obconf::{DebuggerMemory, StopReason, Vm};
+
+pub fn wait_debugger(env: &Vm) {
+    let debug = env.debugger as *mut DebuggerMemory;
+
+    if debug.is_null() {
+        return;
+    }
+
+    unsafe { write_volatile(addr_of_mut!((*debug).stop), StopReason::WaitForDebugger) };
+}

kernel/src/main.rs

@@ -1,6 +1,7 @@
 #![no_std]
 #![cfg_attr(not(test), no_main)]
 
+use crate::config::boot_env;
 use crate::context::Context;
 use crate::malloc::KernelHeap;
 use crate::proc::{ProcMgr, Thread};
@@ -16,6 +17,7 @@ mod arch;
 mod config;
 mod console;
 mod context;
+mod debug;
 mod imgfmt;
 mod lock;
 mod malloc;
@@ -66,6 +68,11 @@ unsafe extern "C" fn _start(env: &'static BootEnv, conf: &'static Config) -> ! {
 }
 
 fn main(pmgr: Arc<ProcMgr>) -> ! {
+    // Wait for debugger.
+    match boot_env() {
+        BootEnv::Vm(vm) => crate::debug::wait_debugger(vm),
+    }
+
     // Activate stage 2 heap.
     info!("Activating stage 2 heap.");
 

src/obconf/src/env/vm.rs

@@ -7,6 +7,8 @@ pub struct Vm {
     pub vmm: usize,
     /// Address of [ConsoleMemory].
     pub console: usize,
+    /// Address of [DebuggerMemory].
+    pub debugger: usize,
     /// Page size on the host.
     pub host_page_size: NonZero<usize>,
 }
@@ -56,3 +58,18 @@ pub enum ConsoleType {
     Warn,
     Error,
 }
+
+/// Layout of a memory for Memory-mapped I/O to communicate with a debugger.
+#[cfg(feature = "virt")]
+#[repr(C)]
+pub struct DebuggerMemory {
+    pub stop: StopReason,
+}
+
+/// Reason why the kernel stopped the execution.
+#[cfg(feature = "virt")]
+#[repr(u8)]
+#[derive(Clone, Copy, PartialEq, Eq, num_enum::IntoPrimitive, num_enum::TryFromPrimitive)]
+pub enum StopReason {
+    WaitForDebugger,
+}