dmnt: add basic gdb packet receive logic

stratosphere/dmnt.gen2/source/dmnt2_debug_log.cpp

@@ -24,11 +24,10 @@ namespace ams::dmnt {
 
     namespace {
 
-        constexpr size_t NumLogBuffers = 16;
+        constexpr size_t NumLogBuffers = 0x200;
         constexpr size_t LogBufferSize = 0x100;
 
-        /* TODO: This shouldn't be so high priority. Come up with a better number? */
+        constexpr inline auto LogThreadPriority = os::HighestThreadPriority - 2;
-        constexpr inline auto LogThreadPriority = 10;
 
         constinit os::MessageQueueType g_buf_mq;
         constinit os::MessageQueueType g_req_mq;

stratosphere/dmnt.gen2/source/dmnt2_debug_log.hpp

@@ -20,8 +20,13 @@ namespace ams::dmnt {
 
     void InitializeDebugLog();
 
-    void DebugLog(const char *prefix, const char *fmt, ...);
+    void DebugLog(const char *prefix, const char *fmt, ...) __attribute((format(printf, 2, 3)));
 
     #define AMS_DMNT2_DEBUG_LOG(fmt, ...) ::ams::dmnt::DebugLog("[dmnt2] ", fmt, ## __VA_ARGS__)
 
+    #define AMS_DMNT2_GDB_LOG_INFO(fmt, ...)  ::ams::dmnt::DebugLog("[gdb-i] ", fmt, ## __VA_ARGS__)
+    #define AMS_DMNT2_GDB_LOG_WARN(fmt, ...)  ::ams::dmnt::DebugLog("[gdb-w] ", fmt, ## __VA_ARGS__)
+    #define AMS_DMNT2_GDB_LOG_ERROR(fmt, ...) ::ams::dmnt::DebugLog("[gdb-e] ", fmt, ## __VA_ARGS__)
+    #define AMS_DMNT2_GDB_LOG_DEBUG(fmt, ...) ::ams::dmnt::DebugLog("[gdb-d] ", fmt, ## __VA_ARGS__)
+
 }

stratosphere/dmnt.gen2/source/dmnt2_gdb_packet_io.cpp

@@ -0,0 +1,194 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stratosphere.hpp>
+#include "dmnt2_gdb_packet_io.hpp"
+#include "dmnt2_debug_log.hpp"
+
+namespace ams::dmnt {
+
+    namespace {
+
+        constexpr char BreakCharacter = '\x03'; /* ctrl-c */
+
+        constexpr int DecodeHex(char c) {
+            if ('a' <= c && c <= 'f') {
+                return 10 + (c - 'a');
+            } else if ('A' <= c && c <= 'F') {
+                return 10 + (c - 'A');
+            } else if ('0' <= c && c <= '9') {
+                return 0 + (c - '0');
+            } else {
+                return -1;
+            }
+        }
+
+        constexpr char EncodeHex(u8 v) {
+            return "0123456789abcdef"[v & 0xF];
+        }
+
+    }
+
+    void GdbPacketIo::SendPacket(bool *out_break, const char *src, HtcsSession *session) {
+        /* Default to not breaked. */
+        *out_break = false;
+
+        /* Send a packet. */
+        while (true) {
+            std::scoped_lock lk(m_mutex);
+
+            size_t len = 0;
+            u8 checksum = 0;
+
+            while (src[len] != 0) {
+                checksum += static_cast<u8>(src[len++]);
+            }
+
+            char buffer[1 + GdbPacketBufferSize + 4];
+            buffer[0] = '$';
+            std::memcpy(buffer + 1, src, len);
+            buffer[1 + len] = '#';
+            buffer[2 + len] = EncodeHex(checksum >> 4);
+            buffer[3 + len] = EncodeHex(checksum >> 0);
+            buffer[4 + len] = 0;
+
+            if (session->PutString(buffer) < 0) {
+                /* Log (truncated) copy of packet. */
+                AMS_DMNT2_GDB_LOG_ERROR("Failed to send packet %s\n", buffer);
+                return;
+            }
+
+            if (m_no_ack) {
+                return;
+            }
+
+            /* Check to see if we need to retransmit. */
+            bool retransmit = false;
+            do {
+                if (const auto char_holder = session->GetChar(); char_holder) {
+                    switch (*char_holder) {
+                        case BreakCharacter:
+                            *out_break = true;
+                            return;
+                        case '+':
+                            return;
+                        case '-':
+                            retransmit = true;
+                            break;
+                        default:
+                            break;
+                    }
+                } else {
+                    /* Log (truncated) copy of packet. */
+                    AMS_DMNT2_GDB_LOG_ERROR("Failed to receive ack for %s\n", buffer);
+                    return;
+                }
+            } while (!retransmit);
+        }
+    }
+
+    char *GdbPacketIo::ReceivePacket(bool *out_break, char *dst, size_t size, HtcsSession *session) {
+        /* Default to not breaked. */
+        *out_break = false;
+
+        /* Receive a packet. */
+        while (true) {
+            /* Wait for data to be available. */
+            if (!session->WaitToBeReadable()) {
+                return nullptr;
+            }
+
+            /* Lock ourselves. */
+            std::scoped_lock lk(m_mutex);
+
+            /* Verify that we still have data immediately available. */
+            if (!session->WaitToBeReadable(0)) {
+                continue;
+            }
+
+            /* Prepare to parse. */
+            enum class State {
+                Initial,
+                PacketData,
+                ChecksumHigh,
+                ChecksumLow
+            };
+
+            State state = State::Initial;
+            u8 checksum = 0;
+            int csum_high = -1, csum_low = -1;
+            size_t count = 0;
+
+            /* Read characters. */
+            while (true) {
+                if (const auto char_holder = session->GetChar(); char_holder) {
+                    const auto c = *char_holder;
+
+                    switch (state) {
+                        case State::Initial:
+                            if (c == '$') {
+                                state = State::PacketData;
+                            } else if (c == BreakCharacter) {
+                                *out_break = true;
+                                return nullptr;
+                            }
+                            break;
+                        case State::PacketData:
+                            /* TODO: Escaped characters. */
+                            if (c == '#') {
+                                dst[count] = 0;
+                                state = State::ChecksumHigh;
+                            } else {
+                                AMS_ABORT_UNLESS(count < size - 1);
+                                checksum += static_cast<u8>(c);
+                                dst[count++] = c;
+                            }
+                            break;
+                        case State::ChecksumHigh:
+                            csum_high = DecodeHex(c);
+                            state = State::ChecksumLow;
+                            break;
+                        case State::ChecksumLow:
+                            csum_low = DecodeHex(c);
+
+                            if (m_no_ack) {
+                                return dst;
+                            } else {
+                                const u8 expectsum = (static_cast<u8>(csum_high) << 4) | (static_cast<u8>(csum_low) << 0);
+
+                                if (csum_high < 0 || csum_low < 0 || checksum != expectsum) {
+                                    /* Request retransmission. */
+                                    state     = State::Initial;
+                                    checksum  = 0;
+                                    csum_high = -1;
+                                    csum_low  = -1;
+                                    count     = 0;
+                                    session->PutChar('-');
+                                } else {
+                                    session->PutChar('+');
+                                    return dst;
+                                }
+                            }
+
+                            break;
+                    }
+                } else {
+                    return nullptr;
+                }
+            }
+        }
+    }
+
+}

stratosphere/dmnt.gen2/source/dmnt2_gdb_packet_io.hpp

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+#include "dmnt2_htcs_session.hpp"
+
+namespace ams::dmnt {
+
+    static constexpr size_t GdbPacketBufferSize = 16_KB;
+
+    class GdbPacketIo {
+        private:
+            os::SdkMutex m_mutex;
+            bool m_no_ack;
+        public:
+            GdbPacketIo() : m_mutex(), m_no_ack(false) { /* ... */ }
+
+            void SetNoAck() { m_no_ack = true; }
+
+            void SendPacket(bool *out_break, const char *src, HtcsSession *session);
+            char *ReceivePacket(bool *out_break, char *dst, size_t size, HtcsSession *session);
+    };
+
+}

stratosphere/dmnt.gen2/source/dmnt2_gdb_server.cpp

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stratosphere.hpp>
+#include "dmnt2_gdb_packet_io.hpp"
+#include "dmnt2_gdb_server.hpp"
+#include "dmnt2_debug_log.hpp"
+
+namespace ams::dmnt {
+
+    namespace {
+
+        constexpr size_t ServerThreadStackSize = util::AlignUp(3 * GdbPacketBufferSize + os::MemoryPageSize, os::ThreadStackAlignment);
+
+        alignas(os::ThreadStackAlignment) constinit u8 g_server_thread_stack[ServerThreadStackSize];
+        constinit os::ThreadType g_server_thread;
+
+        constinit util::TypedStorage<HtcsSession> g_session;
+
+        void OnClientSocketAccepted(int fd) {
+            /* Create htcs session for the socket. */
+            util::ConstructAt(g_session, fd);
+            ON_SCOPE_EXIT { util::DestroyAt(g_session); };
+
+            HtcsSession *session = util::GetPointer(g_session);
+
+            /* Create packet io handler. */
+            GdbPacketIo packet_io;
+
+            /* Process packets. */
+            while (session->IsValid()) {
+                /* Receive a packet. */
+                bool do_break = false;
+                char recv_buf[GdbPacketBufferSize];
+                char *packet = packet_io.ReceivePacket(std::addressof(do_break), recv_buf, sizeof(recv_buf), session);
+
+                if (!do_break && packet != nullptr) {
+                    AMS_DMNT2_GDB_LOG_DEBUG("Received Packet %s\n", packet);
+
+                    /* TODO: Process packets. */
+                    packet_io.SendPacket(std::addressof(do_break), "OK", session);
+                }
+            }
+        }
+
+        void GdbServerThreadFunction(void *) {
+            /* Loop forever, servicing our gdb server. */
+            while (true) {
+                /* Get a socket. */
+                int fd;
+                while ((fd = htcs::Socket()) == -1) {
+                    os::SleepThread(TimeSpan::FromSeconds(1));
+                }
+
+                /* Ensure we cleanup the socket when we're done with it. */
+                ON_SCOPE_EXIT {
+                    htcs::Close(fd);
+                    os::SleepThread(TimeSpan::FromSeconds(1));
+                };
+
+                /* Create a sock addr for our server. */
+                htcs::SockAddrHtcs addr;
+                addr.family    = htcs::HTCS_AF_HTCS;
+                addr.peer_name = htcs::GetPeerNameAny();
+                std::strcpy(addr.port_name.name, "iywys@$gdb");
+
+                /* Bind. */
+                if (htcs::Bind(fd, std::addressof(addr)) == -1) {
+                    continue;
+                }
+
+                /* Listen on our port. */
+                while (htcs::Listen(fd, 0) == 0) {
+                    /* Continue accepting clients, so long as we can. */
+                    int client_fd;
+                    while (true) {
+                        /* Try to accept a client. */
+                        if (client_fd = htcs::Accept(fd, std::addressof(addr)); client_fd < 0) {
+                            break;
+                        }
+
+                        /* Handle the client. */
+                        OnClientSocketAccepted(client_fd);
+
+                        /* Close the client socket. */
+                        htcs::Close(client_fd);
+                    }
+                }
+            }
+        }
+
+
+
+    }
+
+    void InitializeGdbServer() {
+        /* Create and start gdb server thread. */
+        R_ABORT_UNLESS(os::CreateThread(std::addressof(g_server_thread), GdbServerThreadFunction, nullptr, g_server_thread_stack, sizeof(g_server_thread_stack), os::HighestThreadPriority - 1));
+        os::StartThread(std::addressof(g_server_thread));
+    }
+
+}

stratosphere/dmnt.gen2/source/dmnt2_gdb_server.hpp

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::dmnt {
+
+    void InitializeGdbServer();
+
+}

stratosphere/dmnt.gen2/source/dmnt2_htcs_receive_buffer.cpp

@@ -0,0 +1,146 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stratosphere.hpp>
+#include "dmnt2_htcs_receive_buffer.hpp"
+
+namespace ams::dmnt {
+
+    ssize_t HtcsReceiveBuffer::Read(void *dst, size_t size) {
+        /* Acquire exclusive access to ourselves. */
+        std::scoped_lock lk(m_mutex);
+
+        /* Check that we're readable and valid. */
+        if (!(this->IsValid() && this->IsReadable())) {
+            return -1;
+        }
+
+        /* Check that we have data to read. */
+        const size_t readable = std::min(size, m_readable_size);
+        if (readable <= 0) {
+            return  -1;
+        }
+
+        /* Copy the data. */
+        std::memcpy(dst, m_buffer + m_offset, readable);
+
+        /* Advance our pointers. */
+        m_readable_size -= readable;
+        m_offset += readable;
+
+        /* Handle the case where we're done consuming. */
+        if (m_readable_size == 0) {
+            m_offset = 0;
+            m_readable_event.Clear();
+            m_writable_event.Signal();
+        }
+
+        return readable;
+    }
+
+    ssize_t HtcsReceiveBuffer::Write(const void *src, size_t size) {
+        /* Acquire exclusive access to ourselves. */
+        std::scoped_lock lk(m_mutex);
+
+        /* Check that we're readable and valid. */
+        if (!(this->IsValid() && this->IsWritable())) {
+            return -1;
+        }
+
+        /* Copy the data to our buffer. */
+        std::memcpy(m_buffer, src, size);
+
+        /* Set our fields. */
+        m_readable_size = size;
+        m_offset        = 0;
+        m_writable_event.Clear();
+        m_readable_event.Signal();
+
+        return size;
+    }
+
+    bool HtcsReceiveBuffer::WaitToBeReadable() {
+        /* Check if we're already readable. */
+        {
+            std::scoped_lock lk(m_mutex);
+
+            if (this->IsReadable()) {
+                return true;
+            } else if (!this->IsValid()) {
+                return false;
+            } else {
+                m_readable_event.Clear();
+            }
+        }
+
+        /* Wait for us to be readable. */
+        m_readable_event.Wait();
+
+        return this->IsValid();
+    }
+
+    bool HtcsReceiveBuffer::WaitToBeReadable(TimeSpan timeout) {
+        /* Check if we're already readable. */
+        {
+            std::scoped_lock lk(m_mutex);
+
+            if (this->IsReadable()) {
+                return true;
+            } else if (!this->IsValid()) {
+                return false;
+            } else {
+                m_readable_event.Clear();
+            }
+        }
+
+        /* Wait for us to be readable. */
+        const bool res = m_readable_event.TimedWait(timeout);
+
+        return res && this->IsValid();
+    }
+
+    bool HtcsReceiveBuffer::WaitToBeWritable() {
+        /* Check if we're already writable. */
+        {
+            std::scoped_lock lk(m_mutex);
+
+            if (this->IsWritable()) {
+                return true;
+            } else if (!this->IsValid()) {
+                return false;
+            } else {
+                m_writable_event.Clear();
+            }
+        }
+
+        /* Wait for us to be writable. */
+        m_writable_event.Wait();
+
+        return this->IsValid();
+    }
+
+    void HtcsReceiveBuffer::Invalidate() {
+        /* Acquire exclusive access to ourselves. */
+        std::scoped_lock lk(m_mutex);
+
+        /* Set ourselves as invalid. */
+        m_valid = false;
+
+        /* Signal our events. */
+        m_readable_event.Signal();
+        m_writable_event.Signal();
+    }
+
+}

stratosphere/dmnt.gen2/source/dmnt2_htcs_receive_buffer.hpp

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::dmnt {
+
+    class HtcsReceiveBuffer {
+        public:
+            static constexpr size_t ReceiveBufferSize = 4_KB;
+        private:
+            u8 m_buffer[ReceiveBufferSize];
+            os::Event m_readable_event;
+            os::Event m_writable_event;
+            os::SdkMutex m_mutex;
+            size_t m_readable_size;
+            size_t m_offset;
+            bool m_valid;
+        public:
+            HtcsReceiveBuffer() : m_readable_event(os::EventClearMode_ManualClear), m_writable_event(os::EventClearMode_ManualClear), m_mutex(), m_readable_size(), m_offset(), m_valid(true) { /* ... */ }
+
+            ALWAYS_INLINE bool IsReadable() const { return m_readable_size != 0; }
+            ALWAYS_INLINE bool IsWritable() const { return m_readable_size == 0; }
+            ALWAYS_INLINE bool IsValid() const { return m_valid; }
+
+            ssize_t Read(void *dst, size_t size);
+            ssize_t Write(const void *src, size_t size);
+
+            bool WaitToBeReadable();
+            bool WaitToBeReadable(TimeSpan timeout);
+            bool WaitToBeWritable();
+
+            void Invalidate();
+    };
+
+}

stratosphere/dmnt.gen2/source/dmnt2_htcs_session.cpp

@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stratosphere.hpp>
+#include "dmnt2_htcs_session.hpp"
+#include "dmnt2_debug_log.hpp"
+
+namespace ams::dmnt {
+
+    HtcsSession::HtcsSession(int fd) : m_socket(fd), m_valid(true) {
+        /* Create our thread. */
+        R_ABORT_UNLESS(os::CreateThread(std::addressof(m_receive_thread), ReceiveThreadEntry, this, m_receive_thread_stack, sizeof(m_receive_thread_stack), os::HighestThreadPriority - 1));
+
+        /* Start our thread. */
+        os::StartThread(std::addressof(m_receive_thread));
+
+        /* Note that we connected. */
+        AMS_DMNT2_GDB_LOG_INFO("Created Session %d\n", m_socket);
+    }
+
+    HtcsSession::~HtcsSession() {
+        /* Note that we connected. */
+        AMS_DMNT2_GDB_LOG_INFO("Closing Session %d\n", m_socket);
+
+        /* Invalidate our receive buffer. */
+        m_receive_buffer.Invalidate();
+
+        /* Shutdown our socket. */
+        htcs::Shutdown(m_socket, htcs::HTCS_SHUT_RDWR);
+
+        /* Wait for our thread. */
+        os::WaitThread(std::addressof(m_receive_thread));
+        os::DestroyThread(std::addressof(m_receive_thread));
+
+        /* Close our socket. */
+        htcs::Close(m_socket);
+    }
+
+    bool HtcsSession::WaitToBeReadable() {
+        return m_receive_buffer.WaitToBeReadable();
+    }
+
+    bool HtcsSession::WaitToBeReadable(TimeSpan timeout) {
+        return m_receive_buffer.WaitToBeReadable(timeout);
+    }
+
+    util::optional<char> HtcsSession::GetChar() {
+        /* Wait for us to have data. */
+        m_receive_buffer.WaitToBeReadable();
+
+        /* Get our data. */
+        char c;
+        if (m_receive_buffer.Read(std::addressof(c), sizeof(c)) > 0) {
+            return c;
+        } else {
+            return util::nullopt;
+        }
+    }
+
+    ssize_t HtcsSession::PutChar(char c) {
+        /* Send the character. */
+        const auto sent = htcs::Send(m_socket, std::addressof(c), sizeof(c), 0);
+        if (sent < 0) {
+            m_valid = false;
+        }
+
+        return sent;
+    }
+
+    ssize_t HtcsSession::PutString(const char *str) {
+        /* Repeatedly send until all is sent. */
+        const size_t len = std::strlen(str);
+
+        size_t remaining = len;
+        while (remaining > 0) {
+            const auto sent = htcs::Send(m_socket, str, remaining, 0);
+            if (sent >= 0) {
+                remaining -= sent;
+                str += sent;
+            } else {
+                m_valid = false;
+                return sent;
+            }
+        }
+
+        return len;
+    }
+
+    void HtcsSession::ReceiveThreadFunction() {
+        /* Create temporary buffer. */
+        u8 buffer[HtcsReceiveBuffer::ReceiveBufferSize];
+
+        /* Loop receiving data. */
+        while (true) {
+            /* Receive data. */
+            const auto res = htcs::Recv(m_socket, buffer, sizeof(buffer), 0);
+            if (res > 0) {
+                /* Write the data to our buffer. */
+                m_receive_buffer.WaitToBeWritable();
+                m_receive_buffer.Write(buffer, res);
+            } else {
+                /* Otherwise, if we got an error other than "try again", we're done. */
+                if (htcs::GetLastError() != htcs::HTCS_EAGAIN) {
+                    AMS_DMNT2_GDB_LOG_INFO("Session %d invalid, res=%ld, err=%d\n", m_socket, res, static_cast<int>(htcs::GetLastError()));
+                    m_valid = false;
+                    break;
+                }
+            }
+        }
+
+        /* Invalidate our receive buffer. */
+        m_receive_buffer.Invalidate();
+    }
+
+}

stratosphere/dmnt.gen2/source/dmnt2_htcs_session.hpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+#include "dmnt2_htcs_receive_buffer.hpp"
+
+namespace ams::dmnt {
+
+    class HtcsSession {
+        private:
+            alignas(os::ThreadStackAlignment) u8 m_receive_thread_stack[util::AlignUp(os::MemoryPageSize + HtcsReceiveBuffer::ReceiveBufferSize, os::ThreadStackAlignment)];
+            HtcsReceiveBuffer m_receive_buffer;
+            os::ThreadType m_receive_thread;
+            int m_socket;
+            bool m_valid;
+        public:
+            HtcsSession(int fd);
+            ~HtcsSession();
+
+            ALWAYS_INLINE bool IsValid() const { return m_valid; }
+
+            bool WaitToBeReadable();
+            bool WaitToBeReadable(TimeSpan timeout);
+
+            util::optional<char> GetChar();
+            ssize_t PutChar(char c);
+            ssize_t PutString(const char *str);
+
+        private:
+            static void ReceiveThreadEntry(void *arg) {
+                static_cast<HtcsSession *>(arg)->ReceiveThreadFunction();
+            }
+
+            void ReceiveThreadFunction();
+    };
+
+}

stratosphere/dmnt.gen2/source/dmnt2_main.cpp

@@ -15,6 +15,7 @@
  */
 #include <stratosphere.hpp>
 #include "dmnt2_debug_log.hpp"
+#include "dmnt2_gdb_server.hpp"
 
 extern "C" {
     extern u32 __start__;
@@ -143,13 +144,12 @@ int main(int argc, char **argv)
     /* Initialize debug log thread. */
     dmnt::InitializeDebugLog();
 
-    /* TODO: Start GdbServer. */
+    /* Start GdbServer. */
+    dmnt::InitializeGdbServer();
 
     /* TODO */
-    u64 i = 0;
     while (true) {
-        AMS_DMNT2_DEBUG_LOG("Log #%llu\n", i++);
+        os::SleepThread(TimeSpan::FromDays(1));
-        os::SleepThread(TimeSpan::FromSeconds(1));
     }
 
     return 0;