Debugger: Add DebugSession

The DebugSession class wraps the usage of Ptrace.
It is intended to be used by cli & gui debugger programs.

Also, call objdump for disassemly

10 files changed, 463 insertions, 156 deletions

diff --git a/Applications/Debugger/DebugSession.cpp b/Applications/Debugger/DebugSession.cpp
new file mode 100644
index 0000000000..8766ad60b2
--- /dev/null
+++ b/Applications/Debugger/DebugSession.cpp
@@ -0,0 +1,184 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DebugSession.h"
+#include <AK/Optional.h>
+#include <stdlib.h>
+
+DebugSession::DebugSession(int pid)
+    : m_debugee_pid(pid)
+    , m_executable(make<MappedFile>(String::format("/proc/%d/exe", pid)))
+    , m_elf_image(make<ELF::Image>(reinterpret_cast<u8*>(m_executable->data()), m_executable->size()))
+{
+}
+
+DebugSession::~DebugSession()
+{
+    if (!m_is_debugee_dead) {
+        if (ptrace(PT_DETACH, m_debugee_pid, 0, 0) < 0) {
+            perror("PT_DETACH");
+        }
+    }
+}
+
+OwnPtr<DebugSession> DebugSession::exec_and_attach(const String& command)
+{
+    int pid = fork();
+
+    if (!pid) {
+        if (ptrace(PT_TRACE_ME, 0, 0, 0) < 0) {
+            perror("PT_TRACE_ME");
+            exit(1);
+        }
+
+        auto parts = command.split(' ');
+        ASSERT(!parts.is_empty());
+        const char** args = (const char**)calloc(parts.size() + 1, sizeof(const char*));
+        for (size_t i = 0; i < parts.size(); i++) {
+            args[i] = parts[i].characters();
+        }
+        int rc = execvp(args[0], const_cast<char**>(args));
+        if (rc < 0) {
+            perror("execvp");
+        }
+        ASSERT_NOT_REACHED();
+    }
+
+    if (waitpid(pid, nullptr, WSTOPPED) != pid) {
+        perror("waitpid");
+        return nullptr;
+    }
+
+    if (ptrace(PT_ATTACH, pid, 0, 0) < 0) {
+        perror("PT_ATTACH");
+        return nullptr;
+    }
+
+    // TOOD: do we actually need this waitpid?
+    if (waitpid(pid, nullptr, WSTOPPED) != pid) {
+        perror("waitpid");
+        return nullptr;
+    }
+
+    if (ptrace(PT_CONTINUE, pid, 0, 0) < 0) {
+        perror("continue");
+        return nullptr;
+    }
+
+    // We want to continue until the exit from the 'execve' sycsall.
+    // This ensures that when we start debugging the process
+    // it executes the target image, and not the forked image of the tracing process.
+    // NOTE: we only need to do this when we are debugging a new process (i.e not attaching to a process that's already running!)
+
+    if (waitpid(pid, nullptr, WSTOPPED) != pid) {
+        perror("wait_pid");
+        return nullptr;
+    }
+
+    return make<DebugSession>(pid);
+}
+
+bool DebugSession::poke(u32* address, u32 data)
+{
+    if (ptrace(PT_POKE, m_debugee_pid, (void*)address, data) < 0) {
+        perror("PT_POKE");
+        return false;
+    }
+    return true;
+}
+
+Optional<u32> DebugSession::peek(u32* address) const
+{
+    Optional<u32> result;
+    int rc = ptrace(PT_PEEK, m_debugee_pid, (void*)address, 0);
+    if (errno == 0)
+        result = static_cast<u32>(rc);
+    return result;
+}
+
+bool DebugSession::insert_breakpoint(void* address)
+{
+    // We insert a software breakpoint by
+    // patching the first byte of the instruction at 'address'
+    // with the breakpoint instruction (int3)
+
+    if (m_breakpoints.contains(address))
+        return false;
+
+    auto original_bytes = peek(reinterpret_cast<u32*>(address));
+
+    if (!original_bytes.has_value())
+        return false;
+
+    if (!poke(reinterpret_cast<u32*>(address), (original_bytes.value() & ~(uint32_t)0xff) | BREAKPOINT_INSTRUCTION))
+        return false;
+
+    m_breakpoints.set(address, { address, original_bytes.value() });
+    return true;
+}
+
+void DebugSession::remove_breakpoint(const BreakPoint& breakpoint)
+{
+    ASSERT(m_breakpoints.contains(breakpoint.address));
+    poke(reinterpret_cast<u32*>(reinterpret_cast<char*>(breakpoint.address)), breakpoint.original_first_word);
+    m_breakpoints.remove(breakpoint.address);
+}
+
+PtraceRegisters DebugSession::get_registers() const
+{
+    PtraceRegisters regs;
+    if (ptrace(PT_GETREGS, m_debugee_pid, &regs, 0) < 0) {
+        perror("PT_GETREGS");
+        ASSERT_NOT_REACHED();
+    }
+    return regs;
+}
+
+void DebugSession::set_registers(const PtraceRegisters& regs)
+{
+    if (ptrace(PT_SETREGS, m_debugee_pid, reinterpret_cast<void*>(&const_cast<PtraceRegisters&>(regs)), 0) < 0) {
+        perror("PT_SETREGS");
+        ASSERT_NOT_REACHED();
+    }
+}
+
+Optional<DebugSession::BreakPoint> DebugSession::get_matching_breakpoint(const PtraceRegisters& regs) const
+{
+    return m_breakpoints.get(reinterpret_cast<void*>(regs.eip - 1));
+}
+
+void DebugSession::continue_debugee()
+{
+    if (ptrace(PT_CONTINUE, m_debugee_pid, 0, 0) < 0) {
+        perror("continue");
+        ASSERT_NOT_REACHED();
+    }
+}
+
+VirtualAddress DebugSession::get_entry_point() const
+{
+    return m_elf_image->entry();
+}
diff --git a/Applications/Debugger/DebugSession.h b/Applications/Debugger/DebugSession.h
new file mode 100644
index 0000000000..9ac7774f20
--- /dev/null
+++ b/Applications/Debugger/DebugSession.h
@@ -0,0 +1,138 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/MappedFile.h>
+#include <AK/Optional.h>
+#include <AK/OwnPtr.h>
+#include <AK/String.h>
+#include <LibC/sys/arch/i386/regs.h>
+#include <LibELF/Image.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/ptrace.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+class DebugSession {
+public:
+    static OwnPtr<DebugSession> exec_and_attach(const String& command);
+
+    // Has to be public for OwnPtr::make
+    DebugSession(int pid);
+    ~DebugSession();
+
+    int pid() const { return m_debugee_pid; }
+
+    bool poke(u32* address, u32 data);
+    Optional<u32> peek(u32* address) const;
+
+    struct BreakPoint {
+        void* address;
+        u32 original_first_word;
+    };
+
+    bool insert_breakpoint(void* address);
+    void remove_breakpoint(const BreakPoint&);
+    Optional<BreakPoint> get_matching_breakpoint(const PtraceRegisters&) const;
+
+    PtraceRegisters get_registers() const;
+    void set_registers(const PtraceRegisters&);
+
+    void continue_debugee();
+
+    template<typename Callback>
+    void run(Callback callback);
+
+    VirtualAddress get_entry_point() const;
+
+    enum DebugDecision {
+        Continue,
+        Detach,
+        Kill,
+    };
+
+    enum DebugBreakReason {
+        Breakpoint,
+        Exited,
+    };
+
+private:
+    // x86 breakpoint instruction "int3"
+    static constexpr u8 BREAKPOINT_INSTRUCTION
+        = 0xcc;
+
+    int m_debugee_pid { -1 };
+    bool m_is_debugee_dead { false };
+
+    NonnullOwnPtr<MappedFile> m_executable;
+    NonnullOwnPtr<ELF::Image> m_elf_image;
+
+    HashMap<void*, BreakPoint> m_breakpoints;
+};
+
+template<typename Callback>
+void DebugSession::run(Callback callback)
+{
+    for (;;) {
+        continue_debugee();
+
+        int wstatus = 0;
+        if (waitpid(m_debugee_pid, &wstatus, WSTOPPED | WEXITED) != m_debugee_pid) {
+            perror("waitpid");
+            ASSERT_NOT_REACHED();
+        }
+
+        // FIXME: This check actually only checks whether the debugee
+        // Is stopped because it hit a breakpoint or not
+        if (WSTOPSIG(wstatus) != SIGTRAP) {
+            callback(DebugBreakReason::Exited, Optional<PtraceRegisters>());
+            m_is_debugee_dead = true;
+            break;
+        }
+
+        auto regs = get_registers();
+
+        auto current_breakpoint = get_matching_breakpoint(regs);
+        if (current_breakpoint.has_value()) {
+            // FIXME: The current implementation removes a breakpoint
+            // after the first time it has been triggered.
+            remove_breakpoint(current_breakpoint.value());
+
+            // We need to re-execute the instruction we patched for the breakpoint,
+            // so we rollback the instruction pointer to the breakpoint's address
+            regs.eip = reinterpret_cast<u32>(current_breakpoint.value().address);
+            set_registers(regs);
+            DebugDecision decision = callback(DebugBreakReason::Breakpoint, regs);
+            if (decision != DebugDecision::Continue) {
+                // FIXME: implement detach & kill
+                ASSERT_NOT_REACHED();
+            }
+        }
+    }
+}
diff --git a/Applications/Debugger/Makefile b/Applications/Debugger/Makefile
index 2b9e6d7c50..32f18aa799 100755
--- a/Applications/Debugger/Makefile
+++ b/Applications/Debugger/Makefile
@@ -1,8 +1,9 @@
 OBJS = \
+    DebugSession.o \
     main.o
 
 PROGRAM = Debugger
 
-LIB_DEPS = Core
+LIB_DEPS = Core X86
 
 include ../../Makefile.common
diff --git a/Applications/Debugger/main.cpp b/Applications/Debugger/main.cpp
index 24d88dceaf..05fc498487 100644
--- a/Applications/Debugger/main.cpp
+++ b/Applications/Debugger/main.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -24,17 +24,20 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "DebugSession.h"
 #include <AK/Assertions.h>
 #include <AK/ByteBuffer.h>
+#include <AK/LogStream.h>
+#include <AK/StringBuilder.h>
+#include <AK/kmalloc.h>
 #include <LibC/sys/arch/i386/regs.h>
 #include <LibCore/File.h>
-#include <LibELF/ELFImage.h>
+#include <LibX86/Disassembler.h>
+#include <LibX86/Instruction.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/ptrace.h>
-#include <sys/wait.h>
 #include <unistd.h>
 
 static int usage()
@@ -43,178 +46,176 @@ static int usage()
     return 1;
 }
 
-static int g_pid = -1;
+OwnPtr<DebugSession> g_debug_session;
 
 static void handle_sigint(int)
 {
-    if (g_pid == -1)
-        return;
+    printf("Debugger: SIGINT\n");
 
-    if (ptrace(PT_DETACH, g_pid, 0, 0) == -1) {
-        perror("detach");
-    }
+    // The destructor of DebugSession takes care of detaching
+    g_debug_session = nullptr;
 }
 
-void run_child_and_attach(char** argv)
+String get_command()
 {
-    int pid = fork();
-
-    if (!pid) {
-        if (ptrace(PT_TRACE_ME, 0, 0, 0) == -1) {
-            perror("traceme");
-            return exit(1);
-        }
-
-        int rc = execvp(argv[1], &argv[1]);
-        if (rc < 0) {
-            perror("execvp");
+    printf("(sdb) ");
+    fflush(stdout);
+    char* line = nullptr;
+    size_t allocated_size = 0;
+    ssize_t nread = getline(&line, &allocated_size, stdin);
+    if (nread < 0) {
+        if (errno == 0) {
+            fprintf(stderr, "\n");
+        } else {
+            perror("getline");
             exit(1);
         }
-        ASSERT_NOT_REACHED();
     }
+    String command(line);
+    free(line);
+    if (command.ends_with('\n'))
+        command = command.substring(0, command.length() - 1);
+    return command;
+}
 
-    g_pid = pid;
+void handle_print_registers(const PtraceRegisters& regs)
+{
+    printf("eax: 0x%x\n", regs.eax);
+    printf("ecx: 0x%x\n", regs.ecx);
+    printf("edx: 0x%x\n", regs.edx);
+    printf("ebx: 0x%x\n", regs.ebx);
+    printf("esp: 0x%x\n", regs.esp);
+    printf("ebp: 0x%x\n", regs.ebp);
+    printf("esi: 0x%x\n", regs.esi);
+    printf("edi: 0x%x\n", regs.edi);
+    printf("eip: 0x%x\n", regs.eip);
+    printf("eflags: 0x%x\n", regs.eflags);
+}
 
-    if (waitpid(pid, nullptr, WSTOPPED) != pid) {
-        perror("waitpid");
-        exit(1);
+bool handle_disassemble_command(const String& command, void* first_instruction)
+{
+    auto parts = command.split(' ');
+    size_t number_of_instructions_to_disassemble = 5;
+    if (parts.size() == 2) {
+        bool ok;
+        number_of_instructions_to_disassemble = parts[1].to_uint(ok);
+        if (!ok)
+            return false;
     }
 
-    if (ptrace(PT_ATTACH, g_pid, 0, 0) == -1) {
-        perror("attach");
-        exit(1);
+    // FIXME: Instead of using a fixed "dump_size",
+    //        we can feed instructions to the disassembler one by one
+    constexpr size_t dump_size = 0x100;
+    ByteBuffer code;
+    for (size_t i = 0; i < dump_size / sizeof(u32); ++i) {
+        auto value = g_debug_session->peek(reinterpret_cast<u32*>(first_instruction) + i);
+        if (!value.has_value())
+            break;
+        code.append(&value, sizeof(u32));
     }
 
-    if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
-        perror("waitpid");
-        exit(1);
-    }
+    X86::SimpleInstructionStream stream(code.data(), code.size());
+    X86::Disassembler disassembler(stream);
 
-    dbg() << "debugee should continue until before execve exit";
-    if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
-        perror("continue");
-    }
+    for (size_t i = 0; i < number_of_instructions_to_disassemble; ++i) {
+        auto offset = stream.offset();
+        auto insn = disassembler.next();
+        if (!insn.has_value())
+            break;
 
-    // we want to continue until the exit from the 'execve' sycsall
-    // we do this to ensure that when we start debugging the process,
-    // it executes the target image, and not the forked image of the debugger
-    // NOTE: we only need to do this when we are debugging a new process (i.e not attaching to a process that's already running!)
-    // if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
-    //     perror("syscall");
-    //     exit(1);
-    // }
-
-    if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
-        perror("wait_pid");
-        exit(1);
+        printf(String::format("   %08x ", offset + reinterpret_cast<size_t>(first_instruction)).characters());
+        printf("<+%lu>:\t", reinterpret_cast<size_t>(offset));
+        printf("%s\n", insn.value().to_string(offset).characters());
     }
-    // dbg() << "debugee should continue until after execve exit";
-    // sleep(3);
 
-    // if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
-    //     perror("continue");
-    // }
-
-    // sleep(10);
-
-    // if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
-    //     perror("wait_pid");
-    //     exit(1);
-    // }
+    return true;
+}
 
-    // dbg() << "debugee should already be running";
-    // if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
-    //     perror("continue");
-    // }
+bool handle_breakpoint_command(const String& command)
+{
+    auto parts = command.split(' ');
+    if (parts.size() != 2)
+        return false;
+
+    u32 breakpoint_address = strtoul(parts[1].characters(), nullptr, 16);
+    if (errno != 0)
+        return false;
+    bool success = g_debug_session->insert_breakpoint(reinterpret_cast<void*>(breakpoint_address));
+    if (!success) {
+        fprintf(stderr, "coult not insert breakpoint at: 0x%x\n", breakpoint_address);
+        return false;
+    }
+    return true;
 }
 
-VirtualAddress get_entry_point(int pid)
+void print_help()
 {
-    auto path = String::format("/proc/%d/exe", pid);
-    dbg() << "path: " << path;
-    auto file = Core::File::construct(path);
-    if (!file->open(Core::File::ReadOnly)) {
-        fprintf(stderr, "Failed to open Debugged executable");
-        exit(1);
-    }
-    auto data = file->read_all();
-    dbg() << "data size:" << data.size();
-    ELFImage elf(data.data(), data.size());
-    return elf.entry();
+    printf("Options:\n"
+           "cont - Continue execution\n"
+           "regs - Print registers\n"
+           "dis <number of instructions> - Print disassembly\n"
+           "bp <address> - Insert a breakpoint\n");
 }
 
 int main(int argc, char** argv)
 {
     // TODO: pledge & unveil
-    // TOOD: check that we didn't somehow hurt performance. boot seems slower? (or it's just laptop battey)
+    // TODO: check that strace still works
     if (argc == 1)
         return usage();
 
-    struct sigaction sa;
-    memset(&sa, 0, sizeof(struct sigaction));
-    sa.sa_handler = handle_sigint;
-    sigaction(SIGINT, &sa, nullptr);
-
-    run_child_and_attach(argv);
-
-    dbg() << "pid:" << g_pid;
-    auto entry_point = get_entry_point(g_pid);
-    dbg() << "entry point:" << entry_point;
-
-    const uint32_t original_instruction_data = ptrace(PT_PEEK, g_pid, (void*)entry_point.as_ptr(), 0);
-
-    dbg() << "peeked data:" << (void*)original_instruction_data;
-
-    if (ptrace(PT_POKE, g_pid, (void*)entry_point.as_ptr(), (original_instruction_data & ~(uint32_t)0xff) | 0xcc) < 0) {
-        perror("poke");
-        return 1;
+    StringBuilder command;
+    command.append(argv[1]);
+    for (int i = 2; i < argc; ++i) {
+        command.appendf("%s ", argv[i]);
     }
 
-    dbg() << "continuting";
-
-    if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
-        perror("continue");
+    auto result = DebugSession::exec_and_attach(command.to_string());
+    if (!result) {
+        fprintf(stderr, "Failed to start debugging session for: \"%s\"\n", command.to_string().characters());
+        exit(1);
     }
-    dbg() << "continued";
+    g_debug_session = result.release_nonnull();
 
-    // wait for breakpoint
-    if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
-        perror("waitpid");
-        return 1;
-    }
+    struct sigaction sa;
+    memset(&sa, 0, sizeof(struct sigaction));
+    sa.sa_handler = handle_sigint;
+    sigaction(SIGINT, &sa, nullptr);
 
-    printf("hit breakpoint\n");
+    bool rc = g_debug_session->insert_breakpoint(g_debug_session->get_entry_point().as_ptr());
+    ASSERT(rc);
 
-    if (ptrace(PT_POKE, g_pid, (void*)entry_point.as_ptr(), original_instruction_data) < 0) {
-        perror("poke");
-        return 1;
-    }
+    g_debug_session->run([&](DebugSession::DebugBreakReason reason, Optional<PtraceRegisters> optional_regs) {
+        if (reason == DebugSession::DebugBreakReason::Exited) {
+            printf("Program exited.\n");
+            return DebugSession::DebugDecision::Detach;
+        }
 
-    PtraceRegisters regs;
-    if (ptrace(PT_GETREGS, g_pid, &regs, 0) < 0) {
-        perror("getregs");
-        return 1;
-    }
+        ASSERT(optional_regs.has_value());
+        const PtraceRegisters& regs = optional_regs.value();
 
-    dbg() << "eip after breakpoint: " << (void*)regs.eip;
+        printf("Program is stopped at: 0x%x\n", regs.eip);
+        for (;;) {
+            auto command = get_command();
+            bool success = false;
 
-    regs.eip = reinterpret_cast<u32>(entry_point.as_ptr());
-    dbg() << "settings eip back to:" << (void*)regs.eip;
-    if (ptrace(PT_SETREGS, g_pid, &regs, 0) < 0) {
-        perror("setregs");
-        return 1;
-    }
+            if (command == "cont") {
+                return DebugSession::DebugDecision::Continue;
+            }
 
-    dbg() << "continuig";
+            if (command == "regs") {
+                handle_print_registers(regs);
+                success = true;
 
-    if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
-        perror("continue");
-    }
+            } else if (command.starts_with("dis")) {
+                success = handle_disassemble_command(command, reinterpret_cast<void*>(regs.eip));
 
-    // wait for end
+            } else if (command.starts_with("bp")) {
+                success = handle_breakpoint_command(command);
+            }
 
-    if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
-        perror("waitpid");
-        return 1;
-    }
+            if (!success)
+                print_help();
+        }
+    });
 }
diff --git a/Demos/Debugee/Makefile b/Demos/Debugee/Makefile
deleted file mode 100644
index 2c67a05707..0000000000
--- a/Demos/Debugee/Makefile
+++ /dev/null
@@ -1,8 +0,0 @@
-OBJS = \
-    main.o
-
-PROGRAM = Debugee
-
-# LIB_DEPS = Core
-
-include ../../Makefile.common
diff --git a/Demos/Debugee/main.cpp b/Demos/Debugee/main.cpp
deleted file mode 100644
index 6922f27a6f..0000000000
--- a/Demos/Debugee/main.cpp
+++ /dev/null
@@ -1,12 +0,0 @@
-#include <cstdio>
-int main(int, char**)
-{
-    printf("Debuggee main\n");
-    int s = 0;
-    for (int i = 0; i < 10; ++i) {
-        s++;
-    }
-    printf("s: %d\n", s);
-    // asm("int3");
-    return 0;
-}
diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index e6df853499..13054d8f86 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -4935,6 +4935,7 @@ bool Process::has_tracee_thread(int tracer_pid) const
 KResultOr<u32> Process::peek_user_data(u32* address)
 {
     if (!MM.validate_user_read(*this, VirtualAddress(address), sizeof(u32))) {
+        dbg() << "Invalid address for peek_user_data: " << address;
         return KResult(-EFAULT);
     }
     uint32_t result;
@@ -4951,8 +4952,9 @@ KResultOr<u32> Process::peek_user_data(u32* address)
 KResult Process::poke_user_data(u32* address, u32 data)
 {
     // We validate for read (rather than write) because PT_POKE can write to readonly pages.
-    // So we wffectively only care that the poke operation only writes to user pages
+    // So we effectively only care that the poke operation is trying to write to user pages.
     if (!MM.validate_user_read(*this, VirtualAddress(address), sizeof(u32))) {
+        dbg() << "Invalid address for poke_user_data: " << address;
         return KResult(-EFAULT);
     }
     ProcessPagingScope scope(*this);
diff --git a/Kernel/Process.h b/Kernel/Process.h
index 98699701cd..05f9cbe94b 100644
--- a/Kernel/Process.h
+++ b/Kernel/Process.h
@@ -39,6 +39,7 @@
 #include <Kernel/Thread.h>
 #include <Kernel/UnixTypes.h>
 #include <Kernel/VM/RangeAllocator.h>
+#include <LibBareMetal/StdLib.h>
 #include <LibC/signal_numbers.h>
 
 namespace ELF {
diff --git a/Kernel/ThreadTracer.h b/Kernel/ThreadTracer.h
index fae20afcae..1ac492d868 100644
--- a/Kernel/ThreadTracer.h
+++ b/Kernel/ThreadTracer.h
@@ -46,6 +46,7 @@ public:
     void set_trace_syscalls(bool val) { m_trace_syscalls = val; }
 
     void set_regs(const RegisterState& regs);
+    void set_regs(const PtraceRegisters& regs) { m_regs = regs; }
     bool has_regs() const { return m_regs.has_value(); }
     const PtraceRegisters& regs() const
     {
diff --git a/Kernel/build-root-filesystem.sh b/Kernel/build-root-filesystem.sh
index ddc2ee86e3..38950b8a4e 100755
--- a/Kernel/build-root-filesystem.sh
+++ b/Kernel/build-root-filesystem.sh
@@ -146,7 +146,6 @@ cp ../Applications/Browser/Browser mnt/bin/Browser
 cp ../Applications/Debugger/Debugger mnt/bin/sdb
 cp ../Games/Solitaire/Solitaire mnt/bin/Solitaire
 cp ../Demos/HelloWorld/HelloWorld mnt/bin/HelloWorld
-cp ../Demos/Debugee/Debugee mnt/bin/Debugee
 cp ../Demos/WidgetGallery/WidgetGallery mnt/bin/WidgetGallery
 cp ../Demos/Fire/Fire mnt/bin/Fire
 cp ../Demos/DynamicLink/LinkDemo/LinkDemo mnt/bin/LinkDemo