Kernel: Add ptrace commands for reading/writing the debug registers

This adds PT_PEEKDEBUG and PT_POKEDEBUG to allow for reading/writing
the debug registers, and updates the Kernel's debug handler to read the
new information from the debug status register.

Kernel/Arch/i386/CPU.cpp

@@ -363,14 +363,15 @@ void debug_handler(TrapFrame* trap)
         PANIC("Debug exception in ring 0");
     }
     constexpr u8 REASON_SINGLESTEP = 14;
-    bool is_reason_singlestep = (read_dr6() & (1 << REASON_SINGLESTEP));
-    if (!is_reason_singlestep)
+    auto debug_status = read_dr6();
+    auto should_trap_mask = (1 << REASON_SINGLESTEP) | 0b1111;
+    if ((debug_status & should_trap_mask) == 0)
         return;
-
     if (auto tracer = process.tracer()) {
         tracer->set_regs(regs);
     }
     current_thread->send_urgent_signal_to_self(SIGTRAP);
+    write_dr6(debug_status & ~(should_trap_mask));
 }
 
 EH_ENTRY_NO_CODE(3, breakpoint);

Kernel/Syscalls/ptrace.cpp

@@ -153,6 +153,19 @@ static KResultOr<u32> handle_ptrace(const Kernel::Syscall::SC_ptrace_params& par
             return EFAULT;
         return peer->process().poke_user_data(Userspace<u32*> { (FlatPtr)params.addr }, params.data);
 
+    case PT_PEEKDEBUG: {
+        Kernel::Syscall::SC_ptrace_peek_params peek_params {};
+        if (!copy_from_user(&peek_params, reinterpret_cast<Kernel::Syscall::SC_ptrace_peek_params*>(params.addr)))
+            return EFAULT;
+        auto result = peer->peek_debug_register(reinterpret_cast<uintptr_t>(peek_params.address));
+        if (result.is_error())
+            return result.error();
+        if (!copy_to_user(peek_params.out_data, &result.value()))
+            return EFAULT;
+        break;
+    }
+    case PT_POKEDEBUG:
+        return peer->poke_debug_register(reinterpret_cast<uintptr_t>(params.addr), params.data);
     default:
         return EINVAL;
     }
@@ -229,4 +242,56 @@ KResult Process::poke_user_data(Userspace<u32*> address, u32 data)
     return KSuccess;
 }
 
+KResultOr<u32> Thread::peek_debug_register(u32 register_index)
+{
+    u32 data;
+    switch (register_index) {
+    case 0:
+        data = m_debug_register_state.dr0;
+        break;
+    case 1:
+        data = m_debug_register_state.dr1;
+        break;
+    case 2:
+        data = m_debug_register_state.dr2;
+        break;
+    case 3:
+        data = m_debug_register_state.dr3;
+        break;
+    case 6:
+        data = m_debug_register_state.dr6;
+        break;
+    case 7:
+        data = m_debug_register_state.dr7;
+        break;
+    default:
+        return EINVAL;
+    }
+    return data;
+}
+
+KResult Thread::poke_debug_register(u32 register_index, u32 data)
+{
+    switch (register_index) {
+    case 0:
+        m_debug_register_state.dr0 = data;
+        break;
+    case 1:
+        m_debug_register_state.dr1 = data;
+        break;
+    case 2:
+        m_debug_register_state.dr2 = data;
+        break;
+    case 3:
+        m_debug_register_state.dr3 = data;
+        break;
+    case 7:
+        m_debug_register_state.dr7 = data;
+        break;
+    default:
+        return EINVAL;
+    }
+    return KSuccess;
+}
+
 }

Kernel/Thread.h

@@ -972,6 +972,9 @@ public:
     u32 signal_mask() const;
     void clear_signals();
 
+    KResultOr<u32> peek_debug_register(u32 register_index);
+    KResult poke_debug_register(u32 register_index, u32 data);
+
     void set_dump_backtrace_on_finalization() { m_dump_backtrace_on_finalization = true; }
 
     DispatchSignalResult dispatch_one_pending_signal();

Kernel/UnixTypes.h

@@ -690,6 +690,8 @@ struct rtentry {
 #define PT_PEEK 7
 #define PT_POKE 8
 #define PT_SETREGS 9
+#define PT_POKEDEBUG 10
+#define PT_PEEKDEBUG 11
 
 // Used in struct dirent
 enum {

Userland/Libraries/LibC/sys/ptrace.cpp

@@ -40,7 +40,8 @@ int ptrace(int request, pid_t tid, void* addr, int data)
 
     u32 out_data;
     Syscall::SC_ptrace_peek_params peek_params;
-    if (request == PT_PEEK) {
+    auto is_peek_type = request == PT_PEEK || request == PT_PEEKDEBUG;
+    if (is_peek_type) {
         peek_params.address = reinterpret_cast<u32*>(addr);
         peek_params.out_data = &out_data;
         addr = &peek_params;
@@ -54,7 +55,7 @@ int ptrace(int request, pid_t tid, void* addr, int data)
     };
     int rc = syscall(SC_ptrace, &params);
 
-    if (request == PT_PEEK) {
+    if (is_peek_type) {
         if (rc < 0) {
             errno = -rc;
             return -1;

Userland/Libraries/LibC/sys/ptrace.h

@@ -39,6 +39,8 @@ __BEGIN_DECLS
 #define PT_PEEK 7
 #define PT_POKE 8
 #define PT_SETREGS 9
+#define PT_POKEDEBUG 10
+#define PT_PEEKDEBUG 11
 
 // FIXME: PID/TID ISSUE
 // Affects the entirety of LibDebug and Userland/strace.cpp.