Menulis Perulangan Utama Debugger

Debugger menggunakan fungsi WaitForDebugEvent di awal perulangan utamanya. Fungsi ini memblokir debugger hingga peristiwa debugging terjadi. Ketika peristiwa debugging terjadi, sistem menangguhkan semua utas dalam proses yang di-debug dan memberi tahu debugger peristiwa.

Debugger dapat berinteraksi dengan pengguna, atau memanipulasi status proses yang sedang di-debug, dengan menggunakan fungsi GetThreadContext, GetThreadSelectorEntry, ReadProcessMemory, SetThreadContext, dan WriteProcessMemory. GetThreadSelectorEntry mengembalikan entri tabel deskriptor untuk pemilih dan utas tertentu. Debugger menggunakan entri tabel deskriptor untuk mengonversi alamat relatif segmen ke alamat virtual linier. Fungsi ReadProcessMemory dan WriteProcessMemory memerlukan alamat virtual linier.

Debugger sering membaca memori proses yang di-debug dan menulis memori yang berisi instruksi ke cache instruksi. Setelah instruksi ditulis, debugger memanggil fungsi FlushInstructionCache untuk menjalankan instruksi cache.

Debugger menggunakan fungsi ContinueDebugEvent di akhir perulangan utamanya. Fungsi ini memungkinkan proses yang di-debug untuk terus mengeksekusi.

Contoh berikut menggunakan fungsi WaitForDebugEvent dan ContinueDebugEvent untuk mengilustrasikan bagaimana debugger sederhana mungkin diatur.

#include <windows.h>

DWORD OnCreateThreadDebugEvent(const LPDEBUG_EVENT);
DWORD OnCreateProcessDebugEvent(const LPDEBUG_EVENT);
DWORD OnExitThreadDebugEvent(const LPDEBUG_EVENT);
DWORD OnExitProcessDebugEvent(const LPDEBUG_EVENT);
DWORD OnLoadDllDebugEvent(const LPDEBUG_EVENT);
DWORD OnUnloadDllDebugEvent(const LPDEBUG_EVENT);
DWORD OnOutputDebugStringEvent(const LPDEBUG_EVENT);
DWORD OnRipEvent(const LPDEBUG_EVENT);

void EnterDebugLoop(const LPDEBUG_EVENT DebugEv)
{
   DWORD dwContinueStatus = DBG_CONTINUE; // exception continuation 
 
   for(;;) 
   { 
   // Wait for a debugging event to occur. The second parameter indicates
   // that the function does not return until a debugging event occurs. 
 
      WaitForDebugEvent(DebugEv, INFINITE); 

   // Process the debugging event code. 
 
      switch (DebugEv->dwDebugEventCode) 
      { 
         case EXCEPTION_DEBUG_EVENT: 
         // Process the exception code. When handling 
         // exceptions, remember to set the continuation 
         // status parameter (dwContinueStatus). This value 
         // is used by the ContinueDebugEvent function. 
 
            switch(DebugEv->u.Exception.ExceptionRecord.ExceptionCode)
            { 
               case EXCEPTION_ACCESS_VIOLATION: 
               // First chance: Pass this on to the system. 
               // Last chance: Display an appropriate error. 
                  break;
 
               case EXCEPTION_BREAKPOINT: 
               // First chance: Display the current 
               // instruction and register values. 
                  break;
 
               case EXCEPTION_DATATYPE_MISALIGNMENT: 
               // First chance: Pass this on to the system. 
               // Last chance: Display an appropriate error. 
                  break;
 
               case EXCEPTION_SINGLE_STEP: 
               // First chance: Update the display of the 
               // current instruction and register values. 
                  break;
 
               case DBG_CONTROL_C: 
               // First chance: Pass this on to the system. 
               // Last chance: Display an appropriate error. 
                  break;
 
               default:
               // Handle other exceptions. 
                  break;
            } 

            break;
 
         case CREATE_THREAD_DEBUG_EVENT: 
         // As needed, examine or change the thread's registers 
         // with the GetThreadContext and SetThreadContext functions; 
         // and suspend and resume thread execution with the 
         // SuspendThread and ResumeThread functions. 

            dwContinueStatus = OnCreateThreadDebugEvent(DebugEv);
            break;

         case CREATE_PROCESS_DEBUG_EVENT: 
         // As needed, examine or change the registers of the
         // process's initial thread with the GetThreadContext and
         // SetThreadContext functions; read from and write to the
         // process's virtual memory with the ReadProcessMemory and
         // WriteProcessMemory functions; and suspend and resume
         // thread execution with the SuspendThread and ResumeThread
         // functions. Be sure to close the handle to the process image
         // file with CloseHandle.

            dwContinueStatus = OnCreateProcessDebugEvent(DebugEv);
            break;
 
         case EXIT_THREAD_DEBUG_EVENT: 
         // Display the thread's exit code. 

            dwContinueStatus = OnExitThreadDebugEvent(DebugEv);
            break;
 
         case EXIT_PROCESS_DEBUG_EVENT: 
         // Display the process's exit code. 

            dwContinueStatus = OnExitProcessDebugEvent(DebugEv);
            break;
 
         case LOAD_DLL_DEBUG_EVENT: 
         // Read the debugging information included in the newly 
         // loaded DLL. Be sure to close the handle to the loaded DLL 
         // with CloseHandle.

            dwContinueStatus = OnLoadDllDebugEvent(DebugEv);
            break;
 
         case UNLOAD_DLL_DEBUG_EVENT: 
         // Display a message that the DLL has been unloaded. 

            dwContinueStatus = OnUnloadDllDebugEvent(DebugEv);
            break;
 
         case OUTPUT_DEBUG_STRING_EVENT: 
         // Display the output debugging string. 

            dwContinueStatus = OnOutputDebugStringEvent(DebugEv);
            break;

         case RIP_EVENT:
            dwContinueStatus = OnRipEvent(DebugEv);
            break;
      } 
 
   // Resume executing the thread that reported the debugging event. 
 
   ContinueDebugEvent(DebugEv->dwProcessId, 
                      DebugEv->dwThreadId, 
                      dwContinueStatus);
   }
}