Simple WinDebug loop

debugged.cpp

#include <cstdio>
#include <cstdlib>
#include <string>
using namespace std;
int main() {
	for (unsigned int i = 0; i < 10; i++) {
		fprintf(stderr, "Hello, world!\n");
	}
	return 0;
}

debugger.cpp

#include <Windows.h>
#include <cstdio>
//#include "udis86.h"
#include <map>

ULONG mink(ULONG a, ULONG b)
{
	if (a < b) return a; else return b;
}

std::map<DWORD, HANDLE> processes;
std::map<DWORD, HANDLE> threads;
DEBUG_EVENT debug_ev;

void readMemory()
{
	CONTEXT ctx;
	memset(&ctx, 0, sizeof(ctx));
	ctx.ContextFlags = CONTEXT_CONTROL;
	GetThreadContext(threads[debug_ev.dwThreadId], &ctx);
	const ULONG kMaxInstrLength = 15;
	const ULONG kSmallPageSize = (1 << 12);
	BYTE opcode[kMaxInstrLength];
	SIZE_T bytes_read = 0;
	LPBYTE pc = (LPBYTE)ctx.Eip;//<==================
	/*
	  ctx.Eip is 1 affter 0xcc
	  ctx.Eip-1 - 0xcc = int3, but I want previous opcode before set int3
	*/
	while (bytes_read < kMaxInstrLength) {
		SIZE_T remote_bytes_read;
		if (!ReadProcessMemory(processes[debug_ev.dwProcessId],
			&pc[bytes_read],
			&opcode[bytes_read],
			mink(kMaxInstrLength-bytes_read,
			(((SIZE_T)&pc[bytes_read] + kSmallPageSize) & ~(kSmallPageSize - 1))-(SIZE_T)&pc[bytes_read]),
			&remote_bytes_read)) {
			break;
		}
		bytes_read += remote_bytes_read;
	}
	printf("[%.8x] %x\n", ctx.Eip, opcode[0]);
	/*ud_t ud_obj;
	ud_init(&ud_obj);
	ud_set_mode(&ud_obj, 32);
	ud_set_syntax(&ud_obj, UD_SYN_INTEL);
	ud_set_input_buffer(&ud_obj, opcode, bytes_read);
	if (ud_disassemble(&ud_obj) > 0) {
		printf("[%.8x] %s\n", ctx.Eip, ud_insn_asm(&ud_obj));
	}
	else {
		printf("[%.8x] invalid\n", ctx.Eip);
	}*/
}

BOOL SpawnAndAttachProcess(LPTSTR lpApplicationName) {
	STARTUPINFO si;
	PROCESS_INFORMATION pi;
	ZeroMemory(&si, sizeof(si));
	ZeroMemory(&pi, sizeof(pi));
	si.cb = sizeof(si);
	if (!CreateProcess(lpApplicationName, NULL,
		NULL, NULL, FALSE,
		DEBUG_ONLY_THIS_PROCESS,
		NULL, NULL, &si, &pi)) {
		return FALSE;
	}
	do {		
		DWORD cont_status;
		if (!WaitForDebugEvent(&debug_ev, INFINITE)) {
			break;
		}
		switch (debug_ev.dwDebugEventCode) {
		case CREATE_PROCESS_DEBUG_EVENT: 
			printf("CREATE_PROCESS, id: %u, base address: %p, start address: %p\n",
				debug_ev.dwProcessId,
				debug_ev.u.CreateProcessInfo.lpBaseOfImage,
				debug_ev.u.CreateProcessInfo.lpStartAddress);
			if (debug_ev.u.CreateProcessInfo.hFile != NULL) {
				CloseHandle(debug_ev.u.CreateProcessInfo.hFile);
			}
			processes[debug_ev.dwProcessId] = debug_ev.u.CreateProcessInfo.
				hProcess;
			threads[debug_ev.dwThreadId] = debug_ev.u.CreateProcessInfo.hThread;
			break;
		case CREATE_THREAD_DEBUG_EVENT: 
			printf("CREATE_THREAD, tid: %u, TLS: %p, start address: %p\n",
				debug_ev.dwThreadId,
				debug_ev.u.CreateThread.lpThreadLocalBase,
				debug_ev.u.CreateThread.lpStartAddress);
			threads[debug_ev.dwThreadId] = debug_ev.u.CreateThread.hThread;
			break;
		case EXCEPTION_DEBUG_EVENT: 
			cont_status = DBG_EXCEPTION_NOT_HANDLED;
			printf("EXCEPTION, first chance: %u, code: %x, address: %p\n",
				debug_ev.u.Exception.dwFirstChance,
				debug_ev.u.Exception.ExceptionRecord.ExceptionCode,
				debug_ev.u.Exception.ExceptionRecord.ExceptionAddress);
			if (!debug_ev.u.Exception.dwFirstChance) {
				TerminateProcess(processes[debug_ev.dwProcessId], 0);
			}
			readMemory();
			break;		
		case EXIT_PROCESS_DEBUG_EVENT: 
			printf("EXIT_PROCESS, pid: %u, tid: %u, exit code: %u\n",
				debug_ev.dwProcessId, debug_ev.dwThreadId,
				debug_ev.u.ExitProcess.dwExitCode);
			CloseHandle(processes[debug_ev.dwProcessId]);
			CloseHandle(threads[debug_ev.dwThreadId]);
			processes.erase(debug_ev.dwProcessId);
			debug_ev.dwProcessId = 0;
			threads.erase(debug_ev.dwThreadId);
			debug_ev.dwThreadId = 0;
			break;
		case EXIT_THREAD_DEBUG_EVENT: 
			printf("EXIT_THREAD, tid: %u, exit code: %u\n",
				debug_ev.dwThreadId,
				debug_ev.u.ExitThread.dwExitCode);
			CloseHandle(threads[debug_ev.dwThreadId]);
			threads.erase(debug_ev.dwThreadId);
			debug_ev.dwThreadId = 0;
			break;
		case LOAD_DLL_DEBUG_EVENT: 
			printf("LOAD_DLL, base address: %p\n", debug_ev.u.LoadDll.lpBaseOfDll);
			if (debug_ev.u.LoadDll.hFile != NULL) {
				CloseHandle(debug_ev.u.LoadDll.hFile);
			}
			break;
		case OUTPUT_DEBUG_STRING_EVENT: 
			break;
		case RIP_EVENT: break;
		case UNLOAD_DLL_DEBUG_EVENT: break;
		}
		if (debug_ev.dwProcessId == 0) break;
		if (debug_ev.dwThreadId == 0) break;
		ContinueDebugEvent(debug_ev.dwProcessId,
			debug_ev.dwThreadId,
			DBG_CONTINUE);
	}while (!processes.empty());
	CloseHandle(pi.hProcess);
	CloseHandle(pi.hThread);
	return TRUE;
}

int main(int argc, char *argv[])
{
	SpawnAndAttachProcess(L"debugged.exe");
	return 0;
}