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Is The Debugger Attached?

, 22 Oct 2001
Take different actions depending on whether a debugger is attached to your process.
debugger_demo.zip
Debugger.clw
Debugger.dsp
Debugger.dsw
res
Debugger.ico
// DebuggerDlg.cpp : implementation file
//

#include "stdafx.h"
#include "Debugger.h"
#include "DebuggerDlg.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif


BOOL IsDebuggerAttached();

/////////////////////////////////////////////////////////////////////////////
// CAboutDlg dialog used for App About

class CAboutDlg : public CDialog
{
public:
	CAboutDlg();

// Dialog Data
	//{{AFX_DATA(CAboutDlg)
	enum { IDD = IDD_ABOUTBOX };
	//}}AFX_DATA

	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CAboutDlg)
	protected:
	virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support
	//}}AFX_VIRTUAL

// Implementation
protected:
	//{{AFX_MSG(CAboutDlg)
	//}}AFX_MSG
	DECLARE_MESSAGE_MAP()
};

CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
	//{{AFX_DATA_INIT(CAboutDlg)
	//}}AFX_DATA_INIT
}

void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialog::DoDataExchange(pDX);
	//{{AFX_DATA_MAP(CAboutDlg)
	//}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
	//{{AFX_MSG_MAP(CAboutDlg)
		// No message handlers
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CDebuggerDlg dialog

CDebuggerDlg::CDebuggerDlg(CWnd* pParent /*=NULL*/)
	: CDialog(CDebuggerDlg::IDD, pParent)
{
	//{{AFX_DATA_INIT(CDebuggerDlg)
		// NOTE: the ClassWizard will add member initialization here
	//}}AFX_DATA_INIT
	// Note that LoadIcon does not require a subsequent DestroyIcon in Win32
	m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}

void CDebuggerDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialog::DoDataExchange(pDX);
	//{{AFX_DATA_MAP(CDebuggerDlg)
		// NOTE: the ClassWizard will add DDX and DDV calls here
	//}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CDebuggerDlg, CDialog)
	//{{AFX_MSG_MAP(CDebuggerDlg)
	ON_WM_SYSCOMMAND()
	ON_WM_PAINT()
	ON_WM_QUERYDRAGICON()
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CDebuggerDlg message handlers

BOOL CDebuggerDlg::OnInitDialog()
{
	CDialog::OnInitDialog();

	// Add "About..." menu item to system menu.

	// IDM_ABOUTBOX must be in the system command range.
	ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
	ASSERT(IDM_ABOUTBOX < 0xF000);

	CMenu* pSysMenu = GetSystemMenu(FALSE);
	if (pSysMenu != NULL)
	{
		CString strAboutMenu;
		strAboutMenu.LoadString(IDS_ABOUTBOX);
		if (!strAboutMenu.IsEmpty())
		{
			pSysMenu->AppendMenu(MF_SEPARATOR);
			pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
		}
	}

	// Set the icon for this dialog.  The framework does this automatically
	//  when the application's main window is not a dialog
	SetIcon(m_hIcon, TRUE);			// Set big icon
	SetIcon(m_hIcon, FALSE);		// Set small icon
	
	// TODO: Add extra initialization here
	
	return TRUE;  // return TRUE  unless you set the focus to a control
}

void CDebuggerDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
	if ((nID & 0xFFF0) == IDM_ABOUTBOX)
	{
		CAboutDlg dlgAbout;
		dlgAbout.DoModal();
	}
	else
	{
		CDialog::OnSysCommand(nID, lParam);
	}
}

// If you add a minimize button to your dialog, you will need the code below
//  to draw the icon.  For MFC applications using the document/view model,
//  this is automatically done for you by the framework.

void CDebuggerDlg::OnPaint() 
{
	if (IsIconic())
	{
		CPaintDC dc(this); // device context for painting

		SendMessage(WM_ICONERASEBKGND, (WPARAM) dc.GetSafeHdc(), 0);

		// Center icon in client rectangle
		int cxIcon = GetSystemMetrics(SM_CXICON);
		int cyIcon = GetSystemMetrics(SM_CYICON);
		CRect rect;
		GetClientRect(&rect);
		int x = (rect.Width() - cxIcon + 1) / 2;
		int y = (rect.Height() - cyIcon + 1) / 2;

		// Draw the icon
		dc.DrawIcon(x, y, m_hIcon);
	}
	else
	{
		CDialog::OnPaint();
	}
}

// The system calls this to obtain the cursor to display while the user drags
//  the minimized window.
HCURSOR CDebuggerDlg::OnQueryDragIcon()
{
	return (HCURSOR) m_hIcon;
}

void CDebuggerDlg::OnOK() 
{
	LPBYTE lpBuffer = (LPBYTE)0x80000000;


	// Give it a bogus buffer that will crash it for sure
	ReadMemory(lpBuffer, 1024);

}

BOOL CDebuggerDlg::ReadMemory(LPVOID lpBuffer, DWORD dwSize)
{
	// Validate the buffer
	if (IsBadWritePtr(lpBuffer, dwSize))
	{
		// This is bad! Must say something!
		if (IsDebuggerAttached())
		{
			// So we'll break into the debugger
			__asm	int 3

			// If you don't mind the function call overhead, you can call
			// DebugBreak();
			// instead...
		}
		else
		{
			MessageBox("CDebuggerDlg::ReadMemory() : Bad output buffer : lpBuffer!");
		}

		return FALSE;
	}


	// Well, we're not really gonna write anything to the buffer,
	// it's just a demo ;)
	return TRUE;

}

/////////////////////////////////////////////////////////////////////////////

BOOL IsDebuggerAttached()
{
	DWORD dw;


	__asm
	{
		push eax	// Preserve the registers
		push ecx
		mov	eax, fs:[0x18]	// Get the TIB's linear address
		mov	eax, dword ptr [eax + 0x30]
		mov	ecx, dword ptr [eax]	// Get the whole DWORD
		mov	dw, ecx	// Save it
		pop ecx	// Restore the registers
		pop eax
	}


	// The 3rd byte is the byte we really need to check for the
	// presence of a debugger.
	// Check the 3rd byte
	return (BOOL)(dw & 0x00010000 ? TRUE : FALSE);

}

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About the Author

Tim Chew

United States United States
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