Breaking a launched process programmatically - windows

Question

I need to launch a process and then break it immediately so that it can be debugged using Visual Studio.
I wrote this code after searching bits and pieces on the internet. The code is not working. The process gets launched, but it does not break and the calling code keeps waiting infinitely. If I don't launch the process in suspended mode, it runs immediately and exits.
I cannot modify the code of .exe that I am launching. I just have the .exe and symbols file.
Code:
#include<iostream>
#include<Windows.h>
using namespace std;
int main(int argc, char **argv)
{
STARTUPINFO si;
PROCESS_INFORMATION pi;
LPWSTR commandLine;
int commandLength;
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
if (argc != 2)
{
cout << "Usage: Launcher <commandline>" << endl;
return 1;
}
commandLength = MultiByteToWideChar(CP_UTF8, 0, argv[1], -1, NULL, 0);
commandLine = new WCHAR[commandLength];
MultiByteToWideChar(CP_UTF8, 0, argv[1], -1, commandLine, commandLength);
if (!CreateProcess(NULL, commandLine, NULL, NULL, FALSE, CREATE_SUSPENDED, NULL, NULL, &si, &pi))
{
cout << "CreateProcess failed (" << GetLastError() << ")." << endl;
delete[] commandLine;
return 1;
}
cout << pi.dwProcessId << " " << pi.dwThreadId << endl;
delete[] commandLine;
DebugBreakProcess(pi.hProcess);
WaitForSingleObject(pi.hProcess, INFINITE);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return 0;
}
What am I doing wrong here?
EDIT: This is the code after the suggestion by tyson.
#include<iostream>
#include<Windows.h>
using namespace std;
int main(int argc, char **argv)
{
STARTUPINFO si;
PROCESS_INFORMATION pi;
LPWSTR commandLine;
int commandLength;
HANDLE processHandle;
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
if (argc != 2)
{
cout << "Usage: Launcher <commandline>" << endl;
return 1;
}
commandLength = MultiByteToWideChar(CP_UTF8, 0, argv[1], -1, NULL, 0);
commandLine = new WCHAR[commandLength];
MultiByteToWideChar(CP_UTF8, 0, argv[1], -1, commandLine, commandLength);
if (!CreateProcess(NULL, commandLine, NULL, NULL, FALSE, CREATE_SUSPENDED, NULL, NULL, &si, &pi))
{
cout << "CreateProcess failed (" << GetLastError() << ")." << endl;
delete[] commandLine;
return 1;
}
delete[] commandLine;
processHandle = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pi.dwProcessId);
if (processHandle == NULL)
{
cout << "Could not obtain handle (" << GetLastError() << ")." << endl;
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return 2;
}
DebugActiveProcess(pi.dwProcessId);
//ResumeThread(pi.hThread);
WaitForSingleObject(pi.hProcess, INFINITE);
CloseHandle(processHandle);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return 0;
}

Answer 1

EDIT: revised instructions based on updated code.
I see three things that will help. First, you have to obtain a handle to the process with correct access. The handle returned by CreateProcess does not have correct access. Close that process handle (pi.hProcess and pi.hThread) and call OpenProcess requesting PROCESS_ALL_ACCESS. Keep in mind this may fail if the user account running the program does not have the required permissions.
Next, make sure you first initiate debugging by calling DebugActiveProcess with the process handle obtained above. (This may or may not be required.)
Finally, after your edit, I noticed that you are waiting for the process handle using WaitForSingleObject. This has the effect of waiting for the process to terminate. Instead, use WaitForDebugEvent.

Answer 2

You are trying too hard. The system is already well prepared to launch a debugger for any arbitrary process. You only have to set the Image File Execution Options appropriately to launch the debugger automatically.
For reference, here are the instructions quoted from the MSDN:
To setup an application to launch the debugger automatically
Start the Registry Editor (regedit).
In the Registry Editor, open the HKEY_LOCAL_MACHINE folder.
Navigate to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\currentversion\image file execution options.
In the Image File Execution Options folder, locate the name of the application you want to debug, such as myapp.exe. If you cannot find the application you want to debug:
a. Right-click the Image File Execution Options folder, and on the shortcut menu, click New Key.
b. Right-click the new key, and on the shortcut menu, click Rename.
c. Edit the key name to the name of your application; myapp.exe, in this example.
Right-click the myapp.exe folder, and on the shortcut menu, click New String Value.
Right-click the new string value, and on the shortcut menu, click Rename.
Change the name to debugger.
Right-click the new string value, and on the shortcut menu, click Modify.
The Edit String dialog box appears.
In the Value data box, type vsjitdebugger.exe.
Click OK.
From the Registry menu, click Exit.
The directory containing vsjitdebugger.exe must be in your system path. To add it to the system path, follow these steps:
a. Open the Control Panel in Classic view, and double-click System.
b. Click Advanced System Settings.
c. In System Properties, click the Advanced tab.
d. On the Advanced tab, click Environment Variables.
e. In the Environment Variables dialog box, under System variables, select Path, then click the Edit button.
f. In the Edit System Variable dialog box, add the directory to the Variable value box. Use a semicolon to separate it from other entries in the list.
g. Click OK to close the Edit System Variable dialog box.
h. Click OK to close the Environment Variables dialog box.
i. Click OK to close the System Properties dialog box.
Now, use any method to start your application. Visual Studio will start and load the application.