DebugActiveProcess

The DebugActiveProcess function allows a debugger to attach to an active process and then debug it.

BOOL DebugActiveProcess(

DWORD dwProcessId	// process to be debugged
);

Parameters

dwProcessId

Specifies the identifier for the process to be debugged. The debugger gets debugging access to the process as if it created the process with the DEBUG_ONLY_THIS_PROCESS flag.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The debugger must have appropriate access to the target process; it must be able to open the process for PROCESS_ALL_ACCESS access. In the Win32 application programming interface (API) for Windows 95, this is always true if the process identifier is valid. However, in the Win32 API for Windows NT, DebugActiveProcess can fail if the target process was created with a security descriptor that denies the debugger appropriate access.

After the system checks the process identifier and determines that a valid debugging attachment is being made, the function returns TRUE. The debugger is then expected to wait for debugging events by using the WaitForDebugEvent function. The system suspends all threads in the process and sends the debugger events representing the current state of the process.

The system sends the debugger a single CREATE_PROCESS_DEBUG_EVENT debugging event representing the process specified by the dwProcessId parameter. The lpStartAddress member of the CREATE_PROCESS_DEBUG_INFO structure is NULL.

For each thread currently part of the process, the system sends a CREATE_THREAD_DEBUG_EVENT debugging event. The lpStartAddress member of the CREATE_THREAD_DEBUG_INFO structure is NULL.

For each dynamic-link library (DLL) currently loaded into the address space of the target process, the system sends a LOAD_DLL_DEBUG_EVENT debugging event. The system arranges for the first thread in the process to execute a breakpoint instruction after it resumes. Continuing this thread causes it to return to whatever it was doing before the debugger was attached.

After all of this has been done, the system resumes all threads in the process. When the first thread in the process resumes, it executes a breakpoint instruction that causes an EXCEPTION_DEBUG_EVENT debugging event to be sent to the debugger. All future debugging events are sent to the debugger by using the normal mechanism and rules.

See Also

CreateProcess, CREATE_PROCESS_DEBUG_INFO, CREATE_THREAD_DEBUG_INFO, WaitForDebugEvent

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