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Reading a register

Posted on 2007-11-16
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Last Modified: 2010-04-15
Is there a way in C/C++ to read a register such as the stack pointer(SP) ?
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Question by:kipp8r
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Infinity08 earned 100 total points
ID: 20302328
Not with standard C, no. You'll need some inline assembler for that.
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by:UrosVidojevic
UrosVidojevic earned 100 total points
ID: 20302360
Example for VS C++:


#include <iostream>
using namespace std;
 
typedef unsigned short REG_VAL;
 
int main() {
	 REG_VAL reg;
 
	_asm {
		mov reg, sp
	};
 
	cout << "SP register value: " << reg << endl;
 
	__asm mov reg, ax;
	cout << "AX register value: " << reg << endl;
	
	__asm mov reg, bx;
	cout << "BX register value: " << reg << endl;
 
	__asm mov reg, cx;
	cout << "CX register value: " << reg << endl;
	
	__asm mov reg, dx;
	cout << "DX register value: " << reg << endl;
 
	return 0;
}

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Expert Comment

by:UrosVidojevic
ID: 20302382
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by:kipp8r
ID: 20302636
I understand know.  Can this be used to read another processes registers?
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Expert Comment

by:UrosVidojevic
ID: 20302653
No. These values are valid only for current ("RUNNING") process.

Information (register values) for other processes are stored in their PCB structures and are written in the registers when they get processor.
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Author Comment

by:kipp8r
ID: 20303244
Is there anyway to read the registers of another process.  I've noticed windows has a GetWindowThreadProcessId() function.  Basically I'm trying to output the values of the registers when the SP gets to a specific address.  So I can get some debug information on my software.
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Expert Comment

by:fridom
ID: 20303851
Of course there is all debugger do make that. So just search for debugger development and see what you can get from it.

Regards
Friedrich
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Expert Comment

by:Infinity08
ID: 20303881
>> So I can get some debug information on my software.

Maybe it's better to just run your program in a debugger, and get the information that way ?
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Author Comment

by:kipp8r
ID: 20310874
Debugging with another program would be too easy...lol...besides I want to log the values.  I found this though.  The win32 debug API.


            if (WaitForDebugEvent( &devent , 0))
                  {
                  switch(devent.dwDebugEventCode)
                        {
                         case CREATE_PROCESS_DEBUG_EVENT:
                                    h = ::OpenThread(THREAD_ALL_ACCESS, false, devent.dwThreadId);
                        // your handler here
                         break;            
                         case EXIT_PROCESS_DEBUG_EVENT:
                        // your handler here
                        break;
                         case EXCEPTION_DEBUG_EVENT:                   
                        // your handler here
                        break;

                        }      
                  
                  ContinueDebugEvent(devent.dwProcessId , devent.dwThreadId , DBG_CONTINUE);
      
                  }

            else
                  {
                     // other operations
                        
                  }

            }
            ::GetThreadContext(h,&rx);
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