how to allow a process created by another process, use a part of memory of the creator process ?

Question

I got two console processes that second one is created by first one using the API below:

BOOL WINAPI CreateProcess(
  __in_opt     LPCTSTR lpApplicationName,
  __inout_opt  LPTSTR lpCommandLine,
  __in_opt     LPSECURITY_ATTRIBUTES lpProcessAttributes,
  __in_opt     LPSECURITY_ATTRIBUTES lpThreadAttributes,
  __in         BOOL bInheritHandles,
  __in         DWORD dwCreationFlags,
  __in_opt     LPVOID lpEnvironment,
  __in_opt     LPCTSTR lpCurrentDirectory,
  __in         LPSTARTUPINFO lpStartupInfo,
  __out        LPPROCESS_INFORMATION lpProcessInformation
);

Now I wonder that if I pass a pointer to a part of memory of the first process, via IpCommandLine to the second process which is called by first process, will reading the memory to which that pointer points, by the second process definitely cause an access violation error or is it subject to value of some parameter of that API? If I can't use this API alone for my purpose, what method do you propose for the access ?

Answer 1

You can access this memory using ReadProcessMemory/WriteProcessMemory API. Another process needs to know memory address and handle of the process to access its memory.

Answer 2

I believe the use of volatile will allow other processes access to memory. Of course it will need a pointer to it

Answer 3

Here is my uninformed opinion (haven't done much of this thing on windows):

Separate processes (pretty much by definition) normally don't have the access to each other's memory space directly. Therefore you should use one of the interprocess communication (hint: that is something you google for) methods.

I don't know much about windows in this respect, but things like sockets, pipes, memory-mapped files and various forms of RPC come to mind. It, of course, depends on your actual use case.

Answer 4

Alex Farber's answer is correct; you can use Win32 API calls to read another process's memory. However, this is probably a bad idea. If you have a data to move around, you can either pass it as a parameter on the command line, or you can pass a handle to the other process and connect the two processes using a pipe.

Answer 5

I've done this before with #pragma's. I don't have the actual code handy at the moment, but I think something similar to this might work with Visual Studio 2008 C++:

//put this code in a dll that both processes link to

pragma section("shared",read,write,shared)

__declspec(allocate("shared")) int i = 0; // in theory, both processes should be able to access and modify i