Marshalling in WinCE [Windows]

Marshaling Mechanics

- two possible ways that a buffer can be marshaled so that the server can use it:

-- Duplication - Allocate a new buffer for the server to use, and copy data into and out of the buffer as necessary.

- The server owns the buffer for the duration of the call.

- gives the server access to the buffer,

- prevents the caller from asynchronously modifying the buffer after it has been validated by the server.

-- Aliasing:

- Map part of the memory of the caller process into the memory space of the server process.

- Because every process has a separate address space, it is not possible to access another process's memory by using a pointer.

-  Instead, the kernel aliases part of the memory of the caller into the address space of the server, using the VirtualCopyEx function.

- The same piece of physical memory is temporarily shared between the two processes by mapping it to two different virtual address ranges inside the two processes.

- This form of mapping involves allocating a new virtual address range, instead of just re-basing a pointer

Access checking: Verifying that the caller process has sufficient privileges to access a buffer.

Marshaling: Preparing a pointer that a server can use to access a caller’s buffer.

Secure-copy: Making a copy of a buffer to prevent asynchronous modification by the caller.

Pointer parameter: Pointer that is passed as a parameter to an API.

Embedded pointer: Pointer that is passed to an API by storing it inside a buffer or inside of another embedded pointer.