Big Bummer for running Shrinkered files!

[Robert Baruch]

Oops, I misunderstood the purpose of the new frame.

Here's a piece of an article, http://www.microsoft.com/msj/defaultframe.asp?page=/msj/0197/exception/exception.htm&nav=/msj/0197/newnav.htm, figure 14 (KiUserExceptionDispatcher Pseudocode):

int ExecuteHandler( PEXCEPTION_RECORD pExcptRec
                     PEXCEPTION_REGISTRATION pExcptReg
                     CONTEXT * pContext
                     PVOID pDispatcherContext,
                     FARPROC handler ) // Really a ptr to an _except_handler()
{
     // Set up an EXCEPTION_REGISTRATION, where EDX points to the
     // appropriate handler code shown below
     PUSH    EDX
     PUSH    FS:[0]
     MOV     FS:[0],ESP
 
     // Invoke the exception callback function
     EAX = handler( pExcptRec, pExcptReg, pContext, pDispatcherContext );
 
     // Remove the minimal EXCEPTION_REGISTRATION frame 
     MOV     ESP,DWORD PTR FS:[00000000]
     POP     DWORD PTR FS:[00000000]
 
     return EAX;
}


So based on that, I think this is the final code:

// prologue: save esp, ebp and ecx.

push ebp
push ecx
mov ebp, esp
mov ecx, [ebp+1C] // handler

// create a new exception record on the stack
// to catch exceptions in the exception handler.

push [ebp+20]      // nested_handler
push fs:[00000000] // previous frame pointer

// set the new frame to point at that record

mov fs:[00000000], esp

// call the handler

push [ebp+18] // dispatcher
push [ebp+14] // context
push [ebp+10] // frame
push [ebp+0C] // record
call ecx                // exact instruction required by Shrinker

// eax now contains the return code from the exception handler.
// Restore the stack.

mov esp, fs:[00000000]  // exact instruction required by Shrinker

// pop off the previous frame to be the current frame.

pop fs:[00000000]

// epilogue: restore esp, ebp and ecx

mov esp, ebp
pop ecx
pop ebp
ret

Sorry for the Intel-speak rather than the GNU-speak, but I was brought up on x86 assembly in DOS :P

That should do it. I'm going to code this up to see if it works and doesn't kill my system! But first I need to brush up on GNU-assembly :)

--Rob