What global scope variables? The only global scope variable in the replacement
loaded ("if (bNeedInit)"). A static local copy is made; the function to which
it points exists within the EXE's code. Have I got that wrong?
You forgot the data segment of your DLL. You need to change
your installation code to allocate space for your static data and
the wndproc code to reference it in the newly allocated space.
Once you unload your DLL your current wndproc will crash
since it won't find its global-scope variables. (Ah, and you may
need to patch the machine code to achieve data relocation...)
BTW, you may simply allocate 4KB in VirtualAlloc since it
operates on memory pages.
"Vincent Fatica" <vince@blackholespam.net> wrote in message
news:46a6436d$1@news.vefatica.net...
In a DLL (plugin extension for an EXE) I write the following WNDPROC to
the
EXE's address space. Its purpose is simply to turn <WM_SYSCOMMAND,
SC_CLOSE>
into <WM_SYSCOMMAND, SC_MINIMIZE> (make the app hard to exit).
#pragma code_seg(".inject")
LRESULT CALLBACK MyWindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM
lParam)
{
static WNDPROC LocalOldWndProc = NULL;
static BOOL bNeedInit = TRUE;
// CWP = CallWindowProc()
static LRESULT (WINAPI *CWP)(WNDPROC, HWND, UINT, WPARAM, LPARAM);
if ( bNeedInit )
{
LocalOldWndProc = OldWndProc;
HMODULE hUser32 = GetModuleHandle("user32.dll");
(FARPROC&) CWP = GetProcAddress(hUser32, "CallWindowProcA");
bNeedInit = FALSE;
}
if ( uMsg == WM_SYSCOMMAND && (wParam & 0xFFF0) == SC_CLOSE )
wParam = SC_MINIMIZE;
return CWP(LocalOldWndProc, hwnd, uMsg, wParam, lParam);
}
#pragma code_seg()
#pragma comment(linker, "/SECTION:.inject,R")
#define INJECT_SIZE 0x74 // from DUMPBIN.EXE
I inject the code as follows:
BYTE *NewWndProc = (BYTE*) VirtualAlloc(NULL, INJECT_SIZE, MEM_COMMIT,
PAGE_EXECUTE_READWRITE);
BYTE *p = (BYTE*) MyWindowProc, *q = NewWndProc;
for ( INT i=0; i<INJECT_SIZE; i++ ) *q++ = *p++; // inject new wndproc
OldWndProc = (WNDPROC) SetWindowLong(hWndAppFrame, GWL_WNDPROC, (LONG)
NewWndProc);
SendMessage(hWndAppFrame, WM_NULL, 0, 0); // make it initialize
The point of the new WNDPROC's initialization routine is to remove any
future
reference to memory locations in the DLL.
It all works fine but the DLL can't be unloaded (I'd like to unload it,
leaving
the subclassing in place). If the DLL unloads (just before app shutdown
or at
my request) there are two GPF's in module_unknown and one in kernel32.dll
(apparently in DuplicateHandle() (?).
Am I missing something fundamental here, something that would make the
crash
expected?
Thanks.