Switch/case without break inside DllMain
- by Sherwood Hu
I have a Dllmain that allocates Thread local storage when a thread attaches to this DLL. Code as below:
BOOL APIENTRY DllMain(HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved)
{
LPVOID lpvData;
BOOL fIgnore;
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
onProcessAttachDLL();
// Allocate a TLS index.
if ((dwTlsIndex = TlsAlloc()) == TLS_OUT_OF_INDEXES)
return FALSE;
// how can it jump to next case???
case DLL_THREAD_ATTACH:
// Initialize the TLS index for this thread.
lpvData = (LPVOID) LocalAlloc(LPTR, MAX_BUFFER_SIZE);
if (lpvData != NULL)
fIgnore = TlsSetValue(dwTlsIndex, lpvData);
break;
...
}
I know that for the main thread, the DLL_THREAD_ATTACH is not entered, as per Microsoft Documentation. However, the above code worked. I am using VC2005. When I entered the debugger, I saw that after it entered DLL_THREAD_ATTACH case when ul_reason_for_call = 1! How can that happen? If I add `break' at the end of DLL_PROCESS_ATTACH block, the DLL failed to work.
How can this happen?
