[PATCH 2/7] msvcrt: Clean up registered C++ object in handler.

[Piotr Caban]

On 05/31/17 00:59, Daniel Lehman wrote:
> 
> On 05/24/17 02:55, Daniel Lehman wrote:
>> +static DWORD cxx_catch_cleanup(EXCEPTION_RECORD *rec, EXCEPTION_REGISTRATION_RECORD *frame,
>> +                               CONTEXT *context,
>> +EXCEPTION_REGISTRATION_RECORD **pdispatcher) {
>> +    if (rec->ExceptionFlags & (EH_UNWINDING | EH_EXIT_UNWIND))
>> +    {
>> +        thread_data_t *data = msvcrt_get_thread_data();
>> +        frame_info *cur;
>> +
>> +        if (cxx_is_consolidate(rec))
>> Is this condition really needed? Shouldn't we clean the object no matter what's the reason of unwind?
> 
> Yeah.  That's covered by patch 7/7.  The original code only cleaned up if consolidating.
> 
> Since this 2/7 patch was somewhat of a refactoring for the later patches, I kept the consolidate-only cleanup logic.  I can merge them if you want
Yes, it would be preferable to merge the patches.

>>> +                if ((ULONG64)cur <= (ULONG64)frame)
>> This condition is not working. It's making assumption about order of catch_frame and frame_info variables on stack while they are declared this way:
> 
> I see what you mean.  If I forcefully reverse them, my tests crash;  my version of gcc was always putting them in the same place on the stack, regardless of where they were declared
> 
>>> +    EXCEPTION_REGISTRATION_RECORD catch_frame;
>>>        cxx_frame_info frame_info;
>> Shouldn't the cxx_catch_cleanup just unregister the object that was registered in call_catch_block >
> I didn't find a way to be call __CxxUnregisterObject on that one specifically (I'll try suggestions if you got em)
I think that the easiest solution would be to define something like:
struct catch_cleanup_frame {
     EXCEPTION_REGISTRATION_RECORD frame;
     cxx_frame_info frame_info;
}
and just call __CxxUnregisterObject with passed 
catch_cleanup_frame->frame_info in handler.

>> Here's a test case that demonstrate the problem with cur <= frame
>> comparison:
>>
>> 	try {
>> 		try { int *p = NULL; *p = 0x42; }
>> 		catch (klass x) { throw 1; }
>> 	} catch (int i) { }
>>
>> 	try { throw 1; }
>> 	catch(...) {}
> 
> This crashes for me even on Windows because the SEGV is uncaught.  It 'works' if I set an seh translator that throws int, but I get identical results on Wine with my series applied.  Do I need to add something?
It was meant to be run with seh translator set. It might be 
compiler/optimization level specific. On my computer it leads to 
incorrect stack usage caused by "cur <= frame" condition. The 
__CxxUnregisterObject is not called in my case and the registered 
objects list points to invalid stack space.

Thanks,
Piotr