Re: Porting MIDI plug-in from CW to Xcode
Re: Porting MIDI plug-in from CW to Xcode
- Subject: Re: Porting MIDI plug-in from CW to Xcode
- From: Doug Wyatt <email@hidden>
- Date: Tue, 9 Aug 2005 17:31:42 -0700
Hmm, CFPlugInCOM.h doesn't look much different from when I last
pondered it at length (possibly 5 years ago).
So you are deriving a C++ object from IUnknown? That header says:
"This class will work only with compilers that can produce COM-
compatible object layouts for C++ classes." I don't believe that to
be true of gcc as of 4.0 (and I hope someone will correct me if I'm
wrong).
You could have a look at the sample driver in the SDK, notably
MIDIDriverClass.h
see especially GetMIDIDriver, which converts from the COM
object to
your C++ object. Has commentary on exactly what I suspect is
going wrong
here.
MIDIDriver.cpp
Implementation of the above
Doug
--
Doug Wyatt
Core Audio, Apple
On Aug 9, 2005, at 16:22, Pete Gontier wrote:
When this project was last built, CodeWarrior made all that stuff
unnecessary. I just sub-classed IUnknown. There was a period when
Metrowerks tools supported COM better than Apple tools did. That
may still be the case, but my reading of the current version of
<CoreFoundation/CFPlugInCOM.h> suggests Apple tools have caught up.
I would vastly prefer never to code up pseudo-vtables, especially
given the age and stability of this code, so I am presently hoping
that fixing this is going to be a matter of a minor tweak.
— Pete Gontier <http://www.m-audio.com/>
From: Doug Wyatt <email@hidden>
Date: Tue, 9 Aug 2005 14:48:42 -0700
To: Pete Gontier <email@hidden>
Cc: CoreAudio API <email@hidden>, Cobey Gatos
<email@hidden>
Subject: Re: Porting MIDI plug-in from CW to Xcode
Do you have code that obtains a pointer to a C++ object based on a
pointer
to a pointer to a vtable? Does that code think it knows where in
the object
the vtable sits? I have such code and got bitten by those
assumptions when
moving from gcc 2.95 to 3.3 if I remember correctly.
--
Doug Wyatt
Core Audio, Apple
On Aug 8, 2005, at 17:05, Pete Gontier wrote:
> We have a working (shipping) MIDI driver written in C++ and built
> with CodeWarrior which needs to be converted to Xcode. We’ve got it
> building but not running on Panther. (The shipping CodeWarrior
> build runs fine on Panther.)
>
> The CFPlugIn factory function is called but then the plug-in
> interface object it instantiates is being called oddly. It receives
> two calls to AddRef with the same value of ‘this’ but no call to
> QueryInterface. The callers of AddRef are somewhat different; the
> first one is...
>
>> 0x8358bf60 in DriverTable::FindDriversInDirectory(short, unsigned
>> long) ()
>
> ...and the second one is...
>
>> 0x8358bfec in DriverTable::FindDriversInDirectory(short, unsigned
>> long) ()
>
> Same routine with a higher offset. Or perhaps it is only the
> closest symbol to an unnamed function in one or both cases.
>
> The lack of a call to QueryInterface is of course where the plug-in
> instantiates the MIDI driver (if necessary).
>
> I can’t guess why being built by Xcode would cause such oddness to
> occur. Ideas?
>
> — Pete Gontier <http://www.m-audio.com/>
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