[Adium-devl] GPL and Objective C

[Colin Barrett]

Oh yeah? Well I wrote some awesome machine code out on a box of punch  
cards, and it executes your JMP statements, so now I own all *YOUR*  
stuff!

You just can't beat little tiny holes in paper, man. You just can't.

-Colin

On Mar 5, 2006, at 5:16 PM, Adam Iser wrote:

> I just wrote a block of assembly which JMPs into GPL code (A JMP is  
> not
> a function call! HA! HA!).  All your GPL code are belong to me.
>
> - Adam
>
> Ofri Wolfus wrote:
>
>> Hi everyone,
>>
>> A discussion with David in IRC has lead me to talk with a friend of
>> mine (who is a lawyer) about the nature of objc code released under
>> GPL. As you probably know, a message to an object is translated by
>> the compiler to a call to one of the objc_msgSend() functions.
>> Therefor, you never get to call any 'real' function from your code
>> and you only indirectly call GPL functions.
>> Well, GPL code forbids you from linking to it unless your code is GPL
>> as well, but what happens if the GPL code lives in a plugin which is
>> dynamically loaded? This is what GPL has to say about it (taken from
>> http://www.gnu.org/licenses/gpl-faq.html#GPLAndPlugins):
>>
>> "It depends on how the program invokes its plug-ins. If the program
>> uses fork and exec to invoke plug-ins, then the plug-ins are separate
>> programs, so the license of the plug-in makes no requirements about
>> the main program.
>> If the program dynamically links plug-ins, and they make function
>> calls to each other and share data structures, we believe they form a
>> single program, which must be treated as an extension of both the
>> main program and the plug-ins. In order to use the GPL-covered plug-
>> ins, the main program must be released under the GPL or a GPL-
>> compatible free software license, and that the terms of the GPL must
>> be followed when the main program is distributed for use with these
>> plug-ins.
>> If the program dynamically links plug-ins, but the communication
>> between them is limited to invoking the `main' function of the plug-
>> in with some options and waiting for it to return, that is a
>> borderline case."
>>
>> But message sending is not a function call... Therefor, a message
>> being sent to a GPL class, does not force the sender to be GPL as
>> well. As long as your code does not set instance variables of a GPL
>> class (directly - accessors are fine), use IMP caching or use the
>> @defs() directive, your code DOES NOT have to be released under GPL
>> license.
>>
>> But what about the classes themselves? GPL specifically says that one
>> can not use GPL data structures in a non-GPL code. Well... it doesn't
>> bother us at all since classes are translated by the compiler to the
>> objc_class struct which has no effect on us. The same goes with
>> instances of classes which are translated to pointers to an
>> objc_object struct.
>>
>> Quite revolutionary ha? ;-) Using plugins, commercial apps can take
>> advantage of ANY GPL code that can be wrapped in a cocoa class. Not
>> so good... But for us it also means some good stuff. It means that
>> Adium and ChatKit can use protocol libraries which are not GPL. :D
>>
>> - Ofri
>>
>>
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>>
>>
>>
>>
>
>
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