Re: ABI Compatibility (was Re: Installation woes for the average user...)

[Wolfgang Lux]

David Chisnall wrote:

> On 21 May 2009, at 10:34, Wolfgang Lux wrote:
>
> > Have you ever looked at what Apple is doing? I can use executables  
> > compiled on Mac OS X 10.2 on Mac OS X 10.5 without any problems  
> > and Mac OS X does ship with only a single instance of all its  
> > libraries/frameworks
>
> Only half of this is true.  Apple only ships one version of its  
> frameworks.  Each framework, however, contains different versions  
> of the libraries.  You may have noticed all of the OS X version  
> macros in the headers.  Each of those defines the parts of the  
> interface that are visible in a particular version of the  
> framework, but they are also used when compiling.  Each version of  
> OS X has a Foundation.framework containing several  
> libFoundation.dylib files, one compiled for compatibility with each  
> previous version. Without access to their source, I can't be  
> completely sure how they are doing this, but my guess is that each  
> ivar and each method - even each typedef - has the same feature  
> macros in front of it and their build system automatically  
> generates a backwards-compatible version as long as these changes  
> are made.

I'm sorry, but this is just plain wrong. There is just one  
Foundation, AppKit, etc. library on each system. Maybe you are  
thinking of the libraries in the /Developer/SDKs/MacOSX10xxx.sdk  
directories, but these are just stub libraries that are provided in  
order to allow *linking* of executables for another OS version. These  
stub libraries just contain the necessary symbol definitions but no  
code at all.

> It would be nice if GNUstep make had facilities for doing this, but  
> I imagine it would be a lot of effort.  It would also be easier if  
> we could rely on a loader that supported frameworks properly, but I  
> believe Matt Rice is the only person who has one of these on a non- 
> NeXT/Apple platform.

I don't think that frameworks are the issue here. After all,  
frameworks are just a convenient way to group headers, libraries, and  
resources of a particular project together. Sure, they also provide  
for versioning, but Apple does not seem to use that, e.g., Apple's  
Foundation and AppKit libraries are both at version C since the  
advent of Mac OS X.

Wolfgang