[Pythonmac-SIG] building universal binaries

[Kevin Ollivier]

Hi Bob,

On Jan 26, 2006, at 10:55 PM, Bob Ippolito wrote:

[snip]

>> Sorry, I wasn't really thinking about extensions. By Panther I did  
>> mean building against the 10.3.9 SDK, which would give the desired  
>> results for the Python binary itself, but as you said extending  
>> that to correctly build extensions that did the same thing would  
>> be a royal PITA.
>
> You still need to build against two different SDKs, which can't be  
> done with just compiler flags.  You have to do two separate  
> compiles, and then lipo it together.  At that point you might as  
> well use different compilers and target older versions of OS X.

Yes, this was what I meant in my previous email about letting the SDK  
get specified at configure time. I was thinking to have bash script  
that automates the various steps. I guess you could put it into the  
configure script, but that does sound to me to be pretty painful.

> The other thing is that Python's build probably detects a few  
> things at runtime, and at runtime it's seeing 10.4, so it might not  
> actually work on the target version of OS X.

Yeah, if this is the case it'd be a real mess. ;-/

> Ideally all that stuff would be pushed to runtime checks, so that  
> it could choose a different code path based upon which APIs are  
> available... but first you have to isolate the instances where that  
> happens.
>
>>> I think the only approach that doesn't require hacking a  
>>> significant amount of Python's build process and distutils is to  
>>> have two Python installations, one x86 only and one PPC only.   
>>> For distribution, you would cook up some way to lipo it all  
>>> together.
>>
>> I can see how the issues with the strategy I outlined would be  
>> significant, but I don't see how Universal support on Tiger would  
>> be similarly difficult. Apple's Python 2.3.5 already is Universal,  
>> and I'm unaware of any issues with it (except that it doesn't  
>> build Universal extensions ;). The changes they made to the build  
>> process seemed to be fairly minimal.
>
> Yeah, a 10.4+ universal build wouldn't be too big of a deal because  
> you can do that with one invocation of GCC and one set of flags.
>
>> As far as distutils/working with extensions, I admit I'm not very  
>> familiar with that. I did notice when compiling wxPython though  
>> that there weren't any distutils flags passed to gcc that would  
>> conflict with the building of Universal binaries. The main  
>> question in my mind would be whether or not the built Universal  
>> extension libraries could be loaded by Python's dynamic library  
>> loader. If they can be loaded, and we could add the flags to  
>> distutils' default compiler/linker flags, what other major issues  
>> would need to be overcome?
>
> Some extensions aren't going to build cleanly universal, and most  
> users probably aren't going to have all the SDKs installed so if it  
> shipped with universal flags then it wouldn't be able to build  
> extensions.

Unless we had distutils check for the existence of the Universal SDK  
before setting the flags, or probably more accurately, remove them if  
the SDK isn't available. Then perhaps add a distutils 'flag' to  
manually turn off Universal building for extensions that can't be  
fixed. This might be a bit of a hack, but I don't imagine it would be  
too painful. The question is how many extensions would have  
troubles... But I guess the only way we'll know is to test the  
waters. In any case, even if it wouldn't be reasonable to make a  
Universal build the "official" build, it would be very useful to  
people packaging apps, even if it were Tiger+ only.

As far as the SDK dependency issue, IMHO, not everyone would need to  
build Universal - the key would be for distributors/packages to make  
Universal binaries, and I think it would be reasonable for us to tell  
them "have the 10.4u SDK and DevTools installed". (And maybe the  
Panther/Jaguar SDK assuming we could sort the issues you mentioned  
above out...) Again, assuming a Universal build does make a sensible  
default.

Thanks,

Kevin

> -bob
>