[Pythonmac-SIG] building universal binaries

[Bob Ippolito]

On Jan 27, 2006, at 12:19 AM, Ronald Oussoren wrote:

>
> On 27-jan-2006, at 8:46, Kevin Ollivier wrote:
>
>> On Jan 26, 2006, at 10:55 PM, Bob Ippolito wrote:
>>
>>> 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.
>
> I know of one popular extension (cElementTree) that won't build  
> with '-arch i386 -arch ppc' because it calcutes a #define based on  
> the current byte-order. There might be others, I haven't done a  
> thorough search yet.

In my python24-fat branch, I made the following change to  
pyconfig.h.in which I believe will resolve that issue in any  
extension that doesn't do something dumb like trying to grep the  
endianness out of pyconfig.h:

http://svn.red-bean.com/bob/python24-fat/pyconfig.h.in

/* Define to 1 if your processor stores words with the most  
significant byte
    first (like Motorola and SPARC, unlike Intel and VAX). */
#ifdef __BIG_ENDIAN__
#define WORDS_BIGENDIAN 1
#else
#ifndef __LITTLE_ENDIAN__
#undef WORDS_BIGENDIAN
#endif
#endif

GCC defines __BIG_ENDIAN__ to 1 when it's compiling a big endian  
arch... and __LITTLE_ENDIAN__ to 1 when it's compiling on a little  
endian arch.  Configured on i386, this turns into:

#ifdef __BIG_ENDIAN__
#define WORD_BIGENDIAN 1
#else
#ifndef __LITTLE_ENDIAN__
/* #undef WORDS_BIGENDIAN */
#endif
#endif

When configured on PPC, it turns into:

#ifdef __BIG_ENDIAN__
#define WORD_BIGENDIAN 1
#else
#ifndef __LITTLE_ENDIAN__
#define WORDS_BIGENDIAN 1
#endif
#endif

Since this is GCC, the #ifndef __LITTLE_ENDIAN__ branch is always  
false... so I'm making this a compile-time not configure-time value,  
but I left in the configure-time stuff for other platforms.

-bob