[Python-Dev] python, lipo and the future?

[Ronald Oussoren]

On Sep 17, 2006, at 6:53 PM, Martin v. Löwis wrote:

> Ronald Oussoren schrieb:
>> One problem is that python's configure script detects the sizes of
>> various types and those values will be different on 32-bit and 64-bit
>> flavours.
>
> FWIW, the PC build "solves" this problem by providing a hand-crafted
> pyconfig.h file, instead of using an autoconf-generated one.
> That could work for OSX as well, although it is tedious to keep
> the hand-crafted file up-to-date.
>
> For the PC, this isn't really a problem, since Windows doesn't  
> suddenly
> grow new features, at least not those that configure checks for. So
> forking pyconfig.h once and then customizing it for universal binaries
> might work.
>
> Another approach would be to override architecture-specific defines.
> For example, a block
>
> #ifdef __APPLE__
> #include "pyosx.h"
> #endif

Thats what I had started on before Bob came up with the endianness  
check that is in pyconfig.h.in at the moment. I'd to do this instead  
of manually maintaining a fork of pyconfig.h, my guess it is a lot  
less likely that pyconfig.h will grow new size related macros than  
new feature related ones.

One possible issue here is that distutils has an API for fetching  
definitions from pyconfig.h, code that uses this to detect  
architecture features could cause problems.

>
> could be added to the end of pyconfig.h, and then pyosx.h would have
>
> #undef SIZEOF_LONG
>
> #if defined(__i386__) || defined(__ppc__)
> #define SIZEOF_LONG 4
> #elif defined(__amd64__) || defined(__ppc64__)
> #define SIZEOF_LONG 8
> #else
> #error unsupported architecture
> #endif
>
> Out of curiosity: how do the current universal binaries deal with this
> issue?

The sizes of basic types are the same on PPC32 and x86 which helps a  
lot. The byteorder is different, but we can use GCC feature checks  
there. The relevant bit of pyconfig.h.in:

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

Users of pyconfig.h will see the correct definition of  
WORDS_BIGENDIAN regardless of the architecture that was used to  
create the file.

One of the announced features of osx 10.5 is 64-bit support  
throughout the system and I definitely want to see if we can get 4- 
way universal support on such systems. As I don't have a system that  
is capable of running 64-bit code  I'm not going to worry too much  
about this right now :-)

Ronald
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