On Thu, Jul 02, 2009 at 06:54:52PM -0400, Ken Raeburn wrote: > On Jul 2, 2009, at 16:44, Michael Meissner wrote: >> Anyway I had some time during the summit, and I decided to see how >> hard it >> would be to add explicit big/little endian support to the powerpc >> port. It >> only took a few hours to add the support for __little and __big >> qualifier >> keywords, and in fact more time to get the byte swap instructions >> nailed down > > That sounds great! > >> (there are restrictions that named >> address space variables can only be global/static or referenced >> through a >> pointer). > > That sounds like a potential problem, depending on the use cases. No > structure field members with explicit byte order? That could be > annoying for dealing with network protocols or file formats with > explicit byte ordering.
The technical report that named address spaces is based on does not allow you to mix address spaces within a structure (pointers to different address spaces can be mixed, just not the data themselves). For example, stack variables are always in the generic address space. I do tend to think it would be better to have little/big be more offical than a target specific thing. However, most of the places you need to modify for named address spaces are the places you need to modify for mixed endian. > On the other hand, if we're talking about address spaces... I would > guess you could apply it to a structure? That would be good for > memory-mapped devices accepting only one byte order that may not be that > of the main CPU. For that use case, it would be unfortunate to have to > tag every integer field. > > I don't think Paul indicated what his use case was... -- Michael Meissner, IBM 4 Technology Place Drive, MS 2203A, Westford, MA, 01886, USA meiss...@linux.vnet.ibm.com
