Can a C compiler generate an executable 64-bits where pointers are 32-bits?

Technically, it is possible for a compiler to do so. AFAIK, in practice it isn't done. It has been proposed for gcc (even with a patch here: http://gcc.gnu.org/ml/gcc/2007-10/msg00156.html) but never integrated (at least, it was not documented the last time I checked). My understanding is that it needs also support from the kernel and standard library to work (i.e. the kernel would need to set up things in a way not currently possible and using the existing 32 or 64 bit ABI to communicate with the kernel would not be possible).

A simple way to circumvent this is if you'd have only few types for your structures that you are pointing to. Then you could just allocate big arrays for your data and do the indexing with uint32_t.

So a "pointer" in such a model would be just an index in a global array. Usually addressing with that should be efficient enough with a decent compiler, and it would save you some space. You'd loose other things that you might be interested in, dynamic allocation for instance.

Another way to achieve something similar is to encode a pointer with the difference to its actual location. If you can ensure that that difference always fits into 32 bit, you could gain too.

What exactly are the "64-bit features" you need, isn't that a little vague?

Found this while searching myself for an answer: http://www.codeproject.com/KB/cpp/smallptr.aspx

Also pick up the discussion at the bottom...

Never had any need to think about this, but it is interesting to realize that one can be concerned with how much space pointers need...

It's worth noting that there an ABI in development for linux, X32, that lets you build a x86_64 binary that uses 32 bit indices and addresses.

Only relatively new, but interesting nonetheless.

http://en.wikipedia.org/wiki/X32_ABI