Is it possible to dynamically link 32bit program to 64bit shared libraries in Linux64?
Of course the code that calls imported functions should be 64bit. But the other code of the program is 32bit.
So the question is also "Is it possible to mix 32 and 64 bit code in one program?

It is possible, but you need support from the OS to switch modes. Also be aware that the addressing would likely need to all be below the 4G limit and the page tables would need to match. I have no idea if Linux supports such a scheme as this:

http://board.flatassembler.net/topic.php?p=140791#140791

Maybe I have to explain more detailed what I actually need. It is known that 64bit Linux can run 32 bit applications natively but only if they does not use shared libraries. 32bit system calls are kernel supported.
There is a 32bit compatibility package that contains all needed 32bit libraries but it have to be installed. Otherwise, LD linker will not be able to find needed libraries and will fail to load application.

On the other hand, in FreshLib, because of its architecture, I have wrapper functions for all needed functions imported from the shared libraries.
So, I can make Linux64 layer that to import directly from 64bit libraries and this way to allow FreshLib applications to run on 64bit Linux without installing 32bit compatibility package.

Another way is to implement all needed functionality using only system calls, what is possible, but not practical in this moment.

How would your asm file look? Like this?

Well, I have no experience in 64 bit programming. Maybe something like:

You have to get cooperation from the OS to switch operating mode. You can't do it only with user mode code. You have to either change the current segment descriptor or select another descriptor that is already prepared.

Also, if you allocate memory in 64-bit mode then how do you ensure it is accessible in 32-bit mode? The memory regions might be very different.

Yes, I am sure that this is what I have to do. Maybe Linux64 has some syscall about changing modes?

Sorry I can´t give a thorough look into this so this link may not be helpful: http://en.wikipedia.org/wiki/X32_ABI (also notice that perhaps this is not here yet)

That is still running 64-bit code but appears to be using a coding method to reduce code-size/instruction-count if it can be assumed that all pointers and offsets are <=32 bits. This is probably something we do automatically as assembly programmers anyhow so there is no benefit to us.