8/16/32/64 bit aligned lossless compression of .bss and .data for embedded system core dump

Question

I'm looking for a fast / lossless / fix spaced compression algorithm for the following task.

I have an embedded system. Low memory / flash resource.

I want to generate a core dump for it and store the result in flash and / or suck it out over a slow serial line.

All I need essentially is the heap, stack, .data and .bss segments and a few memory mapped registers.

The device is a Leon Sparc Softcore.

Now this data as a couple of oddities which indicate that

1. The usual LZW / Zlib / ... compression libraries won't do as well. (Not a natural language corpus).
2. Sparcs are obsessive about alignment. ie. I can guarantee that every item in the .bss and .data segments is either (effectively) an 8, 16, 32 or 64 bit int aligned correspondingly at 8,16,32,64 bit address boundaries.
3. I'd have to reserve a small fixed space for the compression code.
4. It's a 32 bit machine with the size of the bss and data segments very much smaller than 4gb.
5. Most 32 bit values in the system are addresses of symbols. ie. A very very small subset of the 4 gig possible values.

My current plan is to... Scan the entire .bss / .data segments and compute a complete histogram for 16 bit values.

From this I can get a perfect huffman encoding. But I suspect I can do a lot better contemplating the internal structure of 32 bit / 64 bit values. (eg. The variability in the most significant half of bits is much much much less than the variability of the least significant bits.)

And pointers / suggestions / existing work?