Tiny x86 Length Disassembler
The inspiration for the design of this x86 length disassembler came from Zdisasm by Z0MBiE (I can't actually find this on his page but it's around, just google code search for zdisasm.h) and three ideas presented nicely in a single forum thread:
http://www.devmaster.net/forums/showthread.php?t=2311
The three ideas came from the following posts:
- The original post by Nick (a purely logical length disassembler)
- The post by earlnsk (a Russian switch case length disassembler) The Russian length disassembler can be found here: http://hack-expo.void.ru/groups/blt/text/disasm.txt (Russian) http://z0mbie.daemonlab.org/disasme.txt (English)
- The post by WolfgangSt (bitmap lookup tables)
With these ideas I decided to make a tiny length disassemler in c.
My length disassembler can use logical statements or lookup tables (32 byte bitmap tables) to perform the checks required to determine instruction length. Currently the smallest footprint I have managed is 589 bytes (LengthDisasm function length + 4x32 byte lookup tables). I'm sure there are further optimizations possible (even without using assembly).
I haven't looked into it too much but I don't think it would to too difficult to adapt this approach for x86_64.