There are several areas of potential architectural difference that the tool looks for and flags, but it is not an exhaustive list. The thought process used is sort of the 80/20 rule. Since it is not the front end of a compiler, it will not catch endian problems in structures etc.
Items that are noted are double precision floating point, ioctls, builtins, assembler calls, and mismatches in calling sequences and global variable declarations. The latter can expose endian problems when moving to different hardware.
