I just took a short look at the API and it seems that you have to create a alternative
std something like using cfg to add some "additional" parts for capabilities won't work as some of the syscall's std uses are not available.
The most simple example is
open, the variation of
open in CoudABI is very similar to the
openat system call, except that the mode parameter takes a different struct which does some more then what the mode parameter in linux
But then I think rust, at some point, needs support for alternative stable std's anyway. At last if rust wants to take over micro-controllers (!= microprocessors).