src/librustc_error_codes/error_codes/E0570.md

   1 The requested ABI is unsupported by the current target.
   2
   3 The rust compiler maintains for each target a blacklist of ABIs unsupported on
   4 that target. If an ABI is present in such a list this usually means that the
   5 target / ABI combination is currently unsupported by llvm.
   6
   7 If necessary, you can circumvent this check using custom target specifications.