Genbootstrap prepares GOROOT_BOOTSTRAP tarballs suitable for use on builders. It's a wrapper around bootstrap.bash. After bootstrap.bash produces the full output, genbootstrap trims it up, removing unnecessary and unwanted files.
genbootstrap [-upload] [-rev=rev] [-v] GOOS-GOARCH[-suffix]...
The argument list can be a single glob pattern (for example '*'), which expands to all known targets matching that pattern.