The idea is to provide a path prefix to find binaries that will be relative to the root on the target system.  We're already pretty good about versioning when it comes to kernel files, but we need this mechanism to access userspace paths that may be totally different on the compile host and the target.  So given:

  stap --sysroot=/foo -l 'process("/bin/ls").function("*")'

We'd actually examine /foo/bin/ls for potential probes.  But when they are used, the runtime would match the path on the target without the sysroot prefix.

This mechanism may also be useful for a compile server to isolate access from unwanted paths like autofs /net.