remove usage of absolute rpaths

This is a significant security issue as it adds a hidden library path
based on the location of the build directory. It is *always* wrong in an
installed package, and can be leveraged by an unprivileged user to
inject libraries into a binary called by another user or even root.

Closes #11746

This is a step towards fixing #11747 but is only a partial solution.

src/librustc/back/rpath.rs

@@ -86,10 +86,6 @@ fn get_rpaths(os: abi::Os,
     // crates they depend on.
     let rel_rpaths = get_rpaths_relative_to_output(os, output, libs);
 
-    // Make backup absolute paths to the libraries. Binaries can
-    // be moved as long as the crates they link against don't move.
-    let abs_rpaths = get_absolute_rpaths(libs);
-
     // And a final backup rpath to the global library location.
     let fallback_rpaths = ~[get_install_prefix_rpath(target_triple)];
 
@@ -101,11 +97,9 @@ fn get_rpaths(os: abi::Os,
     }
 
     log_rpaths("relative", rel_rpaths);
-    log_rpaths("absolute", abs_rpaths);
     log_rpaths("fallback", fallback_rpaths);
 
     let mut rpaths = rel_rpaths;
-    rpaths.push_all(abs_rpaths);
     rpaths.push_all(fallback_rpaths);
 
     // Remove duplicates
@@ -145,17 +139,6 @@ pub fn get_rpath_relative_to_output(os: abi::Os,
     prefix+"/"+relative.as_str().expect("non-utf8 component in path")
 }
 
-fn get_absolute_rpaths(libs: &[Path]) -> ~[~str] {
-    libs.iter().map(|a| get_absolute_rpath(a)).collect()
-}
-
-pub fn get_absolute_rpath(lib: &Path) -> ~str {
-    let mut p = os::make_absolute(lib);
-    p.pop();
-    // FIXME (#9639): This needs to handle non-utf8 paths
-    p.as_str().expect("non-utf8 component in rpath").to_owned()
-}
-
 pub fn get_install_prefix_rpath(target_triple: &str) -> ~str {
     let install_prefix = env!("CFG_PREFIX");
 
@@ -182,7 +165,7 @@ pub fn minimize_rpaths(rpaths: &[~str]) -> ~[~str] {
 mod test {
     use std::os;
 
-    use back::rpath::{get_absolute_rpath, get_install_prefix_rpath};
+    use back::rpath::get_install_prefix_rpath;
     use back::rpath::{minimize_rpaths, rpaths_to_flags, get_rpath_relative_to_output};
     use syntax::abi;
     use metadata::filesearch;
@@ -255,15 +238,4 @@ mod test {
                                                &Path::new("lib/libstd.so"));
         assert_eq!(res.as_slice(), "@loader_path/../lib");
     }
-
-    #[test]
-    fn test_get_absolute_rpath() {
-        let res = get_absolute_rpath(&Path::new("lib/libstd.so"));
-        let lib = os::make_absolute(&Path::new("lib"));
-        debug!("test_get_absolute_rpath: {} vs. {}",
-               res.to_str(), lib.display());
-
-        // FIXME (#9639): This needs to handle non-utf8 paths
-        assert_eq!(res.as_slice(), lib.as_str().expect("non-utf8 component in path"));
-    }
 }