diff --git a/Cargo.toml b/Cargo.toml
index 2982f29..1fc98a7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,9 +2,9 @@
 authors = ["The Rust Project Developers"]
 name = "compiletest"
 version = "0.0.0"
-build = "build.rs"
 
 [dependencies]
 log = "0.3"
 env_logger = { version = "0.3.5", default-features = false }
 rustc-serialize = "0.3"
+filetime = "0.1"
diff --git a/build.rs b/build.rs
deleted file mode 100644
index d5164b9..0000000
--- a/build.rs
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-fn main() {
-    println!("cargo:rustc-cfg=cargobuild");
-}
diff --git a/src/header.rs b/src/header.rs
index 71d8d62..522cd22 100644
--- a/src/header.rs
+++ b/src/header.rs
@@ -25,6 +25,7 @@ use extract_gdb_version;
 pub struct EarlyProps {
     pub ignore: bool,
     pub should_fail: bool,
+    pub aux: Vec<String>,
 }
 
 impl EarlyProps {
@@ -32,6 +33,7 @@ impl EarlyProps {
         let mut props = EarlyProps {
             ignore: false,
             should_fail: false,
+            aux: Vec::new(),
         };
 
         iter_header(testfile,
@@ -50,6 +52,10 @@ impl EarlyProps {
                 ignore_lldb(config, ln) ||
                 ignore_llvm(config, ln);
 
+            if let Some(s) = parse_aux_build(ln) {
+                props.aux.push(s);
+            }
+
             props.should_fail = props.should_fail || parse_name_directive(ln, "should-fail");
         });
 
diff --git a/src/main.rs b/src/main.rs
index 40ba66a..5a97f7e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -21,17 +21,11 @@
 extern crate libc;
 extern crate test;
 extern crate getopts;
-
-#[cfg(cargobuild)]
 extern crate rustc_serialize;
-#[cfg(not(cargobuild))]
-extern crate serialize as rustc_serialize;
-
 #[macro_use]
 extern crate log;
-
-#[cfg(cargobuild)]
 extern crate env_logger;
+extern crate filetime;
 
 use std::env;
 use std::ffi::OsString;
@@ -39,6 +33,7 @@ use std::fs;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use filetime::FileTime;
 use getopts::{optopt, optflag, reqopt};
 use common::Config;
 use common::{Pretty, DebugInfoGdb, DebugInfoLldb, Mode};
@@ -58,11 +53,7 @@ mod raise_fd_limit;
 mod uidiff;
 
 fn main() {
-    #[cfg(cargobuild)]
-    fn log_init() { env_logger::init().unwrap(); }
-    #[cfg(not(cargobuild))]
-    fn log_init() {}
-    log_init();
+    env_logger::init().unwrap();
 
     let config = parse_config(env::args().collect());
 
@@ -478,7 +469,7 @@ pub fn make_test(config: &Config, testpaths: &TestPaths) -> test::TestDescAndFn
     };
 
     // Debugging emscripten code doesn't make sense today
-    let mut ignore = early_props.ignore;
+    let mut ignore = early_props.ignore || !up_to_date(config, testpaths, &early_props);
     if (config.mode == DebugInfoGdb || config.mode == DebugInfoLldb) &&
         config.target.contains("emscripten") {
         ignore = true;
@@ -494,6 +485,42 @@ pub fn make_test(config: &Config, testpaths: &TestPaths) -> test::TestDescAndFn
     }
 }
 
+fn stamp(config: &Config, testpaths: &TestPaths) -> PathBuf {
+    let stamp_name = format!("{}-H-{}-T-{}-S-{}.stamp",
+                             testpaths.file.file_name().unwrap()
+                                           .to_str().unwrap(),
+                             config.host,
+                             config.target,
+                             config.stage_id);
+    config.build_base.canonicalize()
+          .unwrap_or(config.build_base.clone())
+          .join(stamp_name)
+}
+
+fn up_to_date(config: &Config, testpaths: &TestPaths, props: &EarlyProps) -> bool {
+    let stamp = mtime(&stamp(config, testpaths));
+    let mut inputs = vec![
+        mtime(&testpaths.file),
+        mtime(&config.rustc_path),
+    ];
+    for aux in props.aux.iter() {
+        inputs.push(mtime(&testpaths.file.parent().unwrap()
+                                         .join("auxiliary")
+                                         .join(aux)));
+    }
+    for lib in config.run_lib_path.read_dir().unwrap() {
+        let lib = lib.unwrap();
+        inputs.push(mtime(&lib.path()));
+    }
+    inputs.iter().any(|input| *input > stamp)
+}
+
+fn mtime(path: &Path) -> FileTime {
+    fs::metadata(path).map(|f| {
+        FileTime::from_last_modification_time(&f)
+    }).unwrap_or(FileTime::zero())
+}
+
 pub fn make_test_name(config: &Config, testpaths: &TestPaths) -> test::TestName {
     // Convert a complete path to something like
     //
diff --git a/src/runtest.rs b/src/runtest.rs
index 9f7d415..bcec1f6 100644
--- a/src/runtest.rs
+++ b/src/runtest.rs
@@ -80,6 +80,8 @@ pub fn run(config: Config, testpaths: &TestPaths) {
     }
 
     base_cx.complete_all();
+
+    File::create(::stamp(&config, &testpaths)).unwrap();
 }
 
 struct TestCx<'test> {