diff --git a/Cargo.lock b/Cargo.lock
index c34a325a47492..bf568cd9e22eb 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2540,6 +2540,7 @@ version = "0.0.0"
 dependencies = [
  "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.82 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-width 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2604,6 +2605,7 @@ dependencies = [
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_cratesio_shim 0.0.0",
  "rustc_data_structures 0.0.0",
+ "serde 1.0.82 (registry+https://github.com/rust-lang/crates.io-index)",
  "serialize 0.0.0",
  "syntax_pos 0.0.0",
  "termcolor 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3217,6 +3219,7 @@ dependencies = [
  "cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_data_structures 0.0.0",
  "scoped-tls 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.82 (registry+https://github.com/rust-lang/crates.io-index)",
  "serialize 0.0.0",
  "unicode-width 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
diff --git a/src/bootstrap/bin/rustc.rs b/src/bootstrap/bin/rustc.rs
index a0c75cd9e9476..d8919ceb8cba9 100644
--- a/src/bootstrap/bin/rustc.rs
+++ b/src/bootstrap/bin/rustc.rs
@@ -109,6 +109,12 @@ fn main() {
         // actually downloaded, so we just always pass the `--sysroot` option.
         cmd.arg("--sysroot").arg(&sysroot);
 
+        // Link crates to the proc macro crate for the target, but use a host proc macro crate
+        // to actually run the macros
+        if env::var_os("RUST_DUAL_PROC_MACROS").is_some() {
+            cmd.arg("-Zdual-proc-macros");
+        }
+
         // When we build Rust dylibs they're all intended for intermediate
         // usage, so make sure we pass the -Cprefer-dynamic flag instead of
         // linking all deps statically into the dylib.
@@ -258,13 +264,6 @@ fn main() {
             }
         }
 
-        // Force all crates compiled by this compiler to (a) be unstable and (b)
-        // allow the `rustc_private` feature to link to other unstable crates
-        // also in the sysroot.
-        if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() {
-            cmd.arg("-Z").arg("force-unstable-if-unmarked");
-        }
-
         if let Ok(map) = env::var("RUSTC_DEBUGINFO_MAP") {
             cmd.arg("--remap-path-prefix").arg(&map);
         }
@@ -284,6 +283,14 @@ fn main() {
         }
     }
 
+    // Force all crates compiled by this compiler to (a) be unstable and (b)
+    // allow the `rustc_private` feature to link to other unstable crates
+    // also in the sysroot. We also do this for host crates, since those
+    // may be proc macros, in which case we might ship them.
+    if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() && (stage != "0" || target.is_some()) {
+        cmd.arg("-Z").arg("force-unstable-if-unmarked");
+    }
+
     if env::var_os("RUSTC_PARALLEL_QUERIES").is_some() {
         cmd.arg("--cfg").arg("parallel_queries");
     }
diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index f742bce180c05..ec6bac51de7a3 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -608,6 +608,7 @@ impl<'a> Builder<'a> {
                     .join(self.target)
                     .join("lib");
                 let _ = fs::remove_dir_all(&sysroot);
+                eprintln!("creating sysroot {:?}", sysroot);
                 t!(fs::create_dir_all(&sysroot));
                 INTERNER.intern_path(sysroot)
             }
@@ -811,6 +812,17 @@ impl<'a> Builder<'a> {
             cargo.env("RUST_CHECK", "1");
         }
 
+        match mode {
+            Mode::Std | Mode::Test | Mode::ToolBootstrap | Mode::ToolStd | Mode::ToolTest=> {},
+            Mode::Rustc | Mode::Codegen | Mode::ToolRustc => {
+                // Build proc macros both for the host and the target
+                if target != compiler.host && cmd != "check" {
+                    cargo.arg("-Zdual-proc-macros");
+                    cargo.env("RUST_DUAL_PROC_MACROS", "1");
+                }
+            },
+        }
+
         cargo.arg("-j").arg(self.jobs().to_string());
         // Remove make-related flags to ensure Cargo can correctly set things up
         cargo.env_remove("MAKEFLAGS");
diff --git a/src/bootstrap/check.rs b/src/bootstrap/check.rs
index cc539d4c89571..e9ad1c9cb971f 100644
--- a/src/bootstrap/check.rs
+++ b/src/bootstrap/check.rs
@@ -42,7 +42,8 @@ impl Step for Std {
                   true);
 
         let libdir = builder.sysroot_libdir(compiler, target);
-        add_to_sysroot(&builder, &libdir, &libstd_stamp(builder, compiler, target));
+        let hostdir = builder.sysroot_libdir(compiler, compiler.host);
+        add_to_sysroot(&builder, &libdir, &hostdir, &libstd_stamp(builder, compiler, target));
     }
 }
 
@@ -88,7 +89,8 @@ impl Step for Rustc {
                   true);
 
         let libdir = builder.sysroot_libdir(compiler, target);
-        add_to_sysroot(&builder, &libdir, &librustc_stamp(builder, compiler, target));
+        let hostdir = builder.sysroot_libdir(compiler, compiler.host);
+        add_to_sysroot(&builder, &libdir, &hostdir, &librustc_stamp(builder, compiler, target));
     }
 }
 
@@ -175,7 +177,8 @@ impl Step for Test {
                   true);
 
         let libdir = builder.sysroot_libdir(compiler, target);
-        add_to_sysroot(builder, &libdir, &libtest_stamp(builder, compiler, target));
+        let hostdir = builder.sysroot_libdir(compiler, compiler.host);
+        add_to_sysroot(builder, &libdir, &hostdir, &libtest_stamp(builder, compiler, target));
     }
 }
 
@@ -222,7 +225,8 @@ impl Step for Rustdoc {
                   true);
 
         let libdir = builder.sysroot_libdir(compiler, target);
-        add_to_sysroot(&builder, &libdir, &rustdoc_stamp(builder, compiler, target));
+        let hostdir = builder.sysroot_libdir(compiler, compiler.host);
+        add_to_sysroot(&builder, &libdir, &hostdir, &rustdoc_stamp(builder, compiler, target));
         builder.cargo(compiler, Mode::ToolRustc, target, "clean");
     }
 }
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index ec04dee6c32f0..f648b40bb2ace 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -224,7 +224,8 @@ impl Step for StdLink {
                 target_compiler.host,
                 target));
         let libdir = builder.sysroot_libdir(target_compiler, target);
-        add_to_sysroot(builder, &libdir, &libstd_stamp(builder, compiler, target));
+        let hostdir = builder.sysroot_libdir(target_compiler, compiler.host);
+        add_to_sysroot(builder, &libdir, &hostdir, &libstd_stamp(builder, compiler, target));
 
         if builder.config.sanitizers && compiler.stage != 0 && target == "x86_64-apple-darwin" {
             // The sanitizers are only built in stage1 or above, so the dylibs will
@@ -426,8 +427,12 @@ impl Step for TestLink {
                 &compiler.host,
                 target_compiler.host,
                 target));
-        add_to_sysroot(builder, &builder.sysroot_libdir(target_compiler, target),
-                    &libtest_stamp(builder, compiler, target));
+        add_to_sysroot(
+            builder,
+            &builder.sysroot_libdir(target_compiler, target),
+            &builder.sysroot_libdir(target_compiler, compiler.host),
+            &libtest_stamp(builder, compiler, target)
+        );
 
         builder.cargo(target_compiler, Mode::ToolTest, target, "clean");
     }
@@ -491,8 +496,8 @@ impl Step for Rustc {
             return;
         }
 
-        // Ensure that build scripts have a std to link against.
-        builder.ensure(Std {
+        // Ensure that build scripts and proc macros have a std / libproc_macro to link against.
+        builder.ensure(Test {
             compiler: builder.compiler(self.compiler.stage, builder.config.build),
             target: builder.config.build,
         });
@@ -587,8 +592,12 @@ impl Step for RustcLink {
                  &compiler.host,
                  target_compiler.host,
                  target));
-        add_to_sysroot(builder, &builder.sysroot_libdir(target_compiler, target),
-                       &librustc_stamp(builder, compiler, target));
+        add_to_sysroot(
+            builder,
+            &builder.sysroot_libdir(target_compiler, target),
+            &builder.sysroot_libdir(target_compiler, compiler.host),
+            &librustc_stamp(builder, compiler, target)
+        );
         builder.cargo(target_compiler, Mode::ToolRustc, target, "clean");
     }
 }
@@ -996,10 +1005,22 @@ impl Step for Assemble {
 ///
 /// For a particular stage this will link the file listed in `stamp` into the
 /// `sysroot_dst` provided.
-pub fn add_to_sysroot(builder: &Builder, sysroot_dst: &Path, stamp: &Path) {
+pub fn add_to_sysroot(
+    builder: &Builder,
+    sysroot_dst: &Path,
+    sysroot_host_dst: &Path,
+    stamp: &Path
+) {
+    //eprintln!("add_to_sysroot - host dir {:?} - stamp {:?}", sysroot_host_dst, stamp);
     t!(fs::create_dir_all(&sysroot_dst));
-    for path in builder.read_stamp_file(stamp) {
-        builder.copy(&path, &sysroot_dst.join(path.file_name().unwrap()));
+    t!(fs::create_dir_all(&sysroot_host_dst));
+    for (path, host) in builder.read_stamp_file(stamp) {
+        if host {
+            eprintln!("add_to_sysroot host - copying {:?} to {:?}", path, sysroot_host_dst);
+            builder.copy(&path, &sysroot_host_dst.join(path.file_name().unwrap()));
+        } else {
+            builder.copy(&path, &sysroot_dst.join(path.file_name().unwrap()));
+        }
     }
 }
 
@@ -1028,8 +1049,14 @@ pub fn run_cargo(builder: &Builder,
     let mut deps = Vec::new();
     let mut toplevel = Vec::new();
     let ok = stream_cargo(builder, cargo, &mut |msg| {
-        let filenames = match msg {
-            CargoMessage::CompilerArtifact { filenames, .. } => filenames,
+        let (filenames, crate_types) = match msg {
+            CargoMessage::CompilerArtifact {
+                filenames,
+                target: CargoTarget {
+                    crate_types,
+                },
+                ..
+            } => (filenames, crate_types),
             _ => return,
         };
         for filename in filenames {
@@ -1044,15 +1071,19 @@ pub fn run_cargo(builder: &Builder,
             let filename = Path::new(&*filename);
 
             // If this was an output file in the "host dir" we don't actually
-            // worry about it, it's not relevant for us.
+            // worry about it, it's not relevant for us
             if filename.starts_with(&host_root_dir) {
+                // Unless it's a proc macro used in the compiler
+                if crate_types.iter().any(|t| t == "proc-macro") {
+                    deps.push((filename.to_path_buf(), true));
+                }
                 continue;
             }
 
             // If this was output in the `deps` dir then this is a precise file
             // name (hash included) so we start tracking it.
             if filename.starts_with(&target_deps_dir) {
-                deps.push(filename.to_path_buf());
+                deps.push((filename.to_path_buf(), false));
                 continue;
             }
 
@@ -1105,10 +1136,10 @@ pub fn run_cargo(builder: &Builder,
             let candidate = format!("{}.lib", path_to_add);
             let candidate = PathBuf::from(candidate);
             if candidate.exists() {
-                deps.push(candidate);
+                deps.push((candidate, false));
             }
         }
-        deps.push(path_to_add.into());
+        deps.push((path_to_add.into(), false));
     }
 
     // Now we want to update the contents of the stamp file, if necessary. First
@@ -1121,12 +1152,13 @@ pub fn run_cargo(builder: &Builder,
     let mut new_contents = Vec::new();
     let mut max = None;
     let mut max_path = None;
-    for dep in deps.iter() {
+    for (dep, proc_macro) in deps.iter() {
         let mtime = mtime(dep);
         if Some(mtime) > max {
             max = Some(mtime);
             max_path = Some(dep.clone());
         }
+        new_contents.extend(if *proc_macro { b"h" } else { b"t" });
         new_contents.extend(dep.to_str().unwrap().as_bytes());
         new_contents.extend(b"\0");
     }
@@ -1138,7 +1170,7 @@ pub fn run_cargo(builder: &Builder,
     if contents_equal && max <= stamp_mtime {
         builder.verbose(&format!("not updating {:?}; contents equal and {:?} <= {:?}",
                 stamp, max, stamp_mtime));
-        return deps
+        return deps.into_iter().map(|(d, _)| d).collect()
     }
     if max > stamp_mtime {
         builder.verbose(&format!("updating {:?} as {:?} changed", stamp, max_path));
@@ -1146,7 +1178,7 @@ pub fn run_cargo(builder: &Builder,
         builder.verbose(&format!("updating {:?} as deps changed", stamp));
     }
     t!(fs::write(&stamp, &new_contents));
-    deps
+    deps.into_iter().map(|(d, _)| d).collect()
 }
 
 pub fn stream_cargo(
@@ -1192,6 +1224,11 @@ pub fn stream_cargo(
     status.success()
 }
 
+#[derive(Deserialize)]
+pub struct CargoTarget<'a> {
+    crate_types: Vec<Cow<'a, str>>,
+}
+
 #[derive(Deserialize)]
 #[serde(tag = "reason", rename_all = "kebab-case")]
 pub enum CargoMessage<'a> {
@@ -1199,6 +1236,7 @@ pub enum CargoMessage<'a> {
         package_id: Cow<'a, str>,
         features: Vec<Cow<'a, str>>,
         filenames: Vec<Cow<'a, str>>,
+        target: CargoTarget<'a>,
     },
     BuildScriptExecuted {
         package_id: Cow<'a, str>,
diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index 7b70236dfe8e6..67c4c4a07e5ce 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -43,6 +43,7 @@ def v(*args):
 o("sccache", None, "invoke gcc/clang via sccache to reuse object files between builds")
 o("local-rust", None, "use an installed rustc rather than downloading a snapshot")
 v("local-rust-root", None, "set prefix for local rust binary")
+v("local-cargo", None, "set prefix for local rust binary")
 o("local-rebuild", "build.local-rebuild", "assume local-rust matches the current version, for rebuilds; implies local-rust, and is implied if local-rust already matches the current version")
 o("llvm-static-stdcpp", "llvm.static-libstdcpp", "statically link to libstdc++ for LLVM")
 o("llvm-link-shared", "llvm.link-shared", "prefer shared linking to LLVM (llvm-config --link-shared)")
@@ -320,6 +321,8 @@ def set(key, value):
     elif option.name == 'local-rust-root':
         set('build.rustc', value + '/bin/rustc')
         set('build.cargo', value + '/bin/cargo')
+    elif option.name == 'local-cargo':
+        set('build.cargo', value)
     elif option.name == 'llvm-root':
         set('target.{}.llvm-config'.format(build()), value + '/bin/llvm-config')
     elif option.name == 'llvm-config':
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 32b03c5fb1b7c..cc61281b0b3b9 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -104,7 +104,7 @@
 //! also check out the `src/bootstrap/README.md` file for more information.
 
 #![deny(bare_trait_objects)]
-#![deny(warnings)]
+//#![deny(warnings)]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 
@@ -1142,7 +1142,7 @@ impl Build {
         ret
     }
 
-    fn read_stamp_file(&self, stamp: &Path) -> Vec<PathBuf> {
+    fn read_stamp_file(&self, stamp: &Path) -> Vec<(PathBuf, bool)> {
         if self.config.dry_run {
             return Vec::new();
         }
@@ -1155,8 +1155,9 @@ impl Build {
             if part.is_empty() {
                 continue
             }
-            let path = PathBuf::from(t!(str::from_utf8(part)));
-            paths.push(path);
+            let host = part[0] as char == 'h';
+            let path = PathBuf::from(t!(str::from_utf8(&part[1..])));
+            paths.push((path, host));
         }
         paths
     }
diff --git a/src/bootstrap/mk/Makefile.in b/src/bootstrap/mk/Makefile.in
index 1c27cf3909b1a..bd5d4d8d52098 100644
--- a/src/bootstrap/mk/Makefile.in
+++ b/src/bootstrap/mk/Makefile.in
@@ -1,9 +1,9 @@
 ifdef VERBOSE
 Q :=
-BOOTSTRAP_ARGS := -v
+BOOTSTRAP_ARGS := -vv
 else
 Q := @
-BOOTSTRAP_ARGS :=
+BOOTSTRAP_ARGS := -vv
 endif
 
 ifdef EXCLUDE_CARGO
@@ -12,11 +12,11 @@ else
 AUX_ARGS := src/tools/cargo src/tools/cargotest
 endif
 
-BOOTSTRAP := $(CFG_PYTHON) $(CFG_SRC_DIR)src/bootstrap/bootstrap.py
+BOOTSTRAP := $(CFG_PYTHON) $(CFG_SRC_DIR)src/bootstrap/bootstrap.py -vv
 
 all:
-	$(Q)$(BOOTSTRAP) build $(BOOTSTRAP_ARGS)
-	$(Q)$(BOOTSTRAP) doc $(BOOTSTRAP_ARGS)
+	$(Q)$(BOOTSTRAP) build -vv $(BOOTSTRAP_ARGS)
+	$(Q)$(BOOTSTRAP) doc -vv $(BOOTSTRAP_ARGS)
 
 help:
 	$(Q)echo 'Welcome to the rustbuild build system!'
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 216649808e2a4..3bf20c9c7e1ea 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -213,7 +213,7 @@ impl Step for Cargo {
         });
         let mut cargo = tool::prepare_tool_cargo(builder,
                                                  compiler,
-                                                 Mode::ToolRustc,
+                                                 Mode::ToolStd,
                                                  self.host,
                                                  "test",
                                                  "src/tools/cargo",
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 9f6db73e6f713..7c4e3d9ae13e9 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -92,7 +92,8 @@ impl Step for ToolBuild {
                 compile::CargoMessage::CompilerArtifact {
                     package_id,
                     features,
-                    filenames
+                    filenames,
+                    target: _,
                 } => {
                     (package_id, features, filenames)
                 }
@@ -514,7 +515,7 @@ impl Step for Cargo {
             compiler: self.compiler,
             target: self.target,
             tool: "cargo",
-            mode: Mode::ToolRustc,
+            mode: Mode::ToolStd,
             path: "src/tools/cargo",
             is_optional_tool: false,
             source_type: SourceType::Submodule,
diff --git a/src/ci/docker/dist-arm-linux/Dockerfile b/src/ci/docker/dist-arm-linux/Dockerfile
index 6ddc5c1e04ae3..e8f2a0b5125ad 100644
--- a/src/ci/docker/dist-arm-linux/Dockerfile
+++ b/src/ci/docker/dist-arm-linux/Dockerfile
@@ -32,5 +32,5 @@ ENV CC_arm_unknown_linux_gnueabi=arm-unknown-linux-gnueabi-gcc \
 
 ENV HOSTS=arm-unknown-linux-gnueabi
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
-ENV SCRIPT python2.7 ../x.py dist --host $HOSTS --target $HOSTS
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs --local-cargo=/cargobin/target/release/cargo
+ENV SCRIPT python2.7 ../x.py dist -vv --host $HOSTS --target $HOSTS
diff --git a/src/ci/docker/run.sh b/src/ci/docker/run.sh
index ad6188568cff2..c65511d653128 100755
--- a/src/ci/docker/run.sh
+++ b/src/ci/docker/run.sh
@@ -127,6 +127,7 @@ exec docker \
   --env TRAVIS_BRANCH \
   --env TOOLSTATE_REPO_ACCESS_TOKEN \
   --env CI_JOB_NAME="${CI_JOB_NAME-$IMAGE}" \
+  --volume "/home/john/dev/cargo:/cargobin" \
   --volume "$HOME/.cargo:/cargo" \
   --volume "$HOME/rustsrc:$HOME/rustsrc" \
   --init \
diff --git a/src/ci/run.sh b/src/ci/run.sh
index b0e1b1651055f..9ef32ad55a6f0 100755
--- a/src/ci/run.sh
+++ b/src/ci/run.sh
@@ -88,6 +88,10 @@ if [ "$RUN_CHECK_WITH_PARALLEL_QUERIES" != "" ]; then
   rm -rf build
 fi
 
+#sh -x -c "curl https://sh.rustup.rs -sSf | sh -s -- -y"
+
+#sh -x -c "cd /cargobin; /cargo/bin/cargo build --release"
+
 travis_fold start configure
 travis_time_start
 $SRC/configure $RUST_CONFIGURE_ARGS
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index e2f4049b1db28..ca75703c29541 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1216,6 +1216,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
          Use with RUST_REGION_GRAPH=help for more info"),
     parse_only: bool = (false, parse_bool, [UNTRACKED],
         "parse only; do not compile, assemble, or link"),
+    dual_proc_macros: bool = (false, parse_bool, [TRACKED],
+        "load proc macros for both target and host, but only link to the target"),
     no_codegen: bool = (false, parse_bool, [TRACKED],
         "run all passes except codegen; no output"),
     treat_err_as_bug: bool = (false, parse_bool, [TRACKED],
diff --git a/src/librustc/session/filesearch.rs b/src/librustc/session/filesearch.rs
index 19f1c7a18fad1..ef83967b8ece3 100644
--- a/src/librustc/session/filesearch.rs
+++ b/src/librustc/session/filesearch.rs
@@ -18,6 +18,7 @@ pub enum FileMatch {
 
 // A module for searching for libraries
 
+#[derive(Clone)]
 pub struct FileSearch<'a> {
     sysroot: &'a Path,
     triple: &'a str,
diff --git a/src/librustc_cratesio_shim/Cargo.toml b/src/librustc_cratesio_shim/Cargo.toml
index b8e494e4040ec..5540521868e88 100644
--- a/src/librustc_cratesio_shim/Cargo.toml
+++ b/src/librustc_cratesio_shim/Cargo.toml
@@ -22,4 +22,5 @@ crate-type = ["dylib"]
 [dependencies]
 bitflags = "1.0"
 log = "0.4"
+serde = { version = "1.0", features = ["serde_derive"] }
 unicode-width = "0.1.4"
diff --git a/src/librustc_cratesio_shim/src/lib.rs b/src/librustc_cratesio_shim/src/lib.rs
index 4024087f4d3ef..fd50cf11ab91e 100644
--- a/src/librustc_cratesio_shim/src/lib.rs
+++ b/src/librustc_cratesio_shim/src/lib.rs
@@ -6,4 +6,5 @@
 extern crate bitflags;
 extern crate log;
 extern crate proc_macro;
+extern crate serde;
 extern crate unicode_width;
diff --git a/src/librustc_errors/Cargo.toml b/src/librustc_errors/Cargo.toml
index b24f8ddf4d9f7..666ea4fd99781 100644
--- a/src/librustc_errors/Cargo.toml
+++ b/src/librustc_errors/Cargo.toml
@@ -14,6 +14,7 @@ serialize = { path = "../libserialize" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_cratesio_shim = { path = "../librustc_cratesio_shim" }
+serde = { version = "1.0", features = ["serde_derive"] }
 unicode-width = "0.1.4"
 atty = "0.2"
 termcolor = "1.0"
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index 64d5ca0c2a742..e16d087dae517 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -16,6 +16,7 @@ extern crate libc;
 #[macro_use]
 extern crate log;
 extern crate rustc_data_structures;
+extern crate serde;
 extern crate serialize as rustc_serialize;
 extern crate syntax_pos;
 extern crate unicode_width;
@@ -35,6 +36,8 @@ use std::cell::Cell;
 use std::{error, fmt};
 use std::panic;
 
+use serde::{Serialize, Deserialize};
+
 use termcolor::{ColorSpec, Color};
 
 mod diagnostic;
@@ -59,7 +62,8 @@ use syntax_pos::{BytePos,
 /// All suggestions are marked with an `Applicability`. Tools use the applicability of a suggestion
 /// to determine whether it should be automatically applied or if the user should be consulted
 /// before applying the suggestion.
-#[derive(Copy, Clone, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Copy, Clone, Debug, PartialEq, Hash,
+         RustcEncodable, RustcDecodable, Serialize, Deserialize)]
 pub enum Applicability {
     /// The suggestion is definitely what the user intended. This suggestion should be
     /// automatically applied.
diff --git a/src/librustc_metadata/creader.rs b/src/librustc_metadata/creader.rs
index e9785e7c88d0d..731eff62586d6 100644
--- a/src/librustc_metadata/creader.rs
+++ b/src/librustc_metadata/creader.rs
@@ -187,13 +187,15 @@ impl<'a> CrateLoader<'a> {
         });
     }
 
-    fn register_crate(&mut self,
-                      root: &Option<CratePaths>,
-                      ident: Symbol,
-                      span: Span,
-                      lib: Library,
-                      dep_kind: DepKind)
-                      -> (CrateNum, Lrc<cstore::CrateMetadata>) {
+    fn register_crate(
+        &mut self,
+        host_lib: Option<Library>,
+        root: &Option<CratePaths>,
+        ident: Symbol,
+        span: Span,
+        lib: Library,
+        dep_kind: DepKind
+    ) -> (CrateNum, Lrc<cstore::CrateMetadata>) {
         let crate_root = lib.metadata.get_root();
         info!("register crate `extern crate {} as {}`", crate_root.name, ident);
         self.verify_no_symbol_conflicts(span, &crate_root);
@@ -221,7 +223,16 @@ impl<'a> CrateLoader<'a> {
         let dependencies: Vec<CrateNum> = cnum_map.iter().cloned().collect();
 
         let proc_macros = crate_root.proc_macro_decls_static.map(|_| {
-            self.load_derive_macros(&crate_root, dylib.clone().map(|p| p.0), span)
+            if self.sess.opts.debugging_opts.dual_proc_macros {
+                let host_lib = host_lib.unwrap();
+                self.load_derive_macros(
+                    &host_lib.metadata.get_root(),
+                    host_lib.dylib.clone().map(|p| p.0),
+                    span
+                )
+            } else {
+                self.load_derive_macros(&crate_root, dylib.clone().map(|p| p.0), span)
+            }
         });
 
         let def_path_table = record_time(&self.sess.perf_stats.decode_def_path_tables_time, || {
@@ -268,6 +279,61 @@ impl<'a> CrateLoader<'a> {
         (cnum, cmeta)
     }
 
+    fn load_proc_macro<'b> (
+        &mut self,
+        locate_ctxt: &mut locator::Context<'b>,
+        path_kind: PathKind,
+    ) -> Option<(LoadResult, Option<Library>)>
+    where
+        'a: 'b
+    {
+        // Use a new locator Context so trying to load a proc macro doesn't affect the error
+        // message we emit
+        let mut proc_macro_locator = locate_ctxt.clone();
+
+        // Try to load a proc macro
+        proc_macro_locator.is_proc_macro = Some(true);
+
+        // Load the proc macro crate for the target
+        let (locator, target_result) = if self.sess.opts.debugging_opts.dual_proc_macros {
+            proc_macro_locator.reset();
+            let result = match self.load(&mut proc_macro_locator)? {
+                LoadResult::Previous(cnum) => return Some((LoadResult::Previous(cnum), None)),
+                LoadResult::Loaded(library) => Some(LoadResult::Loaded(library))
+            };
+            // Don't look for a matching hash when looking for the host crate.
+            // It won't be the same as the target crate hash
+            locate_ctxt.hash = None;
+            // Use the locate_ctxt when looking for the host proc macro crate, as that is required
+            // so we want it to affect the error message
+            (locate_ctxt, result)
+        } else {
+            (&mut proc_macro_locator, None)
+        };
+
+        // Load the proc macro crate for the host
+
+        locator.reset();
+        locator.is_proc_macro = Some(true);
+        locator.target = &self.sess.host;
+        locator.triple = TargetTriple::from_triple(config::host_triple());
+        locator.filesearch = self.sess.host_filesearch(path_kind);
+
+        let host_result = self.load(locator)?;
+
+        Some(if self.sess.opts.debugging_opts.dual_proc_macros {
+            let host_result = match host_result {
+                LoadResult::Previous(..) => {
+                    panic!("host and target proc macros must be loaded in lock-step")
+                }
+                LoadResult::Loaded(library) => library
+            };
+            (target_result.unwrap(), Some(host_result))
+        } else {
+            (host_result, None)
+        })
+    }
+
     fn resolve_crate<'b>(
         &'b mut self,
         root: &'b Option<CratePaths>,
@@ -280,53 +346,39 @@ impl<'a> CrateLoader<'a> {
         mut dep_kind: DepKind,
     ) -> Result<(CrateNum, Lrc<cstore::CrateMetadata>), LoadError<'b>> {
         info!("resolving crate `extern crate {} as {}`", name, ident);
+        let mut locate_ctxt = locator::Context {
+            sess: self.sess,
+            span,
+            ident,
+            crate_name: name,
+            hash: hash.map(|a| &*a),
+            extra_filename: extra_filename,
+            filesearch: self.sess.target_filesearch(path_kind),
+            target: &self.sess.target.target,
+            triple: self.sess.opts.target_triple.clone(),
+            root,
+            rejected_via_hash: vec![],
+            rejected_via_triple: vec![],
+            rejected_via_kind: vec![],
+            rejected_via_version: vec![],
+            rejected_via_filename: vec![],
+            should_match_name: true,
+            is_proc_macro: Some(false),
+            metadata_loader: &*self.cstore.metadata_loader,
+        };
+
         let result = if let Some(cnum) = self.existing_match(name, hash, path_kind) {
-            LoadResult::Previous(cnum)
+            (LoadResult::Previous(cnum), None)
         } else {
             info!("falling back to a load");
-            let mut locate_ctxt = locator::Context {
-                sess: self.sess,
-                span,
-                ident,
-                crate_name: name,
-                hash: hash.map(|a| &*a),
-                extra_filename: extra_filename,
-                filesearch: self.sess.target_filesearch(path_kind),
-                target: &self.sess.target.target,
-                triple: &self.sess.opts.target_triple,
-                root,
-                rejected_via_hash: vec![],
-                rejected_via_triple: vec![],
-                rejected_via_kind: vec![],
-                rejected_via_version: vec![],
-                rejected_via_filename: vec![],
-                should_match_name: true,
-                is_proc_macro: Some(false),
-                metadata_loader: &*self.cstore.metadata_loader,
-            };
-
-            self.load(&mut locate_ctxt).or_else(|| {
+            self.load(&mut locate_ctxt).map(|r| (r, None)).or_else(|| {
                 dep_kind = DepKind::UnexportedMacrosOnly;
-
-                let mut proc_macro_locator = locator::Context {
-                    target: &self.sess.host,
-                    triple: &TargetTriple::from_triple(config::host_triple()),
-                    filesearch: self.sess.host_filesearch(path_kind),
-                    rejected_via_hash: vec![],
-                    rejected_via_triple: vec![],
-                    rejected_via_kind: vec![],
-                    rejected_via_version: vec![],
-                    rejected_via_filename: vec![],
-                    is_proc_macro: Some(true),
-                    ..locate_ctxt
-                };
-
-                self.load(&mut proc_macro_locator)
+                self.load_proc_macro(&mut locate_ctxt, path_kind)
             }).ok_or_else(move || LoadError::LocatorError(locate_ctxt))?
         };
 
         match result {
-            LoadResult::Previous(cnum) => {
+            (LoadResult::Previous(cnum), None) => {
                 let data = self.cstore.get_crate_data(cnum);
                 if data.root.proc_macro_decls_static.is_some() {
                     dep_kind = DepKind::UnexportedMacrosOnly;
@@ -336,9 +388,10 @@ impl<'a> CrateLoader<'a> {
                 });
                 Ok((cnum, data))
             }
-            LoadResult::Loaded(library) => {
-                Ok(self.register_crate(root, ident, span, library, dep_kind))
+            (LoadResult::Loaded(library), host_library) => {
+                Ok(self.register_crate(host_library, root, ident, span, library, dep_kind))
             }
+            _ => panic!()
         }
     }
 
@@ -354,7 +407,7 @@ impl<'a> CrateLoader<'a> {
         // don't want to match a host crate against an equivalent target one
         // already loaded.
         let root = library.metadata.get_root();
-        if locate_ctxt.triple == &self.sess.opts.target_triple {
+        if locate_ctxt.triple == self.sess.opts.target_triple {
             let mut result = LoadResult::Loaded(library);
             self.cstore.iter_crate_data(|cnum, data| {
                 if data.root.name == root.name && root.hash == data.root.hash {
@@ -450,9 +503,9 @@ impl<'a> CrateLoader<'a> {
     fn read_extension_crate(&mut self, span: Span, orig_name: Symbol, rename: Symbol)
                             -> ExtensionCrate {
         info!("read extension crate `extern crate {} as {}`", orig_name, rename);
-        let target_triple = &self.sess.opts.target_triple;
+        let target_triple = self.sess.opts.target_triple.clone();
         let host_triple = TargetTriple::from_triple(config::host_triple());
-        let is_cross = target_triple != &host_triple;
+        let is_cross = target_triple != host_triple;
         let mut target_only = false;
         let mut locate_ctxt = locator::Context {
             sess: self.sess,
@@ -463,7 +516,7 @@ impl<'a> CrateLoader<'a> {
             extra_filename: None,
             filesearch: self.sess.host_filesearch(PathKind::Crate),
             target: &self.sess.host,
-            triple: &host_triple,
+            triple: host_triple,
             root: &None,
             rejected_via_hash: vec![],
             rejected_via_triple: vec![],
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index ad6296e1a3bd8..6f948f3ac8f7e 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -647,7 +647,7 @@ impl<'a, 'tcx> CrateMetadata {
 
     pub fn get_stability(&self, id: DefIndex) -> Option<attr::Stability> {
         match self.is_proc_macro(id) {
-            true => None,
+            true => self.root.proc_macro_stability.clone(),
             false => self.entry(id).stability.map(|stab| stab.decode(self)),
         }
     }
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index afb0218501d18..79942f614a8d0 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -489,7 +489,11 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             } else {
                 None
             },
-
+            proc_macro_stability: if is_proc_macro {
+                tcx.lookup_stability(DefId::local(CRATE_DEF_INDEX)).map(|stab| stab.clone())
+            } else {
+                None
+            },
             compiler_builtins: attr::contains_name(&attrs, "compiler_builtins"),
             needs_allocator: attr::contains_name(&attrs, "needs_allocator"),
             needs_panic_runtime: attr::contains_name(&attrs, "needs_panic_runtime"),
diff --git a/src/librustc_metadata/locator.rs b/src/librustc_metadata/locator.rs
index 6b49d6b9e52cb..20c89569efa53 100644
--- a/src/librustc_metadata/locator.rs
+++ b/src/librustc_metadata/locator.rs
@@ -241,11 +241,13 @@ use flate2::read::DeflateDecoder;
 
 use rustc_data_structures::owning_ref::OwningRef;
 
+#[derive(Clone)]
 pub struct CrateMismatch {
     path: PathBuf,
     got: String,
 }
 
+#[derive(Clone)]
 pub struct Context<'a> {
     pub sess: &'a Session,
     pub span: Span,
@@ -255,7 +257,7 @@ pub struct Context<'a> {
     pub extra_filename: Option<&'a str>,
     // points to either self.sess.target.target or self.sess.host, must match triple
     pub target: &'a Target,
-    pub triple: &'a TargetTriple,
+    pub triple: TargetTriple,
     pub filesearch: FileSearch<'a>,
     pub root: &'a Option<CratePaths>,
     pub rejected_via_hash: Vec<CrateMismatch>,
@@ -299,6 +301,14 @@ impl CratePaths {
 }
 
 impl<'a> Context<'a> {
+    pub fn reset(&mut self) {
+        self.rejected_via_hash.clear();
+        self.rejected_via_triple.clear();
+        self.rejected_via_kind.clear();
+        self.rejected_via_version.clear();
+        self.rejected_via_filename.clear();
+    }
+
     pub fn maybe_load_library_crate(&mut self) -> Option<Library> {
         let mut seen_paths = FxHashSet::default();
         match self.extra_filename {
@@ -396,7 +406,7 @@ impl<'a> Context<'a> {
                                            add);
 
             if (self.ident == "std" || self.ident == "core")
-                && self.triple != &TargetTriple::from_triple(config::host_triple()) {
+                && self.triple != TargetTriple::from_triple(config::host_triple()) {
                 err.note(&format!("the `{}` target may not be installed", self.triple));
             }
             err.span_label(self.span, "can't find crate");
@@ -715,7 +725,7 @@ impl<'a> Context<'a> {
             }
         }
 
-        if &root.triple != self.triple {
+        if root.triple != self.triple {
             info!("Rejecting via crate triple: expected {} got {}",
                   self.triple,
                   root.triple);
diff --git a/src/librustc_metadata/schema.rs b/src/librustc_metadata/schema.rs
index f3ff9747625f5..f3a5cbb2ab88b 100644
--- a/src/librustc_metadata/schema.rs
+++ b/src/librustc_metadata/schema.rs
@@ -187,6 +187,7 @@ pub struct CrateRoot {
     pub has_default_lib_allocator: bool,
     pub plugin_registrar_fn: Option<DefIndex>,
     pub proc_macro_decls_static: Option<DefIndex>,
+    pub proc_macro_stability: Option<attr::Stability>,
 
     pub crate_deps: LazySeq<CrateDep>,
     pub dylib_dependency_formats: LazySeq<Option<LinkagePreference>>,
diff --git a/src/libsyntax_pos/Cargo.toml b/src/libsyntax_pos/Cargo.toml
index 08ee2e0f37626..c6f094a8a7b8c 100644
--- a/src/libsyntax_pos/Cargo.toml
+++ b/src/libsyntax_pos/Cargo.toml
@@ -13,5 +13,6 @@ serialize = { path = "../libserialize" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 arena = { path = "../libarena" }
 scoped-tls = { version = "0.1.1", features = ["nightly"] }
+serde = { version = "1.0", features = ["serde_derive"] }
 unicode-width = "0.1.4"
 cfg-if = "0.1.2"
diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index d9d7f9b0cb492..674abfe045bc8 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -25,6 +25,7 @@ extern crate rustc_data_structures;
 
 #[macro_use]
 extern crate scoped_tls;
+extern crate serde;
 
 use serialize::{Encodable, Decodable, Encoder, Decoder};
 
@@ -36,6 +37,8 @@ extern crate cfg_if;
 
 extern crate unicode_width;
 
+use serde::{Serialize, Deserialize};
+
 pub mod edition;
 pub mod hygiene;
 pub use hygiene::{Mark, SyntaxContext, ExpnInfo, ExpnFormat, CompilerDesugaringKind};
@@ -77,7 +80,10 @@ impl Globals {
 scoped_thread_local!(pub static GLOBALS: Globals);
 
 /// Differentiates between real files and common virtual files.
-#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, RustcDecodable, RustcEncodable)]
+#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash,
+    RustcDecodable, RustcEncodable,
+    Serialize, Deserialize,
+)]
 pub enum FileName {
     Real(PathBuf),
     /// A macro.  This includes the full name of the macro, so that there are no clashes.