diff --git a/.appveyor.yml b/.appveyor.yml
index 294ef26be0be..34887459f6d9 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -1,84 +1,49 @@
+build: off # No Visual Studio auto-build.
 environment:
-    global:
-        PROJECT_NAME: miri
-    matrix:
-        - TARGET: i686-pc-windows-msvc
+  global:
+    PROJECT_NAME: miri
+  matrix:
+    - TARGET: i686-pc-windows-msvc
+matrix:
+  fast_finish: true # Immediately finish build once one of the jobs fails.
+cache:
+- '%USERPROFILE%\.cargo'
+- '%USERPROFILE%\.rustup'
 
 # branches to build
 branches:
   # whitelist
   only:
-    - auto
-    - try
-
-matrix:
-  fast_finish: true     # set this flag to immediately finish build once one of the jobs fails.
-
-cache:
-    - '%USERPROFILE%\.cargo'
-    - '%USERPROFILE%\.rustup'
+  - auto
+  - try
 
 install:
-    # Compute the rust version we use
-    - set /p RUSTC_HASH=<rust-version
-    # Install Rust
-    - curl -sSf --retry 3 -o rustup-init.exe https://win.rustup.rs/
-    - rustup-init.exe -y --default-host %TARGET% --default-toolchain stable --profile minimal
-    - set PATH=%USERPROFILE%\.cargo\bin;%PATH%
-    - rustup default stable
-    - rustup toolchain uninstall beta
-    - rustup update
-    # Install "master" toolchain
-    - cargo install rustup-toolchain-install-master
-    # We need to install cargo here as well or else the DLL search path inside `cargo run`
-    # will be for the wrong toolchain. (On Unix, `./miri` takes care of this, but not here.)
-    - rustup-toolchain-install-master -f -n master %RUSTC_HASH% -c rust-src -c rustc-dev -c cargo
-    - rustup default master
-    - rustc --version
-    - cargo --version
-
-build_script:
-    - set RUSTFLAGS=-C debug-assertions
-    # Build and install miri
-    - cargo build --release --all-features --all-targets --locked
-    - cargo install --all-features --force --path . --locked --offline
+# Compute the Rust version we use.
+- set /p RUSTC_HASH=<rust-version
+# Install Rust. We use the "stable" toolchain for better caching, it is just used to build `rustup-toolchain-install-master`.
+# But we also need to take into account that the build cache might have a different, outdated default.
+- curl -sSf --retry 3 -o rustup-init.exe https://win.rustup.rs/
+- rustup-init.exe -y --default-host %TARGET% --default-toolchain none --profile minimal
+- set PATH=%USERPROFILE%\.cargo\bin;%PATH%
+- rustup default stable
+- rustup toolchain uninstall beta nightly
+- rustup update
+# Install "master" toolchain.
+- cargo install rustup-toolchain-install-master
+- rustup-toolchain-install-master -f -n master %RUSTC_HASH% -c rust-src -c rustc-dev
+- rustup default master
+- rustc --version
+- cargo --version
 
 test_script:
-    - set RUST_TEST_NOCAPTURE=1
-    - set RUST_BACKTRACE=1
-    - set CARGO_INCREMENTAL=0
-    # Test host miri: 32bit Windows
-    - cargo miri setup
-    - set MIRI_SYSROOT=%USERPROFILE%\AppData\Local\rust-lang\miri\cache\HOST
-    - cargo test --release --all-features --locked
-    - cd test-cargo-miri
-    - '"C:\msys64\mingw64\bin\python3.exe" run-test.py'
-    - cd ..
-    - ps: $env:MIRI_SYSROOT = ""
-    # Test foreign miri: 64bit Linux
-    - cargo miri setup --target x86_64-unknown-linux-gnu
-    - set MIRI_SYSROOT=%USERPROFILE%\AppData\Local\rust-lang\miri\cache
-    - set MIRI_TEST_TARGET=x86_64-unknown-linux-gnu
-    - cargo test --release --all-features --locked
-    - cd test-cargo-miri
-    - '"C:\msys64\mingw64\bin\python3.exe" run-test.py'
-    - cd ..
-    - ps: $env:MIRI_SYSROOT = ""
-    # Test foreign miri: 64bit macOS
-    - cargo miri setup --target x86_64-apple-darwin
-    - set MIRI_SYSROOT=%USERPROFILE%\AppData\Local\rust-lang\miri\cache
-    - set MIRI_TEST_TARGET=x86_64-apple-darwin
-    - cargo test --release --all-features --locked
-    - cd test-cargo-miri
-    - '"C:\msys64\mingw64\bin\python3.exe" run-test.py'
-    - cd ..
-    - ps: $env:MIRI_SYSROOT = ""
+- set PYTHON=C:\msys64\mingw64\bin\python3.exe
+- bash ci.sh
 
 after_test:
-    # Don't cache "master" toolchain, it's a waste
-    - rustup default stable
-    - rustup toolchain uninstall master
+# Don't cache "master" toolchain, it's a waste.
+- rustup default stable
+- rustup toolchain uninstall master
 
 notifications:
-    - provider: Email
-      on_build_success: false
+- provider: Email
+  on_build_success: false
diff --git a/.travis.yml b/.travis.yml
index a074d6b14d8d..1605737a7b09 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,41 +1,40 @@
 language: generic
+os:
+- linux
+- osx
+dist: xenial
 cache:
   # Cache the global cargo directory, but NOT the local `target` directory which
   # we cannot reuse anyway when the nightly changes (and it grows quite large
   # over time).
   directories:
-    - $HOME/.cargo
-    - $HOME/.rustup
-
-os:
-- linux
-- osx
-dist: xenial
+  - $HOME/.cargo
+  - $HOME/.rustup
 
 # Run in PRs and for bors, but not on master.
+branches:
+  only:
+  - master
+  - auto
+  - try
 if: branch = auto OR branch = try OR type = pull_request OR type = cron
 
-env:
-  global:
-  - RUST_TEST_NOCAPTURE=1
-  - RUST_BACKTRACE=1
-  - CARGO_INCREMENTAL=0
-
 before_script:
-# Compute the rust version we use. We do not use "language: rust" to have more control here.
+# Compute the Rust version we use. We do not use "language: rust" to have more control here.
 - |
   if [[ "$TRAVIS_EVENT_TYPE" == cron ]]; then
     RUSTC_HASH=$(git ls-remote https://github.com/rust-lang/rust.git master | awk '{print $1}')
   else
     RUSTC_HASH=$(cat rust-version)
   fi
-# Install Rust ("stable" toolchain for better caching, it is just used to build rustup-toolchain-install-master)
-- curl https://build.travis-ci.org/files/rustup-init.sh -sSf | sh -s -- -y --default-toolchain stable --profile minimal
+# Install Rust. We use the "stable" toolchain for better caching, it is just used to build `rustup-toolchain-install-master`.
+# But we also need to take into account that the build cache might have a different, outdated default.
+- curl https://build.travis-ci.org/files/rustup-init.sh -sSf | sh -s -- -y --default-toolchain none --profile minimal
 - export PATH=$HOME/.cargo/bin:$PATH
 - rustup default stable
-- rustup toolchain uninstall beta
+- rustup toolchain uninstall beta nightly
 - rustup update
-# Install "master" toolchain
+# Install "master" toolchain.
 - cargo install rustup-toolchain-install-master
 - travis_retry rustup-toolchain-install-master -f -n master $RUSTC_HASH -c rust-src -c rustc-dev
 - rustup default master
@@ -43,10 +42,10 @@ before_script:
 - cargo --version
 
 script:
-- ./travis.sh
+- ./ci.sh
 
 before_cache:
-# Don't cache "master" toolchain, it's a waste
+# Don't cache "master" toolchain, it's a waste.
 - rustup default stable
 - rustup toolchain uninstall master
 
@@ -54,10 +53,5 @@ notifications:
   email:
     on_success: never
     recipients:
-      - post+travis@ralfj.de
-      - travis-miri@oli-obk.de
-branches:
-  only:
-  - master
-  - auto
-  - try
+    - post+travis@ralfj.de
+    - travis-miri@oli-obk.de
diff --git a/travis.sh b/ci.sh
similarity index 65%
rename from travis.sh
rename to ci.sh
index 590b94b7f5db..a7254f2958a0 100755
--- a/travis.sh
+++ b/ci.sh
@@ -2,8 +2,11 @@
 set -euo pipefail
 
 # Determine configuration
-export CARGO_EXTRA_FLAGS="--all-features"
+export RUST_TEST_NOCAPTURE=1
+export RUST_BACKTRACE=1
 export RUSTC_EXTRA_FLAGS="-D warnings"
+export CARGO_INCREMENTAL=0
+export CARGO_EXTRA_FLAGS="--all-features"
 
 # Prepare
 echo "Build and install miri"
@@ -22,28 +25,26 @@ function run_tests {
   ./miri test --locked
   if ! [ -n "${MIRI_TEST_TARGET+exists}" ]; then
     # Only for host architecture: tests with MIR optimizations
-    MIRI_TEST_FLAGS="-Z mir-opt-level=3" ./miri test
+    MIRI_TEST_FLAGS="-Z mir-opt-level=3" ./miri test --locked
   fi
   # "miri test" has built the sysroot for us, now this should pass without
   # any interactive questions.
-  test-cargo-miri/run-test.py
+  ${PYTHON:-python3} test-cargo-miri/run-test.py
 
   echo
 }
 
 # host
 run_tests
-# cross-test 32bit Linux from everywhere
-MIRI_TEST_TARGET=i686-unknown-linux-gnu run_tests
 
-if [ "$TRAVIS_OS_NAME" == linux ]; then
-  # cross-test 64bit macOS from Linux
+if [ "${TRAVIS_OS_NAME:-}" == linux ]; then
+  MIRI_TEST_TARGET=i686-unknown-linux-gnu run_tests
   MIRI_TEST_TARGET=x86_64-apple-darwin run_tests
-  # cross-test 32bit Windows from Linux
   MIRI_TEST_TARGET=i686-pc-windows-msvc run_tests
-elif [ "$TRAVIS_OS_NAME" == osx ]; then
-  # cross-test 64bit Windows from macOS
+elif [ "${TRAVIS_OS_NAME:-}" == osx ]; then
   MIRI_TEST_TARGET=x86_64-pc-windows-msvc run_tests
-  # cross-test 32bit GNU Windows from macOS
   MIRI_TEST_TARGET=i686-pc-windows-gnu run_tests
+elif [ "${CI_WINDOWS:-}" == True ]; then
+  MIRI_TEST_TARGET=x86_64-unknown-linux-gnu run_tests
+  MIRI_TEST_TARGET=x86_64-apple-darwin run_tests
 fi
diff --git a/src/shims/fs.rs b/src/shims/fs.rs
index 0de0b33fb2e2..8613f6bb0994 100644
--- a/src/shims/fs.rs
+++ b/src/shims/fs.rs
@@ -549,12 +549,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         target_op: OpTy<'tcx, Tag>,
         linkpath_op: OpTy<'tcx, Tag>
     ) -> InterpResult<'tcx, i32> {
-        #[cfg(target_family = "unix")]
+        #[cfg(unix)]
         fn create_link(src: &Path, dst: &Path) -> std::io::Result<()> {
             std::os::unix::fs::symlink(src, dst)
         }
 
-        #[cfg(target_family = "windows")]
+        #[cfg(windows)]
         fn create_link(src: &Path, dst: &Path) -> std::io::Result<()> {
             use std::os::windows::fs;
             if src.is_dir() {
@@ -816,7 +816,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         this.check_no_isolation("mkdir")?;
 
-        let _mode = if this.tcx.sess.target.target.target_os == "macos" {
+        #[cfg_attr(not(unix), allow(unused_variables))]
+        let mode = if this.tcx.sess.target.target.target_os == "macos" {
             u32::from(this.read_scalar(mode_op)?.not_undef()?.to_u16()?)
         } else {
             this.read_scalar(mode_op)?.to_u32()?
@@ -824,14 +825,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         let path = this.read_path_from_c_str(this.read_scalar(path_op)?.not_undef()?)?;
 
+        #[cfg_attr(not(unix), allow(unused_mut))]
         let mut builder = DirBuilder::new();
 
         // If the host supports it, forward on the mode of the directory
         // (i.e. permission bits and the sticky bit)
-        #[cfg(target_family = "unix")]
+        #[cfg(unix)]
         {
             use std::os::unix::fs::DirBuilderExt;
-            builder.mode(_mode.into());
+            builder.mode(mode.into());
         }
 
         let result = builder.create(path).map(|_| 0i32);