diff --git a/cmake/CheckAvxSupport.cmake b/cmake/CheckAvxSupport.cmake
new file mode 100644
index 00000000..ab8ad644
--- /dev/null
+++ b/cmake/CheckAvxSupport.cmake
@@ -0,0 +1,53 @@
+# Copyright 2021 DeepMind Technologies Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+include(CheckCSourceCompiles)
+
+# Assigns compiler options to the given variable based on availability of AVX.
+function(get_avx_compile_options OUTPUT_VAR)
+  message(VERBOSE "Checking if AVX is available...")
+
+  if(MSVC)
+    set(CMAKE_REQUIRED_FLAGS "/arch:AVX")
+  else()
+    set(CMAKE_REQUIRED_FLAGS "-mavx")
+  endif()
+
+  if(APPLE AND "x86_64" IN_LIST CMAKE_OSX_ARCHITECTURES)
+    message(STATUS "Building x86_64 on macOS, forcing CAN_BUILD_AVX to TRUE.")
+    set(CAN_BUILD_AVX TRUE)
+  else()
+    check_c_source_compiles(
+      "
+      #include <immintrin.h>
+      int main(int argc, char* argv[]) {
+        __m256d ymm;
+        return 0;
+      }
+    "
+      CAN_BUILD_AVX
+    )
+  endif()
+
+  if(CAN_BUILD_AVX)
+    message(VERBOSE "Checking if AVX is available... AVX available.")
+    set("${OUTPUT_VAR}"
+        ${CMAKE_REQUIRED_FLAGS}
+        PARENT_SCOPE
+    )
+  else()
+    message(VERBOSE "Checking if AVX is available... AVX not available.")
+    set("${OUTPUT_VAR}" PARENT_SCOPE)
+  endif()
+endfunction()
diff --git a/cmake/FindOrFetch.cmake b/cmake/FindOrFetch.cmake
new file mode 100644
index 00000000..4eeb617e
--- /dev/null
+++ b/cmake/FindOrFetch.cmake
@@ -0,0 +1,128 @@
+# Copyright 2021 DeepMind Technologies Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+#.rst:
+# FindOrFetch
+# ----------------------
+#
+# Find or fetch a package in order to satisfy target dependencies.
+#
+#   FindOrFetch([USE_SYSTEM_PACKAGE [ON/OFF]]
+#               [PACKAGE_NAME [name]]
+#               [LIBRARY_NAME [name]]
+#               [GIT_REPO [repo]]
+#               [GIT_TAG [tag]]
+#               [PATCH_COMMAND [cmd] [args]]
+#               [TARGETS [targets]]
+#               [EXCLUDE_FROM_ALL])
+#
+# The command has the following parameters:
+#
+# Arguments:
+#  - ``USE_SYSTEM_PACKAGE`` one-value argument on whether to search for the
+#    package in the system (ON) or whether to fetch the library from a git
+#    repository (OFF).
+#  - ``PACKAGE_NAME`` name of the system-package. Ignored if
+#    ``USE_SYSTEM_PACKAGE`` is ``OFF``.
+#  - ``LIBRARY_NAME`` name of the library. Ignored if
+#    ``USE_SYSTEM_PACKAGE`` is ``ON``.
+#  - ``GIT_REPO`` git repository to fetch the library from. Ignored if
+#    ``USE_SYSTEM_PACKAGE`` is ``ON``.
+#  - ``GIT_TAG`` tag reference when fetching the library from the git
+#    repository. Ignored if ``USE_SYSTEM_PACKAGE`` is ``ON``.
+#  - ``TARGETS`` list of targets to be satisfied. If any of these targets are
+#    not currently defined, this macro will attempt to either find or fetch the
+#    package.
+
+if(COMMAND FindOrFetch)
+  return()
+endif()
+
+macro(FindOrFetch)
+  if(NOT FetchContent)
+    include(FetchContent)
+  endif()
+
+  # Parse arguments.
+  set(options EXCLUDE_FROM_ALL)
+  set(one_value_args
+      USE_SYSTEM_PACKAGE
+      PACKAGE_NAME
+      LIBRARY_NAME
+      GIT_REPO
+      GIT_TAG
+  )
+  set(multi_value_args PATCH_COMMAND TARGETS)
+  cmake_parse_arguments(
+    _ARGS
+    "${options}"
+    "${one_value_args}"
+    "${multi_value_args}"
+    ${ARGN}
+  )
+
+  # Check if all targets are found.
+  if(NOT _ARGS_TARGETS)
+    message(FATAL_ERROR "mujoco::FindOrFetch: TARGETS must be specified.")
+  endif()
+  set(targets_found TRUE)
+  foreach(target ${_ARGS_TARGETS})
+    if(NOT TARGET ${target})
+      message(STATUS "mujoco::FindOrFetch: target `${target}` not defined.")
+      set(targets_found FALSE)
+      break()
+    endif()
+  endforeach()
+
+  # If targets are not found, use `find_package` or `FetchContent...` to get it.
+  if(NOT targets_found)
+    if(${_ARGS_USE_SYSTEM_PACKAGE})
+      message(
+        STATUS
+          "mujoco::FindOrFetch: Attempting to find `${_ARGS_PACKAGE_NAME}` in system packages..."
+      )
+      find_package(${_ARGS_PACKAGE_NAME} REQUIRED)
+      message(STATUS "mujoco::FindOrFetch: Found `${_ARGS_PACKAGE_NAME}` in system packages.")
+    else()
+      message(
+        STATUS
+          "mujoco::FindOrFetch: Attempting to fetch `${_ARGS_LIBRARY_NAME}` from `${_ARGS_GIT_REPO}`..."
+      )
+      FetchContent_Declare(
+        ${_ARGS_LIBRARY_NAME}
+        GIT_REPOSITORY ${_ARGS_GIT_REPO}
+        GIT_TAG ${_ARGS_GIT_TAG}
+        GIT_SHALLOW FALSE
+        PATCH_COMMAND ${_ARGS_PATCH_COMMAND}
+      )
+      if(${_ARGS_EXCLUDE_FROM_ALL})
+        FetchContent_GetProperties(${_ARGS_LIBRARY_NAME})
+        if(NOT ${${_ARGS_LIBRARY_NAME}_POPULATED})
+          FetchContent_Populate(${_ARGS_LIBRARY_NAME})
+          add_subdirectory(
+            ${${_ARGS_LIBRARY_NAME}_SOURCE_DIR} ${${_ARGS_LIBRARY_NAME}_BINARY_DIR}
+            EXCLUDE_FROM_ALL
+          )
+        endif()
+      else()
+        FetchContent_MakeAvailable(${_ARGS_LIBRARY_NAME})
+      endif()
+      message(
+        STATUS "mujoco::FindOrFetch: Fetched `${_ARGS_LIBRARY_NAME}` from `${_ARGS_GIT_REPO}`."
+      )
+    endif()
+  else()
+    message(STATUS "mujoco::FindOrFetch: `${_ARGS_PACKAGE_NAME}` targets found.")
+  endif()
+endmacro()
diff --git a/cmake/MujocoLinkOptions.cmake b/cmake/MujocoLinkOptions.cmake
new file mode 100644
index 00000000..242767f9
--- /dev/null
+++ b/cmake/MujocoLinkOptions.cmake
@@ -0,0 +1,67 @@
+# Copyright 2021 DeepMind Technologies Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+include(CheckCSourceCompiles)
+
+# Gets the appropriate linker options for building MuJoCo, based on features available on the
+# linker.
+function(get_mujoco_extra_link_options OUTPUT_VAR)
+  if(MSVC)
+    set(EXTRA_LINK_OPTIONS /OPT:REF /OPT:ICF=5)
+  else()
+    set(EXTRA_LINK_OPTIONS)
+
+    if(WIN32)
+      set(CMAKE_REQUIRED_FLAGS "-fuse-ld=lld-link")
+      check_c_source_compiles("int main() {}" SUPPORTS_LLD)
+      if(SUPPORTS_LLD)
+        set(EXTRA_LINK_OPTIONS
+            ${EXTRA_LINK_OPTIONS}
+            -fuse-ld=lld-link
+            -Wl,/OPT:REF
+            -Wl,/OPT:ICF
+        )
+      endif()
+    else()
+      set(CMAKE_REQUIRED_FLAGS "-fuse-ld=lld")
+      check_c_source_compiles("int main() {}" SUPPORTS_LLD)
+      if(SUPPORTS_LLD)
+        set(EXTRA_LINK_OPTIONS ${EXTRA_LINK_OPTIONS} -fuse-ld=lld)
+      else()
+        set(CMAKE_REQUIRED_FLAGS "-fuse-ld=gold")
+        check_c_source_compiles("int main() {}" SUPPORTS_GOLD)
+        if(SUPPORTS_GOLD)
+          set(EXTRA_LINK_OPTIONS ${EXTRA_LINK_OPTIONS} -fuse-ld=gold)
+        endif()
+      endif()
+
+      set(CMAKE_REQUIRED_FLAGS ${EXTRA_LINK_OPTIONS} "-Wl,--gc-sections")
+      check_c_source_compiles("int main() {}" SUPPORTS_GC_SECTIONS)
+      if(SUPPORTS_GC_SECTIONS)
+        set(EXTRA_LINK_OPTIONS ${EXTRA_LINK_OPTIONS} -Wl,--gc-sections)
+      else()
+        set(CMAKE_REQUIRED_FLAGS ${EXTRA_LINK_OPTIONS} "-Wl,-dead_strip")
+        check_c_source_compiles("int main() {}" SUPPORTS_DEAD_STRIP)
+        if(SUPPORTS_DEAD_STRIP)
+          set(EXTRA_LINK_OPTIONS ${EXTRA_LINK_OPTIONS} -Wl,-dead_strip)
+        endif()
+      endif()
+    endif()
+  endif()
+
+  set("${OUTPUT_VAR}"
+      ${EXTRA_LINK_OPTIONS}
+      PARENT_SCOPE
+  )
+endfunction()
diff --git a/cmake/ShellTests.cmake b/cmake/ShellTests.cmake
new file mode 100644
index 00000000..e1a75340
--- /dev/null
+++ b/cmake/ShellTests.cmake
@@ -0,0 +1,52 @@
+# Copyright 2021 DeepMind Technologies Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+function(add_mujoco_shell_test TEST_NAME TARGET_BINARY)
+  find_program(BASH_PROGRAM bash)
+  if(BASH_PROGRAM)
+    # Set up the test directory
+    set(TEST_TMPDIR "${CMAKE_CURRENT_BINARY_DIR}/${TEST_NAME}")
+    add_test(NAME ${TEST_NAME}_setup
+             COMMAND ${BASH_PROGRAM} "${PROJECT_SOURCE_DIR}/cmake/setup_test_dir.sh" ${TEST_TMPDIR}
+    )
+    set_tests_properties(${TEST_NAME}_setup PROPERTIES FIXTURES_SETUP ${TEST_NAME}_fixture)
+    add_test(NAME ${TEST_NAME}_cleanup
+             COMMAND ${BASH_PROGRAM} "${PROJECT_SOURCE_DIR}/cmake/cleanup_test_dir.sh"
+                     ${TEST_TMPDIR}
+    )
+    set_tests_properties(${TEST_NAME}_cleanup PROPERTIES FIXTURES_CLEANUP ${TEST_NAME}_fixture)
+    add_test(
+      NAME ${TEST_NAME}
+      COMMAND ${BASH_PROGRAM} "${CMAKE_CURRENT_SOURCE_DIR}/${TEST_NAME}.sh"
+      WORKING_DIRECTORY $<TARGET_FILE_DIR:${TARGET_BINARY}>
+    )
+    set_tests_properties(${TEST_NAME} PROPERTIES FIXTURES_REQUIRED ${TEST_NAME}_fixture)
+    set_property(
+      TEST "${TEST_NAME}"
+      PROPERTY ENVIRONMENT
+               "CMAKE_SOURCE_DIR=${CMAKE_SOURCE_DIR}"
+               "TARGET_BINARY=$<TARGET_FILE:${TARGET_BINARY}>"
+               "TEST_TMPDIR=${TEST_TMPDIR}"
+    )
+    if(WIN32)
+      # Define the directory containing the mujoco DLL library so that it can be added to the PATH.
+      # We modify the PATH in the script as it is more reliable.
+      set_property(
+        TEST "${TEST_NAME}"
+        APPEND
+        PROPERTY ENVIRONMENT "MUJOCO_DLL_DIR=$<TARGET_FILE_DIR:mujoco_nogl>"
+      )
+    endif()
+  endif()
+endfunction()
diff --git a/python/make_sdist.sh b/python/make_sdist.sh
index a667ca2d..d422ed68 100755
--- a/python/make_sdist.sh
+++ b/python/make_sdist.sh
@@ -47,11 +47,11 @@ python "${package_dir}"/mujoco/codegen/generate_function_traits.py > \
 export PYTHONPATH="${old_pythonpath}"
 
 # Copy over the LICENSE file.
-cp "${package_dir}"/../../LICENSE .
+cp "${package_dir}"/../LICENSE .
 
 # Copy over CMake scripts.
 mkdir cmake
-cp "${package_dir}"/../../cmake/*.cmake cmake
+cp "${package_dir}"/../cmake/*.cmake cmake
 
 python setup.py sdist --formats=gztar
 tar -tf dist/mujoco-*.tar.gz
diff --git a/python/mujoco/errors.h b/python/mujoco/errors.h
index 7dc7d2e7..d805876e 100644
--- a/python/mujoco/errors.h
+++ b/python/mujoco/errors.h
@@ -119,7 +119,12 @@ struct MjErrorIntercepter {
   template <typename Return, typename... Args, typename Callable>
   MUJOCO_ALWAYS_INLINE
   static constexpr auto WrapFunc(Callable&& callable) {
+#if defined(__GNUC__) && !defined(__clang__)
+    // GCC can't inline functions that call setjmp
+    return [callable](Args... args) mutable {
+#else
     return [callable](Args... args) MUJOCO_ALWAYS_INLINE_LAMBDA_MUTABLE {
+#endif
       _mjPRIVATE__set_tls_error_fn(&MjErrorHandler);
 
       // DON'T MIX RAII WITH SETJMP!
diff --git a/python/mujoco/util/crossplatform.h b/python/mujoco/util/crossplatform.h
index be172900..0c71f2b6 100644
--- a/python/mujoco/util/crossplatform.h
+++ b/python/mujoco/util/crossplatform.h
@@ -25,7 +25,11 @@
     (defined(__GNUC__) && !defined(__clang__))
 #define MUJOCO_ALWAYS_INLINE __attribute__((always_inline))
 #define MUJOCO_ALWAYS_INLINE_LAMBDA MUJOCO_ALWAYS_INLINE
+#if defined(__clang__)
 #define MUJOCO_ALWAYS_INLINE_LAMBDA_MUTABLE MUJOCO_ALWAYS_INLINE_LAMBDA mutable
+#else
+#define MUJOCO_ALWAYS_INLINE_LAMBDA_MUTABLE mutable MUJOCO_ALWAYS_INLINE_LAMBDA
+#endif
 #elif defined(_MSC_VER)
 #define MUJOCO_ALWAYS_INLINE __forceinline
 #if _MSC_VER >= 1927 && _MSVC_LANG >= 202002L