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Advanced Build Information

Installing CMake

This project requires at least CMake 3.12. This is probably not available in your package manager's repositories, but we use the OBJECT library feature extensively, so you need to install it either manually from their website, or with our Ansible scripts:

cd openenclave/scripts/ansible
ansible localhost -m import_role -a "name=linux/openenclave tasks_from=environment-setup.yml" --become --ask-become-pass

CMake Configuration

In addition to the standard CMake variables, the following CMake variables control the behavior of the Linux make generator for Open Enclave:

Variable Description
CMAKE_BUILD_TYPE Build configuration (Debug, Release, RelWithDebInfo). Default is Debug.
ENABLE_FULL_LIBCXX_TESTS Enable full Libc++ tests. Default is disabled, enable with setting to "On", "1", ...
ENABLE_REFMAN Enable building of reference manual. Requires Doxygen to be installed. Default is disabled, enable with setting to "On", "1", ...

For example, to generate an optimized release-build with debug info, run the following from your build subfolder:

cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo

The following build types cause the C macro NDEBUG to be defined:

  • CMAKE_BUILD_TYPE="Release"
  • CMAKE_BUILD_TYPE="RelWithDebInfo"

whereas CMAKE_BUILD_TYPE="Debug" causes it to be undefined. Defining the NDEBUG macro affects the behavior of Open Enclave in three ways:

  • The oe_assert() and assert() macros become no-ops.
  • The oe_backtrace() function returns an empty backtrace.
  • The debug allocator is disabled. The debug allocator checks for memory errors during enclave termination.

Multiple variables can be defined in the cmake call with multiple "-DVar=Value" arguments.

Building

Once CMake has run and the build is configured, build with:

make

This builds the entire Open Enclave SDK, creating the following files in your build folder.

Filename Description
output/bin/oegdb Utility for debugging enclaves
output/bin/oesgx Utility for determining the level of SGX support for the given platform
output/bin/oesign Utility for signing enclaves
output/lib/enclave/liboecore.a Core library for building enclave applications (defines enclave intrinsics)
output/lib/enclave/liboeenclave.a Enclave library for building enclave applications (defines enclave features)
output/lib/enclave/liboelibc.a C runtime library for enclave
output/enclave/liboelibcxx.a C++ runtime library for enclave
output/lib/host/liboehost.a Library for building host applications
output/share/doc/openenclave/ HTML API reference for Open Enclave
tools/oeedger8r/oeedger8r Utility for generating ECALL and OCALL stubs from IDL

If there is a build failure, set the VERBOSE make variable to print all invoked commands.

make VERBOSE=1

Building from within a subtree of the build-tree builds all dependencies for that directory as well. make clean is handy before a spot-rebuild in verbose mode.

A successful build only outputs the HTML API reference into the build-tree. To update the Doxygen-generated documentation published to https://openenclave.github.io/openenclave, please follow instructions here

Visualizing the CMake Dependency Graph

CMake comes with built-in support for graphviz which makes it easy to generate an image of the dependency graph for a CMake project. For example, to visualize the entire Open Enclave project from the CMake root:

mkdir graphviz && cd graphviz
cmake --graphviz=graph ..
dot graph -Tsvg -o graph.svg

Although other output image formats such as PNG are support, we recommend using SVG because it keeps the resulting file size reasonably small in spite of the huge number of nodes (targets) in the resulting graph.

To change the ignored targets, edit the file named CMakeGraphVizOptions.cmake at the root of the repo.

As of 2020-03-10, it looks like this:

CMake Dependency Graph

Legend

Nodes:

  • square: interface or shared library
  • diamond: static library
  • circle: external library (static or shared)
  • house: executable

Edges:

  • solid: public dependency
  • dotted: interface dependency
  • dashed: private dependency

LVI Mitigation

In response to the LVI vulnerability, Open Enclave SDK adopts the mitigation based on Intel's prebuilt as/ld binaries .

Newly Added Files

The following list includes necessary files for Open Enclave SDK to support LVI mitigation on both Linux and Windows.

Filename Description
scripts/lvi-mitigation/install_lvi_mitigation_bindir Script for installing necessary compilation tools (Linux).
scripts/lvi-mitigation/generate_wrapper Script for generating compiler wrappers, needed by installation (Linux).
scripts/lvi-mitigation/invoke_compiler Script for invoking compilers, needed by generated wrappers (Linux).
scripts/lvi-mitigation/lvi-mitigation.py Python script for supporting mitigation (Windows).

Dependency Installation

Linux

On Linux, run the install_lvi_mitigation_bindir script to install the dependencies to a desired location. The following example creates a directory lvi_mitigation_bin with all the dependencies in the root of the openenclave directory.

# In the /home/yourname/openenclave directory.
~/openenclave$ ./scripts/lvi-mitigation/install_lvi_mitigation_bindir
Do you want to install in current directory? [yes/no]: yes
...
Installed: /home/yourname/openenclave/lvi_mitigation_bin

If the script ran successfully, the lvi_mitigation_bin should contain a list of files:

~/openenclave/lvi_mitigation_bin$ ls -l
total 16
-rwxrwxr-x 1 yourname yourname 2121936 Mar  10 10:00 as
-rwxrwxr-x 1 yourname yourname     233 Mar  10 10:00 clang++-10
lrwxrwxrwx 1 yourname yourname      18 Mar  10 10:00 clang++-10_symlink -> /usr/bin/clang++-10
-rwxrwxr-x 1 yourname yourname     231 Mar  10 10:00 clang-10
lrwxrwxrwx 1 yourname yourname      16 Mar  10 10:00 clang-10_symlink -> /usr/bin/clang-10
-rwxrwxr-x 1 yourname yourname     227 Mar  10 10:00 g++
lrwxrwxrwx 1 yourname yourname      12 Mar  10 10:00 g++_symlink -> /usr/bin/g++
-rwxrwxr-x 1 yourname yourname     227 Mar  10 10:00 gcc
lrwxrwxrwx 1 yourname yourname      12 Mar  10 10:00 gcc_symlink -> /usr/bin/gcc
-rwxrwxr-x 1 yourname yourname    1093 Mar  10 10:00 invoke_compiler
-rwxrwxr-x 1 yourname yourname 2722256 Mar  10 10:00 ld

as and ld are the customized GNU assembler and linker obtained from Intel, which support the LVI mitigation. clang-10, clang++-10, gcc, and g++ are the copies of previously shown wrappers that invoke the customized as and ld when compiling enclave code with LVI mitigation. The remaining files with the _symlink suffix link to the actual compilers installed in the system, which are required by the wrappers.

Note: clang-10 and clang++-10 may be missing if the system does not have the clang version 10 installed. If you encounter this, you will need to install Clang as GCC is not supported.

Note: If the version of glibc is older than 2.27, the ld will be missing in the above output. Consequently, ld will not be installed. Without a compatible version of ld, debug symbol generation (i.e. use of the -g option) cannot be used when compiling with LVI mitigation.

Example of checking the version of glibc

ldd --version | awk '/ldd/{print $NF}'

Windows

On Windows, this step is not required. Instead of using the customized assembler and linker, the Windows build uses the Python script (modified based on the Intel's version) to instrument the enclave code at the assembly level that achieves similar functionality.

CMake Configuration

Open Enclave SDK adds two CMake variables that allow developers to build enclave libraries with LVI mitigation:

Variable Description
LVI_MITIGATION Enable LVI mitigation to trusted code. The only currently supported values are None or ControlFlow.
LVI_MITIGATION_BINDIR Path to the customized compilation toolchain required by the LVI Mitigation (Linux-only).

Linux

On Linux, the following example configures the build with LVI mitigation (specify the LVI_MITIGATION_BINDIR to the directory created in the previous step).

cmake .. -DLVI_MITIGATION=ControlFlow -DLVI_MITIGATION_BINDIR=/home/yourname/openenclave/lvi_mitigation_bin

Windows

On Windows, only LVI_MITIGATION is required.

cmake .. -DLVI_MITIGATION=ControlFlow

Building

Once CMake has run, and the build is configured, build with:

make

With the LVI mitigation options specified, make generates LVI-mitigated versions of all enclave libraries in addition to the regular versions of them. For example:

Filename Description
output/lib/enclave/liboecore.a Core library for building enclave applications (defines enclave intrinsics).
output/lib/enclave/liboecore-lvi-cfg.a Core library with LVI mitigation.
output/lib/enclave/liboeenclave.a Enclave library for building enclave applications (defines enclave features).
output/lib/enclave/liboeenclave-lvi-cfg.a Enclave library with LVI mitigation.
output/lib/enclave/liboelibc.a C runtime library for enclave.
output/lib/enclave/liboelibc-lvi-cfg.a C runtime library with LVI mitigation.
output/enclave/liboelibcxx.a C++ runtime library for enclave.
output/enclave/liboelibcxx-lvi-cfg.a C++ runtime library with LVI mitigation.

Dependency Graph with LVI Mitigation

To get the dependency graph with LVI mitigation enabled, run

mkdir graphviz && cd graphviz
cmake --graphviz=graph .. -DLVI_MITIGATION=ControlFlow \
-DLVI_MITIGATION_BINDIR=/home/yourname/openenclave/lvi_mitigation_bin
dot graph -Tsvg -o graph-lvi-cfg.svg

As of 2020-03-10, it looks like this:

CMake Dependency Graph with LVI Mitigation

Building Enclaves with LVI Mitigation

With the LVI mitigation enabled, Open Enclave SDK provides a new option that allows users to build enclaves on top of the mitigated version of libraries.

See Build and Run samples with LVI mitigation.