Build

Preliminaries

LLDB relies on many of the technologies developed by the larger LLVM project. In particular, it requires both Clang and LLVM itself in order to build. Due to this tight integration the Getting Started guides for both of these projects come as prerequisite reading:

The following requirements are shared on all platforms.

Depending on your platform and package manager, one might run any of the commands below.

> yum install libedit-devel libxml2-devel ncurses-devel python-devel swig
> sudo apt-get install build-essential subversion swig python2.7-dev libedit-dev libncurses5-dev
> pkg install swig python
> pkgin install swig python27 cmake ninja-build
> brew install swig cmake ninja

Windows

  • Visual Studio 2015 or greater
  • Windows SDK 8.0 or higher. In general it is best to use the latest available version.
  • GnuWin32
  • Python 3.5 or higher or higher. Earlier versions of Python can be made to work by compiling your own distribution from source, but this workflow is unsupported and you are own your own.
  • Python Tools for Visual Studio. If you plan to debug test failures or even write new tests at all, PTVS is an indispensable debugging extension to VS that enables full editing and debugging support for Python (including mixed native/managed debugging)

The steps outlined here describes how to set up your system and install the required dependencies such that they can be found when needed during the build process. They only need to be performed once.

  1. Install Visual Studio and the Windows SDK.
  2. Install GnuWin32, making sure <GnuWin32 install dir>\bin is added to your PATH environment variable.
  3. Install SWIG for Windows, making sure <SWIG install dir> is added to your PATH environment variable.

Any command prompt from which you build LLDB should have a valid Visual Studio environment setup. This means you should run vcvarsall.bat or open an appropriate Visual Studio Command Prompt corresponding to the version you wish to use.

macOS

  • To use the in-tree debug server on macOS, lldb needs to be code signed. For more information see Code Signing on macOS below.
  • If you are building both Clang and LLDB together, be sure to also check out libc++, which is a required for testing on macOS.

Building LLDB with CMake

The LLVM project is migrating to a single monolithic respository for LLVM and its subprojects. This is the recommended way to build LLDB. Check out the source-tree with git:

> git clone https://github.com/llvm/llvm-project.git

CMake is a cross-platform build-generator tool. CMake does not build the project, it generates the files needed by your build tool. The recommended build tool for LLVM is Ninja, but other generators like Xcode or Visual Studio may be used as well. Please also read Building LLVM with CMake.

Regular in-tree builds

Create a new directory for your build-tree. From there run CMake and point it to the llvm directory in the source-tree:

> cmake -G Ninja -DLLVM_ENABLE_PROJECTS="clang;lldb" [<cmake options>] path/to/llvm-project/llvm

We used the LLVM_ENABLE_PROJECTS option here to tell the build-system which subprojects to build in addition to LLVM (for more options see Common CMake options and CMake caches). Parts of the LLDB test suite require lld. Add it to the list in order to run all tests. Once CMake is done, run ninja to perform the actual build. We pass lldb here as the target, so it only builds what is necessary to run the lldb driver:

> ninja lldb

Standalone builds

This is another way to build LLDB. We can use the same source-tree as we checked out above, but now we will have two build-trees:

  • the main build-tree for LLDB in /path/to/lldb-build
  • a provided build-tree for LLVM and Clang in /path/to/llvm-build

Run CMake with -B pointing to a new directory for the provided build-tree1 and the positional argument pointing to the llvm directory in the source-tree. Note that we leave out LLDB here and only include Clang. Then we build the ALL target with ninja:

> cmake -B /path/to/llvm-build -G Ninja \
        -DLLVM_ENABLE_PROJECTS=clang \
        [<more cmake options>] /path/to/llvm-project/llvm
> ninja

Now run CMake a second time with -B pointing to a new directory for the main build-tree and the positional argument pointing to the lldb directory in the source-tree. In order to find the provided build-tree, the build-system needs the options LLVM_DIR and Clang_DIR (CMake variables are case-sensitive!):

> cmake -B /path/to/lldb-build -G Ninja \
        -DLLVM_DIR=/path/to/llvm-build/lib/cmake/llvm \
        -DClang_DIR=/path/to/llvm-build/lib/cmake/clang \
        [<more cmake options>] /path/to/llvm-project/lldb
> ninja lldb

Note

  1. The -B argument was undocumented for a while and is only officially supported since CMake version 3.14

Common CMake options

Following is a description of some of the most important CMake variables which you are likely to encounter. A variable FOO is set by adding -DFOO=value to the CMake command line.

If you want to debug the lldb that you’re building – that is, build it with debug info enabled – pass two additional arguments to cmake before running ninja:

> cmake -G Ninja \
    -DLLDB_EXPORT_ALL_SYMBOLS=1 \
    -DCMAKE_BUILD_TYPE=Debug
    <path to root of llvm source tree>

If you want to run the test suite, you will need a compiler to build the test programs. If you have Clang checked out, that will be used by default. Alternatively, you can specify a C and C++ compiler to be used by the test suite.

> cmake -G Ninja \
    -DLLDB_TEST_USE_CUSTOM_C_COMPILER=On \
    -DLLDB_TEST_USE_CUSTOM_CXX_COMPILER=On \
    -DLLDB_TEST_C_COMPILER=<path to C compiler> \
    -DLLDB_TEST_CXX_COMPILER=<path to C++ compiler> \
    <path to root of llvm source tree>

It is strongly recommend to use a release build for the compiler to speed up test execution.

Windows

On Windows the LLDB test suite requires lld. Either add lld to LLVM_ENABLE_PROJECTS or disable the test suite with LLDB_ENABLE_TESTS=OFF.

Although the following CMake variables are by no means Windows specific, they are commonly used on Windows.

  • LLDB_TEST_DEBUG_TEST_CRASHES (Default=0): If set to 1, will cause Windows to generate a crash dialog whenever lldb.exe or the python extension module crashes while running the test suite. If set to 0, LLDB will silently crash. Setting to 1 allows a developer to attach a JIT debugger at the time of a crash, rather than having to reproduce a failure or use a crash dump.
  • PYTHON_HOME (Required): Path to the folder where the Python distribution is installed. For example, C:\Python35.
  • LLDB_RELOCATABLE_PYTHON (Default=0): When this is 0, LLDB will bind statically to the location specified in the PYTHON_HOME CMake variable, ignoring any value of PYTHONHOME set in the environment. This is most useful for developers who simply want to run LLDB after they build it. If you wish to move a build of LLDB to a different machine where Python will be in a different location, setting LLDB_RELOCATABLE_PYTHON to 1 will cause Python to use its default mechanism for finding the python installation at runtime (looking for installed Pythons, or using the PYTHONHOME environment variable if it is specified).

Sample command line:

> cmake -G Ninja^
    -DLLDB_TEST_DEBUG_TEST_CRASHES=1^
    -DPYTHON_HOME=C:\Python35^
    -DLLDB_TEST_USE_CUSTOM_C_COMPILER=ON^
    -DLLDB_TEST_C_COMPILER=d:\src\llvmbuild\ninja_release\bin\clang.exe^
    <path to root of llvm source tree>

Building with ninja is both faster and simpler than building with Visual Studio, but chances are you still want to debug LLDB with an IDE. One solution is to run cmake twice and generate the output into two different folders. One for compiling (the ninja folder), and one for editing, browsing and debugging.

Follow the previous instructions in one directory, and generate a Visual Studio project in another directory.

> cmake -G "Visual Studio 15 2017 Win64" -Thost=x64 <cmake variables> <path to root of llvm source tree>

Then you can open the .sln file in Visual Studio, set lldb as the startup project, and use F5 to run it. You need only edit the project settings to set the executable and the working directory to point to binaries inside of the ninja tree.

NetBSD

Current stable NetBSD release doesn’t ship with libpanel(3), therefore it’s required to disable curses(3) support with the -DLLDB_DISABLE_CURSES:BOOL=TRUE option. To make sure check if /usr/include/panel.h exists in your system.

macOS

On macOS the LLDB test suite requires libc++. Either add libcxx to LLVM_ENABLE_PROJECTS or disable the test suite with LLDB_ENABLE_TESTS=OFF. Further useful options:

  • LLDB_BUILD_FRAMEWORK:BOOL: Builds the LLDB.framework.
  • LLDB_CODESIGN_IDENTITY:STRING: Set the identity to use for code-signing all executables. If not explicitly specified, only debugserver will be code-signed with identity lldb_codesign (see Code Signing on macOS).
  • LLDB_USE_SYSTEM_DEBUGSERVER:BOOL: Use the system’s debugserver, so lldb is functional without setting up code-signing.

CMake caches

CMake caches allow to store common sets of configuration options in the form of CMake scripts and can be useful to reproduce builds for particular use-cases (see by analogy usage in LLVM and Clang). A cache is passed to CMake with the -C flag, following the absolute path to the file on disk. Subsequent -D options are still allowed. Please find the currently available caches in the lldb/cmake/caches/ directory.

Common configurations on macOS

Build, test and install a distribution of LLDB from the monorepo (see also Building a Distribution of LLVM):

> git clone https://github.com/llvm/llvm-project

> cmake -B /path/to/lldb-build -G Ninja \
        -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-macOS.cmake \
        -DLLVM_ENABLE_PROJECTS="clang;libcxx;lldb" \
        llvm-project/llvm

> DESTDIR=/path/to/lldb-install ninja -C /path/to/lldb-build check-lldb install-distribution

Build LLDB standalone for development with Xcode:

> git clone https://github.com/llvm/llvm-project

> cmake -B /path/to/llvm-build -G Ninja \
        -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-base.cmake \
        -DLLVM_ENABLE_PROJECTS="clang;libcxx" \
        llvm-project/llvm
> ninja -C /path/to/llvm-build

> cmake -B /path/to/lldb-build \
        -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-Xcode.cmake \
        -DLLVM_DIR=/path/to/llvm-build/lib/cmake/llvm \
        -DClang_DIR=/path/to/llvm-build/lib/cmake/clang \
        llvm-project/lldb
> open lldb.xcodeproj
> cmake --build /path/to/lldb-build --target check-lldb

Note

The -B argument was undocumented for a while and is only officially supported since CMake version 3.14

Building The Documentation

If you wish to build the optional (reference) documentation, additional dependencies are required:

  • Sphinx (for the website)
  • Graphviz (for the ‘dot’ tool)
  • doxygen (if you wish to build the C++ API reference)
  • epydoc (if you wish to build the Python API reference)

To install the prerequisites for building the documentation (on Debian/Ubuntu) do:

> sudo apt-get install doxygen graphviz python3-sphinx
> sudo pip install epydoc

To build the documentation, configure with LLVM_ENABLE_SPHINX=ON and build the desired target(s).

> ninja docs-lldb-html
> ninja lldb-cpp-doc
> ninja lldb-python-doc

Cross-compiling LLDB

In order to debug remote targets running different architectures than your host, you will need to compile LLDB (or at least the server component) for the target. While the easiest solution is to just compile it locally on the target, this is often not feasible, and in these cases you will need to cross-compile LLDB on your host.

Cross-compilation is often a daunting task and has a lot of quirks which depend on the exact host and target architectures, so it is not possible to give a universal guide which will work on all platforms. However, here we try to provide an overview of the cross-compilation process along with the main things you should look out for.

First, you will need a working toolchain which is capable of producing binaries for the target architecture. Since you already have a checkout of clang and lldb, you can compile a host version of clang in a separate folder and use that. Alternatively you can use system clang or even cross-gcc if your distribution provides such packages (e.g., g++-aarch64-linux-gnu on Ubuntu).

Next, you will need a copy of the required target headers and libraries on your host. The libraries can be usually obtained by copying from the target machine, however the headers are often not found there, especially in case of embedded platforms. In this case, you will need to obtain them from another source, either a cross-package if one is available, or cross-compiling the respective library from source. Fortunately the list of LLDB dependencies is not big and if you are only interested in the server component, you can reduce this even further by passing the appropriate cmake options, such as:

-DLLDB_DISABLE_LIBEDIT=1
-DLLDB_DISABLE_CURSES=1
-DLLDB_DISABLE_PYTHON=1
-DLLVM_ENABLE_TERMINFO=0

In this case you, will often not need anything other than the standard C and C++ libraries.

Once all of the dependencies are in place, it’s just a matter of configuring the build system with the locations and arguments of all the necessary tools. The most important cmake options here are:

  • CMAKE_CROSSCOMPILING : Set to 1 to enable cross-compilation.
  • CMAKE_LIBRARY_ARCHITECTURE : Affects the cmake search path when looking for libraries. You may need to set this to your architecture triple if you do not specify all your include and library paths explicitly.
  • CMAKE_C_COMPILER, CMAKE_CXX_COMPILER : C and C++ compilers for the target architecture
  • CMAKE_C_FLAGS, CMAKE_CXX_FLAGS : The flags for the C and C++ target compilers. You may need to specify the exact target cpu and abi besides the include paths for the target headers.
  • CMAKE_EXE_LINKER_FLAGS : The flags to be passed to the linker. Usually just a list of library search paths referencing the target libraries.
  • LLVM_TABLEGEN, CLANG_TABLEGEN : Paths to llvm-tblgen and clang-tblgen for the host architecture. If you already have built clang for the host, you can point these variables to the executables in your build directory. If not, you will need to build the llvm-tblgen and clang-tblgen host targets at least.
  • LLVM_HOST_TRIPLE : The triple of the system that lldb (or lldb-server) will run on. Not setting this (or setting it incorrectly) can cause a lot of issues with remote debugging as a lot of the choices lldb makes depend on the triple reported by the remote platform.

You can of course also specify the usual cmake options like CMAKE_BUILD_TYPE, etc.

Example 1: Cross-compiling for linux arm64 on Ubuntu host

Ubuntu already provides the packages necessary to cross-compile LLDB for arm64. It is sufficient to install packages gcc-aarch64-linux-gnu, g++-aarch64-linux-gnu, binutils-aarch64-linux-gnu. Then it is possible to prepare the cmake build with the following parameters:

-DCMAKE_CROSSCOMPILING=1 \
-DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc \
-DCMAKE_CXX_COMPILER=aarch64-linux-gnu-g++ \
-DLLVM_HOST_TRIPLE=aarch64-unknown-linux-gnu \
-DLLVM_TABLEGEN=<path-to-host>/bin/llvm-tblgen \
-DCLANG_TABLEGEN=<path-to-host>/bin/clang-tblgen \
-DLLDB_DISABLE_PYTHON=1 \
-DLLDB_DISABLE_LIBEDIT=1 \
-DLLDB_DISABLE_CURSES=1

An alternative (and recommended) way to compile LLDB is with clang. Unfortunately, clang is not able to find all the include paths necessary for a successful cross-compile, so we need to help it with a couple of CFLAGS options. In my case it was sufficient to add the following arguments to CMAKE_C_FLAGS and CMAKE_CXX_FLAGS (in addition to changing CMAKE_C(XX)_COMPILER to point to clang compilers):

-target aarch64-linux-gnu \
-I /usr/aarch64-linux-gnu/include/c++/4.8.2/aarch64-linux-gnu \
-I /usr/aarch64-linux-gnu/include

If you wanted to build a full version of LLDB and avoid passing -DLLDB_DISABLE_PYTHON and other options, you would need to obtain the target versions of the respective libraries. The easiest way to achieve this is to use the qemu-debootstrap utility, which can prepare a system image using qemu and chroot to simulate the target environment. Then you can install the necessary packages in this environment (python-dev, libedit-dev, etc.) and point your compiler to use them using the correct -I and -L arguments.

Example 2: Cross-compiling for Android on Linux

In the case of Android, the toolchain and all required headers and libraries are available in the Android NDK.

The NDK also contains a cmake toolchain file, which makes configuring the build much simpler. The compiler, include and library paths will be configured by the toolchain file and all you need to do is to select the architecture (ANDROID_ABI) and platform level (ANDROID_PLATFORM, should be at least 21). You will also need to set ANDROID_ALLOW_UNDEFINED_SYMBOLS=On, as the toolchain file defaults to “no undefined symbols in shared libraries”, which is not compatible with some llvm libraries. The first version of NDK which supports this approach is r14.

For example, the following arguments are sufficient to configure an android arm64 build:

-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_HOME/build/cmake/android.toolchain.cmake \
-DANDROID_ABI=arm64-v8a \
-DANDROID_PLATFORM=android-21 \
-DANDROID_ALLOW_UNDEFINED_SYMBOLS=On \
-DLLVM_HOST_TRIPLE=aarch64-unknown-linux-android \
-DCROSS_TOOLCHAIN_FLAGS_NATIVE='-DCMAKE_C_COMPILER=cc;-DCMAKE_CXX_COMPILER=c++'

Note that currently only lldb-server is functional on android. The lldb client is not supported and unlikely to work.

Verifying Python Support

LLDB has a Python scripting capability and supplies its own Python module named lldb. If a script is run inside the command line lldb application, the Python module is made available automatically. However, if a script is to be run by a Python interpreter outside the command line application, the PYTHONPATH environment variable can be used to let the Python interpreter find the lldb module.

The correct path can be obtained by invoking the command line lldb tool with the -P flag:

> export PYTHONPATH=`$llvm/build/Debug+Asserts/bin/lldb -P`

If you used a different build directory or made a release build, you may need to adjust the above to suit your needs. To test that the lldb Python module is built correctly and is available to the default Python interpreter, run:

> python -c 'import lldb'

Code Signing on macOS

To use the in-tree debug server on macOS, lldb needs to be code signed. The Debug, DebugClang and Release builds are set to code sign using a code signing certificate named lldb_codesign. This document explains how to set up the signing certificate.

Note that it’s possible to build and use lldb on macOS without setting up code signing by using the system’s debug server. To configure lldb in this way with cmake, specify -DLLDB_USE_SYSTEM_DEBUGSERVER=ON.

If you have re-installed a new OS, please delete all old lldb_codesign items from your keychain. There will be a code signing certification and a public and private key. Reboot after deleting them. You will also need to delete and build folders that contained old signed items. The darwin kernel will cache code signing using the executable’s file system node, so you will need to delete the file so the kernel clears its cache.

Automatic setup:

  • Run scripts/macos-setup-codesign.sh

Manual setup steps:

  • Launch /Applications/Utilities/Keychain Access.app
  • In Keychain Access select the login keychain in the Keychains list in the upper left hand corner of the window.
  • Select the following menu item: Keychain Access->Certificate Assistant->Create a Certificate…
  • Set the following settings
Name = lldb_codesign
Identity Type = Self Signed Root
Certificate Type = Code Signing
  • Click Create
  • Click Continue
  • Click Done
  • Click on the “My Certificates”
  • Double click on your new lldb_codesign certificate
  • Turn down the “Trust” disclosure triangle, scroll to the “Code Signing” trust pulldown menu and select “Always Trust” and authenticate as needed using your username and password.
  • Drag the new lldb_codesign code signing certificate (not the public or private keys of the same name) from the login keychain to the System keychain in the Keychains pane on the left hand side of the main Keychain Access window. This will move this certificate to the System keychain. You’ll have to authorize a few more times, set it to be “Always trusted” when asked.
  • Remove ~/Desktop/lldb_codesign.cer file on your desktop if there is one.
  • In the Keychain Access GUI, click and drag lldb_codesign in the System keychain onto the desktop. The drag will create a Desktop/lldb_codesign.cer file used in the next step.
  • Switch to Terminal, and run the following:
sudo security add-trust -d -r trustRoot -p basic -p codeSign -k /Library/Keychains/System.keychain ~/Desktop/lldb_codesign.cer
rm -f ~/Desktop/lldb_codesign.cer
  • Drag the lldb_codesign certificate from the System keychain back into the login keychain
  • Quit Keychain Access
  • Reboot
  • Clean by removing all previously creating code signed binaries and rebuild lldb and you should be able to debug.

When you build your LLDB for the first time, the Xcode GUI will prompt you for permission to use the lldb_codesign keychain. Be sure to click “Always Allow” on your first build. From here on out, the lldb_codesign will be trusted and you can build from the command line without having to authorize. Also the first time you debug using a LLDB that was built with this code signing certificate, you will need to authenticate once.