Building#

Getting the Sources#

Please refer to the LLVM Getting Started Guide for general instructions on how to check out the LLVM monorepo, which contains the LLDB sources.

Git browser: https://github.com/llvm/llvm-project/tree/main/lldb

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.

If you want to run the test suite, you’ll need to build LLDB with Python scripting support.

Optional Dependencies#

Although the following dependencies are optional, they have a big impact on LLDB’s functionality. It is strongly encouraged to build LLDB with these dependencies enabled.

By default they are auto-detected: if CMake can find the dependency it will be used. It is possible to override this behavior by setting the corresponding CMake flag to On or Off to force the dependency to be enabled or disabled. When a dependency is set to On and can’t be found it will cause a CMake configuration error.

Feature

Description

CMake Flag

Editline

Generic line editing, history, Emacs and Vi bindings

LLDB_ENABLE_LIBEDIT

Curses

Text user interface

LLDB_ENABLE_CURSES

LZMA

Lossless data compression

LLDB_ENABLE_LZMA

Libxml2

XML

LLDB_ENABLE_LIBXML2

Python

Python scripting

LLDB_ENABLE_PYTHON

Lua

Lua scripting

LLDB_ENABLE_LUA

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 swig python3-dev libedit-dev libncurses5-dev
$ pkg install swig python
$ pkgin install swig python36 cmake ninja-build
$ brew install swig cmake ninja

Note that there’s an incompatibility between Python version 3.7 and later and swig versions older than 4.0.0 which makes builds of LLDB using debug versions of python unusable. This primarily affects Windows, as debug builds of LLDB must use debug python as well.

Windows#

  • Visual Studio 2019.

  • The latest Windows SDK.

  • The Active Template Library (ATL).

  • GnuWin32 for CoreUtils and Make.

  • Python 3. Make sure to (1) get the x64 variant if that’s what you’re targetting and (2) install the debug library if you want to build a debug lldb. The standalone installer is the easiest way to get the debug library.

  • 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).

  • SWIG for Windows

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 with the “Desktop Development with C++” workload and the “Python Development” workload.

  2. Install GnuWin32, making sure <GnuWin32 install dir>\bin is added to your PATH environment variable. Verify that utilities like dirname and make are available from your terminal.

  3. Install SWIG for Windows, making sure <SWIG install dir> is added to your PATH environment variable. Verify that swig is available from your terminal.

  4. Install Python 3 from the standalone installer and include the debug libraries in the install, making sure the Python install path is added to your PATH environment variable.

  5. Register the Debug Interface Access DLLs with the Registry from a privileged terminal.

> regsvr32 "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\DIA SDK\bin\msdia140.dll"
> regsvr32 "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\DIA SDK\bin\amd64\msdia140.dll"

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

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 repository 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.

$ ninja lldb lldb-server

If you only want lldb, or are on a platform where lldb-server is not supported, you can pass just lldb. Ninja will only build 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 multiple build-trees:

  • the main build-tree for LLDB in /path/to/lldb-build

  • one or more provided build-trees for LLVM and Clang; for simplicity we use a single one 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 looks for the path to its CMake modules in LLVM_DIR. If you use a separate build directory for Clang, remember to pass its module path via Clang_DIR (CMake variables are case-sensitive!):

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

If you do not require or cannot build lldb-server on your platform, simply remove it from the Ninja command.

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_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_INCLUDE_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_EMBED_PYTHON_HOME (Default=1 on Windows): When this is 1, 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_EMBED_PYTHON_HOME to 0 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_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 16 2019" -A x64 -T host=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.

macOS#

On macOS the LLDB test suite requires libc++. Either add LLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" or disable the test suite with LLDB_INCLUDE_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;lldb" \
        -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
        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" \
        -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
        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 \
        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 and the Python API reference)

  • Graphviz (for the ‘dot’ tool)

  • doxygen (if you wish to build the C++ API reference)

  • SWIG (for generating Python bindings)

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

$ sudo apt-get install doxygen graphviz swig

To install Sphinx and its dependencies, use the requirements.txt available within LLVM to ensure you get a working configuration:

$ pip3 install -r /path/to/llvm-project/llvm/docs/requirements.txt

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

$ ninja docs-lldb-html
$ ninja docs-lldb-man
$ ninja lldb-cpp-doc

Cross-compiling LLDB#

The advice presented here may not be complete or represent the best practices of CMake at this time. Please refer to CMake’s documentation if you have any doubts or want more in depth information.

In order to debug remote targets running different architectures than your host, you will need to compile LLDB (or at least the server component lldb-server) for the target. While the easiest solution is to 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_ENABLE_PYTHON=0
-DLLDB_ENABLE_LIBEDIT=0
-DLLDB_ENABLE_CURSES=0
-DLLVM_ENABLE_TERMINFO=0

(see Optional Dependencies for more)

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

If you find that CMake is finding a version of an optional dependency that for whatever reason doesn’t work, consider simply disabling it if you don’t know that you need it.

Once all of the dependencies are in place, you need to configure the build system with the locations and arguments of all the necessary tools.

There are 2 ways to do this depending on your starting point and requirements.

1. If you are starting from scratch and only need the resulting cross compiled binaries, you can have LLVM build the native tools for you.

2. If you need a host build too, or already have one, you can tell CMake where that is and it will use those native tools instead.

If you are going to run lldb and lldb-server only on the target machine, choose option 1. If you are going to run lldb on the host machine and connect to lldb-server on the target, choose option 2.

Either way, the most important cmake options when cross-compiling are:

  • CMAKE_SYSTEM_NAME and CMAKE_SYSTEM_PROCESSOR: This tells CMake what the build target is and from this it will infer that you are cross compiling.

  • 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 this is a list of library search paths referencing the target libraries.

  • 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.

  • LLVM_NATIVE_TOOL_DIR (only when using an existing host build): Is a path to the llvm tools compiled for the host. Any tool that must be run on the host during a cross build will be configured from this path, so you do not need to set them all individually. If you are doing a host build only for the purpose of a cross build, you will need it to include at least llvm-tblgen, clang-tblgen and lldb-tblgen. Be aware that the list may grow over time.

  • 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.

To find the possible values of the CMAKE_* options, please refer to the CMake documentation.

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

For testing, you may want to set one of:

  • LLDB_TEST_COMPILER : The compiler used to build programs used in the test suite. If you are also building clang, this will be used but if you want to test remotely from the host, you should choose the cross compiler you are using for the cross build.

  • LLDB_INCLUDE_TESTS=0 : To disable the tests completely.

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.

Configure as follows:

cmake <path-to-monorepo>/llvm-project/llvm -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DLLVM_ENABLE_PROJECTS="clang;lld;lldb" \
  -DCMAKE_SYSTEM_NAME=Linux \
  -DCMAKE_SYSTEM_PROCESSOR=AArch64 \
  -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc \
  -DCMAKE_CXX_COMPILER=aarch64-linux-gnu-g++ \
  -DLLVM_HOST_TRIPLE=aarch64-unknown-linux-gnu \
  -DLLDB_ENABLE_PYTHON=0 \
  -DLLDB_ENABLE_LIBEDIT=0 \
  -DLLDB_ENABLE_CURSES=0

During this build native tools will be built automatically when they are needed. The contents of <build dir>/bin will be target binaries as you’d expect. AArch64 binaries in this case.

Example 2: Cross-compiling for linux arm64 on Ubuntu host using an existing host build#

This build requires an existing host build that includes the required native tools. Install the compiler as in example 1 then run CMake as follows:

cmake <path-to-monorepo>/llvm-project/llvm -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DLLVM_ENABLE_PROJECTS="clang;lld;lldb" \
  -DCMAKE_SYSTEM_NAME=Linux \
  -DCMAKE_SYSTEM_PROCESSOR=AArch64 \
  -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc \
  -DCMAKE_CXX_COMPILER=aarch64-linux-gnu-g++ \
  -DLLVM_HOST_TRIPLE=aarch64-unknown-linux-gnu \
  -DLLVM_NATIVE_TOOL_DIR=<path-to-host>/bin/ \
  -DLLDB_ENABLE_PYTHON=0 \
  -DLLDB_ENABLE_LIBEDIT=0 \
  -DLLDB_ENABLE_CURSES=0

The only difference from example 1 is the addition of DLLVM_NATIVE_TOOL_DIR pointing to your existing host build.

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_ENABLE_PYTHON=0 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 3: 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'

Make sure you’re using the Python interpreter that matches the Python library you linked against. For more details please refer to the caveats.

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.

Automatic setup, run:

  • scripts/macos-setup-codesign.sh

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.

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.