Advanced deb-packaging with CMake

CMake has become our C/C++ build tool of choice because it provides good cross-platform support and very reasonable IDE (Visual Studio, CLion, QtCreator) integration. Another very nice feature is the included packaging support using the CPack module. It allows to create native deployable artifacts for a plethora of systems including NSIS-Installer for Windows, RPM and Deb for Linux, DMG for Mac OS X and a couple more.

While all these binary generators share some CPACK-variables there are specific variables for each generator to use exclusive packaging system features or requirements.

Deb-packaging features

The debian package management system used not only by Debian but also by Ubuntu, Raspbian and many other Linux distributions. In addition to dependency handling and versioning packagers can use several other features, namely:

  • Specifying a section for the packaged software, e.g. Development, Games, Science etc.
  • Specifying package priorities like optional, required, important, standard
  • Specifying the relation to other packages like breaks, enhances, conflicts, replaces and so on
  • Using maintainer scripts to customize the installation and removal process like pre- and post-install, pre- and post-removal
  • Dealing with configuration files to protect end user customizations
  • Installing and linking files and much more without writing shell scripts using ${project-name}.{install | links | ...} files

All these make the software easier to package or easier to manage by your end users.

Using deb-features with CMake

Many of the mentioned features are directly available as appropriately named CMake-variables all starting with CPACK_DEBIAN_.  I would like to specifically mention the CPACK_DEBIAN_PACKAGE_CONTROL_EXTRA variable where you can set the maintainer scripts and one of my favorite features: conffiles.

Deb protects files under /etc from accidental overwriting by default. If you want to protect files located somewhere else you specify them in a file called conffiles each on a separate line:

/opt/myproject/myproject.conf
/opt/myproject/myproject.properties

If the user made changes to these files she will be asked what to do when updating the package:

  • keep the own version
  • use the maintainer version
  • review the situation and merge manually.

For extra security files like myproject.conf.dpkg-dist and myproject.conf.dpkg-old are created so no changes are lost.

Unfortunately, I did not get the linking feature working without using maintainer scripts. Nevertheless I advise you to use CMake for your packaging work instead of packaging using the native debhelper way.

It is much more natural for a CMake-based project and you can reuse much of your metadata for other target platforms. It also shields you from a lot of the gory details of debian packaging without removing too much of the power of deb-packages.

Advertisements

4 Tips for better CMake

We are doing one of those list posts again! This time, I will share some tips and insights on better CMake. Number four will surprise you! Let’s hop right in:

Tip #1

model dependencies with target_link_libraries

I have written about this before, and this is still my number one tip on CMake. In short: Do not use the old functions that force properties down the file hierarchy such as include_directories. Instead set properties on the targets via target_link_libraries and its siblings target_compile_definitions, target_include_directories and target_compile_options and “inherit” those properties via target_link_libraries from different modules.

Tip #2

always use find_package with REQUIRED

Sure, having optional dependencies is nice, but skipping on REQUIRED is not the way you want to do it. In the worst case, some of your features will just not work if those packages are not found, with no explanation whatsoever. Instead, use explicit feature-toggles (e.g. using option()) that either skip the find_package call or use it with REQUIRED, so the user will know that another lib is needed for this feature.

Tip #3

follow the physical project structure

You want your build setup to be as straight forward as possible. One way to simplify it is to follow the file system and and the artifact structure of your code. That way, you only have one structure to maintain. Use one “top level” file that does your global configuration, e.g. find_package calls and CPack configuration, and then only defers to subdirectories via add_subdirectory. Only for direct subdirectories though: if you need extra levels, those levels should have their own CMake files. Then build exactly one artifact (e.g. add_executable or add_library) per leaf folder.

Tip #4

make install() an option()

It is often desirable to include other libraries directly into your build process. For example, we usually do this with googletest for our unit test. However, if you do that and use your install target, it will also install the googletest headers. That is usually not what you want! Some libraries handle this automagically by only doing the install() calls when they are the top level project. Similar to the find_package tip above, I like to do this with an option() for explicit user control!

Generating done

That is it for today! I hope this is helps and we will all see better CMake code in the future.

My C++ Tool Belt

I suspect that every developer has a “tool belt” that he or she uses to be productive. By that I mean a collection of tools, libraries and whatever else helps. With a few exceptions, these tool belts will probably be language specific, or at least platform specific. As my projects updated their compilers and transitioned to C++11 and beyond, my C++ tool belt changed quite a bit. Since things like threading, smart pointers and functional abstractions where added to the standard library, those are now already included by default. Today I wanna write about what is in my modernized C++11 tool belt.

The Standard Library

Ever since the tr1 extensions, the standard library has progressed into becoming truly powerful and exceptional. The smart pointers, containers, algorithms are much more language extensions than “just” a library, and they play perfectly with actual language features, such as lambdas, auto and initializer lists.

fmtlib

fmtlib provides placeholder-based text formatting a la Python’s String.format. There have been a few implementations of this idea over the years, but this is the first where I think that it might just dethrone operator<< overloading for good. It's fast, stable, portable and has a nice API.
I begin to miss this library the moment I need to work on a project that does not have it.
The next best thing is Qt’s QString::arg mechanism, with slightly inferior API, a less inclusive license, and a much bigger dependency.

spdlog

Logging is a powerful tool, both for software development and maintenance. Chances are you are going to need it at one point. spdlog is my favorite choice for this task. It uses fmtlib internally, which is just another plus point. It’s simple, fast and very nice to use due to reuse of fmtlib’s formatting. I usually just include this in my projects and get the included fmtlib for free.

optional

This one is actually part of the most recent C++17, but since that is not widely available yet (meaning not many projects have adopted it), I’m going to list it explicitly. There are also a few alternative implementations, such as the one in Boost or akrzemi1’s single-header variant.
Unlike many other programming languages, C++ has a relatively high emphasis on value types. While reference types usually have a built-in “not available” state (a.k.a. nullptr, NULL, Nothing or nil), an optional can transport intent much clearer. For value types, however, it’s absolutely mandatory to have an optional type. Otherwise, you just end up wrapping the value in a pointer just to make it optional.
Do not, however, fall into the trap of using optional for error handling. It’s not made for that, and other abstractions, such as expected are much better for that.

CMake

There is really only one choice when it comes to build tools, and that’s CMake. It’s got its own bunch of weaknesses, but the goods far outweight the bads. With the target_ functions, it’s actually quite nice and scales really well to bigger projects. The main downside here is that it still does not play nice with some tools, most notably visual studio. CLion and QtCreator fare much better. Then again, CMake enables the use of other tools easily, such as clang-tidy.

A word on Boost

Boost is no longer the must-have it once was. Much of the mandated functionality has already been incorporated into the standard library. It is no longer a requirement for a sane C++ project. On the contrary, boost is notoriously huge and somewhat cumbersome to integrate. Boost is not a library, it is a collection of libraries, therefore you can still decide whether to use Boost on a library by library basis. However, much of that is viral, and using a small part of Boost will easily drag in a few hundreds of other Boost headers. The libraries I tend to include most often are Boost.Utility (for boost::noncopyable) and Boost.Filesystem. The former is obviously easy to do without Boost, especially with = delete; and the latter is a part of the standard library since C++17. I hope to be doing the majority of my projects without it in the future. Boost was a catalyst for most of the C++ progress in recent years. It slowly becoming obsolete, either by being integrated into the standard or it’s idioms no longer being needed, is just a sign of its own success.

My honorable mentions are Qt and the stb single file libraries. What are your go-to tools?

Modern CMake with target_link_libraries

Dependency hell?

One thing that has eluded me in the past was how to efficiently manage dependencies of different components within one CMake project. I’d use the include_directories, add_definitions and add_compile_options command in the top-level or in mid-level CMakeLists.txt files just to get the whole thing to compile. Of course, this is all heavily order-dependent – so the build system breaks as soon as you make an ever so subtle change to the directory layout. I’ve seen projects tackle this problem in various ways – for example by defining specifically named variables for each library and using that for their clients. Other projects defined “interface” files for each library that could be included by other targets. All these homegrown solutions work, but they are rather clumsy and don’t work well when integrating libraries not written in that same convention.

target_link_libraries to the rescue!

It turns out there’s actually a pretty elegant solution built into CMake, which centers around target_link_libraries. But information on this is pretty scarce on the web. The ones that initially put me on the right track were The Ultimate Guide to Modern CMake and CMake – Introduction and best practices. Of course, it’s all in the CMake documentation, but mentioned implicitly at best.

The gist is this: Using target_link_libraries to link A to an internal target B will not only add the linker flags required to link to B, but also the definitions, include paths and other settings – even transitively – if they are configured that way.

To do this, you need to use target_include_directories and target_compile_definitions with the PUBLIC or INTERFACE keywords on your targets. There’s also the PRIVATE keyword that can be used to avoid adding the settings to all dependent targets.

A simple example

Here’s a small example of a library that uses Boost in its headers and therefore wishes to have its clients setup those directories as well:

set(TARGET_NAME cool_lib)

add_library(${TARGET_NAME} STATIC 
  cool_feature.cpp cool_feature.hpp)

target_include_directories(${TARGET_NAME}
  INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})

target_include_directories(${TARGET_NAME} SYSTEM
  PUBLIC ${Boost_INCLUDE_DIR})

Now here’s a program that wants to use that:

set(TARGET_NAME cool_tool)

add_executable(cool_tool main.cpp)

target_link_libraries(cool_tool
  PRIVATE cool_lib)

cool_tool can just #include "cool_feature.hpp" without knowing exactly where it is located in the source tree or without having to worry about setting up the boost includes for itself! Pretty neat!

PRIVATE, PUBLIC and INTERFACE

Typically, you’d use the PRIVATE keyword for includes and definitions that are exclusively used in you implementation, i.e. your *.cpp and *.c files and internal headers. It’s good practice to favor PRIVATE to avoid “leaking” dependencies so they won’t stack up in the dependent libraries and bring down your compile times. The INTERFACE keyword is a bit more curious: For example, with definitions, you can use it to define your .dll interface differently for compilation and usage. For include directories, one common usage is to set the own source directory with INTERFACE if you keep your headers and source files in the same folder. The PUBLIC keyword is used when definitions and includes are relevant for the own and dependent libraries. It pretty much is the combination of PRIVATE and INTERFACE – whenever you’re temped to put something in both of those, put it in PUBLIC instead. It is probably the most common option.

The future!

I hope that all open-source libraries switch to this style sooner rather than later so you can easily include them in your build-trees. Just don’t use the old commands that add properties for all following targets like add_definitions, include_directories etc. and use the commands with the target_ prefix!

CMake as a project model

One thing I actually like about Maven is its attempt to create a project model, conventions and a basic project structure. It allows easy integration IDEs, build servers and so on. For projects in C/C++ I find CMake an attractive way to specify the project model.

Despite its name CMake is not really a build system but more of a cross-platform project description with an integrated build system generator. Cross-platform means not only operating system (OS) here but development environment in general. CMake thus can generate project files for MS Visual Studio 20xx, Eclipse CDT, Code::Blocks, KDevelop and the like. QtCreator can even import a CMake-based project natively which brings you up to speed in almost no time.

CMake allows you organise your project in modules and manage your external dependencies. It does not impose as strict rules as Maven does and lacks an own artifact repository infrastructure but you can use the CMake package definitions or pkg-config information many projects provide.

Packaging and deployment with CPack allows you to deliver releases of your project the way your user would expect it: Depending on the target platform you can package your software as a Windows installer executable (using NSIS), several options for Mac OS X (like Package Maker or Bundle) and the popular DEB and RPM package formats for Linux Distributions.

Conclusion

CMake is more than just another build system. It is a flexible tool to define your project and integrate it with your favorite development tools. It can support the whole project lifecyle from initial creation and normal development to deployment and delivery of your software to the user.

Building Visual C++ Projects with CMake

In previous post my colleague showed how to create RPM packages with CMake. As a really versatile tool it is also able to create and build Visual Studio projects on Windows. This property makes it very valuable when you want to integrate your project into a CI cycle(in our case Jenkins).

Prerequisites:

To be able to compile anything following packages needed to be installed beforehand:

  •  CMake. It is helpful to put it in the PATH environment variable so that absolute paths aren’t needed.
  • Microsoft Windows SDK for Windows 7 and .NET Framework 4 (the web installer or  the ISOs).  The part “.NET Framework 4” is very important, since when the SDK for the .NET Framework 3.5 is installed you will get following parse error for your *.vcxproject files:

    error MSB4066: The attribute “Label” in element is unrecognized

    at the following position:

    <ItemGroup Label=”ProjectConfigurations”>

    Probably equally important is the bitness of the installed SDK. The x64 ISO differs only in one letter from the x86 one. Look for the X if want 64 bit.

  • .NET Framework 4, necessary to make msbuild run

It is possible that you encounter following message during your SDK setup:

A problem occurred while installing selected Windows SDK components. Installation of the “Microsoft Windows SDK for Windows 7” product has reported the following error: Please refer to Samples\Setup\HTML\ConfigDetails.htm document for further information. Please attempt to resolve the problem and then start Windows SDK setup again. If you continue to have problems with this issue, please visit the SDK team support page at http://go.microsoft.com/fwlink/?LinkId=130245. Click the View Log button to review the installation log. To exit, click Finish.

The reason behind this wordy and less informative error message were the Visual C++ Redistributables installed on the system. As suggested by Microsoft KB article removing them all helped.

Makefiles:

For CMake to build anything you need to have a CMakeLists.txt file in your project. For a tutorial on how to use CMake, look at this page. Here is a simple CMakeLists.txt to get you started:

project(MyProject)
 cmake_minimum_required(VERSION 2.6)
 set(source_files
 main.cpp
 )
 include_directories(
 ${CMAKE_CURRENT_SOURCE_DIR}
 )
 add_executable(MyProject ${source_files})

Building:

To build a project there are few steps necessary. You can enter them in your CI directy or put them in a batch file.

call "%ProgramFiles%\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd" /Release /x86

With this call all necessary environment variables are set. Be careful on 64 bit platforms as jenkins slave executes this call in a 32 bit context and so “%ProgramFiles%” is resolved to “ProgramFiles (x86)” where the SDK does not lie.

del CMakeCache.txt

This command is not strictly necessary, but it prevents you from working with outdated generated files when you change your configuration.

cmake -G "Visual Studio 10" .

Generates a Visual Studio 2010 Solution. Every change to the solution and the project files will be gone when you call it, so make sure you track all necessary files in the CMakeLists.txt.

cmake --build . --target ALL_BUILD --config Release

The final step. It will net you the MyProject.exe binary. The target parameter is equal to the name of the project in the solution and the config parameter is one of the solution configurations.

Final words:

The hardest and most time consuming part was the setup of prerequisites. Generic, not informative error messages are the worst you can do to a clueless customer. But… when you are done with it, you are only two small steps apart from an automatically built executable.

Building Windows C++ Projects with CMake and Jenkins

The C++ programming environment where I feel most comfortable is GCC/Linux (lately with some clang here and there). In terms of build systems I use cmake whenever possible. This environment also makes it easy to use Jenkins as CI server and RPM for deployment and distribution tasks.

So when presented with the task to set up a C++ windows project in Jenkins I tried to do it the same way as much as possible.

The Goal:

A Jenkins job should be set up that builds a windows c++ project on a Windows 7 build slave. For reasons that I will not get into here, compatibility with Visual Studio 8 is required.

The first step was to download and install the correct Windows SDK. This provides all that is needed to build C++ stuff under windows.

Then, after installation of cmake, the first naive try looked like this (in an “execute Windows Batch file” build step)

cmake . -DCMAKE_BUILD_TYPE=Release

This cannot work of course, because cmake will not find compilers and stuff.

Problem: Build Environment

When I do cmake builds manually, i.e. not in Jenkins, I open the Visual Studio 2005 Command Prompt which is a normal windows command shell with all environment variables set. So I tried to do that in Jenkins, too:

call “c:\Program Files\Microsoft SDKs\Windows\v6.0\Bin\SetEnv.Cmd” /Release /x86

cmake . -DCMAKE_BUILD_TYPE=Release

This also did not work and even worse, produced strange (to me, at least) error messages like:

‘Cmd’ is not recognized as an internal or external command, operable program or batch file.

The system cannot find the batch label specified – Set_x86

After some digging, I found the solution: a feature of windows batch programming called delayed expansion, which has to be enabled for SetEnv.Cmd to work correctly.

Solution: SetEnv.cmd and delayed expansion

setlocal enabledelayedexpansion

call “c:\Program Files\Microsoft SDKs\Windows\v6.0\Bin\SetEnv.Cmd” /Release /x86

cmake . -DCMAKE_BUILD_TYPE=Release

nmake

Yes! With this little trick it worked perfectly. And feels almost as with GCC/CMake under Linux:  nice, short and easy.