Lazarus for Cross-Platform Development

Lazarus provides an outstanding native code solution. The compiler and most libraries are written with cross-platform in mind. That is why programs written in Free Pascal do not need to run a configure script before compilation. The base types, like char, byte, integer and string, work the same on all platforms. An integer always is a signed 32-bit value. The 64-bit integer is called int64. The native integer for a processor is called PtrInt for signed and PtrUInt for unsigned values. Lazarus itself can be compiled with a simple make or graphically in the IDE itself. And, of course, Lazarus is developed with Lazarus.

FPC's runtime library does not use libc; rather, it uses kernel functions, which change less often. Therefore, the created executables normally work on various Linux distributions and do not need to be recompiled for each new glibc version.

With Lazarus, you can write and debug the biggest part under Linux. But eventually, you'll need to test it on the other targets. However, you do not need to install Lazarus and all the development tools on all your target platforms. Cross compiling can be used to develop under Linux and target another operating system or processor. For example, you could develop under Linux and create Windows executables, and then test them with Wine or in a virtual machine running Windows, or on an actual Windows system. Cross compiling is a big time-saver, because it allows you to test on several platforms quickly and to use your favorite programs while developing.

Note, however, that cross compiling does require you to install the cross-compile tools and libraries, which can be tricky. Precompiled versions do not yet exist for all possible hosts and targets. Easy directions are provided for Linux to Windows, because of Wine, and for Windows to Windows CE, because there are installers with all needed tools.

First, you need to cross compile and install the GNU binutils. This is well documented on several sites, including the Lazarus Wiki (see Resources). For many targets, this is as simple as downloading a single tar.gz and running a script with some parameters.

The next step is to cross compile the Free Pascal libraries. If you want to cross compile to another processor type, you need to cross compile the compiler too. Again, for many targets, complete scripts are available.

If your program requires third-party libraries, these must be cross compiled too. If they are written completely in Object Pascal, normally you can just compile them. Lazarus will do that automatically for you. If they use system libraries, it can become difficult. The problems are then the same as for C/C++ compilers.

Once you've installed the cross compiler and libraries, cross compiling becomes easy in Lazarus. Simply pass the -T option to the compiler. For example, pass -Twin32 to compile a 32-bit Windows executable instead of a Linux binary. The -P option defines the target processor. Normally, you don't even need to pass special search paths, because of the path scheme used. For instance, the Pascal units for the fpc 2.3.1 compiler, for the processor type i386, and for target operating system Linux are installed under /usr/lib/fpc/2.3.1/units/i386-linux/. All filenames and search paths of the compiler and the IDE support macros, which greatly reduces the amount of command-line parameters and configuration settings.

Lazarus reduces the amount of platform-specific settings even further. The IDE allows you to combine several source directories into a Lazarus package. A Lazarus package can be a library or just a logical module of a big project. A package has its own search paths, its own compiler settings and its own macros. All filenames and search paths are stored relative to the configuration file (.lpk file). A package can use other packages and inherit search paths and compiler settings. You can store a package anywhere on the disk. All search paths are adapted automatically on the fly. And, because every source has its own namespace, there is seldom a name conflict. You can switch to another version simply by opening the .lpk file. Each package also has its own output directories, normally one for each platform, which are created automatically.

When a package's source file is changed, the IDE automatically compiles the package and all packages in the current project that depend on it. You can fine-tune this automation for each package.

When you switch the target platform in the IDE, all packages' output directories are switched. The compiler options dialog is shown in Figure 2.

Figure 2. Lazarus Compiler Options