Porting Software to HelenOS

This page shall contain a brief guide for porting software (e.g. from GNU/Linux) to HelenOS. Currently, it only contains assorted links to existing resources.

Links

• Maintenance instructions for binutils
• ​Blog ​posts ​about ​GCC ​porting
• ​Coastline - scripts for porting POSIX-like software to HelenOS (and some ​blog ​posts)
• Python porting: ​repository and ​ML announcement

POSIX emulation layer

HelenOS is not another Unix-like OS and thus it needs an emulation for applications that were written for Unix systems. This emulation is currently in HelenOS provided by libposix library that provides implementation of functions that are part of POSIX standard but were considered inappropriate for HelenOS.

libposix provides an (incomplete) illusion that the application has access to standard POSIX headers and functions. The ported application is then linked with libposix which translates the calls to HelenOS specific implementations in libc.

Implementation detail: some of the functions in libc have the same name as standard POSIX ones or they offer slightly different behaviour. To prevent naming clashes, symbols in libc.a are renamed to avoid the need to rename the POSIX versions (which was an older approach where renaming was done during preprocessing, however this approach has various disadvantages).

General approach

For most (reasonable) GNU/Linux programs, we can assume that they are distributed with a ./configure script. The purpose of this script is to check the environment and prepare Makefiles needed for actual compilation. In order to build the application for HelenOS we "only" need to persuade the configure script to cross-compile it and use HelenOS specific compiler flags and link with libposix.

Although this seems as a simple task because configure offers parameters/variables for exactly this, there are several obstacles.

• HelenOS currently uses Linux ABI and thus the cross-compiler used gives the impression that the target is GNU/Linux system. This could lead to some false expectations.
• There is a lot of compiler/linker flags that are passed. The amount itself obscures a reasonable editing of the command line.
• HelenOS works mostly with static libraries. When linking with static libraries, their order is important and they typically need to come after object files for proper linking. That is not always possible to specify with plain LDFLAGS or CFLAGS settings.

The above means that either patching or some build scripts is sometimes necessary or that the invocation line for configure is rather complex (or both). To simplify the above and, foremost, to allow repeatable builds, the so called Coastline was created.

Coastline

Currently, Coastline is hosted as a separate Git ​repository on GitHub.

Coastline is a set of scripts that allows the developer porting software to HelenOS capture the porting process in a reasonable way. The porting is captured as a shell script that runs the configure and other commands needed to build the ported software. Apart from this it also prepares variables that contains proper path to HelenOS include directories or libraries. Use of Coastline means that the porting process is reproducible and it also allows to factor our common routines.

When the developer uses the Coastline, he is working with 3 directories. The first one is the directory with Coastline checkout, in the scripts referred to as HSCT_HOME. Second one is the build directory where the building happens. And the last one is directory with HelenOS sources (HSCT_HELENOS_ROOT).

The build directory needs to be initialized first. During initialization, headers and libraries from HelenOS source tree are copied to the build directory and used compiler/linker flags are extracted and prepared for further use. These are stored in the helenos/ subdirectory. A shell script helenos/env.sh contains settings of various paths and also the flags for the compiler and the linker. To initialize the build directory, you need to call

$HSCT_HOME/hsct.sh init /path/to/HelenOS/source/tree

If you specify a profile (e.g. ia32) as a third argument, the initialization would prepare the build directory for that profile. Specifying the word build as a last (fourth) argument would force a complete rebuild for the specified profile.

Once the directory is initialized, the user can build the ported software. The build is invoked by calling hsct.sh in the following manner:

hsct.sh build <package>

This would download the tarballs, unpack them and run configure and make (or alternatives) for the given software.

Once the build is complete, the user can either package the software into a tarball or directly copy the application to HelenOS source tree. Running

hsct.sh install <package>

would copy the application (library) to HelenOS source tree that was specified during initialization. Executing

hsct.sh archive <package>

would create a tarball in archives/ subdirectory. Unpacking this tarball into uspace/overlay would effectively install the package.

If you do not want to rebuild the software yourself, you can download ​pre-built packages. Please note that these packages are not 100% up-to-date with mainline and sometimes may not work or may work only partially.

Porting new software

• harbour files
  • $shipname, $shipsources and $shiptugs
  • build() and package() functions
• common issues
  • forcing cross-compilation
  • naming clashes