6. Conclusion

During this second part of the project, we greatly benefited from the experience acquired during the first part Validation of TenDRA Capability to Implement a UNIX-like Operating System. The build environment we used and the way we integrated the TenDRA technology were directly derived from the work on the Unixware platform. Also, the initial set of Linux commands we could reasonably port was derived from the commands we had already ANDFized for Unixware.

We finally ported and validated about 230 commands on the Linux/i386 platform, but we could port only about 150 of them to the Linux/Alpha platform. The main reason for not porting the 80 remaining commands on Linux/Alpha was that we were short of time. Although we are below the target of 300 commands to be ported to both platforms, we believe that the experiment was a success. A significant amount of sometimes complex code was ANDFized, and the portability of this code was demonstrated. The main reasons that the initial objective was not attained were:

• The switch to the second platform was delayed. Initially, we had planned to use the microkernel based version of Linux on PowerPC, but this was not available in time.

• Setting up the Alpha/Linux system took a considerable amount of time. This was mainly due to the fact that Linux has not been ported to “off-the-shelf” hardware, and the system had to be assembled from components (mother board, power supply, disks, etc.).

• In the Linux/Alpha distribution we installed, a number of commands were missing, and others were still not fully validated. This meant that, porting commands from Intel to Alpha, we found several portability bugs which were not fixed, and sometimes not even known, in the Alpha command sources. Finding fixes or asking for help on the Linux/Alpha mailing list slowed down our work.

In the course of the project, Linux has evolved from Linux 1.1 to 1.3, and Linux commands were distributed on Alpha. However, we stuck to the Linux 1.1 commands, and we only used the Linux/Alpha distribution to install the system and to find fixes when we had problems with some commands.

Actually, many of the portability problems we found are now fixed on Linux/Alpha, and it would be much easier to port these commands now than it was a few months ago. However, the first source delivery of commands for Linux/Alpha was only available in December 95, and using this new set of commands would have required to re-do on the Intel platform the work (ANDFization, installation and validation) which was already done. Moreover, this first delivery was still not extensively validated and contained a number of bugs.

This project demonstrated that it is possible to build an API for a -rather large- set of commands. Moreover, this API is mostly based on standard APIs, xpg3, svid3, with a relatively small number of additions (e.g. a more complete bsd API than the TenDRA bsd_extn). However, installation of the standard APIs (Posix, Xpg3,...) with TenDRA has shown that Linux does not fully conform to these standards. In fact, the best support is for the bsd API, since a large number of commands come from bsd sources.

We used a 3-step approach in porting to ANDF, first compiling with the native compiler, second, using the TenDRA compiler with the native header files, and finally using TenDRA with abstract headers files and token libraries. Although we used the second step to find portability errors detected by the TenDRA compiler, this could be done in the third step. However, the third step which consists in making the source code compatible with the abstract API, is not so easy, and thus we found it easier to resolve portability checks in a separate step.

Most of the modifications we made to the source code for the commands came from missing function declarations and other trivial unportable coding, e.g. wrong assumptions on int and pointer sizes.

The TenDRA technology has proven capable of handling the differences between the two platforms. Although the same operating system runs on both platforms, these hardware platforms are sufficiently different to create difficulties. Standard APIs were successfully installed on both platforms, and the specific API developed for the commands could be designed to support the two different implementations. However, defining and installing an API is not an easy process and requires some sometimes extended knowledge of the TenDRA technology. We also detected a very small number of bugs in the TenDRA technology, in particular for the Dec/Alpha installer which has only been recently distributed by DRA.