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Joshua M. Clulow <josh@sysmgr.org>
Robert Mustacchi <rm@fingolfin.org>, Garrett D'Amore <garrett@damore.org>
published

IPD 19 Sunset SPARC

Goal

Officially end SPARC support in illumos and remove the SPARC code from the tree.

Background

When the illumos project was formed in 2010 as a fork of OpenSolaris, the operating system contained support for 32-bit and 64-bit x86 machines, and for various 64-bit SPARC machines from Sun Microsystems. In 2018, we officially dropped support for 32-bit x86 systems, leaving just 64-bit x86 and SPARC.

The most recent SPARC machines for which we have relatively direct and complete support were contemporary at the time of the fork; viz., the UltraSPARC T2 family of servers, such as the T5120 and T5220. The last of these systems reached their end-of-life between 2011 and 2012. In the decade hence, the size and quality of the pool of second hand systems available through eBay and other vendors has dwindled, and prices have risen to match. Desktop systems in particular are popular for collectors, and are thus now staggeringly expensive if you can find them at all. As a result, the pool of machines available to build the software is extremely limited; the project does not currently have access to a permanent official SPARC build machine.

Without ready access to build machines, one might consider cross compilation. Though we have some support for cross-architecture software generation in the tools, the operating system does not currently support being cross compiled in full. Work would be needed to complete surgery to Makefiles and arrange for packaged cross-architecture C compilers, amongst other things.

In theory one might emulate SPARC systems with QEMU, but reports in the field suggest that this does not work well enough to run modern illumos. Even if it did, it may take a very long time -- e.g., weeks! -- to build the operating system under full emulation.

In addition to the core of illumos, the external software ecosystem has changed a lot in ten years. Many new projects have emerged that generate program text at runtime (JIT) or which do not use established code generation systems like LLVM or GCC that have SPARC support; e.g., Go and Node.js. Some projects could in theory support illumos on SPARC, like Rust, but it will still require a not inconsiderable amount of work to get there. There is growing interest for use of Rust in the development of the core of illumos, and lack of current support for SPARC inhibits those efforts.

If a community of users was going to emerge to provide engineering effort and build resources for SPARC, it likely would have done so by now. It is always sad to close a chapter in our history, and SPARC systems represent a strong and positive memory for many of us. Nonetheless, the time has arrived to begin the process of removing SPARC support from the operating system.

What Would This Enable?

A non-exhaustive list of project work that members of the project would like to undertake, where SPARC support presents a barrier today includes:

  • retiring the now-ancient GCC 4.4.4 shadow compiler that remains chiefly to support the SPARC platform
  • use of newer GCC versions and newer C standards to enable improvements such as better compile-time assertions (CTASSERT(), see 12994, etc)
  • cleanup of some of the internals of mac(9E) which have some facilities that exist only for specific SPARC hardware
  • reworking of some of the interpreted programs in usr/src/tools with faster and more featureful tools written in Rust
  • use of Rust to implement new facilities in the kernel, in libraries and in commands

Strategy and Timeline

  1. Replace GCC 4.4.4 shadow with GCC 10 shadow (done, see bug 14149)
  2. Update project documentation to make a clear statement about platform support (immediate)
  3. Stop accepting changes to code for SPARC (immediate)
  4. Delete the SPARC code from the tree (coming months)
    • Care must be taken not to break anything, but one benefit of dropping the platform is cleaning up a lot of code that is mostly not relevant anymore so we should likely do this deliberately and not just clean up occasional files "as we go"
    • Even though there will be just one architecture after the removal, any machinery that exists to support multiple architectures must be kept to enable future porting work (e.g., ARM or RISC-V)
    • We should retain support for interpreting SPARC data where it is not in the way; e.g.,
      • mdb can retain support for SPARC core files, ELF notes, etc
      • dis, libdisasm, etc, can continue to disassemble SPARC program text