Gentoo dropping support of SPARC

Posted Jun 6, 2017 20:35 UTC (Tue) by epa (subscriber, #39769)
Parent article: Gentoo dropping support of SPARC

Is SPARC one of those architectures where you have sparc, sparc64, sparcv5, supersparc, ultrasparc, sparcman or whatever and some of them are really ancient stuff, so you can 'drop' one of them but it doesn't affect any hardware sold in the last twenty years?

Gentoo dropping support of SPARC

Posted Jun 6, 2017 20:42 UTC (Tue) by nix (subscriber, #2304) [Link] (2 responses)

Quite. SPARC32 kernel support is gone, but there is still code in the kernel -- and weird uncommented workarounds in the kernel -- to support things like the Spitfire, released in 1995, an artifact which is actually literally in the Computer History Museum.

The artifact I ran into half an hour ago was code in arch/sparc/kernel/time_64.c:tick_get_tick():

static unsigned long long tick_get_tick(void)
{
        unsigned long ret;

        __asm__ __volatile__("rd        %%tick, %0\n\t"
                             "mov       %0, %0"
                             : "=r" (ret));

        return ret & ~TICK_PRIV_BIT;
}

What's that weird mov for? Well, there was a comment before this code was split up in 2003:

   * Just to be anal we add a workaround for Spitfire
   * Errata 50 by preventing pipeline bypasses on the
   * final read of the %tick register into a compare
   * instruction.  The Errata 50 description states
   * that %tick is not prone to this bug, but I am not
   * taking any chances.

So we have a weird workaround with a long-lost comment in a frequently-called path to handle bugs that, uh, are believed not to affect actual museum artifacts, and certainly don't affect anything more recent (though anything in actual use these days won't use this code path at all because it will have the %stick register).

Gentoo dropping support of SPARC

Posted Jun 14, 2017 22:16 UTC (Wed) by jch (guest, #51929) [Link] (1 responses)

> SPARC32 kernel support is gone, but there is still code in the kernel -- and weird uncommented workarounds in the kernel -- to support things like the Spitfire, released in 1995

Isn't the Spitfire a SPARCv9 (a.k.a. UltraSparc or SPARC64)?

Gentoo dropping support of SPARC

Posted Jun 16, 2017 17:32 UTC (Fri) by nix (subscriber, #2304) [Link]

I think it was the first, or nearly the first, widely-available UltraSPARC. I wasn't suggesting that it was 32-bit: I was noting that even some UltraSPARC stuff is weird and ancient and has little justification for existence any more (and, by extension, that nobody not running a computer museum will miss the ability to boot 32-bit kernels on their SPARC Classic).

Gentoo dropping support of SPARC

Posted Jun 7, 2017 8:58 UTC (Wed) by glaubitz (subscriber, #96452) [Link]

> Is SPARC one of those architectures where you have sparc, sparc64, sparcv5, supersparc, ultrasparc, sparcman or whatever and some of them are really ancient stuff, so you can 'drop' one of them but it doesn't affect any hardware sold in the last twenty years?

sparc64 is fully supported by Oracle:

> http://www.oracle.com/technetwork/server-storage/linux/do...
> https://oss.oracle.com/projects/linux-sparc/

A variant of sparcv8 called LEON is still supported, too, because ESA uses it:

> https://en.wikipedia.org/wiki/LEON