HEADS UP: sparc64 backend for llvm/clang imported

John-Mark Gurney jmg at funkthat.com
Sat Mar 1 01:16:50 UTC 2014

Dimitry Andric wrote this message on Fri, Feb 28, 2014 at 20:22 +0100:
> In r262613 I have merged the clang-sparc64 branch back to head.  This
> imports an updated sparc64 backend for llvm and clang, allowing clang to
> bootstrap itself on sparc64, and to completely build world.  To be able
> to build the GENERIC kernel, there is still one patch to be finalized,
> see below.
> If you have any sparc64 hardware, and are not afraid to encounter rough
> edges, please try out building and running your system with clang.  To
> do so, update to at least r262613, and enable the following options in
> e.g. src.conf, or in your build environment:
> WITH_LIBCPLUSPLUS=y  (optional)
> Alternatively, if you would rather keep gcc as /usr/bin/cc for the
> moment, build world using just WITH_CLANG, enabling clang to be built
> (by gcc) and installed.  After installworld, you can then set CC=clang,
> CXX=clang++ and CPP=clang-cpp for building another world.
> For building the sparc64 kernel, there is one open issue left, which is
> that sys/sparc64/include/pcpu.h uses global register variables, and this
> is not supported by clang.  A preliminary patch for this is attached,
> but it may or may not blow up your system, please beware!
> The patch changes the pcpu and curpcb global register variables into
> inline functions, similar to what is done on other architectures.
> However, the current approach is not optimal, and the emitted code is
> slightly different from what gcc outputs.  Any improvements to this
> patch are greatly appreciated!
> Last but not least, thanks go out to Roman Divacky for his work with
> llvm/clang upstream in getting the sparc64 backend into shape.

Ok, I have a new pcpu patch to try.  I have only compile tested it.

It is available here:

I've also attached it.

Craig, do you mind testing it?

This patch also removes curpcb as it appears to not be used by any
sparc64 C code.  A GENERIC kernel compiles fine, and fxr only turns up
curpcb used in machdep code, and no references to it under sparc64.

This is not a proper solution in that
it can mean counters/stats can be copied/moved to other cpus overwriting
the previous values if a race happens...  We use
PCPU_SET(mem, PCPU_GET(mem) + val) for PCPU_ADD, not great, but it's
no worse than what we were previously using..

Until we get a proper fix which involves mapping all the cpu's PCPU
data on all CPUs, this will have to sufice..

This patch is based upon, I believe, a patch from Marius and possibly
modified by rdivacky.

Thanks for testing..

  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."
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