Re: [ptxdist] Go in ptxdist

[Clemens Gruber <clemens.gruber@pqgruber.com>]

Hi,

On Wed, Oct 05, 2016 at 06:31:17PM +0200, Michael Olbrich wrote:
> This description is a bit vague. In general, whether armel or armhf is used
> does not depend on the ARM architecture, so armel on ARMv7 (and using
> floating point instructions!) is perfectly valid.
> We need to investigate if armhf is just the default for ARMv6/7 or if that
> can be configured.

Yes, I found more information on this topic:

$GOARM (for arm only; default is auto-detected if building on the target
processor, 6 if not)
This sets the ARM floating point co-processor architecture version the
run-time should target. If you are compiling on the target system, its
value will be auto-detected.
- GOARM=5: use software floating point; when CPU doesn't have VFP
  co-processor
- GOARM=6: use VFPv1 only; default if cross compiling; usually ARM11 or
better cores (VFPv2 or better is also supported)
- GOARM=7: use VFPv3; usually Cortex-A cores

See: https://golang.org/doc/install/source#environment

So we have to use 5 for all softfloat architectures, no matter if they
are ARMv5, v6 or v7 based.
So only for ARMv6 and ARMv7 with hardfloat we would use a GOARM value of
6 and 7 respectively.

They also seem to use ARMv7 Data Memory Barrier instructions if GOARM==7
https://github.com/golang/go/blob/master/src/runtime/asm_arm.s#L716

--

Something else I forgot to mention:
Since a few releases, Go is implemented in Go (and a little bit of asm)
and no longer in C, which means, to build Go, you need to bootstrap it
with a binary Go for your host architecture.
They do release official Linux binaries for amd64, 386 and armv6l (with
the l standing for little endian I assume)
Do you think there are PTXdist users out there who are running it on
non-amd64 hosts? What host platforms do we have to support?

Maybe we could also bootstrap it with gccgo (but then we would need a
toolchain containing a GCC built with --enable-languages=c,c++,go).

Clemens

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