Ports/ppc64be: Why does Go1.7 require at least POWER8?

[John Paul Adrian Glaubitz]

Hello!

I just read the draft announcement for Go1.7 [1] and stumbled over this point:

"The experimental port to Linux on big-endian 64-bit PowerPC (linux/ppc64) now requires the POWER8 architecture or later."

Does anyone know what the reasoning behind this is? I understand that POWER8 has more features and instructions that can be used
as compared to POWER4 from which most ppc64-Big-Endian CPUs are derived. However, the problem with this change would be that
a large number of ppc64-Big-Endian systems would no longer be able to run Go and I presume that would affect the vast majority.

Please note that for POWER8 machines, there is a ppc64-Little-Endian port which is actually more popular on these machines. So
I don't think this decision would actually be beneficial for users but just mean that Go would be available on considerably less machines
out there as the number of people who run ppc64 on POWER8 actually run the Little-Endian variant.

Thanks,
Adrian

> [1] https://tip.golang.org/doc/go1.7

[Andrew Austin]

Some previous discussion exists here: https://groups.google.com/d/topic/golang-dev/NovmWlPewRE/discussion

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http://andrewaustin.com

[lab...@linux.vnet.ibm.com]

I opened an issue against the doc to correct this: #16372.

As described in the discussion below, ppc64 BE should continue to work as far back as power5, whereas ppc64le will require power8 in Go 1.7.