cmd/internal/xcoff: move to x/debug/xcoff

[Helflym]

Hi,

Since CL 149957, the tests inside gccgoimporter as long as the gccgo command is available, which is the case on most of AIX machines. However, it's only aware of ELF gccgo files, it doesn't recognize XCOFF files. To add the features, cmd/internal/xcoff must be moved to x/debug/xcoff as it was suggested by issue 28037.
Is that possible ?

Morever, big archive format is only available on AIX, as far as I know. Therefore, is that okay if I implement functions to read them in x/debug/xcoff ? Or I'd rather do a x/debug/ar as it was suggested here:
https://github.com/golang/go/blob/master/src/cmd/internal/buildid/buildid.go#L121

/cc @ianlancetaylor @bradfitz

[ianlancetaylor]

CC @rsc

I don't think we've really decided what is happening with x/debug. Or if we did, I've forgotten.

Note that we could keep postponing that and address this issue by moving cmd/internal/xcoff to internal/xcoff.

[Helflym]

I haven't thought about internal/xcoff. I'd rather have x/debug/xcoff as it could be used by anyone as debug/elf or debug/macho currently are. But it's as you wish.

[bradfitz]

I want to see the aix/ppc64 column all black and "ok" on https://build.golang.org/ before we start doing nice-to-have changes and entering the cherry-picking/branch-management world.

[bradfitz]

Moving to Go 1.13 for now. If AIX is in good shape soon then we could probably do this during the freeze, but it's not important.