x/sys/unix: TestPassFD consistently failing in aix-ppc64 builder on release-branch.go1.12

[bcmills]

golang.org/x/sys/unix is failing in aix-ppc64 on release-branch.go1.12 (https://build.golang.org/log/2ceea003d216da8b55d107004541d477ada9c89f):

--- FAIL: TestPassFD (0.75s)
    syscall_unix_test.go:224: child process: "WriteMsgUnix: write unix : sendmsg: bad file number", <nil>
FAIL
FAIL	golang.org/x/sys/unix	1.041s

The same failure does not occur on release-branch.go1.13. Is there a fix we should backport, or should we skip the test on AIX on 1.12?

CC @Helflym @trex58 @laboger

[Helflym]

https://golang.org/cl/170537 should fix it.

[bcmills]

@Helflym, as far as I can tell that CL is on the master branch (that is, Go 1.14), but the test failure was only observed on release-branch.go1.12. Is there something that can/should be backported to fix the builder?

[Helflym]

Why 1.14 ? Yes, it has been merged in master branch but before 1.13 freeze. That's why golang.org/x/sys/unix is green for release-branch.go1.13 but fails for release-branch.go1.12. Or I'm missing something...
To explain a bit further, the test is failing because in 1.12, we are using recvmsg and sendmsg which aren't compatible with Control and Controllen structures.

[bcmills]

Sorry, my mistake — for some reason I thought that CL hadn't been merged yet.

If it is expected that the golang.org/x/sys/unix test fails on AIX before 1.13, then the test should call t.Skip if runtime.GOOS == "aix" on builds that lack the go1.13 build tag.

[Helflym]

Is it possible to check the go1.13 build tag inside an if or the whole file must be disabled for 1.12 ?

[bcmills]

I'm not sure, but you can always add a separate file that sets a variable:

// […]

// +build aix,!go1.13

package unix

func init() {
	aixHasSendmsgBug = true
}

[gopherbot]

Change https://golang.org/cl/193577 mentions this issue: unix: skip TestPassFD on AIX before 1.13

[tklauser]

Couldn't we just backport https://golang.org/cl/170537 (maybe sans the SockaddrDatalink addition) to release-branch.go1.12 to fix the issue instead of just skipping the test? Or is that not worth the effort?

[Helflym]

I think it's also better to backport it. Syscall package is also using Control and Controllen structures, so nrecvmsg and nsendmsg should be used.

[ianlancetaylor]

Sure, let's backport it.

[gopherbot]

Change https://golang.org/cl/193608 mentions this issue: [release-branch.go1.12] syscall: on AIX use nsendmsg and nrecvmsg, define SockaddrDatalink

[gopherbot]

Closed by merging cf06b9a to release-branch.go1.12.