all: add support for FreeBSD 12

[mikioh]

This is a meta bug for tracking the status of the issues for supporting FreeBSD 12. FreeBSD 12, which will be released in CY18, will contain a few breaking changes on ABI and a few packages in standard library (and probably x/sys/unix repository) need to find out some good way to fill the ABI gap between FreeBSD 11 or below and FreeBSD 12 or above.

• os, syscall, x/sys/unix: add support for FreeBSD 12 #22448 os, syscall, x/sys/unix: add support for FreeBSD 12

[SylvainGarrigues]

I compiled successfully Go 1.10 on FreeBSD 12 / arm. Basic programs seem to work for me: is there anything notably broken?

[mikioh]

@SylvainGarrigues,

I don't know the detail of your basic program and your kernel configuration. See #22448. What happens when the kernel is built without a series of compat flags such as WANT_FREEBSD11_DIRENT?

[paulzhol]

I think it's safe not to switch to the new APIs and require COMPAT_FREEBSD11, at least not while we also support FreeBSD 10.x and 11.x.
I'm particularly worried about this:
https://svnweb.freebsd.org/base?view=revision&revision=320043
Unlike the 64-bit inode ABI change, Kevent (keventt) is used directly in the runtime netpoller. And while 64-bit inodes can be used by applications working on large filesystems and can work in backward-compatible mode (limited to golang.org/x/sys/unix), the runtime won't benefit from the new kevent API.

Rust are explicitly linking to the old symbol versions to handle the FreeBSD 12 changes:
rust-lang/libc@78f9322
rust-lang/libc@969ad2b

Also note that all the ARM kernel configs, even ARMv4/5 which we don't even support - have COMPAT_FREEBSD10 and COMPAT_FREEBSD11 enabled.
(COMPAT_FREEBSD10 is just for pipe, and @tklauser switched all the BSDs to pipe2 recently).

options 	COMPAT_FREEBSD10	# Compatible with FreeBSD10
options 	COMPAT_FREEBSD11	# Compatible with FreeBSD11

https://github.com/freebsd/freebsd/blob/75c7e3b2102b9ecddae188b1c7b60057f87ffdd3/sys/arm/conf/std.arm#L5-L6
https://github.com/freebsd/freebsd/blob/75c7e3b2102b9ecddae188b1c7b60057f87ffdd3/sys/arm/conf/std.armv6#L50-L51
https://github.com/freebsd/freebsd/blob/75c7e3b2102b9ecddae188b1c7b60057f87ffdd3/sys/arm/conf/std.armv7#L50-L51

Unlike the amd64 GENERIC kernel, which has all COMPAT_* options turned on:

options 	COMPAT_FREEBSD4		# Compatible with FreeBSD4
options 	COMPAT_FREEBSD5		# Compatible with FreeBSD5
options 	COMPAT_FREEBSD6		# Compatible with FreeBSD6
options 	COMPAT_FREEBSD7		# Compatible with FreeBSD7
options 	COMPAT_FREEBSD9		# Compatible with FreeBSD9
options 	COMPAT_FREEBSD10	# Compatible with FreeBSD10
options 	COMPAT_FREEBSD11	# Compatible with FreeBSD11

https://github.com/freebsd/freebsd/blob/75c7e3b2102b9ecddae188b1c7b60057f87ffdd3/sys/amd64/conf/GENERIC#L59-L66

[mikioh]

@paulzhol,

Can you please file a separate issue for your concern about kevent?

[paulzhol]

@mikioh I don't think there's a need for another issue, core doesn't use EVFILT_TIMER so the new absolute timer API won't be used anyhow. We can continue using to the current (COMPAT_FREEBSD11) sysnum on all versions.

[mikioh]

@paulzhol,

Would you mind adding a note to doc/go1.12.html (and detailed information in https://github.com/golang/go/wiki/FreeBSD) to clarify the requirements for running Go 1.x on FreeBSD 12-STABLE kernels?

[paulzhol]

@mikioh I've updated the wiki. I see there's a syscall section in doc/go1.12.html (autogenerated?) from Brad's 'RELNOTE=FreeBSD breakages in syscall, use build tags' comment in the CL. I'll update it as well.

[mikioh]

I've checked the network subsystem code of 12-STABLE and found no sign of ABI breaking changes. So it's fine to close this issue (w/ explicit limitations such as requiring COMPAT_SOMETHING) once #22448 is fixed.

PS: The fix for #28896 in Go 1.12 might frighten auto-generated code, but it's fine.

[gopherbot]

Change https://golang.org/cl/160778 mentions this issue: doc: go1.12: document FreeBSD 12.0 requires COMPAT_FREEBSD11