Re: Problems building FreeBSD 9.2 on FreeBSD 10

On Jun 23, 2014, at 7:12 PM, Glen Barber <gjb_at_FreeBSD.org> wrote:

> On Mon, Jun 23, 2014 at 06:57:15PM -0600, Warner Losh wrote:
>> On Jun 23, 2014, at 6:15 PM, Craig Rodrigues <rodrigc_at_FreeBSD.org> wrote:
>>> So, I guess that stable/9 can build properly on a stable/10 box.
>>> For FreeBSD 9.2, there is no easy way out.
>> 
>> You’ll have to back port the patch then. We don’t guarantee forward
>> compatibility like this since 9.2 is frozen in time now.
>> 
> 
> I'd really like to discuss rethinking our forward-compatibility
> policies, since we have (now) 3 active stable/ branches, plus head/. 

Generally, in the past, the rule has been “head will build from the last stable branch tip.” This was extended, for a while, to “last stable branch point” when Ruslan made sure that worked. While -stable has generally built on -head, this was never part of the contract. It usually did, but is very very hard to guarantee given the nature of head’s tools changing in ways that are allowed for head, but that break prior branches.

> What I would like to see, with my RE hat on, is a "best effort"
> backwards compatibility to being able to build the lowest-numbered
> supported stable/ branch on head/.

I think, that as in the past, this will generally work. However, it won’t always work. Things break in this area a lot. More than you might think, especially with the huge amount of churn we’ve had wrt compilers, make, etc. I suspect that new imports of clang will break this every time, since every import of clang has required changes to the tree to either disable warnings, or to fix newly flagged things. I suspect there will be a lot of churn here, and releases will go stale the fastest… With -current starting to support building multiple versions of clang (and gcc), there’s hope for the future, but back-porting this code is beyond what I have the time to do. That’s going to make things increasingly difficult as we march forward.

This isn’t even getting into cross build scenarios….

Or building releases, which is a whole different set of lightly tested code that is mostly host independent, but sometimes isn’t as much as you’d had hoped...

> Sure, this won't always work, but "best effort" is better than "no
> effort", which the latter is why we do not have stable/8 snapshot
> builds, to be honest.  I won't spend the time on the stable/8/release/
> code nor the snapshot build scripts to waste the time.  Building
> stable/9 on head/ is annoying alone.

stable/9 builds on head. If there’s a race, that needs to be fixed in stable/9. That’s quasi supported because people do it. The “best effort” involves people that are interested in the bugs being fixed fixing them, or convincing others to fix them. For me, this scenario is outside the area I care about, have the ability to test, or have time for.

So “best effort” involves more than me making an effort. I may or I may not. It all depends on my time and inclination. If it is going to work, bugs need to be fixed in stable/9 that prevents it from building on head, while not breaking the ability to build on 9. So there’s a lot of heavy lifting that will be needed in short order to keep this working once the clang folks can figure out how to get past the angst of the upgrade path and push forward to 3.5. Some architectures will break when that happens, no doubt.

But 9.2 will never build on head because it is broken with bmake, which is now standard for head. Since 9.2 cannot be changed, and since we’ve removed (or nearly) fmake in current, chances are quite good it will never build on head again without some special handling.

In summary, good luck! there’s a lot of use cases here, and it will take time and effort of multiple people over the long haul to keep it working. Best effort may be larger than you estimate… I won’t stand in your way, but I’m afraid my time available to help is limited.

Warner