freebsd-update 6.2-R -> 6.3-B1 rollback failed

[Jan Henrik Sylvester]

Colin Percival wrote:
> Jan Henrik Sylvester wrote:
>> Colin Percival wrote:
>>> I believe that your system is now 6.3-BETA1 with a few shared libraries
>>> from 6.2-RELEASE mixed in.  If you can get a copy of /lib/*.so.* and
>>> /usr/lib/*.so.* from a 6.3-BETA1 system and install those into place
>>> (in fact, probably all you need is /lib/libc.so.6) your system should
>>> be ok.  Let me know if you need any help with this.
>> I guess I can download a 6.3-BETA1 cd and copy the files over from
>> there. If you have a better way, please, let me know.
> 
> That's probably the safest approach.  Theoretically you could get all of

There are no more BETA1 images on FTP -- I should have thought of that. 
My next idea would be to use libs from a BETA2 cd to try to make the 
system bootable again. If that worked, I would have a system with BETA1 
/ BETA2 mixture... would freebsd-update be able to bring that to BETA2 
or would it fail? (I could answer that myself, if I knew the answer to 
the question at the bottom.)

Or should I install BETA2 from cd on top of it? (I have never done that, 
but I assume that is possible without reinstalling all packages as well.)

> In short, as long as you don't build a custom kernel but call it "GENERIC" or
> "SMP", FreeBSD Update should automatically DTRT.

That is exactly my question. On 6.2-RELEASE, I sometimes used a modified 
ld-elf.so.1 or a single patched module without recompiling the kernel. 
What does using freebsd-update (accidentally or deliberately) do in that 
case? By accident, I discovered that it does not always fail. Does it 
skip the modified files, overwrite them with new versions, or overwrite 
them with an unpredictable bdiff merge that is likely garbage? (From my 
observations, I assume that it does the second -- but maybe that was 
just luck.)

Thanks,
Jan Henrik