Re: [gentoo-user] gcc upgrade - rebuild everything?

[Alan McKinnon <alan.mckinnon@gmail.com>]

Apparently, though unproven, at 21:58 on Thursday 21 October 2010, Grant did 
opine thusly:

> I just upgraded from gcc-4.4.3-r2 to gcc-4.4.4-r2 and I'm wondering if
> I really need to rebuild everything as it says in the guide:
> 
> http://www.gentoo.org/doc/en/gcc-upgrading.xml

No, you do not need to do this. The document is over-reaching (see below)

I ran a mixture of 4.4.3 and 4.4.4 for ages, completely trouble-free.

> If not, when is it necessary?

When you have an ABI change in the code generated by the compiler. In other 
words, when code generated by this version is incompatible with code generated 
by that version, and you have both on the same system. This has not happened 
for a long time in gcc-land.

Now, about that official doc. Your question comes up with unbelievable 
regularity and every time the poster references that doc. But it is not 
necessary to do what the doc says, and a long time ago I think I figured it 
out.

The author's intention is less to give you the absolute complete total 100% 
truth that will always work out just fine, and more to reduce the amount of 
clutter in his inbox or on b.g.o.

The rules about how to detect when a rebuild of world is needed are complex 
and most readers simply will not understand them - they don't understand 
compiler internals (how many people DO?). But if you tell people to just 
rebuild world every time, and weird funny lurking problems are likely to just 
get fixed as a side effect, no real harm is done. Does it hurt the author? No. 
Does it reduce the amount of bugs he has to deal with on the rare occasion it 
is needed? Yes.

What does the user lose? Nothing much, more cpu cycles get used, more bits 
flip on a disk, your video card gets a work out scrolling all that text. Will 
you waste time? Yes. Will you break stuff? No.

So rebuild world if it makes you feel better. But you don't need to this time. 
The authors of gcc will certainly notify the entire world and it's dogs when 
you do need to.

-- 
alan dot mckinnon at gmail dot com