Re: [gentoo-user] Re: Gcc 5.3

[Paul Colquhoun]

On Wed, 30 Dec 2015 17:32:44 lee wrote:
> Neil Bothwick <neil@××××××××××.uk> writes:
> > On Tue, 29 Dec 2015 19:21:01 +0100, lee wrote:
> >> > As 4.9.3 is marked stable, I guess that's what'd you get per
> >> > default.
> >>
> >> 4.8.5
> >>
> >> I'd have to run emerge --sync to know about more recent versions.  How
> >> is that supposed to be used, btw?  I only run that when I do want to
> >> update everything.  Now if I didn't want to update anything but gcc,
> >> could I run emerge --sync and install gcc 5.x without having trouble
> >
> > Emerge --sync only updates the portage tree, so
> >
> > emerge --sync
> > emerge -a sys-devel/gcc:5
> >
> >> with anything else I might install before actually updating everything?
> >> So if I'd never explicitly update everything but run emerge --sync
> >> frequently, things would be updated over time, occasionally?
> >
> > No, nothing would get updated. To do that you need to run emerge @world
> > after emerge --sync.
>
> Well, yes, but what if want to install a package that hasn't been
> installed yet, or re-emerge an installed package with different USE
> flags, after updating the portage tree?  Will a more recent version be
> installed than would have been installed before the tree was updated,
> maybe updating other packages to more recent versions because they are
> needed for the new package?


You have a couple of options.

First, start with "emerge -p whatever" and see what update would happen with 
no adjustments.

Then try again, but specify the version you want and see if that works: 
"emerge -p =whatever-1.2.3"

If it is still trying to install updated versions of libraries or other 
dependencies, make a file like /etc/portage/package.mask/whatever and block 
anything higher than the library/dependency versions you already have.

A bit more work, but probably not much.

However, if you get too far behind, the versions you want may have been 
removed from the portage tree. This is still not a deal breaker. Old ebuilds 
are available from the Gentoo attic at https://sources.gentoo.org/cgi-bin/viewvc.cgi and can be installed in a local overlay. (I put mine in 
/usr/local/portage). Just put "PORTDIR_OVERLAY=/usr/local/portage" into 
/etc/portage/make/conf and you should be set.

You could also use the local overlay to just add the updated ebuilds for 
things you do want to upgrade (and required dependency upgrades, etc) but I 
think that would quickly become very unwieldy.



> Other distributions usually (want to) update a lot of packages once you
> update the information about available packages.
>
> >> > Stuff compiled with older gcc's should run with newer libgcc*[0], but
> >> > stuff compililed with a newer gcc might not run with the older
> >> > libgcc*. Same goes, with more problems IIRC, for libstdc++.
> >> > So beware of that. Apart from that? I'm not aware of problems.
> >>
> >> Uhm ... So I might break the system by switching between compiler
> >> versions?
> >
> > That's highly unlikely as software that has been compiled with the old
> > compiler will still work.
>
> And if not?
>
> Just yesterday I tried to update a Fedora install and it failed so that
> the machine is now unusable because it only keeps rebooting.  I expected
> it to fail, just not that badly ...  If I could find my USB stick, I'd
> be putting Gentoo on it now.
>
> > You may find that some programs fail to
> > recompile with the new compiler, but I didn't experience that with the
> > 4.9>5 step, although I had some that would build with 4.8 but not 4.9.
> >
> > I have an application which I would like to compile with gcc
> >
> >> 5.x just to see if that's even possible.  I could switch, try it, and
> >> then switch back.
> >
> > Exactly, run gcc-config, compile/emerge the program, run gcc-config again.
>
> And what about ccache?  Will it use the new version automatically and
> detect that the compiler version has changed so that files in the cache
> need to be recompiled?

-- 
Reverend Paul Colquhoun, ULC.     http://andor.dropbear.id.au/
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