Re: [gentoo-amd64] Re: About gcc 4.1.1

[Dieter Ries]

What is this emerge libtool? I didnt know about it and just did a 
emerge gcc
gcc-config
emerge -e system

now i am going to start emerge -e world.

cu
Dieter


Am Donnerstag 31 August 2006 20:39 schrieb Duncan:
> Bob Slawson <bslawson@×××××××××××.net> posted
> 44F7199F.6030604@×××××××××××.net, excerpted below, on  Thu, 31 Aug 2006
>
> 13:17:19 -0400:
> > Dieter Ries wrote:
> >> OK so there it is, gcc 4.1.1 is stable.
> >>
> >> i just emerged it and switched gcc-config to 4.1.1.
> >> does it make sense to recompile gcc 4.1.1 with gcc 4.1.1?
> >> (do you know what i mean?
> >
> > No.  As part of the gcc build process, the new gcc is used to compile
> > itself.  'Stage 1'
> > uses an existing compiler to compile the new source to 'xgcc'.  Then in
> > 'stage 2',
> > 'xgcc' compiles the new source to 'gcc', the compiler is compiling
> > itself.
>
> Actually, while you are correct about the gcc build process, the Gentoo
> Linux gcc upgrade guide [1] DOES recommend rebuilding it, but as part of a
> larger full system rebuild.
>
> Quoting the gist of the general instructions:
>
> Code Listing 2.1: Upgrading GCC
> # emerge -uav gcc
>
> (Please substitute "i686-pc-linux-gnu-4.1.1" with the GCC
> version and CHOST settings you've upgraded to:)
> # gcc-config i686-pc-linux-gnu-4.1.1
> # source /etc/profile
>
> If you upgraded from gcc 3 to 4 (e.g. from 3.4.6 to 4.1.1 in this
> example) you will have to run fix_libtool_files.sh manually
> # fix_libtool_files.sh 3.4.6
>
> (Rebuilding libtool)
> # emerge --oneshot -av libtool
>
>    To be completely safe that your system is in a sane state, you must
>    rebuild the toolchain and then world to make use of the new compiler.
>
> Code Listing 2.2: Rebuilding system
> # emerge -eav system
> # emerge -eav world
>
>    It is safe to remove the older GCC version at this time. If you feel the
>    need, please issue the following command (as usual, substitute
>    =sys-devel/gcc-3.4* with the version you want to uninstall):
>
> Code Listing 2.3: Removing older GCC version
> # emerge -aC =sys-devel/gcc-3.4*
>
> End quote.
>
> Thus, the new gcc will actually be compiled three times, first in the
> initial upgrade, second as part of emerge --emptytree system (which builds
> the rest of the toolchain using the new gcc and builds the new gcc using
> itself), third as part of emerge --emptytree world, which rebuilds the
> entire system (including gcc) using the now fully upgraded toolchain.
>
> IOW, first time rebuilds gcc using the old version, second time rebuilds
> it and the toolchain using new gcc but partly old toolchain, third time
> rebuilds it (and everything else) with an entirely fresh toolchain.
>
> Of course, that's going to take some major time...  probably 2-3 days of
> constant compiling.  (I figure a day with my dual Opteron, with the
> portage work dir in a tmpfs based ramdisk in main memory... since I have 8
> gigs of ram I might as well use it.)
>
> OTOH, gcc 4.1.1 is a HUGE boost in performance for amd64, much more so
> than for x86, as amd64 is still new enough for this to be the first version
> to really have support for it fully integrated and optimized.  (gcc 3.x had
> support, but it was bolted on, and optimizations weren't as good as they
> could have been as a result.  gcc 4.0 had it integrated but as the first
> release of the rewrite, was mainly focused on not making things worse. gcc
> 4.1 finally has integrated amd64 support AND is better than 3.x in
> general. gcc 4.1.1 fixed a few minor remaining bugs from 4.1.0.)
>
> [1] http://www.gentoo.org/doc/en/gcc-upgrading.xml
>
> --
> Duncan - List replies preferred.   No HTML msgs.
> "Every nonfree program has a lord, a master --
> and if you use the program, he is your master."  Richard Stallman

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