[gentoo-amd64] Re: cmake error on libkdepim compile

[Duncan]

"Mark Haney" <mhaney@××××××××××××.org> posted
49788889.1080808@××××××××××××.org, excerpted below, on  Thu, 22 Jan 2009
09:54:01 -0500:

> One more thing, when I looked at gcc versions available on my system
> 4.1.2 is the latest stable one.  I take it that 4.3.2 is in ~amd64?

Yes.  One nice thing about Gentoo is that the way it uses gcc-config, you 
can have several gcc versions merged and switch between them.  With the 
exception of C++ programs using libstdc++, there's very little reason to 
worry about switching between versions causing problems, and it's very 
convenient to have multiple versions available to test with, if a compile 
is breaking with one.

As for libstdc++, in the bad old days (early gcc 3, I think, it was 
really before I got into compiling stuff much and possibly before I got 
into Linux much at all), different minor gcc versions sometimes had 
dramatic libstdc++ incompatibilities, but for quite some time it has been 
generally backward compatible and with only a few exceptions, usually 
forward compatible as well.

The one set of exceptions I am aware of was that earlier KDE 3 used a few 
of the (then) newer libstdc++ functions from I believe it was gcc 4.0 or 
4.1 if they were available at compile time, and that specific bit of kde 
(generally Internet related, local stuff seemed to work fine) would fail 
to work if compiled with the newer version then set to run against (due 
to gcc-config-ing back to) the older gcc/libstdc++.  However, that only 
happened if it was compiled against the newer libstdc++ version then was 
run against the older one.  If one compiled with the older version, it 
ran just fine against the newer version.  And I was able to work with it 
just fine compiled against the newer version even when gcc-config-ed to 
an older version -- I just didn't use the broken bits, all Internet 
related, while pointing at the old version, and gcc-config-ed back to the 
newer version as soon as possible.  IOW, I just had gcc-config pointing 
at the old version long enough to compile whatever it was that was still 
giving me trouble in the new version, then switched back to the new 
version, which I was using for normal system operations.

So in general you should be pretty safe installing multiple gcc versions, 
then using gcc-config to temporarily point at whatever one you want to 
try.  Just keep track of which one you're pointed at, and try to keep as 
much of the system as possible compiled with a single version.  Newer 
versions will at first be hard-masked, but due to gcc-config, I've never 
had a problem installing them and even compiling nearly everything with 
them.  At that early stage, there will definitely be packages that won't 
compile and you'll either need to switch back to an early gcc for those 
packages, or search bugzilla and apply necesary patches -- there's very 
often bugs already filed and patches already posted, since some people 
try it before gcc ever gets out of beta, upstream.  Later, certainly as 
gcc-4.3 is now, it has been around long enough that many of those patches 
have already been applied in the newest versions of various ~arch 
packages in the tree.  But if you're conservative, you can still install 
the newer versions and keep gcc-config pointed at your older versions for 
the system in general, only using the newer versions for testing or 
specific packages.  There should be even less problems with that, and 
since you're using the old versions most of the time anyway, you won't 
run into the packages still broken with the new compiler.

Just what I've found.  It should be perfectly safe to have the new 
compilers installed but still point to the old ones for most stuff.  If 
you do want to run the newer compilers for most of your system, you'll 
probably want to run ~arch at least, since otherwise you'll have lots of 
packages with broken compiles because the patches aren't yet backported 
to stable, since that version of gcc isn't yet close to being keyworded 
stable.

-- 
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