Re: [gentoo-dev] RFC: masking old versions of sys-devel/gcc

[Mike Gilbert]

On Wed, Apr 26, 2017 at 5:32 AM, Andreas K. Huettel
<dilfridge@g.o> wrote:
> Am Mittwoch, 26. April 2017, 02:37:17 CEST schrieb Francesco Riosa:
>> 2017-04-26 0:26 GMT+02:00 Andreas K. Huettel <dilfridge@g.o>:
>> > Am Sonntag, 23. April 2017, 14:35:48 CEST schrieb Michał Górny:
>> > > Hi,
>> > >
>> > > I'm thinking of masking old versions of sys-devel/gcc, in particular
>> > > older than the 4.9 branch.
>> >
>> > Masking is fine; some time later (maybe in a few months) I'd even suggest
>> > masking all of gcc-4. After all, unmasking them if you really need them is
>> > rather easy.
>>
>> well if the intent is cleaning adding a package mask is just more burden,
>> not less.
>> If they compile fine with the latest stable gcc better leave them unmasked,
>> right?
>
> Except that "switching back" from gcc-5 to gcc-4 doesn't really work, and that
> gcc-4 will happily use gcc-5 libraries, with unintended consequences.

What do you mean by "gcc-4 will happily use gcc-5 libraries"?

If you mean at build time, it does NOT use gcc-5 libs. If it does, that's a bug.

% gcc-4.9.4 --print-search-dirs | grep ^libraries:
libraries: =/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/../../../../x86_64-pc-linux-gnu/lib/x86_64-pc-linux-gnu/4.9.4/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/../../../../x86_64-pc-linux-gnu/lib/../lib64/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/../../../x86_64-pc-linux-gnu/4.9.4/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/../../../../lib64/:/lib/x86_64-pc-linux-gnu/4.9.4/:/lib/../lib64/:/usr/lib/x86_64-pc-linux-gnu/4.9.4/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/../../../../x86_64-pc-linux-gnu/lib/:/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.4/../../../:/lib/:/usr/lib/

If you mean runtime, that's controlled by
/etc/ld.so.conf.d/05gcc-x86_64-pc-linux-gnu.conf. There's really
nothing wrong with using a newer libstdc++ at runtime; they should be
ABI compatible.