Re: [gentoo-portage-dev] Pre RFC on RFC: Add compiler information to exported a Package Manger's Cached Information.

["Anthony G. Basile" <basile@opensource.dyc.edu>]

On 02/25/15 15:38, Zac Medico wrote:
> On 02/25/2015 12:01 PM, Anthony G. Basile wrote:
>> On 02/25/15 14:51, Anthony G. Basile wrote:
>>> On 02/22/15 01:30, Zac Medico wrote:
>>>> On 02/21/2015 10:22 PM, Zac Medico wrote:
>>>>> If we put the real/canonical libstdc++.so path in the DT_NEEDED
>>>>> section,
>>>>> then it will automatically work with existing soname dependency
>>>>> support.
>>>>
>>>> Actually, we'd also have to add a way for you to put the full path of
>>>> the libstdc++.so in PROVIDES. For example:
>>>>
>>>> PROVIDES_ABSOLUTE="/usr/lib/gcc/*/*/libstdc++.so.6"
>>>>
>>>
>>> I guess I don't understand how this would work exactly.  What if someone
>>> has gcc-4.8.3.  Builds library libfoo.so which uses c++.  Then upgrades
>>> to gcc-4.9, removes 4.8 and then tries to build bar which is also
>>> written in c++ and links against libfoo.so.  We would have mismatching
>>> abis.  How would this catch it and trigger the correct rebuilds?
>>>
>>> Unless I'm misunderstanding your *'s in that line.  Are you using
>>> PROVIDES_ABSOLUTE as a way of recording what version of the compiler
>>> libfoo.so was build with?  So that you'd have a line that says libfoo.so
>>> links against /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/libstdc++.so, so
>>> that parsing that line gives 4.8.3?
>>>
>>> Also if you had the absolute path in VDB somewhere, like in PROVIDES,
>>> then you don't need it in the elf's rpath which would make me feel
>>> better.
>>>
>>
>> Actually no, you'd still need rpath for the elf itslef otherwise you can
>> still link against the wrong version of libstdc++.so.  Note in my
>> following example that even though I build test.cpp with 4.7.3 I still
>> wind up linking aginast 4.8.3.
>
> If DT_NEEDED contains the absolute libstdc++.so path, it's guaranteed to
> link against the correct version, regardless of rpath.
>

How do you get DT_NEEDED to the absolute libstdc++.so path when building?

-- 
Anthony G. Basile, Ph. D.
Chair of Information Technology
D'Youville College
Buffalo, NY 14201
(716) 829-8197