symbol relocation during dynamic loading

[Ian Lance Taylor]

Robert Schweikert <Robert.Schweikert@abaqus.com> writes:

> I am using the --retain-symbols-file <filename> link option to restrict
> the exported symbols from shared libraries. Using elfdump libName
> --export to compare the exported symbols between libraries linked with
> and without the --retain-symbols-file <filename> option indicates that
> things worked as expected and I only get the symbols I want exported.
> Also the size of the "restricted" library is smaller (as expected).
> 
> The question now is why the relocations are the same between the 2
> libraries. If I set the LD_DEBUG environment variable to statistics and
> load both libraries I end up with the same number of relocations. My
> expectation was that the number of relocations would decrease and thus I
> would end up with faster load times.
> 
> Can anyone explain why the number of relocations did not show any
> changes?

Hmmm.  You neglected to mention your target.  The only type of
relocation which is likely to disappear entirely is a PC relative
relocation to a publically visible function.  If the function is
hidden, then the relocation can go away.  All other relocations are
likely to remain, perhaps in the form of R_*_RELATIVE.

That said, there is another way to hide symbols in a shared library,
which is to use a version script.  It is possible that using a version
script will remove relocations where --retain-symbols-file will not.
That is because the implementation of the two options is, I believe,
different.  I haven't checked whether this is so.  But it is possible.
(Yes, if they are indeed different, this probably a bug.)

Ian