[Bug dynamic-link/27977] Unexpected behavior when using DT_FILTER

["alex.ameen.tx at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27977

--- Comment #4 from Alex Ameen <alex.ameen.tx at gmail dot com> ---
Yeah my understanding based on the SunOS docs, which I only referenced because
GNU has basically no documentation on this feature, is the following :

Say you have a big library `libfoo.so' which you cannot modify or rebuild, for
the sake of argument let's say its a commercial 3rd party lib which is licensed
in a way that disallows the use of `objdump' to directly modify the symbol
table.

In our usage we want to link ONLY the symbol `foo' from `libfoo.so', but
nothing else because other global symbols in `libfoo.so' conflict with our own
implementations, listed later in the link. 

To ensure that only `foo' is linked we create a filter library `libfoomin.so'
with only `foo' in its symbol table, listing `libfoo.so' as a `DT_NEEDED'
entry.

The expected behavior is that regardless of what order `libfoomin.so' appears
in our link we will not have to worry about any other symbols except for `foo'
from being bound either during pre-linking or at runtime.

I admit that the use case is niche but this is precisely the situation I've
been trying to solve, making it is a useful feature if implemented as SunOS
described.

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