Suppress the fetch of an archive member via --defsym (glibc/elf/librtld.map.o)

[Florian Weimer]

* Michael Matz:

> On Mon, 16 Mar 2020, Fangrui Song via Binutils wrote:
>> I am concerned that the --defsym's order dependence with archive files is not
>> so obvious, given -u's behavior:
>> 
>> # -u inserts an undefined which fetches b.a(b.o)
>> ld.bfd -u foo b.a       # b.a(b.o) is fetched. free is present
>> # This can't be order dependent because b.a (not in a group) should have been
>> dropped when we saw -u
>> ld.bfd b.a -u foo       # b.a(b.o) is fetched. free is present
>> 
>> Some observations:
>> 
>> 
>> # GNU ld --defsym interacts with an archive
>> ld.bfd a.o b.a --defsym foo=0  # b.a(b.o) is fetched. free is present
>> ld.bfd --defsym foo=0 a.o b.a  # b.a(b.o) is not fetched. free is absent
>
> I consider this the correct linker behaviour.  In that sense I would 
> consider the inconsistency with -u and -T to be the problems of those, not 
> a problem of --defsym (but not necessarily problems we can fix anymore, as 
> people might rely on that).  (i.e. I think the second -u command above 
> should result in an 'undefined foo' output/error, not in b.a(b.o) being 
> fetched).

I agree, the ld.bfd behavior seems the most reasonable one to me.