Re: Reference to discarded section

[Paul Koning <Paul_Koning at dell dot com>]

>>>>> "Cary" == Cary Coutant <ccoutant@google.com> writes:

 >> 1. What does this mean?  3. What causes a link-once section to be
 >> discarded?  There's nothing in ld.info that discusses that topic.

 Cary> Linkonce sections (and the newer notion of comdat groups) are a
 Cary> way for the compiler to emit template instantiations and
 Cary> out-of-line inlined functions without worrying about lots of
 Cary> duplicate copies in the linked output file. There may be a copy
 Cary> of a given instantiated template function in many different
 Cary> object files, but the linker will pick one and discard all the
 Cary> others. In order for this to work, it's important that each
 Cary> copy defines and references exactly the same set of
 Cary> symbols. ...

Great.  That would be nice material to have in the docs.

 >> 2. How do I fix this?

 Cary> Can you rearrange the object modules in the link to try to get
 Cary> the linker to keep the section that defines the symbol you
 Cary> need? Can you recompile the offending module with or without -g
 Cary> (or see if you can match the compilation options with the the
 Cary> other modules in your program)? Can you make sure that all the
 Cary> modules are compiled with the same version of gcc? I'm not sure
 Cary> if any of these will help, but they might.

That worked.  I looked at the way the offending component was built
and noticed some extra GCC switches, including -fno-omit-frame-pointer
and some inlining controls.  There wasn't a good reason for that
anyway so I took them out, and now the linker is happy.

Thanks much for the clear and helpful answer.

       paul