[Bug ipa/64390] New: "-shared" does not resolve symbols from lto generated archives

[htl10 at users dot sourceforge.net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64390

            Bug ID: 64390
           Summary: "-shared" does not resolve symbols from lto generated
                    archives
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: htl10 at users dot sourceforge.net

Upgrading to 4.9.2 from 4.8.x, building R (http://www.r-project.org) with fto
fails. ("./configure --enable-lto AR=gcc-ar").

Specifically, it builds a few static archives of external libraries then tries
build a shared libraries out of it. A simplified procedure is like this:

gcc -flto -c -o routine1.o routine1.c
...
gcc -flto -c -o used_by_routine1.o used_by_routine1.c
...
gcc-ar cr libextra.a used_by_routine1.o ...
...
gcc -shared -o liboutput.so routine1.o ... libextra.a ...

the output shared library is not able to resolve any symbols with libextra.a's
content.

I found two workarounds:

- putting all the dependent *.o on the command line instead of the archive
itself.

- prepending/appending the extra libraries with the whole archive linker
directives: i.e. "-Wl,--whole-archive ../extra/tre/libtre.a
-Wl,--no-whole-archive"

I realise generating shared libraries from static archive is daft, but that's
how R is built.