LTO and undefined reference to typeinfo

[Szabolcs Nagy]

On 23/05/16 12:36, MM wrote:
> Hello,
> 
> g++ (GCC) 5.3.1 20160406 (Red Hat 5.3.1-6)
> GNU gold (version 2.25-17.fc23) 1.11
> I successfully link a executable in debug mode (-std=c++11 -g) but not in
> release mode (-std=c++11 -flto -O3). All sources are compiled with the same
> option. Shared libraries are used.
> The compiler driver is used to launch the final link line:
> /bin/c++    -std=c++11 -Wno-multichar -O3 -DNDEBUG -flto   <listofOfiles>
>  -o <executable> -rdynamic <listofsolibs> Wl,-rpath,<longlistofdirs>
> 
> These are the errors I see (only in release, not in debug):
>  ... [clone .constprop.79]: error: undefined reference to
>      'typeinfo for <ns1>::<ns2>::market [clone .lto_priv.1353]'
> 
> Both the debug and release version of the object referencing this show the
> same with gcc-nm:
> 
>                  U typeinfo for <ns1>::<ns2>::market
>  Note this bit   " [clone .lto_priv.1353]" is not in the symbol at all.
> 
> This is what gcc-nm says for the object where the symbol is defined
> (market.cpp.o, which is part of libmarkets.so):
> 
> 1. In DEBUG
> gcc-nm -C market.cpp.o |  grep 'typeinfo for <ns1>::<ns2>::market'
>      0000000000000000 V typeinfo for <ns1>::<ns2>::market
> 
> 2. In RELEASE
> gcc-nm -C market.cpp.o |  grep 'typeinfo for <ns1>::<ns2>::market'
>     00000000 W typeinfo for <ns1>::<ns2>::market
> This is the one that fails.
> Given the versions of gcc and ld, the default behaviour for lto should be
> straightforward?
> Any ideas what's going on?
> 

typeinfo seems to be a weak object symbol
which is known to be broken with lto, so
this may be related to:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69271


> Thanks
> MM
>