[mpich-discuss] Undefined references to MPL, seems to be caused by --if-needed

[Jed Brown]

MPICH2 1.3.1:

$ cat cxx.C
#include <mpi.h>

int main(int argc,char *argv[])
{
  MPI_Comm comm;

  MPI::Init(argc,argv);
  MPI::Finalize();
  return 0;
}
$ /opt/mpich2/bin/mpicxx cxx.C
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trfree'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_env2str'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trlevel'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trvalid'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trmalloc'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trspace'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_env2range'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trcalloc'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_env2int'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trdump'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_env2bool'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trstrdup'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trrealloc'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_TrSetMaxMem'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trinit'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trDebugLevel'
/opt/mpich2/lib/libmpich.so: undefined reference to `MPL_trid'
collect2: ld returned 1 exit status
$ /opt/mpich2/bin/mpicxx -show cxx.C
c++ -Wl,--hash-style=gnu -Wl,--as-needed cxx.C -I/opt/mpich2/include
-L/opt/mpich2/lib -Wl,-rpath -Wl,/opt/mpich2/lib -lmpichcxx -lmpich -lopa
-lmpl -lpthread -lrt
$ c++ -Wl,--hash-style=gnu cxx.C -I/opt/mpich2/include -L/opt/mpich2/lib
-Wl,-rpath -Wl,/opt/mpich2/lib -lmpichcxx -lmpich -Wl,--as-needed -lopa
-lmpl -lpthread -lrt
$ ./a.out

It's not clear to me why the symbols in libmpich.so are not being marked as
needed.  This does not happen when compiling C programs (with mpicc or
mpicxx).  It's possible that it is a linker bug, but I have not seen this
issue with any other packages.  Perhaps it's a circular reference.

c++ (GCC) 4.5.1
GNU ld (GNU Binutils) 2.20.1.20100521


These link errors aside, I think it is incorrect for MPICH to include
user-specified libraries in the --as-needed sequence:

$ /opt/mpich2/bin/mpicxx -show cxx.C -lfoo
c++ -Wl,--hash-style=gnu -Wl,--as-needed cxx.C -lfoo -I/opt/mpich2/include
-L/opt/mpich2/lib -Wl,-rpath -Wl,/opt/mpich2/lib -lmpichcxx -lmpich -lopa
-lmpl -lpthread -lrt

I think the --as-needed should only come after the last of the user's
parameters (they may turn it on, but it shouldn't be on by default for their
libraries).

Jed
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