Hello, I configured mpich/main (or 4.0a2) with ./configure CC=gcc CXX=g++ --enable-fortran=no on Mac with Apple clang version 12.0.5 (clang-1205.0.22.11). The build failed with ... CCLD hydra_pmi_proxy Undefined symbols for architecture x86_64: "_hwloc_topology_set_io_types_filter", referenced from: _HYDT_topo_hwloc_init in libhydra.a(topo_hwloc.o) --Junchao Zhang