$ nm ./lib/auto/List/Util/Util.so | grep weak                                                    
[77]     |            0|       0|FUNC |GLOB |0|   UNDEF|Perl_sv_rvweaken
[102]    |     67145504|     384|FUNC |GLOB |0|   .text|XS_Scalar__Util_isweak
[66]     |     67145184|     288|FUNC |GLOB |0|   .text|XS_Scalar__Util_weaken