Apple's Linker Ignores Object Files In Static Libraries Consisting Entirely Of Uninitialized Variables

Summary

Apple's linker (ld) appears to have a bug where a .o file is ignored under these conditions:

• The .o is inside a static library
• The .o only contains uninitialized variables (appears as C in nm)

References to any symbols in such an object file become undefined symbols at link time.

Neither GNU's linker nor lld appears to have this problem.

Testing

var.c in this repository fulfills the conditions above if inside a static library.

make test - This will pass since var.o is linked directly.
make test2 - This will fail, since var.o is inside libTest.a and only contains uninitialized variables.

Workaround

You can work around this issue by initializing at least one of the variables (symbol becomes S in nm).
In the case of this repository, modify vars.c and initialize either var1 or var2 to some value.
Then the linker will find all symbols in the .o.