It appears that the $(GEL_file_dir) macro can only be used once for a function call.

For example:

GEL_TextOut("$(GEL_file_dir)/file1.c $(GEL_file_dir)/file2.c\n");

Would result in the GEL output:

CORTEX_M0P: GEL Output: C:\ti\ccs1281\ccs\ccs_base\emulation\gel/file1.c $(GEL_file_dir)/file2.c

The issue occurs with both CCS 12.8.1 and CCS 20.4.0.