I just added #include <os/proc.h> in the bridging header. nothing else at all. Still works fine for me.

Hi, Thanks for your prompt response. macOS version is 12.1. c.withUnsafeMutableBufferPointer{ buf in ... }, buf is simply c. Yes, it is a funny code. While using release build, I din't realize that withUnsafeMutableBufferPointer() was not necessary because it could be built and ran fine. I have eliminated withUnsafeMutableBufferPointer() from the code. Thanks for your pointing that out. But for debug build, it still produces Undefined symbol error. Hikaru