For handling legacy protocols and file formats, can't you just use uint32_t for the timestamp, and then convert that to time_t for the in-memory representation.

For handling legacy protocols and file formats, can't you just use uint32_t for the timestamp, and then convert that to time_t for the in-memory representation. No need to fork the kernel. That's probably what you needed to do anyway, if you want the code to compile correctly on systems with 32 and 64-bit time_t.