here comes SKFU's PS4 FW Tool 1.0.0:
- Show PS4 firmware details
- Unpack PS4 (SLB2 container) firmware
- Pack PS4 (SLB2 container) firmware
- Unpack (inner) PUP
- Pack (inner) PUP
Keep in mind that SLB2 files are the complete firmware files. SLB2 files contain PUP files.
SONY just used the file extension ".PUP" for the actual SLB2 firmware files to make it less confusing for common users.