Function programdata_pubkey 

pub fn programdata_pubkey(program_data: &[u8]) -> Result<[u8; 32], Error>

For a Program account whose owner is the upgradeable loader, return the 32-byte ProgramData address embedded in the account data. The caller fetches that account next.

Layout: UpgradeableLoaderState::Program = 4 bytes Borsh enum tag (value 2) + 32 bytes pubkey = 36 bytes total.