What are these SFP files that SQL Server distributes? What are the SFP files that come with SQL Server 2017?

/opt/mssql/lib/sqlservr.sfp
/opt/mssql/lib/sqldkxplat.sfp
/opt/mssql/lib/secforwarderxplat.sfp
/opt/mssql/lib/system.common.sfp
/opt/mssql/lib/system.certificates.sfp
/opt/mssql/lib/system.netfx.sfp
/opt/mssql/lib/system.sfp
So it turns out these are packed archive. It's part of the "Platform Abstraction Layer" that hosts the operating system in a library, or "Drawbridge" Library OS. Not much is known about Drawbridge yet, but here is one resource on Github that pointed me over to a tool sfpack.

sfpack was able to extract these archives.