Hi, On Thu, Nov 14, 2024 at 11:35:25AM -0500, Peter Geoghegan wrote: > On Thu, Nov 14, 2024 at 11:29 AM Alvaro Herrera <alvhe...@alvh.no-ip.org> > wrote: > > ISTM that we have spare bytes where we could place that boolean without > > breaking ABI. In x86_64 there's a couple of 4-byte holes, but those > > won't be there on x86, so not great candidates. Fortunately there are > > 3-byte and 7-byte holes also, which we can use safely. We can move the > > new boolean to those location. > > Wasn't this part of the official guidelines?
Do you mean in [1] (Maintaining ABI compatibility while backpatching section)? If so, it looks like it's not currently mentioned. What about? " You cannot modify any struct definition in src/include/*. If any new members must be added to a struct, put them in the padding holes (if any) in backbranches (or at the end of the struct if there is no padding holes available). " Also we may need a decision table to ensure 32-bit portability based on the hole size on 64-bit, something like? 64-bit hole size | use on 32-bit? -----------------|--------------- <=3 bytes | safe to use 4 bytes | don't use 5-7 bytes | use first (hole_size - 4) bytes only Does that make sense? Regards, [1]: https://wiki.postgresql.org/wiki/Committing_checklist -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
