On Wed, Sep 11, 2024 at 4:43 AM Petr Pavlu <petr.pavlu@xxxxxxxx> wrote: > > On 8/31/24 02:05, Sami Tolvanen wrote: > > On Fri, Aug 30, 2024 at 9:34 AM Miroslav Benes <mbenes@xxxxxxx> wrote: > >> > >> yes, this is one of the approaches we use in SLES. We add kabi paddings > >> to some structures in advance (see [1] as a random example) and then use > >> it later if needed. > >> > >> It is not the only approach. Much more often we do not have a padding and > >> use alignment holes ([5]), addition of a new member to the end of a > >> structure ([2] or [3]) and such "tricks" ([4] for a newly fully defined > >> structure). > > > > Thanks for bringing this up! Sounds like we're also going to need a > > way to completely exclude specific fields from the output then. I > > think we can use a similar union approach, but instead of instructing > > the tool to use another type, we can just indicate that the field > > should be skipped. I'll come up with a solution for v3. > > It might have been mentioned previously, not sure, but one more case to > consider is handling of enum declarations. New enumerators can be > typically added without breaking ABI, e.g. 'enum E { OLD1, OLD2, NEW }'. > It would be then great to have some ability to hide them from > gendwarfksyms. > > I think neither of the __kabi_reserved or __gendwarfksyms_declonly > mechanism can currently help with that. I thought about this a bit and I wonder if we need a separate mechanism for that, or is it sufficient to just #define any additional hidden values you want to add instead of including them in the enum? enum e { A, B, #define C (B + 1) #define D (C + 1) }; Do you see any issues with this approach? I think Clang would complain about this with -Wassign-enum, but I'm not sure if we even enable that in the kernel, and as long as you don't overflow the underlying type, which is a requirement for not breaking the ABI anyway, it should be fine. Sami