On Fri, Nov 1, 2024 at 2:10 PM Luis Chamberlain <mcgrof@xxxxxxxxxx> wrote: > > On Thu, Oct 31, 2024 at 01:00:28PM -0700, Matthew Maurer wrote: > > > The question is, if only extended moversions are used, what new tooling > > > requirements are there? Can you test using only extended modversions? > > > > > > Luis > > > > I'm not sure precisely what you're asking for. Do you want: > > 1. A kconfig that suppresses the emission of today's MODVERSIONS > > format? > > Yes that's right, a brave new world, and with the warning of that. OK, I can send another revision with a suppression config, perhaps CONFIG_NO_BASIC_MODVERSIONS > > > > This would be fairly easy to do, but I was leaving it enabled > > for compatibility's sake, at least until extended modversions become > > more common. This way existing `kmod` tools and kernels would continue > > to be able to load new-style modules. > > Sure, understood why we'd have both. > > > 2. libkmod support for parsing the new format? I can do that fairly > > easily too, but wanted the format actually decided on and accepted > > before I started modifying things that read modversions. > > This is implied, what I'd like is for an A vs B comparison to be able to > be done on even without rust modules, so that we can see if really > libkmod changes are all that's needed. Does boot fail without a new > libkmod for this? If so the Kconfig should specificy that for this new > brave new world. libkmod changes are not needed for boot - the userspace tools do not examine this data for anything inline with boot at the moment, libkmod only looks at it for kmod_module_get_versions, and modprobe only looks at that with --show-modversions or --dump-modversions, which are not normally part of boot. With the code as is, the only change will be that if a module with EXTENDED_MODVERSIONS set contains an over-length symbol (which wouldn't have been possible before), the overlong symbol's modversion data will not appear in --show-modversions. After patching `libkmod` in a follow-up patch, long symbols would appear as well. If booted against an old kernel, long symbols will not have their CRCs in the list to be checked. However, the old kernel could not export these symbols, so it will fail to resolve the symbol and fail the load regardless. If we add and enable NO_BASIC_MODVERSIONS like you suggested above, today's --show-modversions will claim there is no modversions data. Applying a libkmod patch will result in modversions info being displayed by that command again. If booted against a new kernel, everything will be fine. If booted against an old kernel, it will behave as though there is no modversions information. > > > If a distribution can leverage just one format, why would they not > consider it if they can ensure the proper tooling is in place. We > haven't itemized the differences in practice and this could help > with this. One clear difference so far is the kabi stuff, but that's The kabi stuff is at least partially decoupled - you can (and it sounds like from the responses to Sami's change, occasionally might want to) enable debug symbol based modversions even without extended modversions. You can also enable extended modversions without the debug symbol based modversions, though there are less clear use-cases for that. > just evaluating one way of doing things so far, I suspect we'll get > more review on that from Petr soon. > > Luis
