On Tue, Aug 27, 2019 at 04:34:15PM +0100, Ben Hutchings wrote: > On Tue, 2019-08-27 at 22:42 +1000, Nicholas Piggin wrote: > > Masahiro Yamada's on August 27, 2019 8:49 pm: > > > Hi. > > > > > > On Tue, Aug 27, 2019 at 6:59 PM Nicholas Piggin <npig...@gmail.com> wrote: > > > > Nick Desaulniers's on August 27, 2019 8:57 am: > > > > > On Mon, Aug 26, 2019 at 2:22 PM Nick Desaulniers > > > > > <ndesaulni...@google.com> wrote: > > > > > > I'm looking into a linkage failure for one of our device kernels, > > > > > > and > > > > > > it seems that genksyms isn't producing a hash value correctly for > > > > > > aggregate definitions that contain __attribute__s like > > > > > > __attribute__((packed)). > > > > > > > > > > > > Example: > > > > > > $ echo 'struct foo { int bar; };' | ./scripts/genksyms/genksyms -d > > > > > > Defn for struct foo == <struct foo { int bar ; } > > > > > > > Hash table occupancy 1/4096 = 0.000244141 > > > > > > $ echo 'struct __attribute__((packed)) foo { int bar; };' | > > > > > > ./scripts/genksyms/genksyms -d > > > > > > Hash table occupancy 0/4096 = 0 > > > > > > > > > > > > I assume the __attribute__ part isn't being parsed correctly (looks > > > > > > like genksyms is a lex/yacc based C parser). > > > > > > > > > > > > The issue we have in our out of tree driver (*sadface*) is > > > > > > basically a > > > > > > EXPORT_SYMBOL'd function whose signature contains a packed struct. > > > > > > > > > > > > Theoretically, there should be nothing wrong with exporting a > > > > > > function > > > > > > that requires packed structs, and this is just a bug in the lex/yacc > > > > > > based parser, right? I assume that not having CONFIG_MODVERSIONS > > > > > > coverage of packed structs in particular could lead to potentially > > > > > > not-fun bugs? Or is using packed structs in exported function > > > > > > symbols > > > > > > with CONFIG_MODVERSIONS forbidden in some documentation somewhere I > > > > > > missed? > > > > > > > > > > Ah, looks like I'm late to the party: > > > > > https://lwn.net/Articles/707520/ > > > > > > > > Yeah, would be nice to do something about this. > > > > > > modversions is ugly, so it would be great if we could dump it. > > > > > > > IIRC (without re-reading it all), in theory distros would be okay > > > > without modversions if they could just provide their own explicit > > > > versioning. They take care about ABIs, so they can version things > > > > carefully if they had to change. > > Debian doesn't currently have any other way of detecting ABI changes > (other than eyeballing diffs). > > I know there have been proposals of using libabigail for this instead, > but I'm not sure how far those progressed.
Google has started using libabigail to track api changes in AOSP, here's a patch that updates the ABI file after changing it: https://android-review.googlesource.com/c/kernel/common/+/1108662 Note, there are issues with it, and some rough edges, but I think it can work. But, it means nothing at module load time, this is only at build-check time. At least modversions would prevent module loading in some cases. thanks, greg k-h