On Sat, 10 Dec 2016 13:41:03 +0100 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Dec 09, 2016 at 11:46:54PM +0100, Dodji Seketeli wrote: > > Hello, > > > > Nicholas Piggin <npiggin@xxxxxxxxx> a écrit: > > > > [...] > > > > > That said, a dwarf based checker tool should be able to do as good a job > > > (maybe a bit better because report is very informative and it may pick up > > > compiler alignments or padding options). > > > > So, Nicholas was kind enough to send me the two Linux Kernel binaries > > that he built with the tiny little interface change that we were > > discussing earlier. Here is what the abidiff[1] tools says about that > > interface change: > > > > $ time ~/git/libabigail/kabidiff/build/tools/abidiff vmlinux.abi1.abi vmlinux.abi2.abi > > Functions changes summary: 0 Removed, 1 Changed, 0 Added function > > Variables changes summary: 0 Removed, 0 Changed, 0 Added variable > > > > 1 function with some indirect sub-type change: > > > > [C]'function int foo(blah*)' at memory.c:82:1 has some indirect sub-type changes: > > parameter 1 of type 'blah*' has sub-type changes: > > in pointed to type 'struct blah' at memory.c:78:1: > > type size changed from 32 to 64 bits > > 1 data member insertion: > > 'int blah::y', at offset 0 (in bits) at memory.c:79:1 > > 1 data member change: > > 'int blah::x' offset changed from 0 to 32 (in bits) (by +32 bits) > > > > > > > > real 0m2.595s > > user 0m2.489s > > sys 0m0.108s > > $ > > > > I kept the timing information to give you an idea of the time it takes > > on a non-optimized build of abidiff. > > > > One could for instance want that types that are not defined in header > > files be kept out of the change report. In that case it's possible to > > write a little suppression specification file like this one: > > > > $ cat vmlinux.abignore > > [suppress_type] > > source_location_not_regexp = .*\\.h > > $ > > > > You can then pass that suppression file to the tool: > > > > $ ~/git/libabigail/kabidiff/build/tools/abidiff --suppr vmlinux.abignore vmlinux.abi1.abi vmlinux.abi2.abi > > Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added function > > Variables changes summary: 0 Removed, 0 Changed, 0 Added variable > > > > > > real 0m2.574s > > user 0m2.473s > > sys 0m0.102s > > $ > > > > So this is the kind of interface change analysis tool we are working on > > at the moment. > > > > One could also imagine a tool that would compute a CRC that takes the > > very same suppression specification files into account, letting people > > to decide that some interface changes are OK. That CRC would thus be > > added to the special ELF sections we already have today. We could keep > > the modversion machinery, but with a greater dose of flexibility. > > Whenever modversion detects a change, abidiff would tell people what the > > change is exactly. > > > > What do you guys think? > > YES YES YES!!! > > Now I don't work on a distro anymore, but I would think that something > like this would be really useful, pointing out exactly what changed is > very important for distro maintainers to determine what they want to do > (either fix up the abi change with strange hacks, or ignore it due to > the change being in an area they don't care at all about, i.e. a random > driver subsystem.) > > So yes, I think this is really good stuff. But if the distro > maintainers correct me and think it's useless, then I need to revisit my > view of exactly what they do for their customers :) Agree completely. BTW (for those who might be looking into these tools), we also have https://github.com/skozina/kabi-dw that Stanislav (cc'ed) mentioned earlier. It's true that the current modversions __crc_ matching infrastructure is "just" a symbol versioning system, and we could keep it and just populate it with something other than genksyms (e.g., a symbol version list provided by distros). But the starting point should be *no* versioning and simply using names to break linkage. Unless there's a compelling reason not to, symbols are simpler, easier, everyone knows how they work. The other question would be whether to pull a minimal tool into the kernel source or keep them out of tree (but possibly add some helper scripts etc). I guess we'll need to see what distros want. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
