Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

Nicholas Piggin
2016-11-26T00:56:26Z

On Fri, 25 Nov 2016 10:00:46 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, Nov 24, 2016 at 4:40 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
> >>
> >> Yes, manual "marking" is never going to be a viable solution.
> >
> > I guess it really depends on how exactly you want to use it. For distros
> > that do stable ABI but rarely may have to break something for security
> > reasons, it should work and give exact control.
>
> No. Because nobody else will care, so unless it's like a single symbol
> or something, it will just be a maintenance nightmare.

Yeah that's true, and as I realized a distro can rename a symbol if they
make incompatible changes which happens very rarely. Avoids having to
carry some whole infrastructure upstream for it.

>
> > What else do people *actually* use it for? Preventing mismatched modules
> > when .git version is not attached and release version of the kernel has
> > not been bumped. Is that it?
>
> It used to be very useful for avoiding loading stale modules and then
> wasting days on debugging something that wasn't the case when you had
> forgotten to do "make modules_install". Change some subtle internal
> ABI issue (add/remove a parameter, whatever) and it would really help.
>
> These days, for me, LOCALVERSION_AUTO and module signing are what I
> personally tend to use.
>
> The modversions stuff may just be too painful to bother with. Very few
> people probably use it, and the ones that do likely don't have any
> overriding reason why.
>
> So I'd personally be ok with just saying "let's disable it for now",
> and see if anybody even notices and cares, and then has a good enough
> explanation of why. It's entirely possible that most users are "I
> enabled it ten years ago, I didn't even realize it was still in my
> defconfig".

That sounds good. Should we try to get 4.9 working (which we could
do relatively easily with a few arch reverts), and then disable
modversions for 4.10? (at which point we can un-revert Al's arch
patches)

Thanks,
Nick