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

Nicholas Piggin
2016-11-24T10:04:12Z

On Thu, 24 Nov 2016 10:32:12 +0100
Michal Marek <mmarek@suse.com> wrote:

> On 2016-11-24 08:53, Nicholas Piggin wrote:
> > On Thu, 24 Nov 2016 08:36:39 +0100
> > Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> >
> >> On Thu, Nov 24, 2016 at 06:20:26PM +1100, Nicholas Piggin wrote:
> >>> But still, modversions is pretty complicated for what it gives us. It sends
> >>> preprocessed C into a C parser that makes CRCs using type definitions of
> >>> exported symbols, then turns those CRCs into a linker script which which is
> >>> used to link the .o file with. What we get in return is a quite limited and
> >>> symbol "versioning" system.
> >>>
> >>> What if we ripped all that out and just attached an explicit version to
> >>> each export, and incompatible changes require an increment?
> >>
> >> How would that work for structures? Would that be required for every
> >> EXPORT_SYMBOL* somehow?
> >
> > Yeah just have EXPORT_SYMBOL take another parameter which attaches a version
> > number and use that as the value for the __crc_ symbol versions rather than
> > a calculated CRC.
>
> The problem is that with every kernel release, the structures change in
> a way that you would have to bump the version of virtually every export.
>
> At which point, there would be little difference between
> CONFIG_MODVERSION on and off (without CONFIG_MODVERSION, we compare the
> kernel version strings when loading modules).

I'm not sure about that. If they are truly incompatible changes and
MODVERSIONS does not pick up a different CRC, then it's even worse if
incompatible modules are missed so often.

Thanks,
Nick