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

[Arnd Bergmann <arnd@arndb.de>]

On Thursday, November 24, 2016 6:53:22 PM CET Nicholas Piggin wrote:
> > 
> > > Google tells me
> > > Linus is not a neutral bystander on the topic of symbol versioning, so I'm
> > > bracing for a robust response  (actually I don't much care either way, I'm
> > > happy to put a couple of bandaids on it and keep it going)  
> > 
> > There are tools that people are working on to make it more obvious where
> > API breaks happen by looking at the .o debug data instead of our crazy
> > current system (which is really better than nothing), perhaps we should
> > start using them instead?
> > 
> > See here for more details about this:
> >       https://kernel-recipes.org/en/2016/talks/would-an-abi-changes-visualization-tool-be-useful-to-linux-kernel-maintenance/
> 
> Hmm. I guess it's basically similar to modversions, so has downsides of not
> detecting a semantic change unless it changes the type. But still, if we could
> replace our custom code with a tool like this for modversions functionality,
> that alone would be a massive improvement. But requiring debug info might be
> a bit of a show stopper. I also don't know if that would handle asm functions.

It's certainly not an option for v4.9 at this point. There is also no
realistic way we can get a correct asm/asm-prototypes.h for all the
other architectures in place. At the moment, powerpc is the only
one that actually works with modversions.

We can either make CONFIG_MODVERSIONS a per-architecture opt-in
and let only the ones that have the header file select that, or
revert all of Al's original patches that moved the exports.

	Arnd