Re: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules

[Peter Zijlstra]

On Tue, Jan 26, 2021 at 09:46:51AM -0600, Josh Poimboeuf wrote:
> On Tue, Jan 26, 2021 at 04:15:37PM +0100, Peter Zijlstra wrote:
> > On Tue, Jan 26, 2021 at 08:51:55AM -0600, Josh Poimboeuf wrote:
> > > User space mixes compiler versions all the time.  The C ABI is stable.
> > > 
> > > What specifically is the harder issue you're referring to?
> > 
> > I don't think the C ABI captures nearly enough. Imagine trying to mix a
> > compiler with and without asm-goto support (ok, we fail to build without
> > by now, but just imagine).
> > 
> > No C ABI violated, but having that GCC extention vs not having it
> > radically changes the kernel ABI.
> > 
> > I think I'm with Greg here, just don't do it.
> 
> Ok, thank you for an actual example.  asm goto is a good one.
> 
> But it's not a cut-and-dry issue.  Otherwise how could modversions
> possibly work?
> 
> So yes, we should enforce GCC versions, but I still haven't seen a
> reason it should be more than just "same compiler and *major* version".

Why bother? rebuilding the kernel and all modules is a matter of 10
minutes at most on a decently beefy build box.

What actual problem are we trying to solve here?