Re: Updating *.el files and native compilation

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: emacs-devel@gnu.org
> Date: Mon, 10 May 2021 07:35:53 +0000
> 
> >   . if, for some reason, Emacs loads an incompatible .eln file, then
> >     some Lisp programs could crash the Emacs session, is that correct?
> >     If so, how do we make sure such incompatible changes always cause
> >     a new native compilation that yields a different file name for the
> >     .eln file?
> 
> Yes but this should not happen, every change that can introduce an
> incompatibility has to be accounted in the `comp-abi-hash' computation
> and AFAIK ATM it is.

Some changes don't require updating comp-abi-hash, but still create
*.eln files with different hashes in its name.  AFAIU, that happens
when the primitives don't change, but the .el file itself changes,
isn't that so?

In any case, are you saying that the only situations where loading and
using a .eln file could crash Emacs are those which are handled by
changing comp-abi-hash?  If so, how can we make sure we never fail to
update comp-abi-hash when that is needed?

> > The upshot of all this is that if one keeps multiple Emacs
> > executables, it should be safe to invoke each one of them without
> > risking crashes due to loading incompatible *.eln files that were
> > produced by other, subtly incompatible Emacs executables.  Is this
> > indeed safe, or do we have some "gotchas" that still need to be taken
> > care of?
> 
> As of today I'm not aware of any gotcha here, if we discover a case of
> this we should treat it as bug.

Sure.