From: Andrea Corallo via "Emacs development discussions." <emacs-devel@gnu.org>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: Updating *.el files and native compilation
Date: Mon, 10 May 2021 07:35:53 +0000 [thread overview]
Message-ID: <xjfmtt3rqg6.fsf@sdf.org> (raw)
In-Reply-To: <83mtt5acjw.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 08 May 2021 10:51:15 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
> Andrea,
>
> I'd like to better understand what happens with *.eln files when the
> corresponding *.el files and the Emacs C code are updated and
> recompiled. There are two use cases here that are relevant:
>
> . building Emacs as part of development, while keeping old Emacs
> executables
>
> . updates to locally installed *.el files (e.g., in site-lisp) that
> also target multiple Emacs versions
>
> With byte-compilation, we keep only 1 .elc file for each .el file; if
> one starts an Emacs binary which doesn't fit the .elc file, we could
> have Lisp errors when invoking the affected Lisp functions, but in
> general Emacs should not crash. However, with native-compilation we
> can have several *.eln files in the respective directories (either
> native-comp or eln-cache), even if the ABI hash didn't change. So my
> questions are:
>
> . if the .el file changes in incompatible ways, native-compilation
> will produce a .eln file with a different file name, and each
> Emacs executable will then load the .eln file with which it is
> compatible, is that right?
Hi Eli,
that's correct.
> . 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.
> 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.
Regards
Andrea
next prev parent reply other threads:[~2021-05-10 7:35 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-08 7:51 Updating *.el files and native compilation Eli Zaretskii
2021-05-10 7:35 ` Andrea Corallo via Emacs development discussions. [this message]
2021-05-10 13:34 ` Eli Zaretskii
2021-05-10 15:44 ` Andrea Corallo via Emacs development discussions.
2021-05-10 16:59 ` Eli Zaretskii
2021-05-10 20:45 ` Andrea Corallo via Emacs development discussions.
2021-05-11 2:27 ` Eli Zaretskii
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