Re: --with-native-compilation build failure on 32-bit systems

[Lynn Winebarger <owinebar@gmail.com>]

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On Mon, Aug 8, 2022, 3:44 AM Andrea Corallo <akrl@sdf.org> wrote:

> Lynn Winebarger <owinebar@gmail.com> writes:
>
> > On Fri, Aug 5, 2022, 10:42 AM Andrea Corallo <akrl@sdf.org> wrote:
> >
> >  Andrea Corallo <akrl@sdf.org> writes:
> >
> >  > Lars Ingebrigtsen <larsi@gnus.org> writes:
> >  >
> >  >> Joseph Mingrone <jrm@ftfl.ca> writes:
> >  >>
> >  >>> Could 261d6af have broken --with-native-compilation builds on 32-bit
> >  >>> systems?  This is what I see building in a clean FreeBSD/i386 13.0
> >  >>> jail using 261d6af:
> >  >>>
> http://pkg.ftfl.ca/data/13i386-default/2022-08-04_22h38m28s/logs/errors/emacs-devel-29.0.50.20220804,2.log
> >  >>
> >  >> I guess these are the error messages?
> >  >>
> >  >> emacs: Trying to load incoherent dumped eln file
> >  >>
> >
> /wrkdirs/usr/ports/editors/emacs-devel/work-full/emacs-261d6af/native-lisp/29.0.50-7cc1a43d/preloaded/ediff-hook-0b92f1a2-f843c8a0.eln
> >
> >  >>
> >  >> I don't know what that means; Andrea added to the CCs.
> >  >
> >  > It's very surprising to see 261d6af causing this side effect, at
> least I
> >  > don't see why should effect the 32bit build only.
> >  >
> >  > I'm trying to reproduce it on my 32bit env.
> >
> >  I confirm the build it's broken on my 32bit env as well, (but not on the
> >  64 one).
> >
> >  Loading the second dump, while we are relocating the ediff-hook
> >  compilation unit, we realize (@ pdumper.c:5304) that its file field is
> >  not a cons as expected but just a string.
> >
> >  Now the question is why this is not fixed-up in loadup.el:477 as for the
> >  other compilation units?
> >
> > Are you sure it's actually fixed up in the other compilation units?
>
> Indeed, otherwise an error is signaled.
>
> > This problem should be signaled by loadup if there are any NCUs it does
> not fix up.  It would be a lot easier to diagnose
> > the problem from there.
>
> loadup is in charge of fixing up on all CU's file fields, and indeed if
> something goes wrong in that code an error is signaled.  But evidently
> this is not the case, so there's something more to understand.
>

I just looked, and there are 2 possible paths for NCUs to be in the dump
without an error being signaled:
1 - either the --bin-dest or --eln-dest flag is not specified (or is on the
command line but empty)
2 - there is an NCU loaded for which no symbol is bound to a subr in that
NCU.

Since I put in some code (in loadup) to explicitly test whether any loaded
NCU would be missed by (2), I have seen one instance pop up, though not
while only loading the files in loadup - site-load loads many more.
However, I've removed the requirement of having a cons cell in the NCU in
the dump file, so I don't know if it was destined was garbage collection,
and so discarded by the dump process.

Lynn

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