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

[Andrea Corallo]

Lynn Winebarger <owinebar@gmail.com> writes:

> On Mon, Aug 8, 2022, 9:14 AM Andrea Corallo <akrl@sdf.org> wrote:
>
>  Lynn Winebarger <owinebar@gmail.com> writes:
>
>  > 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)
>
>  This is not the case in our build.
>
> No, but it is one way the dump can produce an unusable file without any error 
> signaled until an Emacs instance attempts
> to load it.

That is understood, but it can't happen using our current build system,
and this is what we are interested in here.

>  > 2 - there is an NCU loaded for which no symbol is bound to a subr in that 
> NCU.
>
>  CUs that are not reachable from the function slot of a symbol are
>  unloaded when GC runs.  We do run GC before dumping so this should not
>  happen.
>
> Yes, "should" is the operative word there.  Why not validate the condition 
> before writing the dump file?  If not in
> loadup, then in the procedure that records the NCU in the dump?  Why wait 
> until load-time to catch something that was
> almost certainly (barring user performing surgery on the dump file) the case 
> when the dump was produced?  Just put the
> same check before the "write" operation that is  done immediately after the 
> corresponding "read" operation.

Just submit a patch.

  Andrea