Re: MPS: Please check if scratch/igc builds with native compilation

[Gerd Möllmann]

Helmut Eller <eller.helmut@gmail.com> writes:

> On Wed, May 22 2024, Gerd Möllmann wrote:
>
>> Helmut Eller <eller.helmut@gmail.com> writes:
>>
>>>> I've checked that d_reloc is indeed scanned by fix_comp_unit. The
>>>> check gives me reasonable confidence that this "should work". But as
>>>> an alternative, I also made all the things like d_reloc in the .elns
>>>> ambiguous roots, so that they cannot possibly be moved, if all works as
>>>> expected.
>>>
>>> Registering the dump as root happens rather late.  The relocation code
>>> allocates a hash table and stores a reference to it in
>>> comp_u->lambda_gc_guard_h.  By that time the dump should already be a
>>> root.  Can we register the dump earlier?  AFAIU, the dumper writes zeros
>>> in the cells for to-be-relocated references and the scan code will
>>> ignore them.  So I think this could work:
>>>
>> AFAIU, at the point above the necessary relocations haven't yet been
>> done, so the dump is still in its "raw" form as it is in the file. Which
>> means, among other things, that Lisp_Objects haven't been changed to
>> point to where the dump is mmap'd or where the data segment of Emacs is
>> and so on. So I don't think that would work.
>
> As I said: NULLs shouldn't cause any trouble.  The scan code ignores
> that.  And pdumper_next_object seems to its own address calculations.
>
> Can you try the patch? 

Yes, of course, sorry.

> (And perhaps delete ~/.emacs.d/eln-cache/* and remove write
> permissions. I've seem elns being loaded from there. Which is not not
> good for repeatability.)

So, clean build and alas no visible change

  igc.c:345: Emacs fatal error: assertion failed: h->obj_type != IGC_OBJ_FWD
  gmake[3]: *** [Makefile:285: ../lisp/files.elc] Abort trap: 6
  gmake[2]: *** [Makefile:933: ../lisp/files.elc] Error 2
    ELC+ELN  ../lisp/emacs-lisp/syntax.elc
    ELC+ELN  ../lisp/emacs-lisp/cconv.elc
    ELC+ELN  ../lisp/emacs-lisp/tabulated-list.elc
    ELC+ELN  ../lisp/faces.elc

  igc.c:345: Emacs fatal error: assertion failed: h->obj_type != IGC_OBJ_FWD
  gmake[3]: *** [Makefile:285: ../lisp/faces.elc] Abort trap: 6

>> But, what if we park MPS while we are loading the dump? WDYT?
>
> Is it possible to allocate from a parked arena?

Yes, that works.