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

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

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:
>
> diff --git a/src/pdumper.c b/src/pdumper.c
> index b039e375c1f..39484a16c95 100644
> --- a/src/pdumper.c
> +++ b/src/pdumper.c
> @@ -5958,6 +5958,7 @@ pdumper_load (const char *dump_filename, char *argv0)
>         & ~(DUMP_ALIGNMENT - 1));
>    void *hot_start = (void *) (dump_base + aligned_header_size);
>    void *hot_end = (void *) (dump_base + header->discardable_start);
> +  igc_on_pdump_loaded (hot_start, hot_end);
>  #endif

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.

>    dump_do_all_dump_reloc_for_phase (header, dump_base, EARLY_RELOCS);
> @@ -6002,10 +6003,6 @@ pdumper_load (const char *dump_filename, char *argv0)
>    dump_private.load_time = timespectod (load_timespec);
>    dump_private.dump_filename = dump_filename_copy;
>  
> -# ifdef HAVE_MPS
> -  igc_on_pdump_loaded (hot_start, hot_end);
> -# endif
> -
>   out:
>    for (int i = 0; i < ARRAYELTS (sections); ++i)
>      dump_mmap_release (&sections[i]);

But, what if we park MPS while we are loading the dump? WDYT?