Re: MPS: Forwording symbols

[Eli Zaretskii <eliz@gnu.org>]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: Emacs Devel <emacs-devel@gnu.org>,  Eli Zaretskii <eliz@gnu.org>
> Date: Sun, 16 Jun 2024 21:39:41 +0200
> 
> Helmut Eller <eller.helmut@gmail.com> writes:
> 
> > On Sun, Jun 16 2024, Gerd Möllmann wrote:
> >
> >> If we don't dump_fwd, we would have to make sure though not to overwrite
> >> the existing values for symbols in lispsym, which happens in
> >> dump_do_dump_relocation
> >>
> >>     case RELOC_DUMP_TO_EMACS_PTR_RAW:
> >>       {
> >>         uintptr_t value = dump_read_word_from_dump (dump_base, reloc_offset);
> >>         eassert (dump_reloc_size (reloc) == sizeof (value));
> >>         value += emacs_basis ();
> >>         dump_write_word_to_dump (dump_base, reloc_offset, value);
> >>         break;
> >>       }
> >>
> >> The name dump_write_word_to_dump is misleading. It does a memcpy to
> >> Emacs' data segment.
> >
> > Hm, why do you think it writes to the data segment?  Confusing names
> > aside, it seems to read a value, which presumably is a pointer, adjusts
> > it to the new basis and then writes it back.
> 
> Becasue of this
> 
>      value += emacs_basis ();
> 
> It has dumnped pointer - basis, and now uses that value to get the
> pointer in the current process.

Isn't this because the dumped data is loaded with a different base
address than the one with which is was dumped?