Re: MPS native subrs

[Helmut Eller <eller.helmut@gmail.com>]

On Wed, Jun 26 2024, Gerd Möllmann wrote:

>> More generally, it seems that the DEFUN macro works much like the DEFVAR
>> macro, in the sense that it creates a struct and puts it in a static
>> variable.  So the Lisp_Subrs structs for primitives are, just like the
>> Lisp_Fwd structs, already in the data section.  We could re-use them
>> instead of re-creating them in the dump.  Of course, only if we can get
>> rid of the command_modes field.
>
> And it would again greatly simplify things. Maybe we should just do it :-)

Curiously, igc-info doesn't show any PVEC_SUBRS.  I think this is going on:

The pdumper does something special for primitives and builtin symbols
(and threads).  Those are dumped to the discardable section.  On load,
it first performs relocations and then copies everything from the
discardable section to the data section.  All builtin symbols can be
copied with a single memcpy to lispsym because they are sorted and
dumped in the correct order.  The same happens for primitives: those are
adjacent because the DEFUN macro sets the SUBR_SECTION_ATTRIBUTE.

This explains why igc-info doesn't show any PVEC_SUBRS (unless
configured with native compilation).  So we already have what we want.
It's probably no problem that we don't trace the subr section, because
the command_modes field is nil anyway.

I'm not sure why it is done this way; maybe it makes walking the object
graph more uniform.