Re: scratch/igc 90e80a9a53e 6/6: Adjust igc.c code to header changes

[Pip Cet <pipcet@protonmail.com>]

On Sunday, July 21st, 2024 at 16:27, Eli Zaretskii <eliz@gnu.org> wrote:
> > Date: Sun, 21 Jul 2024 16:20:57 +0000
> 
> > From: Pip Cet pipcet@protonmail.com
> > Cc: emacs-devel@gnu.org
> > 
> > > Why cannot you identify this kind of object during dumping, and avoid
> > > applying whatever igc_dump_finish_obj does?
> > 
> > You mean you'd prefer to leave the pseudovector header for builtin subrs at its current value? We can do that, but I think the MPS header should still be valid. (It's not with the patch I had attached: that makes it claim an object size of 112 bytes when it's actually just 96 bytes, and that causes us to overwrite the first 16 bytes after the last subr; in my case, stdout... Anyway, next patch attached, which duplicates a bit of code unnecessarily.)
> 
> 
> Then why doesn't your patch do that?

I don't understand why it should. The pseudovector headers of main_thread and the subroutines are, currently, simply wrong:

(gdb) p vectorlike_nbytes(&Scall_interactively)
$1 = 2415919112
(gdb) p vectorlike_nbytes(&main_thread)
$2 = 584
(gdb) p sizeof(main_thread)
$3 = 520
(gdb) p sizeof(Scall_interactively)
$4 = 88

> And this new patch is even more massive than the previous one?

It is "even more massive" than a one-liner because there were additional bugs to fix, yes. As demonstrated above, vectorlike_nbytes doesn't work on subroutines because they lack the pseudovector flag, so I had to duplicate some code from alloc.c to use pseudovector_nbytes instead.
 
> In any case, if we need to change the definition of Aligned_Lisp_Subr,
> let's do that only "#if HAVE_MPS", and leave the old code intact.

No objections there.

I've found two more bugs that popped up testing this in various configurations: not protecting Vinternal_interpreter_environment (fun to debug, as might be imagined) and using xfree rather than igc_xfree in sort.c. Both may have affected dumping, so I'll push all three fixes and then hopefully things will work again.

Pip