GNU bug report logs - #75322
SAFE_ALLOCA assumed to root Lisp_Objects/SSDATA(string)

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Gerd Möllmann <gerd.moellmann <at> gmail.com>
Cc: pipcet <at> protonmail.com, 75322 <at> debbugs.gnu.org
Subject: bug#75322: SAFE_ALLOCA assumed to root Lisp_Objects/SSDATA(string)
Date: Sun, 05 Jan 2025 20:42:37 +0200

> From: Gerd Möllmann <gerd.moellmann <at> gmail.com>
> Cc: pipcet <at> protonmail.com,  75322 <at> debbugs.gnu.org
> Date: Sun, 05 Jan 2025 18:49:56 +0100
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> > This surprises me because on the master branch SAFE_ALLOCA_LISP either
> > calls alloca or xzalloc.  So I don't see why SAFE_ALLOCA_LISP would be
> > safer in the old GC than SAFE_NALLOCA.  It's only on the igc branch
> > that you made SAFE_ALLOCA_LISP make a Lisp vector.
> > But this is a tangent from my POV.  I would like to discuss the new
> > GC, not the old one.
> >
> 
> This in SAFE_ALLOCA_LISP_EXTRA
> 
> 	(buf) = xzalloc (alloca_nbytes);		       \
> 	record_unwind_protect_array (buf, nelt);	       \
> 
> makes a specpdl entry, which makes mark_specpdl do this:
> 
> 	case SPECPDL_UNWIND_ARRAY:
> 	  mark_objects (pdl->unwind_array.array, pdl->unwind_array.nelts);
> 	  break;

Thanks.  I guess it's supposed to be "common knowledge" that
record_unwind_protect_* indirectly causes the objects to be marked...

But then why don't we set the .mark member in SAFE_NALLOCA or some
variant thereof?

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