bug#74224: [PATCH][scratch/igc] pgtk: fix crashing bug in atimer used for checking scaling

[Jeff Walsh <fejfighter@gmail.com>]

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Hi Gerd,

No problems, I'd love to see this go in one day, it's just hard enough to
carve out time to debug crash dumps

I got overzealous with the change in pgtkterm.c, with the call from
`lispstpcpy` (and your explanation there makes sense)
looking at xterm, I see we have not marked that as a root , which is where
I think that code was ported from originally.

I have attached an updated patch, using a rebuilt igc-emacs from that
commit, which is holding up.

Thanks,


On Wed, Nov 6, 2024 at 7:56 PM Gerd Möllmann <gerd.moellmann@gmail.com>
wrote:

> Fejfighter <fejfighter@gmail.com> writes:
>
> > This patch marks 2 outstanding ambiguous roots and appears to solve
> > crashing bugs I had been experiencing with igc/mps and pgtk.
> >
> > I have run this locally today, and I would have normally faced crashes
> > at timer expiration, this appears to be holding up.
>
> Thanks for the report, Jeff! Nice to see that someone besides me is
> using this :-).
>
> I think I see why the change in atimer.c is necessary: pgtk stores a
> struct frame * as client_data in an atimer structure. That's a Lisp
> object that can move during GC. Understood.
>
> The other change in pgtkterm.c I don't understand. AFAICS, x_id_name of
> the display_info structure is indeed only used as a character buffer
> into which characters from Lisp strings are memcpy'd. Could you please
> explain that one? (I'm macOS only, so I don't know anything about pgtk,
> if that matters.)
>

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From 080541ae5463eda9b20d9ec92cb41202ba21d87c Mon Sep 17 00:00:00 2001
From: Jeff Walsh <fejfighter@gmail.com>
Date: Tue, 5 Nov 2024 23:09:56 +1100
Subject: [PATCH] Mark atimer allocation as ambiguous root

* src/atimer.c (start_atimer): Time could be passed a lisp object for
data, we should allocate this as an ambiguous root
---
 src/atimer.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/atimer.c b/src/atimer.c
index 8253ae3a166..5bd282a310d 100644
--- a/src/atimer.c
+++ b/src/atimer.c
@@ -17,6 +17,7 @@
 along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
+#include "igc.h"
 
 #ifdef WINDOWSNT
 #define raise(s) w32_raise(s)
@@ -132,7 +133,13 @@ start_atimer (enum atimer_type type, struct timespec timestamp,
       free_atimers = t->next;
     }
   else
-    t = xmalloc (sizeof *t);
+    {
+#ifdef HAVE_MPS
+      t = igc_xzalloc_ambig (sizeof *t);
+#else
+      t = xmalloc (sizeof *t);
+#endif
+    }
 
   /* Fill the atimer structure.  */
   memset (t, 0, sizeof *t);
-- 
2.47.0