bug#39962: 27.0.90; Crash in Emacs 27.0.90

[Pip Cet <pipcet@gmail.com>]

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On Sat, Mar 14, 2020 at 4:57 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > > The two comments do not seem to agree. Surely second one should say just
> > > something like "P must point into block M."
> >
> > Thanks! Revised patch attached.
>
> Thanks.  I'd prefer not to duplicate code, though.  Can we teach
> live_buffer_holding to disregard whether a buffer is killed or not
> based on an additional argument?

Sure. Patch attached.

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From bf2d92f6387e7bade0567f2081b420084e13b502 Mon Sep 17 00:00:00 2001
From: Pip Cet <pipcet@gmail.com>
Date: Sat, 14 Mar 2020 18:26:33 +0000
Subject: [PATCH] Don't collect reachable killed buffers during GC

* src/alloc.c (live_buffer_holding): Add `all_buffers' argument for
returning killed buffers.
(mark_maybe_object, mark_maybe_pointer): Use it.
---
 src/alloc.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/alloc.c b/src/alloc.c
index 1c6b664b22..aea1f27a39 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -4482,20 +4482,22 @@ live_vector_p (struct mem_node *m, void *p)
 }
 
 /* If P is a pointer into a live buffer, return the buffer.
-   Otherwise, return nil.  M is a pointer to the mem_block for P.  */
+   Otherwise, return nil.  M is a pointer to the mem_block for P.
+   Also return killed buffers if ALL-BUFFERS is true.  */
 
 static Lisp_Object
-live_buffer_holding (struct mem_node *m, void *p)
+live_buffer_holding (struct mem_node *m, void *p, bool all_buffers)
 {
-  /* P must point into the block, and the buffer
-     must not have been killed.  */
+  /* P must point into the block, and the buffer must not
+     have been killed unless ALL-BUFFERS is true.  */
   if (m->type == MEM_TYPE_BUFFER)
     {
       struct buffer *b = m->start;
       char *cb = m->start;
       char *cp = p;
       ptrdiff_t offset = cp - cb;
-      if (0 <= offset && offset < sizeof *b && !NILP (b->name_))
+      if (0 <= offset && offset < sizeof *b &&
+	  (all_buffers || !NILP (b->name_)))
 	{
 	  Lisp_Object obj;
 	  XSETBUFFER (obj, b);
@@ -4508,7 +4510,7 @@ live_buffer_holding (struct mem_node *m, void *p)
 static bool
 live_buffer_p (struct mem_node *m, void *p)
 {
-  return !NILP (live_buffer_holding (m, p));
+  return !NILP (live_buffer_holding (m, p, false));
 }
 
 /* Mark OBJ if we can prove it's a Lisp_Object.  */
@@ -4566,7 +4568,7 @@ mark_maybe_object (Lisp_Object obj)
 
 	case Lisp_Vectorlike:
 	  mark_p = (EQ (obj, live_vector_holding (m, po))
-		    || EQ (obj, live_buffer_holding (m, po)));
+		    || EQ (obj, live_buffer_holding (m, po, true)));
 	  break;
 
 	default:
@@ -4636,7 +4638,7 @@ mark_maybe_pointer (void *p)
 	  break;
 
 	case MEM_TYPE_BUFFER:
-	  obj = live_buffer_holding (m, p);
+	  obj = live_buffer_holding (m, p, true);
 	  break;
 
 	case MEM_TYPE_CONS:
-- 
2.25.1