Subject: Re: bug#61504: 29.0.60; executing byte-code from previous build causes SIGSEGV crash

From: Gregory Heytings <[email-masked]>
Date: Tue, 14 Feb 2023 16:00:35 +0000

> Looks right to me.

Many thanks for your review!

>> @@ -940,10 +940,9 @@ #define DEFINE(name, value) [name] = &&insn_ ## name,
>>  	  }
>>
>>  	CASE (Bsave_restriction):
>> -	  record_unwind_protect (save_restriction_restore,
>> -				 save_restriction_save ());
>> -	  record_unwind_protect (narrowing_locks_restore,
>> -				 narrowing_locks_save ());
>> +	  record_unwind_protect (save_restriction_and_narrowing_locks_restore,
>> +				 Fcons (save_restriction_save (),
>> +					narrowing_locks_save ()));
>>  	  NEXT;
>
> Shouldn't the value returned by `save_restriction_save` include the 
> narrowing locks already?
>
> IOW rather than changing this `bytecode.c` code, the locks handling 
> should be "hidden" inside `save_restriction_restore` and 
> `save_restriction_save`, don't you think?
>

You mean, the attached patch?  That's probably even better, indeed. 
(Again it passes make and make check, with and without native 
compilation.)
From 79c5581d34da4baecf5514c1d0d25cfbcc33f05d Mon Sep 17 00:00:00 2001
From: Gregory Heytings <[email-masked]>
Date: Tue, 14 Feb 2023 15:59:16 +0000
Subject: [PATCH] Improve backward compatibility of save-restriction

* src/editfns.c (save_restriction_save_1): Renamed from
'save_restrictions_save'.
(save_restriction_restore_1): Renamed from
'save_restriction_restore'.
(save_restriction_restore): New function, combining
'save_restriction_save_1' and 'narrowing_locks_save'.
(save_restriction_save): New function, combining
'save_restriction_restore_1' and 'narrowing_locks_restore'.
(Fsave_restriction): Restore the previous code.
(narrowing_locks_save, narrowing_locks_restore): Make them static.

* src/lisp.h: Remove two functions that are not externally visible
anymore.

* src/comp.c (helper_save_restriction): Restore the previous code.

* src/bytecode.c (exec_byte_code): Restore the previous code.

* lisp/emacs-lisp/bytecomp.el (byte-compile-save-restriction):
Decrement unbinding count.
---
 lisp/emacs-lisp/bytecomp.el |  2 +-
 src/bytecode.c              |  2 --
 src/comp.c                  |  2 --
 src/editfns.c               | 26 +++++++++++++++++++-------
 src/lisp.h                  |  2 --
 5 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index c6cda6b588a..5df1205869c 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -4900,7 +4900,7 @@ byte-compile-save-excursion
 (defun byte-compile-save-restriction (form)
   (byte-compile-out 'byte-save-restriction 0)
   (byte-compile-body-do-effect (cdr form))
-  (byte-compile-out 'byte-unbind 2))
+  (byte-compile-out 'byte-unbind 1))
 
 (defun byte-compile-save-current-buffer (form)
   (byte-compile-out 'byte-save-current-buffer 0)
diff --git a/src/bytecode.c b/src/bytecode.c
index 8e214560f30..124348e5b35 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -942,8 +942,6 @@ #define DEFINE(name, value) [name] = &&insn_ ## name,
 	CASE (Bsave_restriction):
 	  record_unwind_protect (save_restriction_restore,
 				 save_restriction_save ());
-	  record_unwind_protect (narrowing_locks_restore,
-				 narrowing_locks_save ());
 	  NEXT;
 
 	CASE (Bcatch):		/* Obsolete since 25.  */
diff --git a/src/comp.c b/src/comp.c
index 0e2dfd3913b..10cf7962ba1 100644
--- a/src/comp.c
+++ b/src/comp.c
@@ -5063,8 +5063,6 @@ helper_save_restriction (void)
 {
   record_unwind_protect (save_restriction_restore,
 			 save_restriction_save ());
-  record_unwind_protect (narrowing_locks_restore,
-			 narrowing_locks_save ());
 }
 
 static bool
diff --git a/src/editfns.c b/src/editfns.c
index ce133785e0b..1534f78ace7 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -2794,7 +2794,7 @@ reset_outermost_narrowings (void)
 
 /* Helper functions to save and restore the narrowing locks of the
    current buffer in Fsave_restriction.  */
-Lisp_Object
+static Lisp_Object
 narrowing_locks_save (void)
 {
   Lisp_Object buf = Fcurrent_buffer ();
@@ -2804,7 +2804,7 @@ narrowing_locks_save (void)
   return Fcons (buf, Fcopy_sequence (locks));
 }
 
-void
+static void
 narrowing_locks_restore (Lisp_Object buf_and_saved_locks)
 {
   Lisp_Object buf = XCAR (buf_and_saved_locks);
@@ -2975,8 +2975,8 @@ DEFUN ("internal--unlock-narrowing", Finternal__unlock_narrowing,
   return Qnil;
 }
 
-Lisp_Object
-save_restriction_save (void)
+static Lisp_Object
+save_restriction_save_1 (void)
 {
   if (BEGV == BEG && ZV == Z)
     /* The common case that the buffer isn't narrowed.
@@ -2999,8 +2999,8 @@ save_restriction_save (void)
     }
 }
 
-void
-save_restriction_restore (Lisp_Object data)
+static void
+save_restriction_restore_1 (Lisp_Object data)
 {
   struct buffer *cur = NULL;
   struct buffer *buf = (CONSP (data)
@@ -3068,6 +3068,19 @@ save_restriction_restore (Lisp_Object data)
     set_buffer_internal (cur);
 }
 
+Lisp_Object
+save_restriction_save (void)
+{
+  return Fcons (save_restriction_save_1 (), narrowing_locks_save ());
+}
+
+void
+save_restriction_restore (Lisp_Object data)
+{
+  save_restriction_restore_1 (XCAR (data));
+  narrowing_locks_restore (XCDR (data));
+}
+
 DEFUN ("save-restriction", Fsave_restriction, Ssave_restriction, 0, UNEVALLED, 0,
        doc: /* Execute BODY, saving and restoring current buffer's restrictions.
 The buffer's restrictions make parts of the beginning and end invisible.
@@ -3092,7 +3105,6 @@ DEFUN ("save-restriction", Fsave_restriction, Ssave_restriction, 0, UNEVALLED, 0
   specpdl_ref count = SPECPDL_INDEX ();
 
   record_unwind_protect (save_restriction_restore, save_restriction_save ());
-  record_unwind_protect (narrowing_locks_restore, narrowing_locks_save ());
   val = Fprogn (body);
   return unbind_to (count, val);
 }
diff --git a/src/lisp.h b/src/lisp.h
index 93197d38176..1276285e2f2 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4684,8 +4684,6 @@ XMODULE_FUNCTION (Lisp_Object o)
 extern void save_excursion_restore (Lisp_Object, Lisp_Object);
 extern Lisp_Object save_restriction_save (void);
 extern void save_restriction_restore (Lisp_Object);
-extern Lisp_Object narrowing_locks_save (void);
-extern void narrowing_locks_restore (Lisp_Object);
 extern Lisp_Object make_buffer_string (ptrdiff_t, ptrdiff_t, bool);
 extern Lisp_Object make_buffer_string_both (ptrdiff_t, ptrdiff_t, ptrdiff_t,
 					    ptrdiff_t, bool);
-- 
2.39.0