From: Paul Eggert <eggert@cs.ucla.edu>
Date: Wed, 31 Oct 2018 03:57:46 +0000 (-0700)
Subject: Improve fix for Bug#33014
X-Git-Tag: emacs-27.0.90~4239
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=cf486a7a920d3d95fa9aa98d7b03ebc61b17518a;p=emacs.git

Improve fix for Bug#33014

Although the previously-applied fix worked for its platform,
it doesn’t suffice in general.
* src/bytecode.c (exec_byte_code): Save VECTOR into stack slot
so that it survives GC.  The stack slot was otherwise unused,
so this doesn’t cost us memory, only a store insn.
* src/eval.c (Ffuncall): Do not make FUN volatile, reverting
2018-10-14T19:12:04Z!gazally@runbox.com.  Adding ‘volatile’
does not suffice, since storage for a volatile local can be
reclaimed after its last access (e.g., by tail recursion
elimination), which would make VECTOR invisible to GC.
---

diff --git a/src/bytecode.c b/src/bytecode.c
index 17457fc5742..40389e08f0e 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -369,6 +369,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
   ptrdiff_t item_bytes = stack_items * word_size;
   Lisp_Object *stack_base = ptr_bounds_clip (alloc, item_bytes);
   Lisp_Object *top = stack_base;
+  *top = vector; /* Ensure VECTOR survives GC (Bug#33014).  */
   Lisp_Object *stack_lim = stack_base + stack_items;
   unsigned char *bytestr_data = alloc;
   bytestr_data = ptr_bounds_clip (bytestr_data + item_bytes, bytestr_length);
diff --git a/src/eval.c b/src/eval.c
index 32cfda24d8c..a51d0c90831 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2820,11 +2820,8 @@ Thus, (funcall \\='cons \\='x \\='y) returns (x . y).
 usage: (funcall FUNCTION &rest ARGUMENTS)  */)
   (ptrdiff_t nargs, Lisp_Object *args)
 {
-  /* Use 'volatile' here to cause optimizing compilers to keep a
-     reference on the stack to the function's bytecode object.  See
-     Bug#33014.  */
-  Lisp_Object volatile fun;
-  Lisp_Object original_fun, funcar;
+  Lisp_Object fun, original_fun;
+  Lisp_Object funcar;
   ptrdiff_t numargs = nargs - 1;
   Lisp_Object val;
   ptrdiff_t count;