Fix alignment-related core dump during GC.

* configure.in (GC_LISP_OBJECT_ALIGNMENT): Remove.
This is now done by src/alloc.c.
* src/alloc.c (GC_LISP_OBJECT_ALIGNMENT): Use offsetof, not __alignof__
or sizeof.  __alignof__ gives the wrong answer on Fedora x86-64
with GCC 4.6.1 when configured with CC='gcc -m32' --with-wide-int;
this makes Emacs dump core during garbage collection on rare
occasions.  sizeof is obviously inferior to offsetof here, so
stick with offsetof.
(GC_POINTER_ALIGNMENT): New macro.
(mark_memory): Omit 3rd (offset) arg; caller changed.
Don't assume EMACS_INT alignment is the same as pointer alignment.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b697ee43376..d2c069b7351 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2011-10-07  Paul Eggert  <eggert@cs.ucla.edu>
+
+        * alloc.c (GC_LISP_OBJECT_ALIGNMENT): Use offsetof, not __alignof__
+        or sizeof.  __alignof__ gives the wrong answer on Fedora x86-64
+        with GCC 4.6.1 when configured with CC='gcc -m32' --with-wide-int;
+        this makes Emacs dump core during garbage collection on rare
+        occasions.  sizeof is obviously inferior to offsetof here, so
+        stick with offsetof.
+        (GC_POINTER_ALIGNMENT): New macro.
+        (mark_memory): Omit 3rd (offset) arg; caller changed.
+        Don't assume EMACS_INT alignment is the same as pointer alignment.
+
 2011-10-03  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * keyboard.c (read_key_sequence_remapped): New var.