From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 22 Apr 2019 04:16:03 +0000 (-0700)
Subject: Fix drain_reloc_list alignment bug
X-Git-Tag: emacs-27.0.90~3153
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=e85bff0bbb60e1d819f8f5e00f8496026f27f7ea;p=emacs.git

Fix drain_reloc_list alignment bug

* src/pdumper.c (dump_charset): Use alignof (struct charset),
not alignof (int), since struct charset might be more strictly
aligned than int.  I think this is just a minor performance
issue, but we might as well use the correct alignment.
(drain_reloc_list): Use an alignment instead of a size for the
output alignment.  This prevents undefined behavior when
alignof (struct emacs_reloc) == 8 and sizeof (dump_off) == 4
when building on x86-64 with gcc -fsanitize=undefined.
---

diff --git a/src/pdumper.c b/src/pdumper.c
index 6ab82769ec9..39931c6807f 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -3167,7 +3167,7 @@ dump_charset (struct dump_context *ctx, int cs_i)
 #if CHECK_STRUCTS && !defined (HASH_charset_317C49E291)
 # error "charset changed. See CHECK_STRUCTS comment."
 #endif
-  dump_align_output (ctx, alignof (int));
+  dump_align_output (ctx, alignof (struct charset));
   const struct charset *cs = charset_table + cs_i;
   struct charset out;
   dump_object_start (ctx, &out, sizeof (out));
@@ -3816,7 +3816,8 @@ drain_reloc_list (struct dump_context *ctx,
   Lisp_Object relocs = Fsort (Fnreverse (*reloc_list),
                               Qdump_emacs_portable__sort_predicate);
   *reloc_list = Qnil;
-  dump_align_output (ctx, sizeof (dump_off));
+  dump_align_output (ctx, max (alignof (struct dump_reloc),
+			       alignof (struct emacs_reloc)));
   struct dump_table_locator locator;
   memset (&locator, 0, sizeof (locator));
   locator.offset = ctx->offset;