[src/trunk]: src/lib/libc/misc More of previous.

[dholland <dholland%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/9689b1267eb5
branches:  trunk
changeset: 349176:9689b1267eb5
user:      dholland <dholland%NetBSD.org@localhost>
date:      Sat Nov 26 21:17:06 2016 +0000

description:
More of previous.

diffstat:

 lib/libc/misc/initfini.c |  18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diffs (39 lines):

diff -r f4d4fae808ca -r 9689b1267eb5 lib/libc/misc/initfini.c
--- a/lib/libc/misc/initfini.c  Sat Nov 26 20:38:20 2016 +0000
+++ b/lib/libc/misc/initfini.c  Sat Nov 26 21:17:06 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: initfini.c,v 1.12 2016/11/26 20:38:20 dholland Exp $    */
+/*     $NetBSD: initfini.c,v 1.13 2016/11/26 21:17:06 dholland Exp $    */
 
 /*-
  * Copyright (c) 2007 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: initfini.c,v 1.12 2016/11/26 20:38:20 dholland Exp $");
+__RCSID("$NetBSD: initfini.c,v 1.13 2016/11/26 21:17:06 dholland Exp $");
 
 #ifdef _LIBC
 #include "namespace.h"
@@ -83,6 +83,20 @@
  * In static binaries the explicit call is first; in dynamically linked
  * binaries the global constructors of libc are called from ld.elf_so
  * before crt0.o is reached.
+ *
+ * Note that __ps_strings is set by crt0.o. So in the dynamic case, it
+ * hasn't been set yet when we get here, and __libc_dlauxinfo is not
+ * (ever) assigned. But this is ok because __libc_dlauxinfo is only
+ * used in static binaries, because it's there to substitute for the
+ * dynamic linker. In static binaries __ps_strings will have been set
+ * up when we get here and we get a valid __libc_dlauxinfo.
+ *
+ * This code causes problems for Emacs because Emacs's undump
+ * mechanism saves the __ps_strings value from the startup execution;
+ * then running the resulting binary it gets here before crt0 has
+ * assigned the current execution's value to __ps_strings, and in an
+ * environment with ASLR this can cause the assignment of
+ * __libc_dlauxinfo to receive SIGSEGV.
  */
 void __section(".text.startup")
 _libc_init(void)