[src/trunk]: src/lib/librumphijack Force gcc to generate a stack frame for th...

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

details:   https://anonhg.NetBSD.org/src/rev/1bab2bdf40e2
branches:  trunk
changeset: 761787:1bab2bdf40e2
user:      pooka <pooka%NetBSD.org@localhost>
date:      Mon Feb 07 19:34:39 2011 +0000

description:
Force gcc to generate a stack frame for the call to dlsym(RTLD_NEXT).
Without this hack at least amd64 -O2 just used jmp and The Wrong
Thing happened.

diffstat:

 lib/librumphijack/hijack.c |  19 ++++++++++++++++---
 1 files changed, 16 insertions(+), 3 deletions(-)

diffs (45 lines):

diff -r 483c558b0386 -r 1bab2bdf40e2 lib/librumphijack/hijack.c
--- a/lib/librumphijack/hijack.c        Mon Feb 07 19:20:35 2011 +0000
+++ b/lib/librumphijack/hijack.c        Mon Feb 07 19:34:39 2011 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: hijack.c,v 1.31 2011/02/07 12:23:05 pooka Exp $       */
+/*      $NetBSD: hijack.c,v 1.32 2011/02/07 19:34:39 pooka Exp $       */
 
 /*-
  * Copyright (c) 2011 Antti Kantee.  All Rights Reserved.
@@ -26,7 +26,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: hijack.c,v 1.31 2011/02/07 12:23:05 pooka Exp $");
+__RCSID("$NetBSD: hijack.c,v 1.32 2011/02/07 19:34:39 pooka Exp $");
 
 #define __ssp_weak_name(fun) _hijack_ ## fun
 
@@ -174,12 +174,25 @@
 /*
  * This is called from librumpclient in case of LD_PRELOAD.
  * It ensures correct RTLD_NEXT.
+ *
+ * ... except, it's apparently extremely difficult to force
+ * at least gcc to generate an actual stack frame here.  So
+ * sprinkle some volatile foobar and baz to throw the optimizer
+ * off the scent and generate a variable assignment with the
+ * return value.  The posterboy for this meltdown is amd64
+ * with -O2.  At least with gcc 4.1.3 i386 works regardless of
+ * optimization.
  */
+volatile int rumphijack_unrope; /* there, unhang yourself */
 static void *
 hijackdlsym(void *handle, const char *symbol)
 {
+       void *rv;
 
-       return dlsym(handle, symbol);
+       rv = dlsym(handle, symbol);
+       rumphijack_unrope = *(volatile int *)rv;
+
+       return (void *)rv;
 }
 
 /* low calorie sockets? */