From 2b41a37b3c4127d4a7f95d032ef63f9f8b9e5035 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Wed, 13 Oct 2010 21:18:44 +0200
Subject: [PATCH] fix bug in with-fluids in a non-tail position

* libguile/vm-i-system.c (VM_DEFINE_INSTRUCTION): Drop the stack items
  corresponding the the with-fluids object. Thanks very much to Stefan
  Israelsson Tampe for the fix.
---
 libguile/vm-i-system.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/libguile/vm-i-system.c b/libguile/vm-i-system.c
index 16b74e2b6..62b5e1a9c 100644
--- a/libguile/vm-i-system.c
+++ b/libguile/vm-i-system.c
@@ -1575,11 +1575,12 @@ VM_DEFINE_INSTRUCTION (89, wind_fluids, "wind-fluids", 1, -1, 0)
   unsigned n = FETCH ();
   SCM wf;
   
-  if (sp - 2*n < SCM_FRAME_UPPER_ADDRESS (fp))
-    goto vm_error_stack_underflow;
-
   SYNC_REGISTER ();
-  wf = scm_i_make_with_fluids (n, sp + 1 - 2*n, sp + 1 - n);
+  sp -= 2 * n;
+  CHECK_UNDERFLOW ();
+  wf = scm_i_make_with_fluids (n, sp + 1, sp + 1 + n);
+  NULLSTACK (2 * n);
+
   scm_i_swap_with_fluids (wf, dynstate);
   scm_i_set_dynwinds (scm_cons (wf, scm_i_dynwinds ()));
   NEXT;