From 08cf30f2a0fc6c9e0851e229a11c09ab9aaacec0 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Mon, 20 Jul 2015 16:24:49 +0200
Subject: Fix error printing some wrong-num-args backtraces

* module/system/repl/debug.scm (print-frame): Pass #:top-frame? #t for
  the top frame.

* module/system/vm/frame.scm (available-bindings): Be permissive and
  allow #:top-frame? #f even when the IP is at the start of the
  function.
---
 module/system/repl/debug.scm | 5 +++--
 module/system/vm/frame.scm   | 5 ++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/module/system/repl/debug.scm b/module/system/repl/debug.scm
index 300145d16..6fff660e5 100644
--- a/module/system/repl/debug.scm
+++ b/module/system/repl/debug.scm
@@ -1,6 +1,6 @@
 ;;; Guile VM debugging facilities
 
-;;; Copyright (C) 2001, 2009, 2010, 2011, 2013, 2014 Free Software Foundation, Inc.
+;;; Copyright (C) 2001, 2009, 2010, 2011, 2013, 2014, 2015 Free Software Foundation, Inc.
 ;;;
 ;;; This library is free software; you can redistribute it and/or
 ;;; modify it under the terms of the GNU Lesser General Public
@@ -134,7 +134,8 @@
         (format port "~&In ~a:~&" file))
     (format port "~9@a~:[~*~3_~;~3d~] ~v:@y~%"
             (if line (format #f "~a:~a" line col) "")
-            index index width (frame-call-representation frame))
+            index index width
+            (frame-call-representation frame #:top-frame? (zero? index)))
     (if full?
         (print-locals frame #:width width
                       #:per-line-prefix "     "))))
diff --git a/module/system/vm/frame.scm b/module/system/vm/frame.scm
index ac5fbf6f5..b84f6683e 100644
--- a/module/system/vm/frame.scm
+++ b/module/system/vm/frame.scm
@@ -206,7 +206,10 @@
       (when (< offset 0)
         (error "ip did not correspond to an instruction boundary?"))
       (if (zero? offset)
-          (let ((live (if top-frame?
+          ;; It shouldn't be the case that both OFFSET and N are zero
+          ;; but TOP-FRAME? is false.  Still, it could happen, as is
+          ;; currently the case in frame-arguments.
+          (let ((live (if (or top-frame? (zero? n))
                           (vector-ref inv n)
                           ;; If we're not at a top frame, the IP points
                           ;; to the continuation -- but we haven't
-- 
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