From 11e906139b99652a2e0d89a6d6bfb2c149a7ddcd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Lindqvist?= <bjourne@gmail.com>
Date: Sun, 4 Jan 2015 15:30:04 +0100
Subject: [PATCH] VM: code_block::scan, make it so the method always returns -1
 if scan can't be determined, part of the fix for #1265

---
 core/kernel/kernel-docs.factor |  8 +++++++-
 vm/code_blocks.cpp             | 31 +++++++++++++------------------
 2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/core/kernel/kernel-docs.factor b/core/kernel/kernel-docs.factor
index d4a00de05d..ca07d52a9a 100644
--- a/core/kernel/kernel-docs.factor
+++ b/core/kernel/kernel-docs.factor
@@ -44,7 +44,13 @@ HELP: set-retainstack
 
 HELP: callstack
 { $values { "callstack" callstack } }
-{ $description "Outputs a copy of the call stack contents, with the top of the stack at the end of the vector. The stack frame of the caller word is " { $emphasis "not" } " included." } ;
+{ $description "Outputs a copy of the call stack contents, with the top of the stack at the end of the vector. The stack frame of the caller word is " { $emphasis "not" } " included. Each group of three elements in the callstack is frame:"
+  { $list
+    "The first element is the executing word or quotation."
+    "The second element is the executing quotation."
+    "The third element is the offset in the executing quotation, or -1 if the offset can't be determined."
+  }
+} ;
 
 HELP: set-callstack
 { $values { "callstack" callstack } }
diff --git a/vm/code_blocks.cpp b/vm/code_blocks.cpp
index bb993f1ff4..19f8f4946b 100644
--- a/vm/code_blocks.cpp
+++ b/vm/code_blocks.cpp
@@ -9,26 +9,21 @@ cell code_block::owner_quot() const {
   return executing.value();
 }
 
+/* If the code block is an unoptimized quotation, we can calculate the
+   scan offset. In all other cases -1 is returned. */
 cell code_block::scan(factor_vm* vm, void* addr) const {
-  switch (type()) {
-    case code_block_unoptimized: {
-      tagged<object> obj(owner);
-      if (obj.type_p(WORD_TYPE))
-        obj = obj.as<word>()->def;
-
-      if (obj.type_p(QUOTATION_TYPE))
-        return tag_fixnum(
-            vm->quot_code_offset_to_scan(obj.value(), offset(addr)));
-      else
-        return false_object;
-    }
-    case code_block_optimized:
-    case code_block_pic:
-      return false_object;
-    default:
-      critical_error("Bad frame type", type());
-      return false_object;
+  if (type() != code_block_unoptimized) {
+    return tag_fixnum(-1);
   }
+
+  tagged<object> obj(owner);
+  if (obj.type_p(WORD_TYPE))
+    obj = obj.as<word>()->def;
+  if (!obj.type_p(QUOTATION_TYPE))
+    return tag_fixnum(-1);
+
+  cell ofs = offset(addr);
+  return tag_fixnum(vm->quot_code_offset_to_scan(obj.value(), ofs));
 }
 
 cell factor_vm::compute_entry_point_address(cell obj) {