From 8e1f3a0e5162a223e77c2af8dd7f8d1b32c68653 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Lindqvist?= <bjourne@gmail.com>
Date: Fri, 22 May 2015 16:52:13 +0200
Subject: [PATCH] VM: after reset_datastack and retainstack clear the stack
 segment. makes it easier to find bad accesses to shadow data

---
 vm/contexts.cpp     | 10 ++++++++++
 vm/contexts.hpp     |  1 +
 vm/slot_visitor.hpp | 20 ++++++++------------
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/vm/contexts.cpp b/vm/contexts.cpp
index df698b38e8..e829bfd4b2 100644
--- a/vm/contexts.cpp
+++ b/vm/contexts.cpp
@@ -17,10 +17,12 @@ context::context(cell datastack_size, cell retainstack_size,
 
 void context::reset_datastack() {
   datastack = datastack_seg->start - sizeof(cell);
+  fill_stack_seg(datastack, datastack_seg, 0x11111111);
 }
 
 void context::reset_retainstack() {
   retainstack = retainstack_seg->start - sizeof(cell);
+  fill_stack_seg(retainstack, retainstack_seg, 0x22222222);
 }
 
 void context::reset_callstack() {
@@ -32,6 +34,14 @@ void context::reset_context_objects() {
               context_object_count * sizeof(cell));
 }
 
+void context::fill_stack_seg(cell top_ptr, segment* seg, cell pattern) {
+#ifdef FACTOR_DEBUG
+  cell clear_start = top_ptr + sizeof(cell);
+  cell clear_size = seg->end - clear_start;
+  memset_cell((void*)clear_start, pattern, clear_size);
+#endif
+}
+
 void context::reset() {
   reset_datastack();
   reset_retainstack();
diff --git a/vm/contexts.hpp b/vm/contexts.hpp
index b898d78c0b..b9e04fe302 100644
--- a/vm/contexts.hpp
+++ b/vm/contexts.hpp
@@ -48,6 +48,7 @@ struct context {
   void reset_context_objects();
   void reset();
   void fix_stacks();
+  void fill_stack_seg(cell top_ptr, segment* seg, cell pattern);
 
   cell peek() { return *(cell*)datastack; }
 
diff --git a/vm/slot_visitor.hpp b/vm/slot_visitor.hpp
index 6db92c592e..7bd7a1c7ea 100644
--- a/vm/slot_visitor.hpp
+++ b/vm/slot_visitor.hpp
@@ -381,23 +381,19 @@ void slot_visitor<Fixup>::visit_context(context* ctx) {
      stacks. */
   visit_callstack(ctx);
 
-  cell* ds_ptr = (cell*)ctx->datastack;
-  cell* rs_ptr = (cell*)ctx->retainstack;
-  visit_stack_elements(ctx->datastack_seg, ds_ptr);
-  visit_stack_elements(ctx->retainstack_seg, rs_ptr);
+  cell ds_ptr = ctx->datastack;
+  cell rs_ptr = ctx->retainstack;
+  segment* ds_seg = ctx->datastack_seg;
+  segment* rs_seg = ctx->retainstack_seg;
+  visit_stack_elements(ds_seg, (cell*)ds_ptr);
+  visit_stack_elements(rs_seg, (cell*)rs_ptr);
   visit_object_array(ctx->context_objects,
                      ctx->context_objects + context_object_count);
 
   /* Clear out the space not visited with a known pattern. That makes
      it easier to see if uninitialized reads are made. */
-  #ifdef FACTOR_DEBUG
-  cell ds_clear_start = (cell)(ds_ptr + 1);
-  cell ds_clear_size = ctx->datastack_seg->end - ds_clear_start;
-  memset_cell((void*)ds_clear_start, 0xbaadbaad, ds_clear_size);
-  cell rs_clear_start = (cell)(rs_ptr + 1);
-  cell rs_clear_size = ctx->retainstack_seg->end - rs_clear_start;
-  memset_cell((void*)rs_clear_start, 0xdaabdaab, rs_clear_size);
-  #endif
+  ctx->fill_stack_seg(ds_ptr, ds_seg, 0xbaadbadd);
+  ctx->fill_stack_seg(rs_ptr, rs_seg, 0xdaabdaab);
 }
 
 template <typename Fixup> void slot_visitor<Fixup>::visit_contexts() {