From c896e6dfbc4240a4d042dd43a8f66c5127f94707 Mon Sep 17 00:00:00 2001
From: Robin Watts <robin.watts@artifex.com>
Date: Sat, 26 Mar 2016 09:28:34 +0000
Subject: Memento: Cope with wrapped blocks.

If another routine 'wraps' memento blocks (such as a chunk allocator
or the 'trace' allocator in mudraw), then the address passed to
Memento_label, Memento_takeRef etc, can be inside the block rather
than at the start of the block.

Update Memento to cope with this.
---
 source/fitz/memento.c | 44 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

(limited to 'source/fitz/memento.c')

diff --git a/source/fitz/memento.c b/source/fitz/memento.c
index b29e07a1..36693366 100644
--- a/source/fitz/memento.c
+++ b/source/fitz/memento.c
@@ -676,6 +676,9 @@ static void Memento_storeDetails(Memento_BlkHeader *head, int type)
     int count;
     int skip;
 
+    if (head == NULL)
+        return;
+
 #ifdef MEMENTO_STACKTRACE_METHOD
     count = Memento_getStacktrace(stack, &skip);
 #else
@@ -1560,16 +1563,47 @@ int Memento_breakAt(int event)
     return event;
 }
 
+static void *safe_find_block(void *ptr)
+{
+    Memento_BlkHeader *block;
+    int valid;
+
+    block = MEMBLK_FROMBLK(ptr);
+    /* Sometimes wrapping allocators can mean Memento_label
+     * is called with a value within the block, rather than
+     * at the start of the block. If we detect this, find it
+     * the slow way. */
+    VALGRIND_MAKE_MEM_DEFINED(&block->child, sizeof(block->child));
+    VALGRIND_MAKE_MEM_DEFINED(&block->sibling, sizeof(block->sibling));
+    valid = (block->child == MEMENTO_CHILD_MAGIC &&
+             block->sibling == MEMENTO_SIBLING_MAGIC);
+    VALGRIND_MAKE_MEM_NOACCESS(&block->child, sizeof(block->child));
+    VALGRIND_MAKE_MEM_NOACCESS(&block->sibling, sizeof(block->sibling));
+    if (!valid);
+    {
+        findBlkData data;
+
+        data.addr  = ptr;
+        data.blk   = NULL;
+        data.flags = 0;
+        Memento_appBlocks(&memento.used, Memento_containsAddr, &data);
+	if (data.blk == NULL)
+            return ptr;
+	block = data.blk;
+    }
+    return block;
+}
+
 void *Memento_label(void *ptr, const char *label)
 {
     Memento_BlkHeader *block;
 
     if (ptr == NULL)
         return NULL;
-    block = MEMBLK_FROMBLK(ptr);
+    block = safe_find_block(ptr);
     VALGRIND_MAKE_MEM_DEFINED(&block->label, sizeof(block->label));
     block->label = label;
-    VALGRIND_MAKE_MEM_UNDEFINED(&block->label, sizeof(block->label));
+    VALGRIND_MAKE_MEM_NOACCESS(&block->label, sizeof(block->label));
     return ptr;
 }
 
@@ -1675,21 +1709,21 @@ static void do_reference(Memento_BlkHeader *blk, int event)
 void *Memento_takeRef(void *blk)
 {
     if (blk)
-        do_reference(MEMBLK_FROMBLK(blk), Memento_EventType_takeRef);
+        do_reference(safe_find_block(blk), Memento_EventType_takeRef);
     return blk;
 }
 
 void *Memento_dropRef(void *blk)
 {
     if (blk)
-        do_reference(MEMBLK_FROMBLK(blk), Memento_EventType_dropRef);
+        do_reference(safe_find_block(blk), Memento_EventType_dropRef);
     return blk;
 }
 
 void *Memento_reference(void *blk)
 {
     if (blk)
-        do_reference(MEMBLK_FROMBLK(blk), Memento_EventType_reference);
+        do_reference(safe_find_block(blk), Memento_EventType_reference);
     return blk;
 }
 
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