Memento: Ensure that Memento_BlkHeader is a multiple of 32 bytes.

This is so that Memento wrapped blocks get the same alignment % 32
as the underlying malloc blocks. This is important for setjmp
buffer usage on Windows (at least, probably linux too).

1 files changed, 43 insertions, 22 deletions

diff --git a/base/memento.c b/base/memento.c
index ea809a51c..aa60999bb 100644
--- a/base/memento.c
+++ b/base/memento.c
@@ -385,33 +385,54 @@ struct Memento_BlkDetails
 
 typedef struct Memento_BlkHeader Memento_BlkHeader;
 
-struct Memento_BlkHeader
-{
-    size_t               rawsize;
-    int                  sequence;
-    int                  lastCheckedOK;
-    int                  flags;
+#ifdef MEMENTO_DETAILS
+#define MEMENTO_DETAIL_FIELDS \
+    Memento_BlkDetails  *details;\
+    Memento_BlkDetails **details_tail;
+#else
+#define MEMENTO_DETAIL_FIELDS
+#endif
 
-    const char          *label;
+#define MEMENTO_BLKHEADER_FIELDS \
+    size_t               rawsize;                       \
+    int                  sequence;                      \
+    int                  lastCheckedOK;                 \
+    int                  flags;                         \
+                                                        \
+    const char          *label;                         \
+                                                        \
+    /* Blocks are held in a linked list for LRU */      \
+    Memento_BlkHeader   *next;                          \
+    /* Reused as 'parent' when printing nested list */  \
+    Memento_BlkHeader   *prev;                          \
+                                                        \
+    /* Blocks are held in a splay tree for position. */ \
+    Memento_BlkHeader   *parent;                        \
+    Memento_BlkHeader   *left;                          \
+    Memento_BlkHeader   *right;                         \
+                                                        \
+    /* Entries for nesting display calculations. Set    \
+     * to magic values at all other time.  */           \
+    Memento_BlkHeader   *child;                         \
+    Memento_BlkHeader   *sibling;                       \
+                                                        \
+    MEMENTO_DETAIL_FIELDS
 
-    /* Blocks are held in a linked list for LRU */
-    Memento_BlkHeader   *next;
-    Memento_BlkHeader   *prev; /* Reused as 'parent' when printing nested list */
+typedef struct
+{
+    MEMENTO_BLKHEADER_FIELDS
+} Memento_BlkHeader_unpadded;
 
-    /* Blocks are held in a splay tree for position. */
-    Memento_BlkHeader   *parent;
-    Memento_BlkHeader   *left;
-    Memento_BlkHeader   *right;
+#define MEMENTO_BLKHEADER_UNPADDED_SIZE (sizeof(Memento_BlkHeader_unpadded)+Memento_PreSize)
 
-    /* Entries for nesting display calculations. Set to magic
-     * values at all other time.  */
-    Memento_BlkHeader   *child;
-    Memento_BlkHeader   *sibling;
+struct Memento_BlkHeader
+{
+    MEMENTO_BLKHEADER_FIELDS
 
-#ifdef MEMENTO_DETAILS
-    Memento_BlkDetails  *details;
-    Memento_BlkDetails **details_tail;
-#endif
+    /* Ensure that Memento_BlkHeader is a multiple of 32. This is required
+     * for setjmp/longjmp etc on many platforms. We want to ensure that
+     * we preserve the relative 32byte alignment to the underlying malloc. */
+    char alignment_padding[32-(MEMENTO_BLKHEADER_UNPADDED_SIZE & 31)];
 
     char                 preblk[Memento_PreSize];
 };