1 files changed, 47 insertions, 21 deletions

diff --git a/src/alloc.c b/src/alloc.c
index ad1741e308f..ead5c8a8ca4 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -490,19 +490,45 @@ buffer_memory_full (EMACS_INT nbytes)
 /* Check for overrun in malloc'ed buffers by wrapping a header and trailer
    around each block.
 
-   The header consists of 16 fixed bytes followed by sizeof (size_t) bytes
-   containing the original block size in little-endian order,
-   while the trailer consists of 16 fixed bytes.
+   The header consists of XMALLOC_OVERRUN_CHECK_SIZE fixed bytes
+   followed by XMALLOC_OVERRUN_SIZE_SIZE bytes containing the original
+   block size in little-endian order.  The trailer consists of
+   XMALLOC_OVERRUN_CHECK_SIZE fixed bytes.
 
    The header is used to detect whether this block has been allocated
-   through these functions -- as it seems that some low-level libc
-   functions may bypass the malloc hooks.
-*/
-
+   through these functions, as some low-level libc functions may
+   bypass the malloc hooks.  */
 
 #define XMALLOC_OVERRUN_CHECK_SIZE 16
 #define XMALLOC_OVERRUN_CHECK_OVERHEAD \
-  (2 * XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t))
+  (2 * XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE)
+
+/* Define XMALLOC_OVERRUN_SIZE_SIZE so that (1) it's large enough to
+   hold a size_t value and (2) the header size is a multiple of the
+   alignment that Emacs needs for C types and for USE_LSB_TAG.  */
+#define XMALLOC_BASE_ALIGNMENT                          \
+  offsetof (                                            \
+    struct {                                            \
+      union { long double d; intmax_t i; void *p; } u;  \
+      char c;                                           \
+    },                                                  \
+    c)
+#ifdef USE_LSB_TAG
+/* A common multiple of the positive integers A and B.  Ideally this
+   would be the least common multiple, but there's no way to do that
+   as a constant expression in C, so do the best that we can easily do.  */
+# define COMMON_MULTIPLE(a, b) \
+    ((a) % (b) == 0 ? (a) : (b) % (a) == 0 ? (b) : (a) * (b))
+# define XMALLOC_HEADER_ALIGNMENT \
+    COMMON_MULTIPLE (1 << GCTYPEBITS, XMALLOC_BASE_ALIGNMENT)
+#else
+# define XMALLOC_HEADER_ALIGNMENT XMALLOC_BASE_ALIGNMENT
+#endif
+#define XMALLOC_OVERRUN_SIZE_SIZE                               \
+   (((XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t)              \
+      + XMALLOC_HEADER_ALIGNMENT - 1)                           \
+     / XMALLOC_HEADER_ALIGNMENT * XMALLOC_HEADER_ALIGNMENT)     \
+    - XMALLOC_OVERRUN_CHECK_SIZE)
 
 static char const xmalloc_overrun_check_header[XMALLOC_OVERRUN_CHECK_SIZE] =
   { '\x9a', '\x9b', '\xae', '\xaf',
@@ -522,9 +548,9 @@ static void
 xmalloc_put_size (unsigned char *ptr, size_t size)
 {
   int i;
-  for (i = 0; i < sizeof (size_t); i++)
+  for (i = 0; i < XMALLOC_OVERRUN_SIZE_SIZE; i++)
     {
-      *--ptr = size & (1 << CHAR_BIT) - 1;
+      *--ptr = size & ((1 << CHAR_BIT) - 1);
       size >>= CHAR_BIT;
     }
 }
@@ -534,8 +560,8 @@ xmalloc_get_size (unsigned char *ptr)
 {
   size_t size = 0;
   int i;
-  ptr -= sizeof (size_t);
-  for (i = 0; i < sizeof (size_t); i++)
+  ptr -= XMALLOC_OVERRUN_SIZE_SIZE;
+  for (i = 0; i < XMALLOC_OVERRUN_SIZE_SIZE; i++)
     {
       size <<= CHAR_BIT;
       size += *ptr++;
@@ -579,7 +605,7 @@ overrun_check_malloc (size_t size)
   if (val && check_depth == 1)
     {
       memcpy (val, xmalloc_overrun_check_header, XMALLOC_OVERRUN_CHECK_SIZE);
-      val += XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t);
+      val += XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
       xmalloc_put_size (val, size);
       memcpy (val + size, xmalloc_overrun_check_trailer,
               XMALLOC_OVERRUN_CHECK_SIZE);
@@ -603,7 +629,7 @@ overrun_check_realloc (POINTER_TYPE *block, size_t size)
   if (val
       && check_depth == 1
       && memcmp (xmalloc_overrun_check_header,
-                 val - XMALLOC_OVERRUN_CHECK_SIZE - sizeof (size_t),
+                 val - XMALLOC_OVERRUN_CHECK_SIZE - XMALLOC_OVERRUN_SIZE_SIZE,
                  XMALLOC_OVERRUN_CHECK_SIZE) == 0)
     {
       size_t osize = xmalloc_get_size (val);
@@ -611,8 +637,8 @@ overrun_check_realloc (POINTER_TYPE *block, size_t size)
                   XMALLOC_OVERRUN_CHECK_SIZE))
         abort ();
       memset (val + osize, 0, XMALLOC_OVERRUN_CHECK_SIZE);
-      val -= XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t);
-      memset (val, 0, XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t));
+      val -= XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
+      memset (val, 0, XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE);
     }
 
   val = (unsigned char *) realloc ((POINTER_TYPE *)val, size + overhead);
@@ -620,7 +646,7 @@ overrun_check_realloc (POINTER_TYPE *block, size_t size)
   if (val && check_depth == 1)
     {
       memcpy (val, xmalloc_overrun_check_header, XMALLOC_OVERRUN_CHECK_SIZE);
-      val += XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t);
+      val += XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
       xmalloc_put_size (val, size);
       memcpy (val + size, xmalloc_overrun_check_trailer,
               XMALLOC_OVERRUN_CHECK_SIZE);
@@ -640,7 +666,7 @@ overrun_check_free (POINTER_TYPE *block)
   if (val
       && check_depth == 1
       && memcmp (xmalloc_overrun_check_header,
-                 val - XMALLOC_OVERRUN_CHECK_SIZE - sizeof (size_t),
+                 val - XMALLOC_OVERRUN_CHECK_SIZE - XMALLOC_OVERRUN_SIZE_SIZE,
                  XMALLOC_OVERRUN_CHECK_SIZE) == 0)
     {
       size_t osize = xmalloc_get_size (val);
@@ -648,12 +674,12 @@ overrun_check_free (POINTER_TYPE *block)
                   XMALLOC_OVERRUN_CHECK_SIZE))
         abort ();
 #ifdef XMALLOC_CLEAR_FREE_MEMORY
-      val -= XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t);
+      val -= XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
       memset (val, 0xff, osize + XMALLOC_OVERRUN_CHECK_OVERHEAD);
 #else
       memset (val + osize, 0, XMALLOC_OVERRUN_CHECK_SIZE);
-      val -= XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t);
-      memset (val, 0, XMALLOC_OVERRUN_CHECK_SIZE + sizeof (size_t));
+      val -= XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
+      memset (val, 0, XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE);
 #endif
     }