diff --git a/xen/common/debugtrace.c b/xen/common/debugtrace.c
index 07e2746846..51ab41f7a7 100644
--- a/xen/common/debugtrace.c
+++ b/xen/common/debugtrace.c
@@ -15,34 +15,40 @@
 #include <xen/watchdog.h>
 
 /* Send output direct to console, or buffer it? */
-static volatile int debugtrace_send_to_console;
+static volatile bool debugtrace_send_to_console;
 
-static char        *debugtrace_buf; /* Debug-trace buffer */
-static unsigned int debugtrace_prd; /* Producer index     */
-static unsigned int debugtrace_kilobytes = 128, debugtrace_bytes;
-static unsigned int debugtrace_used;
+struct debugtrace_data {
+    unsigned long prd;   /* Producer index. */
+    char          buf[];
+};
+
+static struct debugtrace_data *dt_data;
+
+static unsigned int debugtrace_kilobytes = 128;
+static unsigned long debugtrace_bytes;
 static bool debugtrace_buf_empty;
+static bool debugtrace_used;
 static DEFINE_SPINLOCK(debugtrace_lock);
 integer_param("debugtrace", debugtrace_kilobytes);
 
 static void debugtrace_dump_worker(void)
 {
-    if ( (debugtrace_bytes == 0) || !debugtrace_used )
+    if ( !debugtrace_used )
         return;
 
     printk("debugtrace_dump() starting\n");
 
     /* Print oldest portion of the ring. */
-    if ( debugtrace_buf[debugtrace_prd] != '\0' )
-        console_serial_puts(&debugtrace_buf[debugtrace_prd],
-                            debugtrace_bytes - debugtrace_prd);
+    if ( dt_data->buf[dt_data->prd] != '\0' )
+        console_serial_puts(&dt_data->buf[dt_data->prd],
+                            debugtrace_bytes - dt_data->prd);
 
     /* Print youngest portion of the ring. */
-    debugtrace_buf[debugtrace_prd] = '\0';
-    console_serial_puts(&debugtrace_buf[0], debugtrace_prd);
+    dt_data->buf[dt_data->prd] = '\0';
+    console_serial_puts(&dt_data->buf[0], dt_data->prd);
 
-    memset(debugtrace_buf, '\0', debugtrace_bytes);
-    debugtrace_prd = 0;
+    memset(dt_data->buf, '\0', debugtrace_bytes);
+    dt_data->prd = 0;
     debugtrace_buf_empty = true;
 
     printk("debugtrace_dump() finished\n");
@@ -68,7 +74,6 @@ static void debugtrace_toggle(void)
 
     spin_unlock_irqrestore(&debugtrace_lock, flags);
     watchdog_enable();
-
 }
 
 void debugtrace_dump(void)
@@ -90,26 +95,27 @@ static void debugtrace_add_to_buf(char *buf)
 
     for ( p = buf; *p != '\0'; p++ )
     {
-        debugtrace_buf[debugtrace_prd++] = *p;
-        if ( debugtrace_prd == debugtrace_bytes )
-            debugtrace_prd = 0;
+        dt_data->buf[dt_data->prd++] = *p;
+        if ( dt_data->prd == debugtrace_bytes )
+            dt_data->prd = 0;
     }
 }
 
 void debugtrace_printk(const char *fmt, ...)
 {
     static char buf[1024], last_buf[1024];
-    static unsigned int count, last_count, last_prd;
+    static unsigned int count, last_count;
+    static unsigned long last_prd;
 
     char          cntbuf[24];
     va_list       args;
     unsigned long flags;
     unsigned int nr;
 
-    if ( debugtrace_bytes == 0 )
+    if ( !dt_data )
         return;
 
-    debugtrace_used = 1;
+    debugtrace_used = true;
 
     spin_lock_irqsave(&debugtrace_lock, flags);
 
@@ -129,14 +135,14 @@ void debugtrace_printk(const char *fmt, ...)
         if ( debugtrace_buf_empty || strcmp(buf, last_buf) )
         {
             debugtrace_buf_empty = false;
-            last_prd = debugtrace_prd;
+            last_prd = dt_data->prd;
             last_count = ++count;
             safe_strcpy(last_buf, buf);
             snprintf(cntbuf, sizeof(cntbuf), "%u ", count);
         }
         else
         {
-            debugtrace_prd = last_prd;
+            dt_data->prd = last_prd;
             snprintf(cntbuf, sizeof(cntbuf), "%u-%u ", last_count, ++count);
         }
         debugtrace_add_to_buf(cntbuf);
@@ -154,23 +160,27 @@ static void debugtrace_key(unsigned char key)
 static int __init debugtrace_init(void)
 {
     int order;
-    unsigned int kbytes, bytes;
+    unsigned long kbytes;
+    struct debugtrace_data *data;
 
     /* Round size down to next power of two. */
     while ( (kbytes = (debugtrace_kilobytes & (debugtrace_kilobytes-1))) != 0 )
         debugtrace_kilobytes = kbytes;
 
-    bytes = debugtrace_kilobytes << 10;
-    if ( bytes == 0 )
+    debugtrace_bytes = debugtrace_kilobytes << 10;
+    if ( debugtrace_bytes == 0 )
         return 0;
 
-    order = get_order_from_bytes(bytes);
-    debugtrace_buf = alloc_xenheap_pages(order, 0);
-    ASSERT(debugtrace_buf != NULL);
+    order = get_order_from_bytes(debugtrace_bytes);
+    data = alloc_xenheap_pages(order, 0);
+    if ( !data )
+        return -ENOMEM;
 
-    memset(debugtrace_buf, '\0', bytes);
+    debugtrace_bytes = PAGE_SIZE << order;
+    memset(data, '\0', debugtrace_bytes);
+    debugtrace_bytes -= sizeof(*data);
 
-    debugtrace_bytes = bytes;
+    dt_data = data;
 
     register_keyhandler('T', debugtrace_key,
                         "toggle debugtrace to console/buffer", 0);
