memory: info mtree check mr range overflow

The address of memory regions might overflow when something wrong
happened, like reported in:

https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg02043.html

For easier debugging, let's try to detect it.
Reported-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <1489496187-624-1-git-send-email-peterx@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

memory.c

@@ -2494,6 +2494,7 @@ static void mtree_print_mr(fprintf_function mon_printf, void *f,
     MemoryRegionListHead submr_print_queue;
     const MemoryRegion *submr;
     unsigned int i;
+    hwaddr cur_start, cur_end;
 
     if (!mr) {
         return;
@@ -2503,6 +2504,18 @@ static void mtree_print_mr(fprintf_function mon_printf, void *f,
         mon_printf(f, MTREE_INDENT);
     }
 
+    cur_start = base + mr->addr;
+    cur_end = cur_start + MR_SIZE(mr->size);
+
+    /*
+     * Try to detect overflow of memory region. This should never
+     * happen normally. When it happens, we dump something to warn the
+     * user who is observing this.
+     */
+    if (cur_start < base || cur_end < cur_start) {
+        mon_printf(f, "[DETECTED OVERFLOW!] ");
+    }
+
     if (mr->alias) {
         MemoryRegionList *ml;
         bool found = false;
@@ -2522,8 +2535,7 @@ static void mtree_print_mr(fprintf_function mon_printf, void *f,
         mon_printf(f, TARGET_FMT_plx "-" TARGET_FMT_plx
                    " (prio %d, %s): alias %s @%s " TARGET_FMT_plx
                    "-" TARGET_FMT_plx "%s\n",
-                   base + mr->addr,
-                   base + mr->addr + MR_SIZE(mr->size),
+                   cur_start, cur_end,
                    mr->priority,
                    memory_region_type((MemoryRegion *)mr),
                    memory_region_name(mr),
@@ -2534,8 +2546,7 @@ static void mtree_print_mr(fprintf_function mon_printf, void *f,
     } else {
         mon_printf(f,
                    TARGET_FMT_plx "-" TARGET_FMT_plx " (prio %d, %s): %s%s\n",
-                   base + mr->addr,
-                   base + mr->addr + MR_SIZE(mr->size),
+                   cur_start, cur_end,
                    mr->priority,
                    memory_region_type((MemoryRegion *)mr),
                    memory_region_name(mr),
@@ -2562,7 +2573,7 @@ static void mtree_print_mr(fprintf_function mon_printf, void *f,
     }
 
     QTAILQ_FOREACH(ml, &submr_print_queue, queue) {
-        mtree_print_mr(mon_printf, f, ml->mr, level + 1, base + mr->addr,
+        mtree_print_mr(mon_printf, f, ml->mr, level + 1, cur_start,
                        alias_print_queue);
     }