Fix #1457 - warn if monitor info mem is invalid (#1480)

* Fix #1457 - warn if monitor info mem is invalid

* Fixes

* fix lint

pwndbg/gdblib/vmmap.py

@@ -450,6 +450,9 @@ def kernel_vmmap_via_page_tables():
     return tuple(retpages)
 
 
+monitor_info_mem_not_warned = True
+
+
 def kernel_vmmap_via_monitor_info_mem():
     """
     Returns Linux memory maps information by parsing `monitor info mem` output
@@ -469,6 +472,7 @@ def kernel_vmmap_via_monitor_info_mem():
     # ffff90358009b000-ffff903582200000 0000000002165000 -rw
     # ffff903582200000-ffff903582803000 0000000000603000 -r-
     """
+    global monitor_info_mem_not_warned
     monitor_info_mem = None
     try:
         monitor_info_mem = gdb.execute("monitor info mem", to_string=True)
@@ -505,7 +509,19 @@ def kernel_vmmap_via_monitor_info_mem():
         start = int(line[:dash_idx], 16)
         end = int(line[dash_idx + 1 : space_idx], 16)
         size = int(line[space_idx + 1 : rspace_idx], 16)
-        assert end - start == size, "monitor info mem output didn't pass a sanity check"
+        if end - start != size and monitor_info_mem_not_warned:
+            print(
+                M.warn(
+                    (
+                        "The vmmap output may be incorrect as `monitor info mem` output assertion/assumption\n"
+                        "that end-start==size failed. The values are:\n"
+                        "end=%#x; start=%#x; size=%#x; end-start=%#x\n"
+                        "Note that this warning will not show up again in this Pwndbg/GDB session."
+                    )
+                    % (end, start, size, end - start)
+                )
+            )
+            monitor_info_mem_not_warned = False
         perm = line[rspace_idx + 1 :]
 
         flags = 0