[tools] Improve j6stack GDB command

Improve the j6stack command in two ways: first, swap the order of the
arguments, as depth is much more likely to be changed. Second, on any
exception accessing memory in the stack, print the exception and
continue instead of failing the whole command.

assets/debugging/jsix.elf-gdb.py

@@ -16,10 +16,14 @@ class PrintStackCommand(gdb.Command):
             depth = int(args[1])
 
         for i in range(depth-1, -1, -1):
+            try:
                 offset = i * 8
                 base_addr = gdb.parse_and_eval(base)
                 value = gdb.parse_and_eval(f"*(uint64_t*)({base} + {offset})")
                 print("{:016x} (+{:04x}): {:016x}".format(int(base_addr) + offset, offset, int(value)))
+            except Exception as e:
+                print(e)
+                continue
 
 
 class PrintBacktraceCommand(gdb.Command):
@@ -29,13 +33,13 @@ class PrintBacktraceCommand(gdb.Command):
     def invoke(self, arg, from_tty):
         args = gdb.string_to_argv(arg)
 
-        frame = "$rbp"
-        if len(args) > 0:
-            frame = args[0]
-
         depth = 30
+        if len(args) > 0:
+            depth = int(args[0])
+
+        frame = "$rbp"
         if len(args) > 1:
-            depth = int(args[1])
+            frame = args[1]
 
         for i in range(depth-1, -1, -1):
             ret = gdb.parse_and_eval(f"*(uint64_t*)({frame} + 8)")