scripts: gdb: Added some useful GDB scripts to test.py --gdb

These just invoke the existing dbg*.py python scripts, but allow quick
references to variables in the debugginged process:

  (gdb) dbgflags o file->b.o.flags
  LFS3_O_RDWR    0x00000002  Open a file as read and write
  LFS3_o_REG     0x10000000  Type = regular-file
  LFS3_o_UNSYNC  0x01000000  File's metadata does not match disk

Quite neat and useful!

This works by injecting dbg.gdb.py via gdb -x, which includes the
necessary python hooks to add these commands to gdb. This can be
overridden/extended with test.py/bench.py's --gdb-script flag.

Currently limited to scripts that seem the most useful for process
internals:

- dbgerr - Decode littlefs error codes
- dbgflags - Decode littlefs flags
- dbgtag - Decode littlefs tags

scripts/dbg.gdb.py

@@ -0,0 +1,97 @@
+#
+# hooks for gdb:
+# (gdb) source ./scripts/dbg.gdb.py
+#
+#
+
+
+# dbgerr
+class DbgErr(gdb.Command):
+    """Decode littlefs error codes. See -h/--help for more info."""
+
+    def __init__(self):
+        super().__init__("dbgerr",
+                gdb.COMMAND_DATA,
+                gdb.COMPLETE_EXPRESSION)
+
+    def invoke(self, args, *_):
+        args = args.split()
+        # find nonflags
+        nonflags = []
+        for i, a in enumerate(args):
+            if not a.startswith('-'):
+                nonflags.append(i)
+        # parse and eval
+        for i, n in enumerate(nonflags):
+            try:
+                args[n] = '%d' % gdb.parse_and_eval(args[n])
+            except gdb.error as e:
+                raise gdb.GdbError(e)
+
+        # execute
+        gdb.execute(' '.join(['!./scripts/dbgerr.py'] + args))
+
+DbgErr()
+
+
+# dbgflags
+class DbgFlags(gdb.Command):
+    """Decode littlefs flags. See -h/--help for more info."""
+
+    def __init__(self):
+        super().__init__("dbgflags",
+                gdb.COMMAND_DATA,
+                gdb.COMPLETE_EXPRESSION)
+
+    def invoke(self, args, *_):
+        args = args.split()
+        # hack, but don't eval if -l or --list specified
+        if '-l' not in args and '--list' not in args:
+            # find nonflags
+            nonflags = []
+            for i, a in enumerate(args):
+                if not a.startswith('-'):
+                    nonflags.append(i)
+            # parse and eval
+            for i, n in enumerate(nonflags):
+                # dbgflags is special in that first arg may be prefix
+                if i > 0 or len(nonflags) <= 1:
+                    try:
+                        args[n] = '%d' % gdb.parse_and_eval(args[n])
+                    except gdb.error as e:
+                        raise gdb.GdbError(e)
+
+        # execute
+        gdb.execute(' '.join(['!./scripts/dbgflags.py'] + args))
+
+DbgFlags()
+
+
+# dbgtag
+class DbgTag(gdb.Command):
+    """Decode littlefs tags. See -h/--help for more info."""
+
+    def __init__(self):
+        super().__init__("dbgtag",
+                gdb.COMMAND_DATA,
+                gdb.COMPLETE_EXPRESSION)
+
+    def invoke(self, args, *_):
+        args = args.split()
+        # find nonflags
+        nonflags = []
+        for i, a in enumerate(args):
+            if not a.startswith('-'):
+                nonflags.append(i)
+        # parse and eval
+        for i, n in enumerate(nonflags):
+            try:
+                args[n] = '%d' % gdb.parse_and_eval(args[n])
+            except gdb.error as e:
+                raise gdb.GdbError(e)
+
+        # execute
+        gdb.execute(' '.join(['!./scripts/dbgtag.py'] + args))
+
+DbgTag()
+