From 1f1f01722424779fccf438d2134534c5909affa5 Mon Sep 17 00:00:00 2001
From: Mathieu Maret <mathieu.maret@gmail.com>
Date: Wed, 19 Aug 2020 15:02:56 +0200
Subject: [PATCH] Add gdb custom commands

---
 custom_gdb_extension.py | 44 +++++++++++++++++++++++++++++++++++++++++
 debug.gdb               |  1 +
 2 files changed, 45 insertions(+)
 create mode 100644 custom_gdb_extension.py

diff --git a/custom_gdb_extension.py b/custom_gdb_extension.py
new file mode 100644
index 0000000..cd11ba0
--- /dev/null
+++ b/custom_gdb_extension.py
@@ -0,0 +1,44 @@
+class KthreadListDumpCmd(gdb.Command):
+    """Prints the kthread list"""
+
+    def __init__(self):
+        super(KthreadListDumpCmd, self).__init__(
+            "kthread_list_dump", gdb.COMMAND_USER
+        )
+
+    def _kthread_list_to_str(self, val):
+        """Walk through the Kthread list.
+
+        We will simply follow the 'next' pointers until we encounter the HEAD again
+        """
+        idx = 0
+        head = val
+        kthread_ptr = val
+        result = ""
+        while kthread_ptr != 0 and (idx == 0 or kthread_ptr != head) :
+            name = kthread_ptr["name"]
+            result += "\n%d: Addr: 0x%x, name: %s" % (idx, kthread_ptr, name)
+            kthread_ptr = kthread_ptr["next"]
+            idx += 1
+        result = ("Found a Linked List with %d kthread:" % idx) + result
+        return result
+
+    def complete(self, text, word):
+        # We expect the argument passed to be a symbol so fallback to the
+        # internal tab-completion handler for symbols
+        return gdb.COMPLETE_SYMBOL
+
+    def invoke(self, args, from_tty):
+        # We can pass args here and use Python CLI utilities like argparse
+        # to do argument parsing
+        print("Args Passed: %s" % args)
+
+        kthread_ptr_val = gdb.parse_and_eval(args)
+        if str(kthread_ptr_val.type) != "struct kthread *":
+            print("Expected pointer argument of type (struct kthread *)")
+            return
+
+        print(self._kthread_list_to_str(kthread_ptr_val))
+
+KthreadListDumpCmd()
+
diff --git a/debug.gdb b/debug.gdb
index f0b1431..316464e 100644
--- a/debug.gdb
+++ b/debug.gdb
@@ -1,2 +1,3 @@
 add-symbol-file kernel.sym
+source custom_gdb_extension.py
 target remote | qemu-system-i386 -S -gdb stdio -kernel kernel