[PATCH v2] scripts/gdb: Add command to check list consistency

["Thiébaud Weksteen" <thiebaud@weksteen.fr>]

Add a gdb script to verify the consistency of lists.

Signed-off-by: Thiébaud Weksteen <thiebaud@weksteen.fr>
---
Implement suggestions from Jan.

Changes in v2:
 - Add copyright line
 - Rename check_list to list_check
 - Remove casting and only accept (struct list_head) object
 - Add error message if argument is missing
 - Reformat error messages to include address of nodes

Example of use:
(gdb) lx-list-check workqueues
Starting with: {next = 0xf3aea5a8, prev = 0xf580e668}
list is consistent: 30 node(s)
(gdb) set *((int *) 0xf3934908) = 0x0
(gdb) lx-list-check workqueues
Starting with: {next = 0xf3aea5a8, prev = 0xf580e668}
next is not accessible: current@0xf3934908={next = 0x0, prev = 0xf3aea5a8}
(gdb) set *((int *) 0xf3934908) = 0xdeadbeef
(gdb) lx-list-check workqueues
Starting with: {next = 0xf3aea5a8, prev = 0xf580e668}
next.prev != current: current@0xf3934908={next = 0xdeadbeef, prev = 0xf3aea5a8}
    next@0xdeadbeef={next = 0x0, prev = 0x0}
(gdb) set *((int *) 0xf3934908) = 0xf537f188
(gdb) lx-list-check workqueues
Starting with: {next = 0xf3aea5a8, prev = 0xf580e668}
list is consistent: 30 node(s)


 scripts/gdb/linux/lists.py | 89 ++++++++++++++++++++++++++++++++++++++++++++++
 scripts/gdb/vmlinux-gdb.py |  1 +
 2 files changed, 90 insertions(+)
 create mode 100644 scripts/gdb/linux/lists.py

diff --git a/scripts/gdb/linux/lists.py b/scripts/gdb/linux/lists.py
new file mode 100644
index 0000000..2a94b54
--- /dev/null
+++ b/scripts/gdb/linux/lists.py
@@ -0,0 +1,89 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  list tools
+#
+# Copyright (c) Thiebaud Weksteen, 2015
+#
+# Authors:
+#  Thiebaud Weksteen <thiebaud@weksteen.fr>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import utils
+
+list_head = utils.CachedType("struct list_head")
+
+
+def list_check(head):
+    nb = 0
+    c = head
+    if (c.type != list_head.get_type()):
+        raise gdb.GdbError('The argument should be of type (struct list_head)')
+    try:
+        gdb.write("Starting with: {}\n".format(c))
+    except gdb.MemoryError:
+        gdb.write('head is not accessible\n')
+        return
+    while True:
+        p = c['prev'].dereference()
+        n = c['next'].dereference()
+        try:
+            if p['next'] != c.address:
+                gdb.write('prev.next != current: '
+                          'current@{current_addr}={current} '
+                          'prev@{p_addr}={p}\n'.format(
+                              current_addr=c.address,
+                              current=c,
+                              p_addr=p.address,
+                              p=p,
+                          ))
+                return
+        except gdb.MemoryError:
+            gdb.write('prev is not accessible: '
+                      'current@{current_addr}={current}\n'.format(
+                          current_addr=c.address,
+                          current=c
+                      ))
+            return
+        try:
+            if n['prev'] != c.address:
+                gdb.write('next.prev != current: '
+                          'current@{current_addr}={current} '
+                          'next@{n_addr}={n}\n'.format(
+                              current_addr=c.address,
+                              current=c,
+                              n_addr=n.address,
+                              n=n,
+                          ))
+                return
+        except gdb.MemoryError:
+            gdb.write('next is not accessible: '
+                      'current@{current_addr}={current}\n'.format(
+                          current_addr=c.address,
+                          current=c
+                      ))
+            return
+        c = n
+        nb += 1
+        if c == head:
+            gdb.write("list is consistent: {} node(s)\n".format(nb))
+            return
+
+
+class LxListChk(gdb.Command):
+    """Verify a list consistency"""
+
+    def __init__(self):
+        super(LxListChk, self).__init__("lx-list-check", gdb.COMMAND_DATA)
+
+    def invoke(self, arg, from_tty):
+        argv = gdb.string_to_argv(arg)
+        if len(argv) != 1:
+            raise gdb.GdbError("lx-list-check takes one argument")
+        list_check(gdb.parse_and_eval(argv[0]))
+
+LxListChk()
diff --git a/scripts/gdb/vmlinux-gdb.py b/scripts/gdb/vmlinux-gdb.py
index 4848928..ce82bf5 100644
--- a/scripts/gdb/vmlinux-gdb.py
+++ b/scripts/gdb/vmlinux-gdb.py
@@ -28,3 +28,4 @@ else:
     import linux.dmesg
     import linux.tasks
     import linux.cpus
+    import linux.lists
-- 
2.1.0