[PATCH 12/18] scripts/gdb: Add a Radix Tree Parser

[Jan Kiszka]

From: Kieran Bingham <kieran.bingham@xxxxxxxxxx>

Linux makes use of the Radix Tree data structure to store pointers indexed
by integer values. This structure is utilised across many structures in
the kernel including the IRQ descriptor tables, and several filesystems.

This module provides a method to lookup values from a structure given
its head node.

Usage:

The function lx_radix_tree_lookup, must be given a symbol of type
struct radix_tree_root, and an index into that tree.

The object returned is a generic integer value, and must be cast
correctly to the type based on the storage in the data structure.

For example, to print the irq descriptor in the sparse irq_desc_tree at
index 18, try the following:

 (gdb) print (struct irq_desc)$lx_radix_tree_lookup(irq_desc_tree, 18)

Signed-off-by: Kieran Bingham <kieran.bingham@xxxxxxxxxx>
Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
---
 scripts/gdb/linux/constants.py.in |  7 +++
 scripts/gdb/linux/radixtree.py    | 97 +++++++++++++++++++++++++++++++++++++++
 scripts/gdb/vmlinux-gdb.py        |  1 +
 3 files changed, 105 insertions(+)
 create mode 100644 scripts/gdb/linux/radixtree.py

diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
index 7986f4e..07e6c2b 100644
--- a/scripts/gdb/linux/constants.py.in
+++ b/scripts/gdb/linux/constants.py.in
@@ -14,6 +14,7 @@
 
 #include <linux/fs.h>
 #include <linux/mount.h>
+#include <linux/radix-tree.h>
 
 /* We need to stringify expanded macros so that they can be parsed */
 
@@ -50,3 +51,9 @@ LX_VALUE(MNT_NOEXEC)
 LX_VALUE(MNT_NOATIME)
 LX_VALUE(MNT_NODIRATIME)
 LX_VALUE(MNT_RELATIME)
+
+/* linux/radix-tree.h */
+LX_VALUE(RADIX_TREE_INDIRECT_PTR)
+LX_GDBPARSED(RADIX_TREE_HEIGHT_MASK)
+LX_GDBPARSED(RADIX_TREE_MAP_SHIFT)
+LX_GDBPARSED(RADIX_TREE_MAP_MASK)
diff --git a/scripts/gdb/linux/radixtree.py b/scripts/gdb/linux/radixtree.py
new file mode 100644
index 0000000..0fdef4e
--- /dev/null
+++ b/scripts/gdb/linux/radixtree.py
@@ -0,0 +1,97 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  Radix Tree Parser
+#
+# Copyright (c) 2016 Linaro Ltd
+#
+# Authors:
+#  Kieran Bingham <kieran.bingham@xxxxxxxxxx>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import utils
+from linux import constants
+
+radix_tree_root_type = utils.CachedType("struct radix_tree_root")
+radix_tree_node_type = utils.CachedType("struct radix_tree_node")
+
+
+def is_indirect_ptr(node):
+    long_type = utils.get_long_type()
+    return (node.cast(long_type) & constants.LX_RADIX_TREE_INDIRECT_PTR)
+
+
+def indirect_to_ptr(node):
+    long_type = utils.get_long_type()
+    node_type = node.type
+    indirect_ptr = node.cast(long_type) & ~constants.LX_RADIX_TREE_INDIRECT_PTR
+    return indirect_ptr.cast(node_type)
+
+
+def maxindex(height):
+    height = height & constants.LX_RADIX_TREE_HEIGHT_MASK
+    return gdb.parse_and_eval("height_to_maxindex["+str(height)+"]")
+
+
+def lookup(root, index):
+    if root.type == radix_tree_root_type.get_type().pointer():
+        root = root.dereference()
+    elif root.type != radix_tree_root_type.get_type():
+        raise gdb.GdbError("Must be struct radix_tree_root not {}"
+                           .format(root.type))
+
+    node = root['rnode']
+    if node is 0:
+        return None
+
+    if not (is_indirect_ptr(node)):
+        if (index > 0):
+            return None
+        return node
+
+    node = indirect_to_ptr(node)
+
+    height = node['path'] & constants.LX_RADIX_TREE_HEIGHT_MASK
+    if (index > maxindex(height)):
+        return None
+
+    shift = (height-1) * constants.LX_RADIX_TREE_MAP_SHIFT
+
+    while True:
+        new_index = (index >> shift) & constants.LX_RADIX_TREE_MAP_MASK
+        slot = node['slots'][new_index]
+
+        node = slot.cast(node.type.pointer()).dereference()
+        if node is 0:
+            return None
+
+        shift -= constants.LX_RADIX_TREE_MAP_SHIFT
+        height -= 1
+
+        if (height <= 0):
+            break
+
+    return node
+
+
+class LxRadixTree(gdb.Function):
+    """ Lookup and return a node from a RadixTree.
+
+$lx_radix_tree_lookup(root_node [, index]): Return the node at the given index.
+If index is omitted, the root node is dereferenced and returned."""
+
+    def __init__(self):
+        super(LxRadixTree, self).__init__("lx_radix_tree_lookup")
+
+    def invoke(self, root, index=0):
+        result = lookup(root, index)
+        if result is None:
+            raise gdb.GdbError("No entry in tree at index {}".format(index))
+
+        return result
+
+LxRadixTree()
diff --git a/scripts/gdb/vmlinux-gdb.py b/scripts/gdb/vmlinux-gdb.py
index 6e0b0af..3a80ad6 100644
--- a/scripts/gdb/vmlinux-gdb.py
+++ b/scripts/gdb/vmlinux-gdb.py
@@ -31,3 +31,4 @@ else:
     import linux.lists
     import linux.proc
     import linux.constants
+    import linux.radixtree
-- 
2.1.4