scripts/gdb: add a Radix Tree Parser

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)

Link: http://lkml.kernel.org/r/d2028c55e50cf95a9b7f8ca0d11885174b0cc709.1462865983.git.jan.kiszka@siemens.com
Signed-off-by: Kieran Bingham <kieran.bingham@linaro.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kieran Bingham 2016-05-23 16:25:07 -07:00 committed by Linus Torvalds
parent 4bc393dbcf
commit e127a73d41
3 changed files with 105 additions and 0 deletions

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@ -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)

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@ -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@linaro.org>
#
# 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()

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@ -31,3 +31,4 @@ else:
import linux.lists
import linux.proc
import linux.constants
import linux.radixtree