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

From: Jan Kiszka
Date: Thu Apr 23 2015 - 08:10:51 EST


On 2015-04-22 09:32, ThiÃbaud Weksteen wrote:
> Add a gdb script to verify the consistency of lists.
>
> Signed-off-by: ThiÃbaud Weksteen <thiebaud@xxxxxxxxxxx>
> ---
> scripts/gdb/linux/lists.py | 78 ++++++++++++++++++++++++++++++++++++++++++++++
> scripts/gdb/vmlinux-gdb.py | 1 +
> 2 files changed, 79 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..d512f62
> --- /dev/null
> +++ b/scripts/gdb/linux/lists.py
> @@ -0,0 +1,78 @@
> +#
> +# gdb helper commands and functions for Linux kernel debugging
> +#
> +# list tools
> +#
> +# Authors:
> +# Thiebaud Weksteen <thiebaud@xxxxxxxxxxx>

Who is the copyright holder, also you, your employer etc.? Please
clarify, ideally by just having a copyright line like in the other scripts.

> +#
> +# 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 check_list(head):

In general - applies to internal naming as well as the command itself -
I would prefer "list check". That would create a namespace under which
we may add further list helpers later on.

> + nb = 0
> + list_head_ptr_type = list_head.get_type().pointer()
> + c = head.cast(list_head_ptr_type)

Why casting? Is it a common use case to not have the list head as a
variable at hand? The user could still do

lx_list_check (struct list_head *)0x...

when needed.

> + try:
> + gdb.write("Starting with: {} {}\n".format(c, c.dereference()))
> + except gdb.MemoryError:
> + gdb.write('head is not accessible\n')
> + return
> + while True:
> + p = c['prev']
> + n = c['next']
> + try:
> + if p['next'] != c:
> + gdb.write('prev.next != current: current={current} '
> + 'prev={p} prev.next={pnext}\n'.format(
> + current=c,
> + p=p,
> + pnext=p['next']
> + ))

This is not pep8-conforming. Please fix (even if the exiting scripts
have some issues as well - just noticed...).

> + return
> + except gdb.MemoryError:
> + gdb.write('prev is not accessible: current={current} '
> + 'current.prev={p}\n'.format(
> + current=c,
> + p=p
> + ))
> + return
> + try:
> + if n['prev'] != c:
> + gdb.write('next.prev != current: current={current} '
> + 'next={n}, next.prev={nprev}\n'.format(
> + current=c,
> + n=n,
> + nprev=n['prev']
> + ))
> + return
> + except gdb.MemoryError:
> + gdb.write('next is not accessible: current={current} '
> + 'current.next={n}\n'.format(
> + current=c,
> + n=n
> + ))
> + return
> + c = n
> + nb += 1
> + if c == head:
> + gdb.write("list is consistent: {} node(s)\n".format(nb))
> + return
> +
> +class LxChkList(gdb.Command):
> + """Verify a list consistency"""
> +
> + def __init__(self):
> + super(LxChkList, self).__init__("lx-check-list", gdb.COMMAND_DATA)
> +
> + def invoke(self, arg, from_tty):
> + argv = gdb.string_to_argv(arg)
> + check_list(gdb.parse_and_eval(argv[0]))
> +
> +LxChkList()
> 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
>

Looks useful! As indicated, I could imagine extending this module by
further helpers, for the other list types or for walking a list,
executing some gdb command for each element.

Thanks,
Jan

--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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