Subject: Re: [PATCH 1/2] scripts/gdb: add lx-fdtdump command
To: Peter Griffin <peter.griffin@linaro.org>
References: <1476803249-23328-1-git-send-email-peter.griffin@linaro.org>
 <c8a1898e-e60f-b25a-f4d2-7384f04b6f3f@siemens.com>
 <20161018160638.GA24851@griffinp-ThinkPad-X1-Carbon-2nd>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        kernel@stlinux.com, kieran@ksquared.org.uk, lee.jones@linaro.org,
        devicetree@vger.kernel.org
From: Jan Kiszka <jan.kiszka@siemens.com>
Message-ID: <0143426e-7e92-aaff-7641-519e1f63e075@siemens.com>
Date: Tue, 18 Oct 2016 18:10:02 +0200
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On 2016-10-18 18:06, Peter Griffin wrote:
> Hi Jan,
> 
> On Tue, 18 Oct 2016, Jan Kiszka wrote:
> 
>> On 2016-10-18 17:07, Peter Griffin wrote:
>>> lx-fdtdump dumps the flatenned device tree passed to the kernel
>>> from the bootloader to a file called fdtdump.dtb to allow further
>>> post processing on the machine running GDB. The fdt header is also
>>> also printed in the GDB console. For example:
>>>
>>> (gdb) lx-fdtdump
>>> fdt_magic:         0xD00DFEED
>>> fdt_totalsize:     0xC108
>>> off_dt_struct:     0x38
>>> off_dt_strings:    0x3804
>>> off_mem_rsvmap:    0x28
>>> version:           17
>>> last_comp_version: 16
>>> Dumped fdt to fdtdump.dtb
>>>
>>>> fdtdump fdtdump.dtb | less
>>>
>>> This command is useful as the bootloader can often re-write parts
>>> of the device tree, and this can sometimes cause the kernel to not
>>> boot.
>>>
>>> Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
>>> ---
>>>  scripts/gdb/linux/constants.py.in |  8 +++++
>>>  scripts/gdb/linux/proc.py         | 70 ++++++++++++++++++++++++++++++++++++++-
>>>  2 files changed, 77 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
>>> index 7986f4e..43c6241 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/of_fdt.h>
>>>  
>>>  /* We need to stringify expanded macros so that they can be parsed */
>>>  
>>> @@ -50,3 +51,10 @@ LX_VALUE(MNT_NOEXEC)
>>>  LX_VALUE(MNT_NOATIME)
>>>  LX_VALUE(MNT_NODIRATIME)
>>>  LX_VALUE(MNT_RELATIME)
>>> +
>>> +/* linux/of_fdt.h> */
>>> +LX_VALUE(OF_DT_HEADER)
>>> +
>>> +/* Kernel Configs */
>>> +LX_CONFIG(CONFIG_OF)
>>> +
>>> diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
>>> index 38b1f09..f20fcfa 100644
>>> --- a/scripts/gdb/linux/proc.py
>>> +++ b/scripts/gdb/linux/proc.py
>>> @@ -16,7 +16,7 @@ from linux import constants
>>>  from linux import utils
>>>  from linux import tasks
>>>  from linux import lists
>>> -
>>> +from struct import *
>>>  
>>>  class LxCmdLine(gdb.Command):
>>>      """ Report the Linux Commandline used in the current kernel.
>>> @@ -195,3 +195,71 @@ values of that process namespace"""
>>>                          info_opts(MNT_INFO, m_flags)))
>>>  
>>>  LxMounts()
>>> +
>>> +class LxFdtDump(gdb.Command):
>>> +    """Output Flattened Device Tree header and dump FDT blob to a file
>>> +       Equivalent to 'cat /proc/fdt > fdtdump.dtb' on a running target"""
>>> +
>>> +    def __init__(self):
>>> +        super(LxFdtDump, self).__init__("lx-fdtdump", gdb.COMMAND_DATA)
>>> +
>>> +    def fdthdr_to_cpu(self, fdt_header):
>>> +
>>> +            fdt_header_be = ">IIIIIII"
>>> +            fdt_header_le = "<IIIIIII"
>>> +
>>> +            if utils.get_target_endianness() == 1:
>>> +                output_fmt = fdt_header_le
>>> +            else:
>>> +                output_fmt = fdt_header_be
>>> +
>>> +            return unpack(output_fmt, pack(fdt_header_be,
>>> +                                           fdt_header['magic'],
>>> +                                           fdt_header['totalsize'],
>>> +                                           fdt_header['off_dt_struct'],
>>> +                                           fdt_header['off_dt_strings'],
>>> +                                           fdt_header['off_mem_rsvmap'],
>>> +                                           fdt_header['version'],
>>> +                                           fdt_header['last_comp_version']))
>>> +
>>> +    def invoke(self, arg, from_tty):
>>> +
>>> +        if constants.LX_CONFIG_OF:
>>> +
>>> +            filename = "fdtdump.dtb"
>>
>> Why not specifying the file name as argument? Safer than silently
>> overwriting potentially pre-existing files or failing without
>> alternatives if the current directory is not writable.
> 
> Good idea, I will update to have the filename as the command argument in v2.
> 

Also check gdb.COMPLETE_FILENAME [1] at that chance. :)

Jan

[1]
https://sourceware.org/gdb/onlinedocs/gdb/Commands-In-Python.html#Commands-In-Python

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