Date: Tue, 18 Oct 2016 17:31:42 +0100
From: Peter Griffin <peter.griffin@linaro.org>
To: Kieran Bingham <kieran@ksquared.org.uk>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        kernel@stlinux.com, jan.kiszka@siemens.com, lee.jones@linaro.org,
        devicetree@vger.kernel.org
Subject: Re: [PATCH 1/2] scripts/gdb: add lx-fdtdump command
Message-ID: <20161018163142.GB28359@griffinp-ThinkPad-X1-Carbon-2nd>
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Hi Kieran,

Thanks for reviewing.

On Tue, 18 Oct 2016, Kieran Bingham wrote:

> Hi Pete,
> 
> Thanks for your patch.
> 
> On 18/10/16 16:07, Peter Griffin wrote:
> > lx-fdtdump dumps the flatenned device tree passed to the kernel
> 
> s/flatenned/flattened/
> 
> > 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:
> > 
> 
> Excellent - I've been looking forward to this
> 
> General comment: It would be good to see the output filename
> configurable as a parameter, defaulting to fdtdump.dtb if none provided.
> 
> Is this something you have time to add?

Have added this in v2 :)

> 
> > (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"
> > +
> 
> You could parse the arguments here to allow users to write to their own
> file / path ... arg is just a string, so you can either parse it as such
> or convert to argv with
> 	argv = gdb.string_to_argv(arg)
> 
> 
> Aha - I see Jan beat me to it :)
> 
> 
> > +            py_fdt_header_ptr = gdb.parse_and_eval(
> > +                "(const struct fdt_header *) initial_boot_params")
> > +            py_fdt_header = py_fdt_header_ptr.dereference()
> > +
> > +            fdt_header = self.fdthdr_to_cpu(py_fdt_header)
> > +
> > +            if fdt_header[0] != constants.LX_OF_DT_HEADER:
> > +                raise gdb.GdbError("No flattened device tree magic found\n")
> > +
> > +            gdb.write("fdt_magic:         0x{:02X}\n".format(fdt_header[0]))
> > +            gdb.write("fdt_totalsize:     0x{:02X}\n".format(fdt_header[1]))
> > +            gdb.write("off_dt_struct:     0x{:02X}\n".format(fdt_header[2]))
> > +            gdb.write("off_dt_strings:    0x{:02X}\n".format(fdt_header[3]))
> > +            gdb.write("off_mem_rsvmap:    0x{:02X}\n".format(fdt_header[4]))
> > +            gdb.write("version:           {}\n".format(fdt_header[5]))
> > +            gdb.write("last_comp_version: {}\n".format(fdt_header[6]))
> > +
> > +            inf = gdb.inferiors()[0]
> > +            fdt_buf = utils.read_memoryview(inf, py_fdt_header_ptr,
> > +                                            fdt_header[1]).tobytes()
> > +
> > +            try:
> > +                f = open(filename, 'wb')
> > +            except:
> > +                raise gdb.GdbError("Could not open file to dump fdt")
> > +
> > +            f.write(fdt_buf)
> > +            f.close()
> > +
> > +            gdb.write("Dumped fdt to " + filename + "\n")
> > +
> > +        else:
> > +            gdb.write("Kernel not compiled with CONFIG_OF\n")
> 
> Would it be cleaner to write
>   if not constants.LX_CONFIG_OF:
>       raise gdb.GdbError("Kernel not compiled with CONFIG_OF\n")
> 
> at the beginning, and reduce the indentation level required ?

Good idea, have updated like you suggest in V2 and reduced the
indentation.

regards,

Peter