[PATCH 1/2] scripts/gdb: add lx-fdtdump command

[Peter Griffin]

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@xxxxxxxxxx>
---
 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"
+
+            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")
+
+LxFdtDump()
-- 
1.9.1