scripts/gdb: add lx-fdtdump command

lx-fdtdump dumps the flattened device tree passed to the kernel from the
bootloader to the filename specified as the command argument.  If no
argument is provided it defaults to fdtdump.dtb.  This then allows
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.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Griffin <[email protected]>
Signed-off-by: Kieran Bingham <[email protected]>
Cc: Jason Wessel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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 +51,9 @@ 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)

scripts/gdb/linux/proc.py

@@ -16,6 +16,7 @@
 from linux import utils
 from linux import tasks
 from linux import lists
+from struct import *
 
 
 class LxCmdLine(gdb.Command):
@@ -195,3 +196,75 @@ def invoke(self, arg, from_tty):
                         info_opts(MNT_INFO, m_flags)))
 
 LxMounts()
+
+
+class LxFdtDump(gdb.Command):
+    """Output Flattened Device Tree header and dump FDT blob to the filename
+       specified as the command argument. Equivalent to
+       'cat /proc/fdt > fdtdump.dtb' on a running target"""
+
+    def __init__(self):
+        super(LxFdtDump, self).__init__("lx-fdtdump", gdb.COMMAND_DATA,
+                                        gdb.COMPLETE_FILENAME)
+
+    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 not constants.LX_CONFIG_OF:
+            raise gdb.GdbError("Kernel not compiled with CONFIG_OF\n")
+
+        if len(arg) == 0:
+            filename = "fdtdump.dtb"
+        else:
+            filename = arg
+
+        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 blob to " + filename + "\n")
+
+LxFdtDump()