[v2] scripts/gdb: add lx-fdtdump command

Commit Message

Peter Griffin Oct. 18, 2016, 4:33 p.m. UTC

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.

Signed-off-by: Peter Griffin <[e-mail]>

---

Changes since v1
 - s/flatenned/flattened/ (Kieran)
 - Add filename as argument to command (Jan / Kieran)
 - Check LX_CONFIG_OF early to reduce indendation (Kieran)
 - Add gdb.COMPLETE_FILENAME to get auto completion (Jan)
 - Squash pep8 fixup patch (Kieran)
---
 scripts/gdb/linux/constants.py.in |  8 +++++
 scripts/gdb/linux/proc.py         | 73 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

Patch

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..086d272 100644
--- a/scripts/gdb/linux/proc.py
+++ b/scripts/gdb/linux/proc.py
@@ -16,6 +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):
@@ -195,3 +196,75 @@  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 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()