[PATCH] scripts/gdb: fix lx-dmesg when CONFIG_PRINTK_CALLER is set

[Joel Colledge <joel.colledge@linbit.com>]

When CONFIG_PRINTK_CALLER is set, struct printk_log contains an
additional member caller_id. As a result, the offset of the log text is
different.

This fixes the following error:

  (gdb) lx-dmesg
  Python Exception <class 'ValueError'> embedded null character:
  Error occurred in Python command: embedded null character

Signed-off-by: Joel Colledge <joel.colledge@linbit.com>
---
 scripts/gdb/linux/constants.py.in | 1 +
 scripts/gdb/linux/dmesg.py        | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
index 2efbec6b6b8d..3c9794a0bf55 100644
--- a/scripts/gdb/linux/constants.py.in
+++ b/scripts/gdb/linux/constants.py.in
@@ -74,4 +74,5 @@ LX_CONFIG(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST)
 LX_CONFIG(CONFIG_HIGH_RES_TIMERS)
 LX_CONFIG(CONFIG_NR_CPUS)
 LX_CONFIG(CONFIG_OF)
+LX_CONFIG(CONFIG_PRINTK_CALLER)
 LX_CONFIG(CONFIG_TICK_ONESHOT)
diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
index 6d2e09a2ad2f..1352680ef731 100644
--- a/scripts/gdb/linux/dmesg.py
+++ b/scripts/gdb/linux/dmesg.py
@@ -14,6 +14,7 @@
 import gdb
 import sys
 
+from linux import constants
 from linux import utils
 
 
@@ -53,7 +54,8 @@ class LxDmesg(gdb.Command):
                 continue
 
             text_len = utils.read_u16(log_buf[pos + 10:pos + 12])
-            text = log_buf[pos + 16:pos + 16 + text_len].decode(
+            text_start = pos + (20 if constants.LX_CONFIG_PRINTK_CALLER else 16)
+            text = log_buf[text_start:text_start + text_len].decode(
                 encoding='utf8', errors='replace')
             time_stamp = utils.read_u64(log_buf[pos:pos + 8])
 
-- 
2.17.1