52 lines
1.6 KiB
ReStructuredText
52 lines
1.6 KiB
ReStructuredText
Debugging
|
|
=========
|
|
|
|
|
|
.. _dev-debugging-kernel-oops:
|
|
|
|
Kernel Oops
|
|
-----------
|
|
|
|
Sometimes a running Linux kernel detects an error during runtime that can't
|
|
be corrected.
|
|
This usually generates a stack trace that points to the location in the code
|
|
that caused the oops.
|
|
|
|
Linux kernels in Gluon (and OpenWrt) are stripped.
|
|
That means they do not contain any debug symbols.
|
|
On one hand this leads to a smaller binary and faster loading times on the
|
|
target.
|
|
On the other hand this means that in a case of a stack trace the unwinder
|
|
can only print memory locations and no further debugging information.
|
|
|
|
Gluon stores a compressed kernel with debug symbols for every target
|
|
in the directory `output/debug/`.
|
|
These kernels should be kept along with the images as long as the images
|
|
are in use.
|
|
This allows the developer to analyse a stack trace later.
|
|
|
|
Decoding Stacktraces
|
|
....................
|
|
|
|
The tooling is contained in the kernel source tree in the file
|
|
`decode_stacktrace.sh <https://github.com/torvalds/linux/blob/master/scripts/decode_stacktrace.sh>`__.
|
|
This file and the needed source tree are available in the directory: ::
|
|
|
|
openwrt/build_dir/target-<architecture>/linux-<architecture>/linux-<version>/
|
|
|
|
.. note::
|
|
Make sure to use a kernel tree that matches the version and patches
|
|
that was used to build the kernel.
|
|
If in doubt just re-build the images for the target.
|
|
|
|
Some more information on how to use this tool can be found at
|
|
`LWN <https://lwn.net/Articles/592724/>`__.
|
|
|
|
Obtaining Stacktraces
|
|
.....................
|
|
|
|
On many targets stacktraces can be read from the following
|
|
location after reboot: ::
|
|
|
|
/sys/kernel/debug/crashlog
|