2020-06-04 20:35:58 +00:00
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Debugging
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=========
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.. _dev-debugging-kernel-oops:
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Kernel Oops
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-----------
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2020-08-13 11:25:45 +00:00
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Sometimes a running Linux kernel detects an error during runtime that can't
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2020-06-04 20:35:58 +00:00
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be corrected.
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This usually generates a stack trace that points to the location in the code
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that caused the oops.
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Linux kernels in Gluon (and OpenWrt) are stripped.
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That means they do not contain any debug symbols.
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On one hand this leads to a smaller binary and faster loading times on the
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target.
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On the other hand this means that in a case of a stack trace the unwinder
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can only print memory locations and no further debugging information.
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Gluon stores a compressed kernel with debug symbols for every target
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in the directory `output/debug/`.
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These kernels should be kept along with the images as long as the images
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are in use.
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This allows the developer to analyse a stack trace later.
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Decoding Stacktraces
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....................
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The tooling is contained in the kernel source tree in the file
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`decode_stacktrace.sh <https://github.com/torvalds/linux/blob/master/scripts/decode_stacktrace.sh>`__.
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This file and the needed source tree are available in the directory: ::
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openwrt/build_dir/target-<architecture>/linux-<architecture>/linux-<version>/
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.. note::
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Make sure to use a kernel tree that matches the version and patches
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that was used to build the kernel.
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If in doubt just re-build the images for the target.
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Some more information on how to use this tool can be found at
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`LWN <https://lwn.net/Articles/592724/>`__.
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Obtaining Stacktraces
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.....................
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On many targets stacktraces can be read from the following
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location after reboot: ::
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/sys/kernel/debug/crashlog
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