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How to create vmcores for tests
===============================
1. Boot a FreeBSD VM with as little memory as possible and create a core dump
per `FreeBSD Handbook Kernel Debugging Chapter`_. Note that you may need to
reboot with more memory after the kernel panic as otherwise savecore(8) may
fail.
For instance, I was able to boot FreeBSD and qemu-system-x86_64 with 128 MiB
RAM but had to increase it to 256 MiB for the boot after kernel panic.
2. Transfer the kernel image (``/boot/kernel/kernel``) and vmcore
(``/var/crash/vmcore.latest``) from the VM.
3. Patch libfbsdvmcore using ``libfbsdvmcore-hacks.patch`` and build LLDB
against the patched library.
4. Patch LLDB using ``lldb-minimize-processes.patch`` and build it.
WARNING: LLDB will now modify core files in order to make the resulting
test vmcores smaller. Make a backup if necessary.
5. Do a test run of ``test.script`` in LLDB against the kernel + vmcore::
lldb -b -s test.script --core /path/to/core /path/to/kernel
If everything works fine, the LLDB output should be interspersed with
``%RD`` lines. The vmcore will also be modified to shorten the process
list in ``allproc``.
6. Open the vmcore in the patched LLDB again and choose interesting threads
for testing. Update thread numbers in ``test.script`` if necessary.
7. Use the ``copy-sparse.py`` tool to create a sparse version of the vmcore::
lldb -b -s test.script --core /path/to/core /path/to/kernel |
grep '^% RD' | python copy-sparse.py /path/to/core vmcore.sparse
8. Compress the sparse vmcore file using ``bzip2``::
bzip2 -9 vmcore.sparse
.. _FreeBSD Handbook Kernel Debugging Chapter:
https://docs.freebsd.org/en/books/developers-handbook/kerneldebug/
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