[PATCH 0/2] Expose kallsyms data in vmcoreinfo note

Stephen Brennan
2022-05-17T00:06:11Z

The kernel can be configured to contain a lot of introspection or
debugging information built-in, such as ORC for unwinding stack traces,
BTF for type information, and of course kallsyms. Debuggers could use
this information to navigate a core dump or live system, but they need
to be able to find it.

This patch series adds the necessary symbols into vmcoreinfo, which
would allow a debugger to find and interpret the kallsyms table. Using
the kallsyms data, the debugger can then lookup any symbol, allowing it
to find ORC, BTF, or any other useful data.

This would allow a live kernel, or core dump, to be debugged without
any DWARF debuginfo. This is useful for many cases: the debuginfo may
not have been generated, or you may not want to deploy the large files
everywhere you need them.

I've demonstrated a proof of concept for this at LSF/MM+BPF during a
lighting talk. Using a work-in-progress branch of the drgn debugger, and
an extended set of BTF generated by a patched version of dwarves, I've
been able to open a core dump without any DWARF info and do basic tasks
such as enumerating slab caches, block devices, tasks, and doing
backtraces. I hope this series can be a first step toward a new
possibility of "DWARFless debugging".

Related discussion around the BTF side of this:
https://lore.kernel.org/bpf/586a6288-704a-f7a7-b256-e18a675927df@oracle.com/T/#u

Some work-in-progress branches using this feature:
https://github.com/brenns10/dwarves/tree/remove_percpu_restriction_1
https://github.com/brenns10/drgn/tree/kallsyms_plus_btf

Stephen Brennan (2):
kallsyms: Move declarations to internal header
vmcoreinfo: Include kallsyms symbols

kernel/crash_core.c | 14 ++++++++++++++
kernel/kallsyms.c | 23 +----------------------
kernel/kallsyms_internal.h | 30 ++++++++++++++++++++++++++++++
3 files changed, 45 insertions(+), 22 deletions(-)
create mode 100644 kernel/kallsyms_internal.h

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2.30.2