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https://github.com/JakeHillion/drgn.git
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e6abfeac03
There are a few reasons for this: 1. dwfl_core_file_report() crashes on elfutils 0.183-0.185. Those versions are still used by several distros. 2. In order to support --main-symbols and --symbols properly, we need to report things ourselves. 3. I'm considering moving away from libdwfl in the long term. We provide an escape hatch for now: setting the environment variable DRGN_USE_LIBDWFL_REPORT=1 opts out of drgn's reporting and uses libdwfl's. Fixes #130. Signed-off-by: Omar Sandoval <osandov@osandov.com>
118 lines
4.2 KiB
ReStructuredText
118 lines
4.2 KiB
ReStructuredText
Advanced Usage
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==============
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.. highlight:: pycon
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The :doc:`user_guide` covers basic usage of drgn, but drgn also supports more
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advanced use cases which are covered here.
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Loading Debugging Symbols
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-------------------------
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drgn will automatically load debugging information based on the debugged
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program (e.g., from loaded kernel modules or loaded shared libraries).
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:meth:`drgn.Program.load_debug_info()` can be used to load additional debugging
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information::
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>>> prog.load_debug_info(['./libfoo.so', '/usr/lib/libbar.so'])
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Library
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-------
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In addition to the CLI, drgn is also available as a library.
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:func:`drgn.program_from_core_dump()`, :func:`drgn.program_from_kernel()`, and
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:func:`drgn.program_from_pid()` correspond to the ``-c``, ``-k``, and ``-p``
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command line options, respectively; they return a :class:`drgn.Program` that
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can be used just like the one initialized by the CLI::
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>>> import drgn
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>>> prog = drgn.program_from_kernel()
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C Library
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---------
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The core functionality of drgn is implemented in C and is available as a C
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library, ``libdrgn``. See |drgn.h|_.
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.. |drgn.h| replace:: ``drgn.h``
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.. _drgn.h: https://github.com/osandov/drgn/blob/main/libdrgn/drgn.h.in
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Full documentation can be generated by running ``doxygen`` in the ``libdrgn``
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directory of the source code. Note that the API and ABI are not yet stable.
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Custom Programs
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---------------
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The main components of a :class:`drgn.Program` are the program memory, types,
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and symbols. The CLI and equivalent library interfaces automatically determine
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these. However, it is also possible to create a "blank" ``Program`` and plug in
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the main components.
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:meth:`drgn.Program.add_memory_segment()` defines a range of memory and how to
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read that memory. The following example uses a Btrfs filesystem image as the
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program "memory":
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.. code-block:: python3
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import drgn
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import os
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import sys
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def btrfs_debugger(dev):
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file = open(dev, 'rb')
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size = file.seek(0, 2)
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def read_file(address, count, physical, offset):
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file.seek(offset)
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return file.read(count)
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platform = drgn.Platform(drgn.Architecture.UNKNOWN,
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drgn.PlatformFlags.IS_LITTLE_ENDIAN)
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prog = drgn.Program(platform)
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prog.add_memory_segment(0, size, read_file)
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prog.load_debug_info([f'/lib/modules/{os.uname().release}/kernel/fs/btrfs/btrfs.ko'])
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return prog
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prog = btrfs_debugger(sys.argv[1] if len(sys.argv) >= 2 else '/dev/sda')
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print(drgn.Object(prog, 'struct btrfs_super_block', address=65536))
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:meth:`drgn.Program.add_type_finder()` and
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:meth:`drgn.Program.add_symbol_finder()` are the equivalent methods for
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plugging in types and symbols.
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Environment Variables
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---------------------
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Some of drgn's behavior can be modified through environment variables:
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``DRGN_MAX_DEBUG_INFO_ERRORS``
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The maximum number of individual errors to report in a
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:exc:`drgn.MissingDebugInfoError`. Any additional errors are truncated. The
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default is 5; -1 is unlimited.
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``DRGN_PREFER_ORC_UNWINDER```
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Whether to prefer using `ORC
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<https://www.kernel.org/doc/html/latest/x86/orc-unwinder.html>`_ over DWARF
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for stack unwinding (0 or 1). The default is 0. Note that drgn will always
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fall back to ORC for functions lacking DWARF call frame information and
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vice versa. This environment variable is mainly intended for testing and
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may be ignored in the future.
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``DRGN_USE_LIBDWFL_REPORT``
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Whether drgn should use libdwfl to find debugging information for core
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dumps instead of its own implementation (0 or 1). The default is 0. This
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environment variable is mainly intended as an escape hatch in case of bugs
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in drgn's implementation and will be ignored in the future.
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``DRGN_USE_LIBKDUMPFILE_FOR_ELF``
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Whether drgn should use libkdumpfile for ELF vmcores (0 or 1). The default
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is 0. This functionality will be removed in the future.
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``DRGN_USE_PROC_AND_SYS_MODULES``
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Whether drgn should use ``/proc/modules`` and ``/sys/module`` to find
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loaded kernel modules for the running kernel instead of getting them from
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the core dump (0 or 1). The default is 1. This environment variable is
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mainly intended for testing and may be ignored in the future.
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