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Hello folks,
I have released kdump2gdb 0.2, a small tool that converts a kdump core to
an ELF core that can be used with gdb. It now enables kernel-level
backtracing of all processes from within gdb.
Download it from here:
http://jeanmarc.saffroy.free.fr/kdump2gdb/
Each process is seen as a thread, so you can use gdb's internal
thread-related commands (which are much faster and richer than scripts):
"info threads" to list them, "thread <NN>" to switch to any thread (no VMM
context switch here), "bt" and "bt full", "up" and "down", as with a
userland multithreaded core file. Due to optimizations (?), the stack
frames decoded by gdb can be unaccurate, and should be taken with a grain
of salt; I suspect setting CONFIG_STACK_UNWIND could yield better results.
Below is the README. Feedback is welcome!
Cheers,
--
[email protected]
kdump2gdb
---------
The kdump2gdb script converts a kdump core file (which is essentially an ELF
core) into a slightly different ELF core that can be directly used with gdb.
It also produces a gdb script that loads the required kernel modules.
Features:
- completely automated: run kdump2gdb, then start gdb on your new core file,
load modules, and enjoy!
- the power of gdb to explore stack frames with full debug infos on all
tasks
Limitations:
- currently limited to x86-64; but support for other arches should not be
difficult to add
- gdb scripting is *slow*! But a patch that improves this is already
available, and I suspect there could be more in the near future.
Sample session
--------------
Below is an example of how I use kdump2gdb (from the tarball). As you can see,
even on a 2GHz Athlon box with a patched gdb, it takes several minutes to
complete.
$ cd kdump2gdb-0.2
$ make
gcc -Wall -g -lelf kdumpfix.c -o kdumpfix
$ time ./kdump2gdb -k /var/dump/dump-2006-09-21_11\:15\:21 \
-d ~/kernel/build-2.6.18 -o /tmp/core -g modload
Restoring low identity-mapped areas...
Gathering vmalloc-mapped areas...
warning: shared library handler failed to enable breakpoint
Gathering thread data...
warning: shared library handler failed to enable breakpoint
Restoring vmalloc-mapped areas...
Preparing gdb script to map modules...
warning: shared library handler failed to enable breakpoint
All done. Now you can do:
$ gdb /home/saffroy/kernel/build-2.6.18/vmlinux /tmp/core
(gdb) source modload
(gdb) bt
real 7m42.250s
user 6m15.658s
sys 0m6.520s
(The warnings are produced by gdb, they are harmless.)
Gdb patches
-----------
I use gdb 6.5, and encountered the following problems:
- gdb crashes in realloc on add-symbol-file:
the fix is here:
http://sources.redhat.com/ml/gdb-patches/2006-10/msg00056.html
- gdb scripts are sooooooooooo sloooooow:
a significant improvement is observed with the patch mentioned here:
http://sources.redhat.com/ml/gdb/2006-10/msg00023.html
You should edit the kdump2gdb script to use a specific gdb binary if needed.
Licensing
---------
This program is free software, distributed under the terms of the
GNU General Public License version 2.
Contact
-------
Jean-Marc Saffroy <[email protected]>
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