Dump C level and Ruby level backtrace from living ruby process or core file using gdb
MIT License
Dump C level and Ruby level backtrace from living ruby process or core file using gdb.
$ gem install gdbdump
sudo gdb
must be allowed to dump backtrace of living ruby processIt was verified that gdbdump works with ruby executables built by rbenv/ruby-build.
Usage: gdbdump [options] [ pid | /path/to/ruby pid | /path/to/ruby core ]
-d, --[no-]debug print debug log (default: false)
-x, --gdbinit FILE path to ruby repo's .gdbinit (default: some of ruby repo's .gdbinit is pre-bundle in this gem)
--gdb PATH path to gdb command (default: gdb)
Default supported ruby versions: 2.1.x - 2.4.x
Ruby repo's .gdbinit file defines useful helper functions and it is maintained by ruby core team. gdbdump
uses it. .gdbinit
of some versions written on above are pre-bundled in this gem. But, if you want to use gdbdump
for older or newer ruby versions:
-x
optiongdbdump
gem.With live ruby process of pid 1897,
$ gdbdump 1897
You will see C and Ruby level backtrace as:
$1 = (rb_vm_t *) 0x7f46bb071f20
* #<Thread:0x7f46bb0a5ee8 rb_thread_t:0x7f46bb0725d0 native_thread:0x7f46ba514740>
0x7f46ba16d700 <thread_join_m at thread.c:980>:in `join'
loop.rb:17:in `<main>'
* #<Thread:0x7f46bb202750 rb_thread_t:0x7f46bb3e03d0 native_thread:0x7f46b89c0700>
0x7f46ba0e4f30 <rb_f_sleep at process.c:4388>:in `sleep'
loop.rb:6:in `block (2 levels) in <main>'
0x7f46ba1a72b0 <rb_f_loop at vm_eval.c:1137>:in `loop'
loop.rb:4:in `block in <main>'
* #<Thread:0x7f46bb202660 rb_thread_t:0x7f46bb3e47e0 native_thread:0x7f46b87be700>
0x7f46ba0e4f30 <rb_f_sleep at process.c:4388>:in `sleep'
loop.rb:13:in `block (2 levels) in <main>'
0x7f46ba1a72b0 <rb_f_loop at vm_eval.c:1137>:in `loop'
loop.rb:11:in `block in <main>'
With core file, you have to specify path of ruby executable.
$ gdbdump $HOME/.rbenv/versions/2.4.1/bin/ruby core.1897
You can get a core file with gcore
command as:
$ sudo gcore 1897
rb_ps
defined in gdbinit. That's it.sigdump
gem and require 'sigdump/setup'
unlike gdbdump.gdbdump
can replace gdbruby
.After checking out the repo, run bin/setup
to install dependencies. Then, run rake test
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
. To release a new version, update the version number in version.rb
, and then run bundle exec rake release
, which will create a git tag for the version, push git commits and tags, and push the .gem
file to rubygems.org.
Belows are my investigation notes about how to print C level and Ruby level backtrace via gdb.
CRuby itself has rb_print_backtrace function to print C level backtrace, and rb_backtrace function to print Ruby level backtrace. I first tried to use them.
However, they print a backtrace of only current thread. Furthermore, rb_print_backtrace supports printing outputs to only STDERR. Also, because it calls C function, it works only for a living process, and does not work for core file.
def print_backtrace
run do |gdb|
gdb.cmd_exec('call write(2, "== c backtrace ==\n", 18)')
gdb.cmd_exec('call rb_print_backtrace()')
gdb.cmd_exec('call write(2, "== ruby backtrace ==\n", 21)')
gdb.cmd_exec('call rb_backtrace()')
end
end
I secondly tried to use GDB's info threads
and bt
command to print C level backtrace. This was fine.
I also tried to print Ruby level backtrace by calling rb_eval_string with Ruby codes as:
def ruby_backtrace_code
code = +%Q[File.open('#{dumpfile}', 'a') {|f|]
code << %q[
Thread.list.each {|th|
f.write %Q[ Thread #{th} status=#{th.status} priority=#{th.priority}\n]
th.backtrace.each {|bt|
f.write %Q[ #{bt}\n]
}
}
}]
code.split("\n").map(&:strip).join('; ')
end
def print_backtrace
run do |gdb|
gdb.cmd_exec(%Q[call rb_eval_string("#{ruby_backtrace_code}")])
end
end
However, the debugee (target) process got stuck after call rb_eval_string
. It seemed the ruby process will be broken if ruby codes are executed via gdb.
I thirdly tried to use rb_ps
function defined in .gdbinit of ruby repository to print C level and Ruby level backtrace of all threads.
Since .gdbinit
is maintained by ruby core team, I do not need to follow changes of C level interfaces of CRuby as long as I follow .gdbinit
.
Because rb_ps
does not call any C functions inside, it can print C and Ruby level backtrace for core file.
The drawback of this way is that
.gdbinit
in newer ruby versionsrb_ps
takes somewhat long time like 2.6 seconds to print backtrace.Currently, I am taking this way.
Bug reports and pull requests are welcome on GitHub at https://github.com/sonots/gdbdump. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.
The gem is available as open source under the terms of the MIT License.
Everyone interacting in the Gdbdump project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.