Hey José, I was able to get elixir to work with cerl, such as elixir -e "IO.puts :ok". But I could not get it to work in the release environment running in docker. I get this error:
root:~# releases/0.1.0/elixir -e "IO.puts :ok"
{"init terminating in
do_boot",{undef,[{elixir,start_cli,[],[]},{init,start_em,1,[]},{init,do_boot,3,[]}]}}
init terminating in do_boot
({undef,[{elixir,start_cli,[],[]},{init,start_em,1,[]},{init,do_boot,3,[]}]})
Crash dump is being written to: erl_crash.dump...done
In my dockerfile I replace the elixir bin with my elixir debug like so:
....
COPY --from=build /app/_build/prod/rel/app ./
# Copy erlang source, along with erlang debug binary
COPY --from=build /OTP/subdir /OTP/subdir
# Symlink erlang debug binary to erts bin dir
RUN ln -s /OTP/subdir/bin/cerl
/app/releases/0.1.0/../../erts-11.2.2.15/bin/cerl
# Replace elixir script with our scrip that runs the erlang debug binary
COPY elixir-debug releases/0.1.0/elixir
RUN chmod +x releases/0.1.0/elixir
...
The source image for my app docker file
is hexpm/elixir:1.10.4-erlang-23.3.4.16-ubuntu-bionic-20210930 but modified
to keep the erlang source code and build cerl debug vm.
I don't think I can reasonably share a minimal app that reproduces the
issue (without sharing my app code which I cannot). The seg fault happens
randomly after x hours and I do not know what is causing it.
Attached is my modified elixir bin.
On Monday, August 22, 2022 at 9:14:52 AM UTC-7 José Valim wrote:
> Or perhaps please provide a minimal app that reproduces it. :)
>
> On Mon, Aug 22, 2022 at 6:13 PM José Valim <jose....@dashbit.co> wrote:
>
>> Running Elixir with cerl should just work. Can you expand on the on_boot
>> errors you get in a release?
>>
>> On Mon, Aug 22, 2022 at 5:46 PM Stephen Baldwin <stephen...@syncromsp.com>
>> wrote:
>>
>>> Hello I've been trying to debug a seg fault in my elixir app for a bit.
>>> I've learned that if debugging symbols are enabled on the erlang vm you can
>>> use gdb to debug a linux core file to deduce where the seg fault is
>>> occuring. Now I've rebuilt erlang from source to have the debugging symbols
>>> and that all works fine, but using it with an elixir release seems to be a
>>> bit difficult.
>>>
>>> I modified the elixir bin similar to
>>> https://github.com/elixir-lang/elixir/pull/11082 but I am getting
>>> on_boot errors when running the release. So replacing cerl with erl isn't a
>>> path to success.
>>>
>>> I need some help as I don't fully understand the path from an elixir
>>> release to the erlang vm. Any quick ways to get this to work? Otherwise I
>>> think it would be worthwhile to have an option when building an elixir
>>> release to use a cerl vm (debug, valgrind, etc).
>>>
>>> Regards,
>>> Stephen
>>>
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elixir-debug
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