[Debug BEAM VM] How can I debug Segmentation fault from 3rd party lib?

Questions / Help
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1

Hello,

first a bit of context:

I am using Elixir with Kafka extensively.

Lib for connecting to Kafka I am using is GitHub - silviucpp/erlkaf: Erlang kafka driver based on librdkafka

It depends on a well known C++ Kafka driver GitHub - edenhill/librdkafka: The Apache Kafka C/C++ library

librdkafka works great most of the time, but sometimes on startup it throws Segmentation fault errors, and I would like to debug the C++ code.

Question:

Is there a way to compile the BEAM VM with C debug flags and connect it to some C debugger (prob not gdb but something for LLVM, right?)

I am using Mac with i7 Intel proc, installed Erlang and Elixir with asdf.

Tnx in advance,
Vlx

2

If I’m reading the docs right, asdf uses kerl under the hood, so you should be able to pass kerl options when installing:

$ export KERL_BUILD_DEBUG_VM="true"
$ asdf install erlang <version>

You should then be able to use cerl -debug -lldb to start LLDB with the debug emulator.

3 Likes
3

False alarm, I mistakenly used openssl@3 for compile

uuuugh, now my asdf installation doesn’t work. OpenSSL issues

$ echo $KERL_BUILD_DEBUG_VM
true
$ echo $KERL_CONFIGURE_OPTIONS 
--without-javac --with-ssl=/usr/local/opt/openssl@3
$ asdf install erlang 24.1.7 
asdf_24.1.7 is not a kerl-managed Erlang/OTP installation
No build named asdf_24.1.7
Downloading 24.1.7 to /Users/y/.asdf/plugins/erlang/kerl-home/archives...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   654  100   654    0     0   6812      0 --:--:-- --:--:-- --:--:--  6812
100  102M  100  102M    0     0  27.9M      0  0:00:03  0:00:03 --:--:-- 37.0M
Extracting source code
Building Erlang/OTP 24.1.7 (asdf_24.1.7), please wait...
APPLICATIONS DISABLED (See: /Users/y/.asdf/plugins/erlang/kerl-home/builds/asdf_24.1.7/otp_build_24.1.7.log)
 * jinterface     : Java compiler disabled by user

Build failed.
#   define OSSL_DEPRECATEDIN_3_0                OSSL_DEPRECATED(3.0)
                                                ^
/usr/local/opt/openssl@3/include/openssl/macros.h:62:52: note: expanded from macro 'OSSL_DEPRECATED'
#     define OSSL_DEPRECATED(since) __attribute__((deprecated))
                                                   ^
25 warnings generated.
make[3]: *** [opt] Error 2
make[2]: *** [opt] Error 2
make[1]: *** [opt] Error 2
make: *** [libs] Error 2
4

I successfully compiled erlang with debug flags, thank you very much!

Now I am really struggling with runnig the Elixir app in interactive mode (iex -S mix) and connecting it to the lldb

I suppose I should run the lldb first, then run BEAM machine and then point it to the Elixir project to run it?

5

Sorry, I’m afraid I can’t be of much help with the Elixir side of things. :frowning: