`jiffy.so: undefined symbol: _nif_init` with LTO

[ldgabbay]

When I compile and run a project with jiffy 1.1.0+ on Ubuntu 24.04 and actually try to call jiffy functions, I get the error:

1> jiffy:module_info().
=WARNING REPORT==== 1-Feb-2026::18:20:55.091035 ===
The on_load function for module jiffy returned:
{error,{bad_lib,"Failed to find library init function: '.../_build/default/lib/jiffy/priv/jiffy.so: undefined symbol: _nif_init'"}}

** exception error: undefined function jiffy:module_info/0

I have determined this is caused by Link Time Optimization (LTO), which is enabled by default on Ubuntu and possibly other Linux based systems. The rebar.config.script looks for LTO support and automatically enables it, but the aggressive optimization strips symbols that it thinks are not used and removes _nif_init and others.

I have been able to patch the problem by including:

{overrides, [
  {override, jiffy, [
    {port_env, [
      {".*", "FLTO_FLAG", "-fno-lto"}
    ]}
  ]}
]}.

in my project's rebar.config, but this should be fixed in the jiffy library itself.

[nickva]

@ldgabbay wonder if other NIFs have the same issue? Or I guess not too many others try to use LTO.

Do you know what compiler is used on Ubuntu 24.04, gcc or llvm? And what settings it used compile and link the NIF? Rebar2 at least used to generate a compile_commands.json file, not sure if rebar3 + pc does that...

Also noticed a recent change in Erlang regard visibility of symbols, erlang/otp#9864, what Erlang version are you using? I see the PR moved this to a new define:

#elif defined(__GNUC__) && __GNUC__ >= 4
#  define ERL_NAPI_EXPORT __attribute__ ((visibility("default")))

It's checking that it's GNUC and GNUC >=4 as before.

I guess we can try to set -Wl,--undefined=nif_init as a linker flag, but ideally Erlang/OTP ERL_NIF_INIT would do that. If worse comes to worse can just disable FLTO.

[nickva]

@ldgabbay I was trying to reproduce the issue on Ubuntu 24.04 in Docker with both the default gcc and gcc-14 with Erlang OTP 26 (apache/couchdbci-ubuntu:noble-erlang-26.2.5.17).

I got the jiffy to build and run eunit tests in both cases. Wondering the if it's a specific version of Erlang OTP, clang compiler or maybe some extra LTO options your environment might have had?

To make sure the specified CC/CXX variables were actually used the rebar pc (port compiler) plugin has a config flag to dump all the compiled command to compile_commands.json file:

 cat compile_commands.json
[
{ "file"      : "c_src/decoder.c"
, "directory" : "/home/jenkins/jiffy"
, "command"   : "gcc-14 -c -Ic_src/ -g -Wall -flto -Werror -O3 -fvisibility=hidden -g -Wall -fPIC -MMD -I\"/usr/local/lib/erlang/lib/erl_interface-5.5.1/include\" -I\"/usr/local/lib/erlang/erts-14.2.5.13/include\" c_src/decoder.c -o c_src/decoder.o"
}

[nickva]

To avoid any issues with FLTO I opted to remove it altogether and switched jiffy to a unity build, so we get the same benefit (and more) from a single compiled file and not have worry about LTO edge cases. With that, I'll close the issue. The new feature will be available in the upcoming 2.0 release.