erts: Allow erlang:load_nif/2 to load a NIF library from an in-memory binary

[saleyn]

Add support for passing #{memory => NifSO::binary(), filename => Filename::string()} as the first argument to erlang:load_nif/2. When a map is given, the NIF shared object is loaded directly from the binary image in memory instead of from the file system.

Why is this needed?

Presently build tools (i.e. rebar3, mix) cannot bundle all dependencies into a single executable archive escript (a.k.a. escriptizing) that have dependencies with NIF shared object libraries. This PR addresses that gap, and extends the erlang:load_nif/2 call with the missing functionality. After it's merged, the build tools will be able to be modified to take advantage of it. See #4476 issue.

Implementation

• erts_dlopen_mem() — new static helper in erl_nif.c (Linux/POSIX only). On Linux >= 3.17 it uses memfd_create(2) to create an anonymous in-memory file, writes the SO image into it, and calls dlopen(3) via /proc/self/fd/. On older Linux kernels and other POSIX systems it falls back to shm_open(3) + /dev/shm/. The implementation is derived from the https://github.com/saleyn/memfd_create proof of concept.

• erts_load_nif() — extended argument parsing:

  • Plain filename :: string()|binary() continues to work unchanged.
  • #{filename => string()|binary()}: same as passing the filename string
  • #{memory => Binary, filename => string()|binary()} map: Binary is extracted via erts_get_aligned_binary_bytes(), passed to erts_dlopen_mem(), and the resulting dlopen handle is used directly. The optional filename string serves only as a label inside the memory-backed file descriptor, and is only valid on non-MacOS systems.
  • The open-from-memory step is performed before the existing else-if validation chain (version checks, module-name check, create_lib) so both code paths share the same validation and bookkeeping.
  • erts_sys_ddll_open() is skipped (via !load_from_mem guard) when a handle was already obtained from memory.

• The feature is guarded by #if defined(HAVE_DLOPEN) && defined(unix). On unsupported platforms load_nif/2 returns {error,{load_failed,…}}.

Testing

• nif_SUITE: new test case load_nif_from_mem

  • Happy path: reads nif_mod.1.so into a binary, calls erlang:load_nif(#{memory => Binary, filename => Filename}, []) via nif_mod:load_nif_lib_from_mem/3, and asserts lib_version() == 1.
  • Error path: non-binary second element returns {error,{bad_lib,_}}.

• nif_mod.erl: new exported helper load_nif_lib_from_mem/3 so that the load_nif call site lives inside the NIF module (required by the BIF).

[github-actions]

CT Test Results

    3 files    136 suites   52m 23s ⏱️
1 676 tests 1 620 ✅ 56 💤 0 ❌
2 318 runs  2 244 ✅ 74 💤 0 ❌

Results for commit 67cf2fa.

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// Erlang/OTP Github Action Bot

[essen]

This could be used for Windows: https://github.com/fancycode/MemoryModule

[saleyn]

This could be used for Windows: https://github.com/fancycode/MemoryModule

After I get the tests pass on all Unix/Mac flavors, I welcome a PR on top of mine to add the Windows support.