Direct Mojo proof

Copy Markdown View Source

This file records how the loaded NIF was shown to be the Mojo build of native/poc.mojo, rather than a C file compiled beside it.

Build command

scripts/build-native.sh runs only:

.venv/bin/mojo build native/poc.mojo \
  --emit shared-lib \
  -o priv/native/libpoc.so \
  -Xlinker -undefined \
  -Xlinker dynamic_lookup

The script does not pass a .c, .cc, or .o file. experiments/abi/diagnostic/layout.c is compiled only by scripts/run-abi-experiments.sh, and that binary is experiments/abi/diagnostic/layout, not priv/native/libpoc.so.

Exported and imported symbols

scripts/inspect-abi.sh on the built library:

0000000000000754 T _nif_init

Undefined symbols:

_abort
_calloc
_enif_get_long
_enif_make_badarg
_enif_make_long
dyld_stub_binder

nm without -gU also shows one local text symbol, the mangled add callback (t _poc::add(...)). The BEAM does not dlsym that name. nif_init stores the thin function pointer in the ErlNifFunc it returns.

There is no undefined enif_get_int64. On this OTP that name is a preprocessor macro.

Linked images

otool -L:

priv/native/libpoc.so
@rpath/libKGENCompilerRTShared.dylib
/usr/lib/libSystem.B.dylib

The rpath is .venv/lib/python3.12/site-packages/modular/lib. libKGENCompilerRTShared.dylib is the Mojo compiler runtime that mojo build linked. It is not a NIF shim written for this project. libSystem supplies calloc and abort.

IR check

mojo build native/poc.mojo --emit llvm contains direct declarations:

declare i64 @enif_make_badarg(ptr)
declare i32 @enif_get_long(ptr, i64, ptr)
declare i64 @enif_make_long(ptr, i64)
declare i64 @calloc(i64, i64)
declare void @abort()

The same file also declares write, dup, fdopen, fflush, fclose, and KGEN_CompilerRT_AlignedFree. Those are inserted by the compiler. They are part of the honest dependency list. They are not a second source file that implements add.

Load check

ExUnit loads this .so through :erlang.load_nif/2 and asserts Mojoler.POC.add(20, 22) == 42, plus the nm expectations above. A separate OS process does the same load and exits 0.