OpenRA/OpenRA · critical

Could not load hostfxr_run_app(): %s

Error message

Could not load hostfxr_run_app(): %s

What it means

Printed by the macOS apphost when dlsym(lib, "hostfxr_run_app") returns NULL. hostfxr_initialize_for_dotnet_command_line resolved successfully, so the library is recognizably hostfxr, but it does not export the run_app entrypoint — indicating a partial, stub, or ABI-incompatible hostfxr. dlerror() gives the loader's 'symbol not found' detail.

Source

Thrown at packaging/macos/apphost.c:58

{
	void *lib = dlopen(argv[1], RTLD_LAZY);
	if (lib == NULL)
	{
		fprintf(stderr, "Failed to load %s: %s\n", argv[1], dlerror());
		return 1;
	}

	hostfxr_initialize_for_dotnet_command_line_fn hostfxr_initialize_for_dotnet_command_line = (hostfxr_initialize_for_dotnet_command_line_fn)dlsym(lib, "hostfxr_initialize_for_dotnet_command_line");
	if (!hostfxr_initialize_for_dotnet_command_line)
	{
		fprintf(stderr, "Could not load hostfxr_initialize_for_dotnet_command_line(): %s\n", dlerror());
		return 1;
	}

	hostfxr_run_app_fn hostfxr_run_app = (hostfxr_run_app_fn)dlsym(lib, "hostfxr_run_app");
	if (!hostfxr_run_app)
	{
		fprintf(stderr, "Could not load hostfxr_run_app(): %s\n", dlerror());
		return 1;
	}

	hostfxr_close_fn hostfxr_close = (hostfxr_close_fn)dlsym(lib, "hostfxr_close");
	if (!hostfxr_close)
	{
		fprintf(stderr, "Could not load hostfxr_close(): %s\n", dlerror());
		return 1;
	}

	struct hostfxr_initialize_parameters params;
	params.size = sizeof(params);
	params.host_path = argv[0];
	params.dotnet_root = dirname(argv[1]);

	hostfxr_handle host_context_handle;
	hostfxr_initialize_for_dotnet_command_line(
	    argc - 2,

View on GitHub (pinned to a520984d91)

Solutions

1. Confirm the export set: `nm -gU libhostfxr.dylib | grep hostfxr_run_app` — absence confirms an incomplete/wrong hostfxr.
2. Replace the dylib with the matching libhostfxr.dylib from the same .NET runtime version the app was published against.
3. Repackage the app via `dotnet publish` so runtime + hostfxr + apphost are consistent.
4. Verify file integrity (not truncated) with `codesign --verify` and `file`/`otool -L`.
5. If building custom hostfxr, ensure the full public hostfxr API (incl. hostfxr_run_app) is exported.

Example fix

// before: incomplete hostfxr lacks run_app
hostfxr_run_app = dlsym(lib, "hostfxr_run_app"); // NULL

// after: ship the full matching runtime
$ nm -gU OpenRA.app/Contents/MacOS/libhostfxr.dylib | grep hostfxr_run_app
000000000000abcd T hostfxr_run_app   // present
$ dotnet publish -r osx-arm64 --self-contained   // bundles complete hostfxr

// Packaging-time symbol check (fail fast, not at user runtime):
// nm -gU libhostfxr.dylib | grep -q hostfxr_run_app || { echo 'hostfxr missing run_app'; exit 1; }

if (!hostfxr_run_app) {
    fprintf(stderr, "Loaded hostfxr is incomplete (no run_app). Re-bundle the full matching .NET runtime.\n");
    dlclose(lib);
    return 1;
}

When it happens

Trigger: A hostfxr build/variant that omits hostfxr_run_app (e.g. a minimal or wrong runtime pack); ABI drift where run_app was renamed/removed; loading a hostpolicy stub instead of the full hostfxr.

Common situations: Shipping a trimmed/wrong runtime pack that lacks run_app; bundling hostfxr from a preview/SDK build whose export set differs; corrupt or truncated dylib that resolves some symbols but not others.

Related errors

• Could not load hostfxr_initialize_for_dotnet_command_line():
• Could not load hostfxr_close(): %s
• Failed to load %s: %s

AI-assisted analysis of OpenRA/OpenRA@a520984d91 (2026-08-13). Data as JSON: /api/errors/088580e02ca857f1. Report an issue: GitHub.