[WasmFS] Ensure error codes are negative in the Node backend

[kleisauke]

See commit 48459c6 for details.

Split out from #24733, this fixes a test failure in core0.test_fs_js_api_wasmfs_rawfs from that PR.

[sbc100]

Why no tests failing because of this bug?

[kleisauke]

Why no tests failing because of this bug?

Good question, I suspect it's because absolute path access doesn't work with -sWASMFS -sNODERAWFS (so this code is never reached in that test), but I'll dig into this later.

[kleisauke]

For reference, see the CircleCI log at https://circleci.com/gh/emscripten-core/emscripten/1164699 for the failure.

Details

======================================================================
FAIL [0.001s]: test_fs_js_api_wasmfs_rawfs (test_core.core0)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/root/project/test/common.py", line 377, in resulting_test
    return func(self, *args)
  File "/root/project/test/decorators.py", line 324, in metafunc
    return func(self, *args, **kwargs)
  File "/root/project/test/test_core.py", line 5915, in test_fs_js_api
    self.do_runf('fs/test_fs_js_api.c', 'success')
  File "/root/project/test/common.py", line 1408, in do_runf
    return self._build_and_run(filename, expected_output, **kwargs)
  File "/root/project/test/common.py", line 1456, in _build_and_run
    js_output = self.run_js(js_file, engine, args,
  File "/root/project/test/common.py", line 1040, in run_js
    self.fail('JS subprocess failed (%s): %s (expected=%s).  Output:\n%s' % (error.cmd, error.returncode, assert_returncode, ret))
AssertionError: JS subprocess failed (/root/emsdk/node/22.16.0_64bit/bin/node --stack-trace-limit=50 --trace-uncaught /tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js): 1 (expected=0).  Output:
Aborted(Assertion failed: err < 0, at: /emsdk/emscripten/system/lib/wasmfs/syscalls.cpp,1067,__syscall_renameat)
Aborted(Assertion failed)
/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:552
  var e = new WebAssembly.RuntimeError(what);
          ^

RuntimeError: Aborted(Assertion failed)
    at abort (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:552:11)
    at assert (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:269:5)
    at test_fs_rename (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:2763:456)
    at wasm://wasm/000901ea:wasm-function[49]:0x152b
    at wasm://wasm/000901ea:wasm-function[50]:0x1562
    at /tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:567:12
    at callMain (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:3044:15)
    at doRun (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:3097:24)
    at run (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:3110:5)
    at removeRunDependency (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:798:11)
    at receiveInstance (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:671:5)
    at receiveInstantiationResult (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:688:12)
    at createWasm (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:714:17)
Thrown at:
    at abort (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:552:11)
    at assert (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:269:5)
    at test_fs_rename (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:2763:456)
    at $func49 (wasm://wasm/000901ea:1:5420)
    at $main (wasm://wasm/000901ea:1:5475)
    at /tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:567:12
    at callMain (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:3044:15)
    at doRun (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:3097:24)
    at run (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:3110:5)
    at removeRunDependency (/tmp/emtest_7ktg8cnu/emscripten_test_core0_v8vtv858/test_fs_js_api.js:798:11)


Node.js v22.16.0


----------------------------------------------------------------------
Ran 1145 tests in 674.466s

FAILED (failures=1, skipped=67)

Which is this assert():

emscripten/system/lib/wasmfs/syscalls.cpp

Line 1067 in 57df161

assert(err < 0);

[sbc100]

Actually I think this is wrong. IIUC, there are 3 classes of functions at play:

1. The _wasmfs_node_xxx API. These return positive error codes.
2. The internal C++ API for wasm (e.g. insertMove). These also return positive error codes.
3. The __syscall_xxx API: These return negative error codes.

[kleisauke]

Are you sure about point (2)? See for example:

emscripten/system/lib/wasmfs/file.h

Lines 409 to 416 in bc56904

	// Move the file represented by `file` from its current directory to this
	// directory with the new `name`, possibly overwriting another file that
	// already exists with that name. The old directory may be the same as this
	// directory. On success return 0 and otherwise return a negative error code
	// without changing any underlying state. This should only be called from
	// renameat with the locks on the old and new parents already held.
	[[nodiscard]] int insertMove(const std::string& name,
	std::shared_ptr<File> file);

[sbc100]

Oh.. I stand corrected. Sorry about that.

[sbc100]

lgtm!