wasm_standalone fopen operation not permitted

[Rochet2]

I am trying to compile and run the examples depicted here:
https://github.com/bytecodealliance/wasmtime/blob/fbe29da5cc1c0847af176f151f114a6a535534ff/docs/WASI-tutorial.md
The tools I try to use are emscripten and wasmtime.

When compiling the module with wasi-sdk (clang), the example works as expected.
However, when using emscripten to compile the module, when trying to run the example the following error occurs:

emcc test.c -o test.wasm
echo hello world > test.txt
./wasmtime test.wasm test.txt test2.txt
Error: failed to run main module `test.wasm`

Caused by:
    0: failed to instantiate "test.wasm"
    1: unknown import: `env::__sys_read` has not been defined

I wanted to try to debug the issue to try to see if I can avoid the import and started by creating the following minimal program.

#include <stdlib.h>
#include <stdio.h>

int main() {
    printf("Hello world!\n");
    FILE* f = fopen("test.txt", "r");
    printf("Handle %p\n", f);
    perror("fopen():");
    return 0;
}

When compiling the module with emscripten and running it with wasmtime I get the following.

emcc test.c -o test.wasm
echo hello world > test.txt
./wasmtime test.wasm
Hello world!
Handle 0
fopen():: Operation not permitted

Setting the file permissions with chmod 777 test.txt does not help.
Using the wasmtime flags for enabling the program to use the folder where the text file is in does not help either: ./wasmtime --dir=. test.wasm.
Wasmtime produces a different error about insufficient capabilities in case the folder permissions are an issue, and the same example works when compiled with clang (wasi-sdk).

Getting the example to work would be great, but getting the file opening to work at all would be great as well.
I am unsure if I have missed some flag or similar, I will keep on looking through emscripten documentation.
If I cant find anything I will just implement a host defined function to read/write files instead of using WASI.

Emscripten version: 2.0.0 (d81f400)

[kripken]

I think this is a current limitation, see

emscripten/system/lib/standalone/standalone.c

Lines 74 to 93 in ec6d3d4

	// open(), etc. - we just support the standard streams, with no
	// corner case error checking; everything else is not permitted.
	// TODO: full file support for WASI, or an option for it
	// open()
	long __syscall5(const char* path, long flags, ...) {
	if (!strcmp(path, "/dev/stdin")) return STDIN_FILENO;
	if (!strcmp(path, "/dev/stdout")) return STDOUT_FILENO;
	if (!strcmp(path, "/dev/stderr")) return STDERR_FILENO;
	return -EPERM;
	}
	// ioctl()
	int __syscall54(int fd, int op, ...) {
	return -ENOSYS;
	}
	// fcntl64()
	long __syscall221(long fd, long cmd, ...) {
	return -ENOSYS;
	}

Improving that is being discussed in #12073

Note that if you do want 100% WASI file support, using the wasi-sdk may make more sense. (But long-term I hope they converge as mentioned in that issue.)

[stale]

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